QUIC                                                     J. Iyengar, Ed.
Internet-Draft                                                    Google
Intended status: Standards Track                         M. Thomson, Ed.
Expires: July 18, September 14, 2017                                      Mozilla
                                                        January 14,
                                                          March 13, 2017

           QUIC: A UDP-Based Multiplexed and Secure Transport
                      draft-ietf-quic-transport-01
                      draft-ietf-quic-transport-02

Abstract

   QUIC is a multiplexed and secure transport protocol that runs on top
   of UDP.  QUIC builds on past transport experience, and implements
   mechanisms that make it useful as a modern general-purpose transport
   protocol.  Using UDP as the basis of QUIC is intended to address
   compatibility issues with legacy clients and middleboxes.  QUIC
   authenticates all of its headers, preventing third parties from
   changing them.  QUIC encrypts most of its headers, thereby limiting
   protocol evolution to QUIC endpoints only.  Therefore, middleboxes,
   in large part, are not required to be updated as new protocol
   versions are deployed.

   This document describes defines the core QUIC
   protocol, including the conceptual design, wire format, and
   mechanisms of the QUIC protocol for transport protocol.  This
   document describes connection establishment, stream
   multiplexing, stream and connection-level flow control, packet format,
   multiplexing and data reliability.  Accompanying documents describe QUIC's loss recovery
   and congestion control, and the use of TLS 1.3 for key negotiation.
   cryptographic handshake and loss detection.

Note to Readers

   Discussion of this draft takes place on the QUIC working group
   mailing list (quic@ietf.org), which is archived at
   https://mailarchive.ietf.org/arch/search/?email_list=quic .

   Working Group information can be found at https://github.com/quicwg ;
   source code and issues list for this draft can be found at
   https://github.com/quicwg/base-drafts/labels/transport .

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
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   Drafts is at http://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months
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   This Internet-Draft will expire on July 18, September 14, 2017.

Copyright Notice

   Copyright (c) 2017 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   4
   2.  Conventions and Definitions . . . . . . . . . . . . . . . . .   4
     2.1.  Notational Conventions  . . . . . . . . . . . . . . . . .   5
   3.  A QUIC Overview . . . . . . . . . . . . . . . . . . . . . . .   5
     3.1.  Low-Latency Connection Establishment  . . . . . . . . . .   5   6
     3.2.  Stream Multiplexing . . . . . . . . . . . . . . . . . . .   6
     3.3.  Rich Signaling for Congestion Control and Loss Recovery .   6
     3.4.  Stream and Connection Flow Control  . . . . . . . . . . .   6
     3.5.  Authenticated and Encrypted Header and Payload  . . . . .   7
     3.6.  Connection Migration and Resilience to NAT Rebinding  . .   7
     3.7.  Version Negotiation . . . . . . . . . . . . . . . . . . .   7   8
   4.  Versions  . . . . . . . . . . . . . . . . . . . . . . . . . .   7   8
   5.  Packet Types and Formats  . . . . . . . . . . . . . . . . . .   8
     5.1.  Common  Long Header . . . . . . . . . . . . . . . . . . . . . .   8
       5.1.1.  Identifying Packet Types .   9
     5.2.  Short Header  . . . . . . . . . . . . . . .  10
       5.1.2.  Handling Packets from Different Versions . . . . . .  10
     5.2.  Regular Packets .  11
     5.3.  Version Negotiation Packet  . . . . . . . . . . . . . . .  12
     5.4.  Cleartext Packets . . . . .  11
       5.2.1.  Packet Number Compression and Reconstruction . . . .  12
       5.2.2.  Frames and Frame Types . . . . . . . . . . .  13
     5.5.  Encrypted Packets . . . . .  13
     5.3.  Version Negotiation Packet . . . . . . . . . . . . . . .  14
     5.4.
     5.6.  Public Reset Packet . . . . . . . . . . . . . . . . . . .  15
   6.  Life of a Connection
       5.6.1.  Public Reset Proof  . . . . . . . . . . . . . . . . .  15
     5.7.  Connection ID . . .  15
     6.1.  Version Negotiation . . . . . . . . . . . . . . . . . . .  15
     6.2.  Crypto and Transport Handshake  16
     5.8.  Packet Numbers  . . . . . . . . . . . . .  16
       6.2.1.  Transport Parameters and Options . . . . . . . .  16
       5.8.1.  Initial Packet Number . .  16
       6.2.2.  Proof of Source Address Ownership . . . . . . . . . .  17
       6.2.3.  Crypto Handshake Protocol Features . . . .  17
     5.9.  Handling Packets from Different Versions  . . . . .  18
       6.2.4.  Version Negotiation Validation . . .  17
   6.  Frames and Frame Types  . . . . . . . .  19
     6.3.  Connection Migration . . . . . . . . . . .  18
   7.  Life of a Connection  . . . . . . .  19
     6.4.  Connection Termination . . . . . . . . . . . . .  19
     7.1.  Version Negotiation . . . .  19
   7.  Frame Types and Formats . . . . . . . . . . . . . . . .  19
       7.1.1.  Using Reserved Versions . . .  20
     7.1.  STREAM Frame . . . . . . . . . . . .  20
     7.2.  Cryptographic and Transport Handshake . . . . . . . . . .  21
     7.2.  ACK Frame
     7.3.  Transport Parameters  . . . . . . . . . . . . . . . . . .  22
       7.3.1.  Transport Parameter Definitions . . . . . .  22
       7.2.1.  Ack Block Section . . . . .  24
       7.3.2.  Values of Transport Parameters for 0-RTT  . . . . . .  24
       7.3.3.  New Transport Parameters  . . . . . . .  24
       7.2.2.  Timestamp Section . . . . . . .  25
       7.3.4.  Version Negotiation Validation  . . . . . . . . . . .  25
     7.3.  STOP_WAITING Frame
     7.4.  Proof of Source Address Ownership . . . . . . . . . . . .  27
       7.4.1.  Client Address Validation Procedure . . . . . . .  26
     7.4.  WINDOW_UPDATE Frame . .  27
       7.4.2.  Address Validation on Session Resumption  . . . . . .  28
       7.4.3.  Address Validation Token Integrity  . . . . . . . . .  29
     7.5.  Connection Migration  . .  27
     7.5.  BLOCKED Frame . . . . . . . . . . . . . . . .  29
     7.6.  Connection Termination  . . . . . .  27
     7.6.  RST_STREAM Frame . . . . . . . . . . .  30
   8.  Frame Types and Formats . . . . . . . . .  28
     7.7.  PADDING Frame . . . . . . . . . .  31
     8.1.  STREAM Frame  . . . . . . . . . . . .  28
     7.8.  PING frame . . . . . . . . . .  31
     8.2.  ACK Frame . . . . . . . . . . . . .  29
     7.9.  CONNECTION_CLOSE frame . . . . . . . . . . .  32
       8.2.1.  ACK Block Section . . . . . .  29
     7.10. GOAWAY Frame . . . . . . . . . . . .  34
       8.2.2.  Timestamp Section . . . . . . . . . .  29
   8.  Packetization and Reliability . . . . . . . .  35
       8.2.3.  ACK Frames and Packet Protection  . . . . . . . .  30
   9.  Streams: QUIC's Data Structuring Abstraction . .  37
     8.3.  WINDOW_UPDATE Frame . . . . . .  32
     9.1.  Life of a Stream . . . . . . . . . . . . .  38
     8.4.  BLOCKED Frame . . . . . . .  32
       9.1.1.  idle . . . . . . . . . . . . . . .  39
     8.5.  RST_STREAM Frame  . . . . . . . . .  34
       9.1.2.  reserved . . . . . . . . . . .  39
     8.6.  PADDING Frame . . . . . . . . . . .  34
       9.1.3.  open . . . . . . . . . . .  40
     8.7.  PING frame  . . . . . . . . . . . . .  35
       9.1.4.  half-closed (local) . . . . . . . . . .  40
     8.8.  CONNECTION_CLOSE frame  . . . . . . .  35
       9.1.5.  half-closed (remote) . . . . . . . . . .  40
     8.9.  GOAWAY Frame  . . . . . .  35
       9.1.6.  closed . . . . . . . . . . . . . . . .  41
   9.  Packetization and Reliability . . . . . . .  36
     9.2.  Stream Identifiers . . . . . . . . .  42
     9.1.  Special Considerations for PMTU Discovery . . . . . . . .  44
   10. Streams: QUIC's Data Structuring Abstraction  . .  37
     9.3.  Stream Concurrency . . . . . .  45
     10.1.  Life of a Stream . . . . . . . . . . . . .  37
     9.4.  Sending and Receiving Data . . . . . . .  45
       10.1.1.  idle . . . . . . . .  37
   10. Flow Control . . . . . . . . . . . . . . . .  47
       10.1.2.  open . . . . . . . .  38
     10.1.  Edge Cases and Other Considerations . . . . . . . . . .  39
       10.1.1.  Mid-stream RST_STREAM . . . . . .  47
       10.1.3.  half-closed (local)  . . . . . . . . .  39
       10.1.2.  Response to a RST_STREAM . . . . . . .  48
       10.1.4.  half-closed (remote) . . . . . . .  40
       10.1.3.  Offset Increment . . . . . . . . .  48
       10.1.5.  closed . . . . . . . . .  40
       10.1.4.  BLOCKED frames . . . . . . . . . . . . . .  48
     10.2.  Stream Identifiers . . . . .  40
   11. Error Codes . . . . . . . . . . . . . .  50
     10.3.  Stream Concurrency . . . . . . . . . . .  41
   12. Security . . . . . . . .  50
     10.4.  Sending and Privacy Considerations Receiving Data . . . . . . . . . . . . .  44
     12.1.  Spoofed Ack Attack . .  51
     10.5.  Stream Prioritization  . . . . . . . . . . . . . . . . .  44
   13. IANA  51
   11. Flow Control  . . . . . . . . . . . . . . . . . . . . . . . .  52
     11.1.  Edge Cases and Other Considerations  . . . . . . . . . .  54
       11.1.1.  Mid-stream RST_STREAM  . . . . . . . . . . .  45
   14. References . . . .  54
       11.1.2.  Response to a RST_STREAM . . . . . . . . . . . . . .  54
       11.1.3.  Offset Increment . . . . . . .  45
     14.1.  Normative References . . . . . . . . . . .  54
       11.1.4.  BLOCKED frames . . . . . . .  45
     14.2.  Informative References . . . . . . . . . . . .  55
   12. Error Handling  . . . . .  45
     14.3.  URIs . . . . . . . . . . . . . . . . . .  55
     12.1.  Connection Errors  . . . . . . . .  46
   Appendix A.  Contributors . . . . . . . . . . .  55
     12.2.  Stream Errors  . . . . . . . . .  46
   Appendix B.  Acknowledgments . . . . . . . . . . . .  56
     12.3.  Error Codes  . . . . . .  46
   Appendix C.  Change Log . . . . . . . . . . . . . . . .  56
   13. Security and Privacy Considerations . . . . .  46
     C.1.  Since draft-ietf-quic-transport-00: . . . . . . . .  60
     13.1.  Spoofed ACK Attack . . .  47
     C.2.  Since draft-hamilton-quic-transport-protocol-01: . . . .  47
   Authors' Addresses . . . . . . . . . . . .  60
   14. IANA Considerations . . . . . . . . . . .  47

1.  Introduction

   QUIC is a multiplexed and secure transport protocol that runs on top
   of UDP.  QUIC builds on past transport experience and implements
   mechanisms that make it useful as a modern general-purpose transport
   protocol.  Using UDP as the substrate, QUIC seeks to be compatible
   with legacy clients and middleboxes.  QUIC authenticates all of its
   headers, preventing middleboxes and other third parties from changing
   them, and encrypts most of its headers, limiting protocol evolution
   largely to QUIC endpoints only.

   This document describes the core QUIC protocol, including the
   conceptual design, wire format, and mechanisms of the . . . . . . . . . .  61
     14.1.  QUIC protocol
   for connection establishment, stream multiplexing, stream and
   connection-level flow control, and data reliability.  Accompanying
   documents describe QUIC's loss detection and congestion control
   [QUIC-RECOVERY], and the use of TLS 1.3 for key negotiation
   [QUIC-TLS]. Transport Parameter Registry  . . . . . . . . . . .  61
   15. References  . . . . . . . . . . . . . . . . . . . . . . . . .  62
     15.1.  Normative References . . . . . . . . . . . . . . . . . .  62
     15.2.  Informative References . . . . . . . . . . . . . . . . .  63
     15.3.  URIs . . . . . . . . . . . . . . . . . . . . . . . . . .  64
   Appendix A.  Contributors . . . . . . . . . . . . . . . . . . . .  64
   Appendix B.  Acknowledgments  . . . . . . . . . . . . . . . . . .  64
   Appendix C.  Change Log . . . . . . . . . . . . . . . . . . . . .  64
     C.1.  Since draft-ietf-quic-transport-01: . . . . . . . . . . .  64
     C.2.  Since draft-ietf-quic-transport-00: . . . . . . . . . . .  66
     C.3.  Since draft-hamilton-quic-transport-protocol-01:  . . . .  67
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  67

1.  Introduction

   QUIC is a multiplexed and secure transport protocol that runs on top
   of UDP.  QUIC aims to provide a flexible set of features that allow
   it to be a general-purpose transport for multiple applications.

   QUIC implements techniques learned from experience with TCP, SCTP and
   other transport protocols.  Using UDP as the substrate, QUIC seeks to
   be compatible with legacy clients and middleboxes.  QUIC
   authenticates all of its headers and encrypts most of the data it
   exchanges, including its signaling.  This allows the protocol to
   evolve without incurring a dependency on upgrades to middleboxes.

   This document describes the core QUIC protocol, including the
   conceptual design, wire format, and mechanisms of the QUIC protocol
   for connection establishment, stream multiplexing, stream and
   connection-level flow control, and data reliability.

   Accompanying documents describe QUIC's loss detection and congestion
   control [QUIC-RECOVERY], and the use of TLS 1.3 for key negotiation
   [QUIC-TLS].

2.  Conventions and Definitions Definitions

   The words "MUST", "MUST NOT", "SHOULD", and "MAY" are used in this
   document.  It's not shouting; when they are capitalized, they have
   the special meaning defined in [RFC2119].

   Definitions of terms that are used in this document:

   Client:  The endpoint initiating a QUIC connection.

   Server:  The endpoint accepting incoming QUIC connections.

   Endpoint:  The client or server end of a connection.

   Stream:  A logical, bi-directional channel of ordered bytes within a
      QUIC connection.

   Connection:  A conversation between two QUIC endpoints with a single
      encryption context that multiplexes streams within it.

   Connection ID:  The identifier for a QUIC connection.

   QUIC packet:  A well-formed UDP payload that can be parsed by a QUIC
      receiver.  QUIC packet size in this document refers to the UDP
      payload size.

2.1.  Notational Conventions

   Packet and frame diagrams use the format described in [RFC2360]
   Section 3.1, with the following additional conventions:

   [x]  Indicates that x is optional

   {x}  Indicates that x is encrypted

   x (A)  Indicates that x is A bits long

   x (A/B/C) ...  Indicates that x is one of A, B, or C bits long

   x (*) ...  Indicates that x is variable-length

3.  A QUIC Overview

   This section briefly describes QUIC's key mechanisms and benefits.
   Key strengths of QUIC include:

   o  Low-latency connection establishment

   o  Multiplexing without head-of-line blocking

   o  Authenticated and encrypted header and payload

   o  Rich signaling for congestion control and loss recovery

   o  Stream and connection flow control

   o  Connection migration and resilience to NAT rebinding

   o  Version negotiation

3.1.  Low-Latency Connection Establishment

   QUIC relies on a combined cryptographic and transport handshake for
   setting up a secure transport connection.  QUIC connections are
   expected to commonly use 0-RTT handshakes, meaning that for most QUIC
   connections, data can be sent immediately following the client
   handshake packet, without waiting for a reply from the server.  QUIC
   provides a dedicated stream (Stream ID 1) to be used for performing
   the cryptographic handshake and QUIC options negotiation.  The format
   of the QUIC options and parameters used during negotiation are
   described in this document, but the handshake protocol that runs on
   Stream ID 1 is described in the accompanying cryptographic handshake
   draft [QUIC-TLS].

3.2.  Stream Multiplexing

   When application messages are transported over TCP, independent
   application messages can suffer from head-of-line blocking.  When an
   application multiplexes many streams atop TCP's single-bytestream
   abstraction, a loss of a TCP segment results in blocking of all
   subsequent segments until a retransmission arrives, irrespective of
   the application streams that are encapsulated in subsequent segments.
   QUIC ensures that lost packets carrying data for an individual stream
   only impact that specific stream.  Data received on other streams can
   continue to be reassembled and delivered to the application.

3.3.  Rich Signaling for Congestion Control and Loss Recovery

   QUIC's packet framing and acknowledgments carry rich information that
   help both congestion control and loss recovery in fundamental ways.
   Each QUIC packet carries a new packet number, including those
   carrying retransmitted data.  This obviates the need for a separate
   mechanism to distinguish acknowledgments for retransmissions from
   those for original transmissions, avoiding TCP's retransmission
   ambiguity problem.  QUIC acknowledgments also explicitly encode the
   delay between the receipt of a packet and its acknowledgment being
   sent, and together with the monotonically-increasing packet numbers,
   this allows for precise network roundtrip-time (RTT) calculation.
   QUIC's ACK frames support up to 256 ACK blocks, so QUIC is more
   resilient to reordering than TCP with SACK support, as well as able
   to keep more bytes on the wire when there is reordering or loss.

3.4.  Stream and Connection Flow Control

   QUIC implements stream- and connection-level flow control, closely
   following HTTP/2's flow control mechanisms.  At a high level, a QUIC
   receiver advertises the absolute byte offset within each stream up to
   which the receiver is willing to receive data.  As data is sent,
   received, and delivered on a particular stream, the receiver sends
   WINDOW_UPDATE frames that increase the advertised offset limit for
   that stream, allowing the peer to send more data on that stream.  In
   addition to this stream-level flow control, QUIC implements
   connection-level flow control to limit the aggregate buffer that a
   QUIC receiver is willing to allocate to all streams on a connection.
   Connection-level flow control works in the same way as stream-level
   flow control, but the bytes delivered and highest received offset are
   all aggregates across all streams.

3.5.  Authenticated and Encrypted Header and Payload

   TCP headers appear in plaintext on the wire and are not
   authenticated, causing a plethora of injection and header
   manipulation issues for TCP, such as receive-window manipulation and
   sequence-number overwriting.  While some of these are mechanisms used
   by middleboxes to improve TCP performance, others are active attacks.
   Even "performance-enhancing" middleboxes that routinely interpose on
   the transport state machine end up limiting the evolvability of the
   transport protocol, as has been observed in the design of MPTCP
   [RFC6824] and in its subsequent deployability issues.

   Generally, QUIC packets are always authenticated and the payload is
   typically fully encrypted.  The parts of the packet header which are
   not encrypted are still authenticated by the receiver, so as to
   thwart any packet injection or manipulation by third parties.  Some
   early handshake packets, such as the Version Negotiation packet, are
   not encrypted, but information sent in these unencrypted handshake
   packets is later verified as part of cryptographic processing.

   PUBLIC_RESET packets that reset a connection are currently not
   authenticated.

3.6.  Connection Migration and Resilience to NAT Rebinding

   QUIC connections are identified by a 64-bit Connection ID, randomly
   generated by the client.  QUIC's consistent connection ID allows
   connections to survive changes to the client's IP and port, such as
   those caused by NAT rebindings or by the client changing network
   connectivity to a new address.  QUIC provides automatic cryptographic
   verification of a rebound client, since the client continues to use
   the same session key for encrypting and decrypting packets.  The
   consistent connection ID can be used to allow migration of the
   connection to a new server IP address as well, since the Connection
   ID remains consistent across changes in the client's and the server's
   network addresses.

3.7.  Version Negotiation

   QUIC version negotiation allows for multiple versions of the protocol
   to be deployed and used concurrently.  Version negotiation is
   described in Section 7.1.

4.  Versions

   QUIC versions are identified using a 32-bit value.

   The version 0x00000000 is reserved to represent an invalid version.
   This version of the specification is identified by the number
   0x00000001.

   Versions with the most significant 16 bits of the version number
   cleared are reserved for use in future IETF consensus documents.

   Versions that follow the pattern 0x?a?a?a?a are reserved for use in
   forcing version negotiation to be exercised.  That is, any version
   number where the low four bits of all octets is 1010 (in binary).  A
   client or server MAY advertise support for any of these reserved
   versions.

   Reserved version numbers will probably never represent a real
   protocol; a client MAY use one of these version numbers with the
   expectation that the server will initiate version negotiation; a
   server MAY advertise support for one of these versions and can expect
   that clients ignore the value.

   [[RFC editor: please remove the remainder of this section before
   publication.]]

   The version number for the final version of this specification
   (0x00000001), is reserved for the version of the protocol that is
   published as an RFC.

   Version numbers used to identify IETF drafts are created by adding
   the draft number to 0xff000000.  For example, draft-ietf-quic-
   transport-13 would be identified as 0xff00000D.

   Implementors are encouraged to register version numbers of QUIC that
   they are using for private experimentation on the github wiki [4].

5.  Packet Types and Formats

   We first describe QUIC's packet types and their formats, since some
   are referenced in subsequent mechanisms.

   All numeric values are encoded in network byte order (that is, big-
   endian) and all field sizes are in bits.  When discussing individual
   bits of fields, the least significant bit is referred to as bit 0.
   Hexadecimal notation is used for describing the value of fields.

   Any QUIC packet has either a long or a short header, as indicated by
   the Header Form bit.  Long headers are expected to be used early in
   the connection before version negotiation and establishment of 1-RTT
   keys, and for public resets.  Short headers are minimal version-
   specific headers, which can be used after version negotiation and
   1-RTT keys are established.

5.1.  Long Header

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+
   |1|   Type (7)  |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                                                               |
   +                       Connection ID (64)                      +
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                       Packet Number (32)                      |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                         Version (32)                          |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                          Payload (*)                        ...
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                       Figure 1: Long Header Format

   Long headers are used for packets that are sent prior to the
   completion of version negotiation and establishment of 1-RTT keys.
   Once both conditions are met, a sender SHOULD switch to sending
   short-form headers.  While inefficient, long headers MAY be used for
   packets encrypted with 1-RTT keys.  The long form allows for special
   packets, such as the Version Negotiation and the Public Reset packets
   to be represented in this uniform fixed-length packet format.  A long
   header contains the following fields:

   Header Form:  The most significant bit (0x80) of the first octet is
      set to 1 for long headers and 0 for short headers.

   Long Packet Type:  The remaining seven bits of first octet of a long
      packet is the packet type.  This field can indicate one of 128
      packet types.  The types specified for this version are listed in
      Table 1.

   Connection ID:  Octets 1 through 8 contain the connection ID.
      Section 5.7 describes the use of this field in more detail.

   Packet Number:  Octets 9 to 12 contain the packet number.  {{packet-
      numbers} describes the use of packet numbers.

   Version:  Octets 13 to 16 contain the selected protocol version.
      This field indicates which version of QUIC is in use and
      determines how the rest of the protocol fields are interpreted.

   Payload:  Octets from 17 onwards (the rest of QUIC packet) are the
      payload of the packet.

   The following packet types are defined:

          +------+-------------------------------+-------------+
          | Type | Name                          | Section     |
          +------+-------------------------------+-------------+
          | 01   | Version Negotiation           | Section 5.3 |
          |      |                               |             |
          | 02   | Client Cleartext              | Section 5.4 |
          |      |                               |             |
          | 03   | Non-Final Server Cleartext    | Section 5.4 |
          |      |                               |             |
          | 04   | Final Server Cleartext        | Section 5.4 |
          |      |                               |             |
          | 05   | 0-RTT Encrypted               | Section 5.5 |
          |      |                               |             |
          | 06   | 1-RTT Encrypted (key phase 0) | Section 5.5 |
          |      |                               |             |
          | 07   | 1-RTT Encrypted (key phase 1) | Section 5.5 |
          |      |                               |             |
          | 08   | Public Reset                  | Section 5.6 |
          +------+-------------------------------+-------------+

                     Table 1: Long Header Packet Types

   The header form, packet type, connection ID, packet number and
   version fields of a long header packet are version-independent.  The
   types of packets defined in Table 1 are version-specific.  See
   Section 5.9 for details on how packets from different versions of
   QUIC are interpreted.

   (TODO: Should the list of packet types be version-independent?)

   The interpretation of the fields and the payload are specific to a
   version and packet type.  Type-specific semantics for this version
   are described in Section 5.3, Section 5.6, Section 5.4, and
   Section 5.5.

5.2.  Short Header

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+
   |0|C|K| Type (5)|
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                                                               |
   +                     [Connection ID (64)]                      +
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                      Packet Number (8/16/32)                ...
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                     Encrypted Payload (*)                   ...
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                       Figure 2: Short Header Format

   The short header can be used after the version and 1-RTT keys are
   negotiated.  This header form has the following fields:

   Header Form:  The most significant bit (0x80) of the first octet of a
      packet is the header form.  This bit is set to 0 for the short
      header.

   Connection ID Flag:  The second bit (0x40) of the first octet
      indicates whether the Connection ID field is present.  If set to
      1, then the Connection ID field is present; if set to 0, the
      Connection ID field is omitted.

   Key Phase Bit:  The third bit (0x20) of the first octet indicates the
      key phase, which allows a recipient of a packet to identify the
      packet protection keys that are used to protect the packet.  See
      [QUIC-TLS] for details.

   Short Packet Type:  The remaining 5 bits of the first octet include
      one of 32 packet types.  Table 2 lists the types that are defined
      for short packets.

   Connection ID:  If the Connection ID Flag is set, a connection ID
      occupies octets 1 through 8 of the packet.  See Section 5.7 for
      more details.

   Packet Number:  The length of the packet number field depends on the
      packet type.  This field can be 1, 2 or 4 octets long depending on
      the short packet type.

   Encrypted Payload:  Packets with a short header always include a
      1-RTT protected payload.

   The packet type in a short header currently determines only the size
   of the packet number field.  Additional types can be used to signal
   the presence of other fields.

                       +------+--------------------+
                       | Type | Packet Number Size |
                       +------+--------------------+
                       | 01   | 1 octet            |
                       |      |                    |
                       | 02   | 2 octets           |
                       |      |                    |
                       | 03   | 4 octets           |
                       +------+--------------------+

                    Table 2: Short Header Packet Types

   The header form, connection ID flag and connection ID of a short
   header packet are version-independent.  The remaining fields are
   specific to the selected QUIC version.  See Section 5.9 for details
   on how packets from different versions of QUIC are interpreted.

5.3.  Version Negotiation Packet

   A Version Negotiation packet is sent only by servers and is a
   response to a client packet of an unsupported version.  It uses a
   long header and contains:

   o  Octet 0: 0x81

   o  Octets 1-8: Connection ID (echoed)

   o  Octets 9-12: Packet Number (echoed)

   o  Octets 13-16: Version (echoed)

   o  Octets 17+: Payload

   The payload of the Version Negotiation packet is a list of 32-bit
   versions which the server supports, as shown below.

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                    Supported Version 1 (32)                 ...
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                   [Supported Version 2 (32)]                ...
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                                  ...
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                   [Supported Version N (32)]                ...
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                   Figure 3: Version Negotiation Packet

   See Section 7.1 for a description of the version negotiation process.

5.4.  Cleartext Packets

   Cleartext packets are sent during the handshake prior to key
   negotiation.  A Client Cleartext packet contains:

   o  Octet 0: 0x82

   o  Octets 1-8: Connection ID (initial)

   o  Octets 9-12: Packet number

   o  Octets 13-16: Version

   o  Octets 17+: Payload

   Non-Final Server Cleartext packets contain:

   o  Octet 0: 0x83

   o  Octets 1-8: Connection ID (echoed)

   o  Octets 9-12: Packet Number

   o  Octets 13-16: Version

   o  Octets 17+: Payload

   Final Server Cleartext packets contains:

   o  Octet 0: 0x84

   o  Octets 1-8: Connection ID (final)
   o  Octets 9-12: Packet Number

   o  Octets 13-16: Version

   o  Octets 17+: Payload

   The client MUST choose a random 64-bit value and use it as the
   initial Connection ID in all packets until the server replies with
   the final Connection ID.  The server echoes the client's Connection
   ID in Non-Final Server Cleartext packets.  The first Final Server
   Cleartext and all subsequent packets MUST use the final Connection
   ID, as described in Section 5.7.

   The payload of a Cleartext packet consists of a sequence of frames,
   as described in Section 6.

   (TODO: Add hash before frames.)

5.5.  Encrypted Packets

   Packets encrypted with either 0-RTT or 1-RTT keys may be sent with
   long headers.  Different packet types explicitly indicate the
   encryption level for ease of decryption.  These packets contain:

   o  Octet 0: 0x85, 0x86 or 0x87

   o  Octets 1-8: Connection ID (initial or final)

   o  Octets 9-12: Packet Number

   o  Octets 13-16: Version

   o  Octets 17+: Encrypted Payload

   A first octet of 0x85 indicates a 0-RTT packet.  After the 1-RTT keys
   are established, key phases are used by the QUIC packet protection to
   identify the correct packet protection keys.  The words "MUST", "MUST NOT", "SHOULD", initial key phase
   is 0.  See [QUIC-TLS] for more details.

   The encrypted payload is both authenticated and "MAY" are used encrypted using
   packet protection keys.  [QUIC-TLS] describes packet protection in this
   document.  It's not shouting; when they are capitalized, they have
   detail.  After decryption, the special meaning defined plaintext consists of a sequence of
   frames, as described in [RFC2119].

   Definitions Section 6.

5.6.  Public Reset Packet

   A Public Reset packet is only sent by servers and is used to abruptly
   terminate communications.  Public Reset is provided as an option of terms
   last resort for a server that are used in this document:

   o  Client: The endpoint initiating does not have access to the state of a QUIC
   connection.

   o  Server: The endpoint accepting incoming QUIC connections.

   o  Endpoint: The client  This is intended for use by a server that has lost state
   (for example, through a crash or outage).  A server end of that wishes to
   communicate a connection.

   o  Stream: fatal connection error MUST use a CONNECTION_CLOSE
   frame if it has sufficient state to do so.

   A logical, bi-directional channel Public Reset packet contains:

   o  Octet 0: 0x88

   o  Octets 1-8: Echoed data (octets 1-8 of ordered bytes within
      a QUIC connection. received packet)

   o  Connection:  Octets 9-12: Echoed data (octets 9-12 of received packet)

   o  Octets 13-16: Version

   o  Octets 17+: Public Reset Proof

   For a client that sends a connection ID on every packet, the
   Connection ID field is simply an echo of the initial Connection ID,
   and the Packet Number field includes an echo of the client's packet
   number (and, depending on the client's packet number length, 0, 2, or
   3 additional octets from the client's packet).

   A conversation between two QUIC endpoints Public Reset packet sent by a server indicates that it does not
   have the state necessary to continue with a
      single encryption context connection.  In this
   case, the server will include the fields that multiplexes streams within it.

   o  Connection ID: The identifier prove that it
   originally participated in the connection (see Section 5.6.1 for
   details).

   Upon receipt of a QUIC Public Reset packet that contains a valid proof, a
   client MUST tear down state associated with the connection.

   o  QUIC packet:  The
   client MUST then cease sending packets on the connection and SHOULD
   discard any subsequent packets that arrive.  A well-formed UDP payload Public Reset that can does
   not contain a valid proof MUST be parsed ignored.

5.6.1.  Public Reset Proof

   TODO: Details to be added.

5.7.  Connection ID

   QUIC connections are identified by their 64-bit Connection ID.  All
   long headers contain a
      QUIC receiver.  QUIC packet size in this document refers to Connection ID.  Short headers indicate the
      UDP payload size.

2.1.  Notational Conventions

   Packet and frame diagrams use
   presence of a Connection ID using the format described in [RFC2360]
   Section 3.1, with CONNECTION_ID flag.  When
   present, the following additional conventions:

   [x]  Indicates that x is optional

   {x}  Indicates that x is encrypted

   x (*) ...  Indicates that x is variable-length

   x (A/B/C) ...  Indicates that x Connection ID is one of A, B, or C bits long

3.  A QUIC Overview

   This section briefly describes QUIC's key mechanisms and benefits.
   Key strengths of QUIC include:

   o  Low-latency connection establishment

   o  Multiplexing without head-of-line blocking

   o  Authenticated and encrypted header and payload

   o  Rich signaling in the same location in all packet
   headers, making it straightforward for congestion control and loss recovery

   o  Stream middleboxes, such as load
   balancers, to locate and use it.

   When a connection flow control

   o  Connection migration is initiated, the client MUST choose a random value
   and resilience to NAT rebinding

   o  Version negotiation

3.1.  Low-Latency use it as the initial Connection Establishment

   QUIC relies on ID until the final value is
   available.  The initial Connection ID is a combined crypto and transport suggestion to the server.
   The server echoes this value in all packets until the handshake for setting
   up is
   successful (see [QUIC-TLS]).  On a secure transport connection.  QUIC connections are expected to
   commonly use 0-RTT handshakes, meaning that successful handshake, the server
   MUST select the final Connection ID for most QUIC
   connections, data can the connection and use it in
   Final Server Cleartext packets.  This final Connection ID MAY be sent immediately following the
   one proposed by the client
   handshake packet, without waiting for or MAY be a reply new server-selected value.
   All subsequent packets from the server.  QUIC
   provides a dedicated stream (Stream ID 1) server MUST contain this value.  On
   handshake completion, the client MUST switch to be used using the final
   Connection ID for performing all subsequent packets.

   Thus, all Client Cleartext packets, 0-RTT Encrypted packets, and Non-
   Final Server Cleartext packets MUST use the crypto handshake client's randomly-
   generated initial Connection ID.  Final Server Cleartext packets,
   1-RTT Encrypted packets, and QUIC options negotiation.  The format of all short-header packets MUST use the
   QUIC options
   final Connection ID.

5.8.  Packet Numbers

   The packet number is a 64-bit unsigned number and parameters is used during negotiation are described in
   this document, but as part of
   a cryptographic nonce for packet encryption.  Each endpoint maintains
   a separate packet number for sending and receiving.  The packet
   number for sending MUST increase by at least one after sending any
   packet.

   A QUIC endpoint MUST NOT reuse a packet number within the same
   connection (that is, under the same cryptographic keys).  If the
   packet number for sending reaches 2^64 - 1, the handshake protocol that runs on Stream ID 1 sender MUST close the
   connection by sending a CONNECTION_CLOSE frame with the error code
   QUIC_SEQUENCE_NUMBER_LIMIT_REACHED (connection termination is
   described in Section 7.6.)

   To reduce the accompanying crypto handshake draft [QUIC-TLS].

3.2.  Stream Multiplexing

   When application messages are transported over TCP, independent
   application messages can suffer from head-of-line blocking.  When an
   application multiplexes many streams atop TCP's single-bytestream
   abstraction, a loss of a TCP segment results in blocking number of all
   subsequent segments until a retransmission arrives, irrespective bits required to represent the packet number
   over the wire, only the least significant bits of the application streams that packet number
   are encapsulated in subsequent segments.
   QUIC ensures that lost packets carrying data for an individual stream
   only impact that specific stream.  Data received on other streams can
   continue to be reassembled and delivered to transmitted over the application.

3.3.  Rich Signaling wire, up to 32 bits.  The actual packet
   number for Congestion Control and Loss Recovery

   QUIC's each packet framing and acknowledgments carry rich information that
   help both congestion control and loss recovery in fundamental ways.
   Each QUIC is reconstructed at the receiver based on the
   largest packet carries number received on a new successfully authenticated
   packet.

   A packet number, including those
   carrying retransmitted data.  This obviates number is decoded by finding the need for a separate
   mechanism packet number value that is
   closest to distinguish acks for retransmissions from those for
   original transmissions, avoiding TCP's retransmission ambiguity
   problem.  QUIC acknowledgments also explicitly encode the delay
   between next expected packet.  The next expected packet is the receipt
   highest received packet number plus one.  For example, if the highest
   successfully authenticated packet had a packet number of 0xaa82f30e,
   then a packet and its acknowledgment being sent,
   and together with the monotonically-increasing containing a 16-bit value of 0x1f94 will be decoded as
   0xaa831f94.

   The sender MUST use a packet numbers, this
   allows for precise network roundtrip-time (RTT) calculation.  QUIC's
   ACK frames support up number size able to 256 ack blocks, so QUIC is represent more resilient to
   reordering than TCP with SACK support,
   twice as well as able to keep more
   bytes on large a range than the wire when there is reordering or loss.

3.4.  Stream and Connection Flow Control

   QUIC implements stream- difference between the largest
   acknowledged packet and connection-level flow control, closely
   following HTTP/2's flow control mechanisms.  At a high level, a QUIC
   receiver advertises packet number being sent.  A peer receiving
   the absolute byte offset within each stream up to
   which packet will then correctly decode the receiver packet number, unless the
   packet is willing delayed in transit such that it arrives after many higher-
   numbered packets have been received.  An endpoint MAY use a larger
   packet number size to receive data. safeguard against such reordering.

   As data is sent,
   received, and delivered on a particular stream, result, the receiver sends
   WINDOW_UPDATE frames that increase the advertised offset limit for
   that stream, allowing size of the peer to send packet number encoding is at least one
   more data on that stream.  In
   addition to this stream-level flow control, QUIC implements
   connection-level flow control to limit than the aggregate buffer that base 2 logarithm of the number of contiguous
   unacknowledged packet numbers, including the new packet.

   For example, if an endpoint has received an acknowledgment for packet
   0x6afa2f, sending a
   QUIC receiver packet with a number of 0x6b4264 requires a
   16-bit or larger packet number encoding; whereas a 32-bit packet
   number is willing to allocate needed to all streams on send a connection.
   Connection-level flow control works in the same way as stream-level
   flow control, but packet with a number of 0x6bc107.

5.8.1.  Initial Packet Number

   The initial value for packet number MUST be a 31-bit random number.
   That is, the bytes delivered and highest received offset are
   all aggregates across all streams.

3.5.  Authenticated and Encrypted Header value is selected from an uniform random distribution
   between 0 and Payload

   TCP headers appear in plaintext 2^31-1.  [RFC4086] provides guidance on the wire and are not
   authenticated, causing a plethora generation
   of injection and header
   manipulation issues for TCP, such as receive-window manipulation and
   sequence-number overwriting.  While some random values.

   The first set of these are mechanisms used packets sent by middleboxes to improve TCP performance, others are active attacks.
   Even "performance-enhancing" middleboxes that routinely interpose on
   the transport state machine end up limiting an endpoint MUST include the evolvability low
   32-bits of the
   transport protocol, as packet number.  Once any packet has been observed acknowledged,
   subsequent packets can use a shorter packet number encoding.

5.9.  Handling Packets from Different Versions

   Between different versions the following things are guaranteed to
   remain constant:

   o  the location of the header form flag,

   o  the location of the Connection ID flag in short headers,

   o  the design location and size of MPTCP the Connection ID field in both header
      forms,

   o  the location and size of the Version field in its subsequent deployability issues.

   Generally, QUIC packets are always authenticated long headers, and
   o  the location and size of the Packet Number field in long headers.

   Implementations MUST assume that an unsupported version uses an
   unknown packet format.  All other fields MUST be ignored when
   processing a packet that contains an unsupported version.

6.  Frames and the payload is
   typically fully encrypted. Frame Types

   The parts payload of cleartext packets and the packet header which are
   not plaintext after decryption
   of encrypted are still authenticated by the receiver, so payloads consists of a sequence of frames, as to
   thwart any shown in
   Figure 4.

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                          Frame 1 (*)                        ...
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                          Frame 2 (*)                        ...
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                                  ...
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                          Frame N (*)                        ...
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                  Figure 4: Contents of Encrypted Payload

   Encrypted payloads MUST contain at least one frame, and MAY contain
   multiple frames and multiple frame types.

   Frames MUST fit within a single QUIC packet injection or manipulation and MUST NOT span a QUIC
   packet boundary.  Each frame begins with a Frame Type byte,
   indicating its type, followed by third parties.  Some
   early handshake packets, such as the Version Negotiation packet, additional type-dependent fields:

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |   Type (8)    |           Type-Dependent Fields (*)         ...
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                      Figure 5: Generic Frame Layout

   Frame types are
   not encrypted, but information sent listed in these unencrypted handshake
   packets is later verified under crypto cover.

   PUBLIC_RESET packets Table 3.  Note that reset a connection are currently not
   authenticated.

3.6.  Connection Migration the Frame Type byte in
   STREAM and Resilience ACK frames is used to NAT Rebinding

   QUIC connections are identified by a 64-bit Connection ID, randomly
   generated by carry other frame-specific flags.
   For all other frames, the client.  QUIC's consistent connection ID allows
   connections to survive changes to Frame Type byte simply identifies the client's IP and port, such
   frame.  These frames are explained in more detail as
   those caused by NAT rebindings or by they are
   referenced later in the client changing network
   connectivity to a new address.  QUIC provides automatic cryptographic
   verification document.

           +------------------+------------------+-------------+
           | Type-field value | Frame type       | Definition  |
           +------------------+------------------+-------------+
           | 0x00             | PADDING          | Section 8.6 |
           |                  |                  |             |
           | 0x01             | RST_STREAM       | Section 8.5 |
           |                  |                  |             |
           | 0x02             | CONNECTION_CLOSE | Section 8.8 |
           |                  |                  |             |
           | 0x03             | GOAWAY           | Section 8.9 |
           |                  |                  |             |
           | 0x04             | WINDOW_UPDATE    | Section 8.3 |
           |                  |                  |             |
           | 0x05             | BLOCKED          | Section 8.4 |
           |                  |                  |             |
           | 0x07             | PING             | Section 8.7 |
           |                  |                  |             |
           | 0x40 - 0x7f      | ACK              | Section 8.2 |
           |                  |                  |             |
           | 0x80 - 0xff      | STREAM           | Section 8.1 |
           +------------------+------------------+-------------+

                           Table 3: Frame Types

7.  Life of a rebound client, since the client continues to use
   the same session key for encrypting and decrypting packets.  The
   consistent connection ID can be used to allow migration of the Connection

   A QUIC connection to is a new server IP address as well, since the Connection
   ID remains consistent across changes in the client's and the server's
   network addresses.

3.7.  Version Negotiation single conversation between two QUIC
   endpoints.  QUIC's connection establishment intertwines version
   negotiation allows for multiple versions of with the protocol
   to be deployed cryptographic and used concurrently.  Version negotiation is transport handshakes to reduce
   connection establishment latency, as described in Section 6.1.

4.  Versions

   QUIC versions are identified using 7.2.  Once
   established, a 32-bit value.

   The version 0x00000000 is reserved to represent an invalid version.
   This version of the specification is identified by the number
   0x00000001.

   Versions with the most significant 16 bits of the version number
   cleared are reserved for use in future IETF consensus documents.

   [[RFC editor: please remove the remainder of this section before
   publication.]]

   The version number for the final version of this specification
   (0x00000001), is reserved for the version of the protocol that is
   published as an RFC.

   Version numbers used connection may migrate to identify IETF drafts are created by adding
   the draft number a different IP or port at
   either endpoint, due to 0xff000000.  For example, draft-ietf-quic-
   transport-13 would be identified NAT rebinding or mobility, as 0xff00000D.

   Versions of QUIC that are used for experimentation are coordinated on
   the github wiki [4].

5.  Packet Types and Formats

   We first describe QUIC's packet types and their formats, since some
   are referenced in subsequent mechanisms.

   All numeric values are encoded in network byte order (that is, big-
   endian) and all field sizes are described in bits.  When discussing individual
   bits of fields, the least significant bit is referred to
   Section 7.5.  Finally a connection may be terminated by either
   endpoint, as bit 0.
   Hexadecimal notation is used for describing described in Section 7.6.

7.1.  Version Negotiation

   QUIC's connection establishment begins with version negotiation,
   since all communication between the value of fields.

5.1.  Common Header

   All endpoints, including packet and
   frame formats, relies on the two endpoints agreeing on a version.

   A QUIC packets begin connection begins with a QUIC Common header, as shown below.

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+
   |   Flags (8)   |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                                                               |
   +                     [Connection ID (64)]                      +
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                   Type-Dependent Fields (*)                 ...
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ client sending a handshake packet.
   The fields in details of the Common Header handshake mechanisms are the following:

   o  Flags:

      *  0x01 = VERSION.  The semantics described in Section 7.2,
   but all of this flag depends on whether the packet is initial packets sent by from the client to the server or
   MUST use the client.  A client MAY
         set this flag long header format and include exactly one proposed version.  A MUST specify the version of the
   protocol being used.

   When the server may set this flag when receives a packet from a client with the long header
   format, it compares the client-proposed client's version was
         unsupported, to the versions it supports.

   If the version selected by the client is not acceptable to the
   server, the server discards the incoming packet and may then provide responds with a
   Version Negotiation packet (Section 5.3).  This includes a list (0 or more) of
         acceptable
   versions as a part of version negotiation (described
         in Section 6.1.)

      *  0x02 = PUBLIC_RESET.  Set to indicate that the packet is server will accept.  A server MUST send a
         Public Reset packet.

      *  0x04 = KEY_PHASE.  This is used by Version
   Negotiation packet for every packet that it receives with an
   unacceptable version.

   If the QUIC packet protection contains a version that is acceptable to identify the correct packet protection keys, see [QUIC-TLS].

      *  0x08 = CONNECTION_ID.  Indicates server,
   the Connection ID is present
         in server proceeds with the packet. handshake (Section 7.2).  This must be set in all packets until
         negotiated to a different value for a given direction.  For
         instance, if a client indicates that commits
   the 5-tuple fully
         identifies server to the connection at version that the client, client selected.

   When the connection ID is
         optional in client receives a Version Negotiation packet from the server-to-client direction.

      *  0x30 = PACKET_NUMBER_SIZE.  These two bits indicate
   server, it should select an acceptable protocol version.  If the number
         of low-order-bytes of
   server lists an acceptable version, the packet number client selects that are present in
         each packet.

         +  11 indicates version
   and reattempts to create a connection using that 6 bytes of version.  Though the packet number are present

         +  10 indicates that 4 bytes
   contents of the a packet number are present

         +  01 indicates that 2 bytes of might not change in response to version
   negotiation, a client MUST increase the packet number are present

         +  00 indicates that 1 byte of the it uses on
   every packet number is present

      *  0x40 = MULTIPATH.  This bit is reserved for multipath use.

      *  0x80 is currently unused, and must be set it sends.  Packets MUST continue to 0.

   o  Connection ID: An unsigned 64-bit random number chosen by use long headers and
   MUST include the
      client, used as new negotiated protocol version.

   The client MUST use the identifier of long header format and include its selected
   version on all packets until it has 1-RTT keys and it has received a
   packet from the server which is not a Version Negotiation packet.

   A client MUST NOT change the connection.  Connection ID version it uses unless it is tied in response
   to a QUIC connection, and remains consistent across Version Negotiation packet from the server.  Once a client
      and/or
   receives a packet from the server IP and port changes.

5.1.1.  Identifying Packet Types

   While all QUIC which is not a Version Negotiation
   packet, it MUST ignore Version Negotiation packets have on the same common header, there are three
   types of packets: Regular packets,
   connection.

   Version Negotiation packets, and
   Public Reset packets. negotiation uses unprotected data.  The flowchart below shows how a packet is
   classified into one result of these three packet types:

   Check the flags
   negotiation MUST be revalidated as part of the cryptographic
   handshake (see Section 7.3.4).

7.1.1.  Using Reserved Versions

   For a server to use a new version in the common header
                 |
                 |
                 V
           +--------------+
           | PUBLIC_RESET |  YES
           | flag set?    |-------> Public Reset packet
           +--------------+
                 |
                 | NO
                 V
           +------------+         +-------------+
           | VERSION    |  YES    | Packet sent |  YES future, clients must
   correctly handle unsupported versions.  To help ensure this, a server
   SHOULD include a reserved version (see Section 4) while generating a
   Version
           | flag set?  |-------->| by server?  |--------> Negotiation
           +------------+         +-------------+          packet
                 |                       |
                 | NO                    | NO
                 V                       V
         Regular packet with       Regular packet with
     no QUIC Version in header    QUIC Version in header

                      Figure 1: Types packet.

   The design of QUIC Packets

5.1.2.  Handling Packets from Different Versions

   Version version negotiation (Section 6.1) is performed using permits a server to avoid
   maintaining state for packets that
   have it rejects in this fashion.
   However, when the VERSION bit set.  This bit is always set on packets that are
   sent prior to connection establishment.  When receiving a packet that
   is not associated with an existing connection, packets without server generates a
   VERSION bit MUST be discarded.

   Implementations MUST assume that an unsupported Version Negotiation packet, it
   cannot randomly generate a reserved version uses an
   unknown packet format.

   Between different versions number.  This is because
   the following things are guaranteed server is required to
   remain constant are:

   o  the location and size of the Flags field,

   o include the location and same value of the VERSION bit in its transport
   parameters (see Section 7.3.4).  To avoid the Flags field,
   o  the location and size of the Connection ID field, and

   o selected version number
   changing during connection establishment, the Version (or Supported Versions, Section 5.3) field.

   All other values MUST reserved version SHOULD
   be ignored when processing a packet that
   contains an unsupported version.

5.2.  Regular Packets

   Each Regular packet contains additional header fields followed by an
   encrypted payload, generated as shown below:

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                        [Version (32)]                         |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                  Packet Number (8/16/32/48)                 ...
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                    {Encrypted Payload (*)}                  ...
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                         Figure 2: Regular Packet

   The fields in a Regular packet past the Common Header are function of values that will be available to the
   following:

   o  QUIC Version:
   server when later generating its handshake packets.

   A 32-bit opaque tag pseudorandom function that represents the version of
      the QUIC protocol.  Only present in the client-to-server
      direction, takes client address information (IP and
   port) and if the VERSION flag is set.  Version Negotiation client selected version as input would ensure that
   there is
      described sufficient variability in Section 6.1.

   o  Packet Number: The lower 8, 16, 32, or 48 bits of the values that a server uses.

   A client MAY send a packet
      number, based using a reserved version number.  This can
   be used to solicit a list of supported versions from a server.

7.2.  Cryptographic and Transport Handshake

   QUIC relies on the PACKET_NUMBER_SIZE flag.  Each Regular packet
      is assigned a packet number by combined cryptographic and transport handshake to
   minimize connection establishment latency.  QUIC allocates stream 1
   for the sender.  The first packet sent
      by an endpoint MUST have a packet number cryptographic handshake.  This version of 1.

   o  Encrypted Payload: The remainder QUIC uses TLS 1.3
   [QUIC-TLS].

   QUIC provides this stream with reliable, ordered delivery of data.
   In return, the cryptographic handshake provides QUIC with:

   o  authenticated key exchange, where

      *  a Regular packet server is both
      authenticated always authenticated,

      *  a client is optionally authenticated,

      *  every connection produces distinct and encrypted once unrelated keys,

      *  keying material is usable for packet protection for both 0-RTT
         and 1-RTT packets, and

      *  1-RTT keys are
      available.  [QUIC-TLS] describes packet protection in detail.
      After decryption, have forward secrecy

   o  authenticated values for the plaintext consists transport parameters of a sequence the peer (see
      Section 7.3)

   o  authenticated confirmation of frames,
      as shown in Figure 3.  Frames are described in version negotiation (see
      Section 5.2.2.

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                          Frame 1 (*)                        ...
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                          Frame 2 (*)                        ...
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                                  ...
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                          Frame N (*)                        ...
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                  Figure 3: Contents 7.3.4)

   o  authenticated negotiation of Encrypted Payload

5.2.1.  Packet Number Compression and Reconstruction

   The complete packet number an application protocol (TLS uses
      ALPN [RFC7301] for this purpose)

   o  for the server, the ability to carry data that provides assurance
      that the client can receive packets that are addressed with the
      transport address that is claimed by the client (see Section 7.4)

   The initial cryptographic handshake message MUST be sent in a 64-bit unsigned number and single
   packet.  Any second attempt that is used as
   part of triggered by address validation
   MUST also be sent within a cryptographic nonce for packet encryption.  To reduce the
   number of bits required single packet.  This avoids having to represent the packet number over
   reassemble a message from multiple packets.  Reassembling messages
   requires that a server maintain state prior to establishing a
   connection, exposing the wire,
   at most 48 bits server to a denial of the service risk.

   The first client packet number are transmitted over of the wire.
   A QUIC endpoint cryptographic handshake protocol MUST NOT reuse a complete packet number
   fit within a 1280 octet QUIC packet.  This includes overheads that
   reduce the
   same connection (that is, under space available to the same cryptographic keys).  If the
   total number handshake protocol.

   Details of packets transmitted in this connection reaches 2^64 -
   1, the sender MUST close the connection by sending a CONNECTION_CLOSE
   frame how TLS is integrated with the error code QUIC_SEQUENCE_NUMBER_LIMIT_REACHED
   (connection termination QUIC is described provided in Section 6.4.)  For
   unambiguous reconstruction more detail
   in [QUIC-TLS].

7.3.  Transport Parameters

   During connection establishment, both endpoints make authenticated
   declarations of their transport parameters.  These declarations are
   made unilaterally by each endpoint.  Endpoints are required to comply
   with the complete packet number restrictions implied by a
   receiver from these parameters; the lower-order bits, a QUIC sender MUST NOT have more
   than 2^(packet_number_size - 2) in flight at any point in description of
   each parameter includes rules for its handling.

   The format of the
   connection.  In other words,

   o  If a sender sets PACKET_NUMBER_SIZE bits to 11, it MUST NOT have
      more than (2^46) packets in flight.

   o  If a sender sets PACKET_NUMBER_SIZE bits to 10, it MUST NOT have
      more than (2^30) packets transport parameters is the TransportParameters
   struct from Figure 6.  This is described using the presentation
   language from Section 3 of [I-D.ietf-tls-tls13].

      uint32 QuicVersion;

      enum {
         stream_fc_offset(0),
         connection_fc_offset(1),
         concurrent_streams(2),
         idle_timeout(3),
         truncate_connection_id(4),
         (65535)
      } TransportParameterId;

      struct {
         TransportParameterId parameter;
         opaque value<0..2^16-1>;
      } TransportParameter;

      struct {
         select (Handshake.msg_type) {
            case client_hello:
               QuicVersion negotiated_version;
               QuicVersion initial_version;

            case encrypted_extensions:
               QuicVersion supported_versions<2..2^8-4>;
         };
         TransportParameter parameters<30..2^16-1>;
      } TransportParameters;

                Figure 6: Definition of TransportParameters

   The "extension_data" field of the quic_transport_parameters extension
   defined in flight.

   o  If [QUIC-TLS] contains a sender sets PACKET_NUMBER_SIZE bits TransportParameters value.  TLS
   encoding rules are therefore used to 01, it MUST NOT have
      more than (2^14) packets in flight.

   o  If encode the transport parameters.

   QUIC encodes transport parameters into a sender sets PACKET_NUMBER_SIZE bits to 00, it MUST NOT have
      more than (2^6) packets sequence of octets, which
   are then included in flight.

      DISCUSS: Should the receiver be required to enforce this rule that cryptographic handshake.  Once the sender MUST NOT exceed handshake
   completes, the inflight limit?  Specifically,
      should transport parameters declared by the receiver drop packets that are received outside this
      window?
      Any truncated packet number received from a peer MUST be
      reconstructed as are
   available.  Each endpoint validates the value closest to the next expected packet
      number from that provided by its peer.

   (TODO: Clarify how packet number size can change mid-connection.)

5.2.2.  Frames and Frame Types

   A Regular packet MUST contain at least one frame, and MAY contain
   multiple frames and multiple frame types.  Frames MUST fit within a
   single QUIC packet and
   In particular, version negotiation MUST NOT span a QUIC packet boundary.  Each
   frame begins with a Frame Type byte, indicating its type, followed by
   additional type-dependent fields:

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |   Type (8)    |           Type-Dependent Fields (*)         ...
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                      Figure 4: Generic Frame Layout

   The following table lists currently be validated (see
   Section 7.3.4) before the connection establishment is considered
   properly complete.

   Definitions for each of the defined frame types.  Note that transport parameters are included
   in Section 7.3.1.

7.3.1.  Transport Parameter Definitions

   An endpoint MUST include the Frame Type byte following parameters in STREAM and ACK frames its encoded
   TransportParameters:

   stream_fc_offset (0x0000):  The initial stream level flow control
      offset parameter is used to carry other
   frame-specific flags.  For all other frames, encoded as an unsigned 32-bit integer in units
      of octets.  The sender of this parameter indicates that the Frame Type byte
   simply identifies flow
      control offset for all stream data sent toward it is this value.

   connection_fc_offset (0x0001):  The connection level flow control
      offset parameter contains the frame.  These frames are explained in more
   detail initial connection flow control
      window encoded as they are referenced later an unsigned 32-bit integer in units of 1024
      octets.  That is, the document.

        +---+------------------+------------------+--------------+
        |   | Type-field value | Frame type       | Definition   |
        +---+------------------+------------------+--------------+
        |   | "1FDOOOSS"       | STREAM           | Section 7.1  |
        |   |                  |                  |              |
        |   | "01NULLMM"       | ACK              | Section 7.2  |
        |   |                  |                  |              |
        |   | 00000000 (0x00)  | PADDING          | Section 7.7  |
        |   |                  |                  |              |
        |   | 00000001 (0x01)  | RST_STREAM       | Section 7.6  |
        |   |                  |                  |              |
        |   | 00000010 (0x02)  | CONNECTION_CLOSE | Section 7.9  |
        |   |                  |                  |              |
        |   | 00000011 (0x03)  | GOAWAY           | Section 7.10 |
        |   |                  |                  |              |
        |   | 00000100 (0x04)  | WINDOW_UPDATE    | Section 7.4  |
        |   |                  |                  |              |
        |   | 00000101 (0x05)  | BLOCKED          | Section 7.5  |
        |   |                  |                  |              |
        |   | 00000110 (0x06)  | STOP_WAITING     | Section 7.3  |
        |   |                  |                  |              |
        |   | 00000111 (0x07)  | PING             | Section 7.8  |
        +---+------------------+------------------+--------------+

5.3.  Version Negotiation Packet

   A Version Negotiation packet here is only sent multiplied by 1024 to
      determine the actual flow control offset.  The sender of this
      parameter sets the server, MUST have byte offset for connection level flow control
      to this value.  This is equivalent to sending a WINDOW_UPDATE
      (Section 8.3) for the VERSION flag set, and MUST include connection immediately after completing the full 64-bit Connection ID.
      handshake.

   concurrent_streams (0x0002):  The remainder maximum number of concurrent
      streams parameter is encoded as an unsigned 32-bit integer.

   idle_timeout (0x0003):  The idle timeout is a value in seconds that
      is encoded as an unsigned 16-bit integer.  The maximum value is
      600 seconds (10 minutes).

   An endpoint MAY use the Version Negotiation packet following transport parameters:

   truncate_connection_id (0x0004):  The truncated connection identifier
      parameter indicates that packets sent to the peer can omit the
      connection ID.  This can be used by an endpoint where the 5-tuple
      is sufficient to identify a list connection.  This parameter is zero
      length.  Omitting the parameter indicates that the endpoint relies
      on the connection ID being present in every packet.

7.3.2.  Values of 32-bit
   versions which Transport Parameters for 0-RTT

   Transport parameters from the server supports, SHOULD be remembered by the
   client for use with 0-RTT data.  A client that doesn't remember
   values from a previous connection can instead assume the following
   values: stream_fc_offset (65535), connection_fc_offset (65535),
   concurrent_streams (10), idle_timeout (600), truncate_connection_id
   (absent).

   If assumed values change as shown below.

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                    Supported Version 1 (32)                 ...
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                    Supported Version 2 (32)                 ...
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                                  ...
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                    Supported Version N (32)                 ...
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                   Figure 5: Version Negotiation Packet

5.4.  Public Reset Packet a result of completing the handshake, the
   client is expected to respect the new values.  This introduces some
   potential problems, particularly with respect to transport parameters
   that establish limits:

   o  A Public Reset packet MUST have client might exceed a newly declared connection or stream flow
      control limit with 0-RTT data.  If this occurs, the PUBLIC_RESET flag set, and client ceases
      transmission as though the flow control limit was reached.  Once
      WINDOW_UPDATE frames indicating an increase to the affected flow
      control offsets is received, the client can recommence sending.

   o  Similarly, a client might exceed the concurrent stream limit
      declared by the server.  A client MUST
   include reset any streams that
      exceed this limit.  A server SHOULD reset any streams it cannot
      handle with a code that allows the full 64-bit client to retry any application
      action bound to those streams.

   A server MAY close a connection ID.  The content of the Public
   Reset packet if remembered or assumed 0-RTT
   transport parameters cannot be supported, using an error code that is TBD.

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                    Public Reset Fields (*)                  ...
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                       Figure 6: Public Reset Packet

6.  Life of
   appropriate to the specific condition.  For example, a Connection
   QUIC_FLOW_CONTROL_RECEIVED_TOO_MUCH_DATA might be used to indicate
   that exceeding flow control limits caused the error.  A QUIC client that
   has a connection closed due to an error condition SHOULD NOT attempt
   0-RTT when attempting to create a new connection.

7.3.3.  New Transport Parameters

   New transport parameters can be used to negotiate new protocol
   behavior.  An endpoint MUST ignore transport parameters that it does
   not support.  Absence of a transport parameter therefore disables any
   optional protocol feature that is a single conversation between two QUIC
   endpoints.  QUIC's connection establishment intertwines version
   negotiation with negotiated using the crypto and parameter.

   The definition of a transport handshakes to reduce
   connection establishment latency, as described in Section 6.2.  Once
   established, parameter SHOULD include a connection may migrate to default
   value that a different IP or port at
   either endpoint, due to NAT rebinding or mobility, as described in
   Section 6.3.  Finally client can use when establishing a connection may new connection.  If
   no default is specified, the value can be terminated by either
   endpoint, as described assumed to be absent when
   attempting 0-RTT.

   New transport parameters can be registered according to the rules in
   Section 6.4.

6.1. 14.1.

7.3.4.  Version Negotiation

   QUIC's connection establishment begins with Validation

   The transport parameters include three fields that encode version negotiation,
   since all communication between
   information.  These retroactively authenticate the endpoints, including packet and
   frame formats, relies on version
   negotiation (see Section 7.1) that is performed prior to the two endpoints agreeing on a version.

   A QUIC connection begins with a client sending a handshake packet.
   cryptographic handshake.

   The details cryptographic handshake provides integrity protection for the
   negotiated version as part of the handshake mechanisms are described in transport parameters (see
   Section 6.2,
   but all 7.3).  As a result, modification of the initial version negotiation
   packets sent from the by an attacker can be detected.

   The client to includes two fields in the server
   MUST have transport parameters:

   o  The negotiated_version is the VERSION flag set, and version that was finally selected
      for use.  This MUST specify be identical to the version of value that is on the
   protocol being used.

   When
      packet that carries the ClientHello.  A server that receives a packet from a client with the VERSION flag
   set, it compares
      negotiated_version that does not match the client's version to of QUIC that is
      in use MUST terminate the versions it supports.

   If connection with a
      QUIC_VERSION_NEGOTIATION_MISMATCH error code.

   o  The initial_version is the version selected by that the client is not acceptable initially
      attempted to the
   server, use.  If the server discards the incoming packet and responds with did not send a version
      negotiation packet (Section 5.3).  This includes the VERSION
   flag and a list of versions that the server Section 5.3, this will accept. be identical to the
      negotiated_version.

   A server
   MUST send that processes all packets in a stateful fashion can
   remember how version negotiation packet was performed and validate the
   initial_version value.

   A server that does not maintain state for every packet that it receives with an unacceptable version.

   If the packet contains
   (i.e., a version that is acceptable to stateless server) uses a different process.  If the server, initial
   and negotiated versions are the same, a stateless server proceeds with can accept
   the handshake (Section 6.2).  All subsequent
   packets sent by value.

   If the initial version is different from the negotiated_version, a
   stateless server MUST check that it would have sent a version
   negotiation packet if it had received a packet with the VERSION flag unset.  This
   commits the indicated
   initial_version.  If a server to would have accepted the version that
   included in the client selected.

   When initial_version and the client receives a Version Negotiation packet value differs from the
   server, it should select an acceptable protocol version.  If value
   of negotiated_version, the server lists an acceptable version, MUST terminate the client selects connection with
   a QUIC_VERSION_NEGOTIATION_MISMATCH error.

   The server includes a list of versions that it would send in any
   version
   and resends all packets using that version.  The resent packets MUST
   use new negotiation packet numbers.  These packets MUST continue to have the
   VERSION flag set and MUST include the new negotiated protocol
   version.

   The client MUST (Section 5.3) in supported_versions.  This
   value is set the VERSION flag on all packets until even if it did not send a version negotiation concludes.  Version negotiation successfully concludes
   when the client receives a packet from the server with packet.

   The client can validate that the VERSION
   flag unset.  All subsequent packets sent by negotiated_version is included in
   the client SHOULD supported_versions list and - if version negotiation was
   performed - that it would have selected the VERSION flag unset.

   Once negotiated version.  A
   client MUST terminate the server receives connection with a packet from
   QUIC_VERSION_NEGOTIATION_MISMATCH error code if the
   negotiated_version value is not included in the supported_versions
   list.  A client MUST terminate with the VERSION
   flag unset, a
   QUIC_VERSION_NEGOTIATION_MISMATCH error code if version negotiation
   occurred but it MUST ignore would have selected a different version based on the flag in subsequently received packets.

   Version negotiation uses unprotected data.  The result
   value of the
   negotiation MUST be revalidated once the cryptographic handshake has
   completed (see Section 6.2.4).

6.2.  Crypto and supported_versions list.

7.4.  Proof of Source Address Ownership

   Transport Handshake

   QUIC relies on protocols commonly spend a combined crypto round trip checking that a
   client owns the transport address (IP and port) that it claims.
   Verifying that a client can receive packets sent to its claimed
   transport handshake address protects against spoofing of this information by
   malicious clients.

   This technique is used primarily to minimize
   connection establishment latency. avoid QUIC provides a dedicated stream
   (Stream ID 1) to be from being used for performing
   traffic amplification attack.  In such an attack, a combined connection and
   security handshake (streams are described in detail packet is sent to
   a server with spoofed source address information that identifies a
   victim.  If a server generates more or larger packets in Section 9).
   The crypto handshake protocol encapsulates and delivers QUIC's
   transport handshake response to
   that packet, the peer on the crypto stream.  The first QUIC
   packet from the client to attacker can use the server MUST carry handshake information
   as to send more data on Stream ID 1.

6.2.1.  Transport Parameters and Options

   During connection establishment, toward
   the handshake must negotiate various
   transport parameters.  The currently defined transport parameters victim than it would be able to send on its own.

   Several methods are
   described later used in QUIC to mitigate this attack.  Firstly,
   the document.

   The transport component of the initial handshake packet from a client is responsible for
   exchanging and negotiating the following parameters for padded to at least 1280
   octets.  This allows a QUIC
   connection.  Not all parameters are negotiated, some are parameters
   sent in just one direction.  These parameters and options are encoded
   and handed off server to send a similar amount of data
   without risking causing an amplication attack toward an unproven
   remote address.

   A server eventually confirms that a client has received its messages
   when the crypto cryptographic handshake protocol to successfully completes.  This might
   be transmitted insufficient, either because the server wishes to avoid the peer.

6.2.1.1.  Encoding

   (TODO: Describe format with example)

   QUIC encodes
   computational cost of completing the transport parameters and options as tag-value pairs,
   all as 7-bit ASCII strings.  QUIC parameter tags are listed below.

6.2.1.2.  Required Transport Parameters

   o  SFCW: Stream Flow Control Window.  The stream level flow control
      byte offset advertised by handshake, or it might be that
   the sender size of this parameter.

   o  CFCW: Connection Flow Control Window.  The connection level flow
      control byte offset advertised by the sender of this parameter.

   o  MSPC: Maximum number of incoming streams per connection.

   o  ICSL: Idle timeout in seconds.  The maximum value packets that are sent during the handshake is 600 seconds
      (10 minutes).

6.2.1.3.  Optional Transport Parameters

   o  TCID: Indicates support too
   large.  This is especially important for truncated Connection IDs.  If sent by 0-RTT, where the server
   might wish to provide application data traffic - such as a peer, indicates that connection IDs sent response
   to a request - in response to the peer should be
      truncated data carried in the early data from
   the client.

   To send additional data prior to 0 bytes.  This is expected completing the cryptographic
   handshake, the server then needs to commonly be used by an
      endpoint where validate that the 5-tuple client owns the
   address that it claims.

   Source address validation is sufficient to identify therefore performed during the
   establishment of a connection.
      For instance, if  TLS provides the 5-tuple tools that support
   the feature, but basic validation is unique at performed by the client, core transport
   protocol.

7.4.1.  Client Address Validation Procedure

   QUIC uses token-based address validation.  Any time the client
      MAY send a TCID parameter server wishes
   to validate a client address, it provides the server.  When client with a TCID parameter token.
   As long as the token cannot be easily guessed (see Section 7.4.3), if
   the client is
      received, an endpoint MAY choose able to return that token, it proves to not send the connection ID on
      subsequent packets.

   o  COPT: Connection Options are a repeated tag field.  The field
      contains any connection options being requested by server that
   it received the client or
      server.  These are typically used for experimentation and will
      evolve over time.  Example use cases include changing congestion
      control algorithms and parameters such as initial window.  (TODO:
      List connection options.)

6.2.2.  Proof token.

   During the processing of Source Address Ownership

   Transport protocols commonly use a roundtrip time to verify a
   client's address ownership for protection the cryptographic handshake messages from malicious clients a
   client, TLS will request that
   spoof their source address. QUIC uses make a cookie, called decision about whether to
   proceed based on the Source
   Address Token (STK), information it has.  TLS will provide QUIC with
   any token that was provided by the client.  For an initial packet,
   QUIC can decide to mostly eliminate this roundtrip of delay.

   This technique is similar abort the connection, allow it to TCP Fast Open's use of a cookie proceed, or
   request address validation.

   If QUIC decides to avoid request address validation, it provides the
   cryptographic handshake with a roundtrip token.  The contents of delay in TCP connection establishment.

   On this token are
   consumed by the server that generates the token, so there is no need
   for a new connection, single well-defined format.  A token could include information
   about the claimed client address (IP and port), a QUIC timestamp, and any
   other supplementary information the server sends an STK, which is opaque will need to
   and stored validate the
   token in the future.

   The cryptographic handshake is responsible for enacting validation by
   sending the address validation token to the client.  On  A legitimate
   client will include a subsequent connection, copy of the client
   echoes token when it in attempts to continue
   the transport handshake.  The cryptographic handshake as proof of IP ownership.

   A extracts the token then
   asks QUIC server also uses a second time whether the STK to store server-designated connection
   IDs for Stateless Rejects, to verify that an incoming connection
   contains token is acceptable.  In
   response, QUIC can either abort the correct connection ID. or permit it to
   proceed.

   A QUIC server connection MAY additionally store other data in be accepted without address validation - or with
   only limited validation - but a server SHOULD limit the STK, such as
   measured bandwidth and measured minimum RTT to data it sends
   toward an unvalidated address.  Successful completion of the client
   cryptographic handshake implicitly provides proof that may
   help the server better bootstrap a subsequent connection client has
   received packets from the
   same client. server.

7.4.2.  Address Validation on Session Resumption

   A server MAY send provide clients with an updated STK message mid-connection
   to update server state address validation token during
   one connection that can be used on a subsequent connection.  Address
   validation is stored at the especially important with 0-RTT because a server
   potentially sends a significant amount of data to a client in
   response to 0-RTT data.

   A different type of token is needed when resuming.  Unlike the STK.

   (TODO: Describe server token
   that is created during a handshake, there might be some time between
   when the token is created and client actions on STK, encoding,
   recommendations for what to put in an STK.  Describe SCUP messages.)

6.2.3.  Crypto Handshake Protocol Features

   QUIC's current crypto handshake mechanism when the token is documented in
   [QUICCrypto].  QUIC does not restrict itself to using subsequently used.
   Thus, a specific
   handshake protocol, so resumption token SHOULD include an expiration time.  It is
   also unlikely that the client port number is the details of a specific handshake protocol
   are out of this document's scope.  If not explicitly specified in same on two
   different connections; validating the
   application mapping, TLS port is assumed therefore unlikely to
   be successful.

   This token can be provided to the default crypto cryptographic handshake protocol, as described in [QUIC-TLS].  An application that
   maps to immediately
   after establishing a connection.  QUIC MAY however specify might also generate an alternative crypto handshake
   protocol to be used.

   The following list of requirements and recommendations documents
   properties of updated
   token if significant time passes or the current prototype handshake which should be
   provided by client address changes for
   any handshake protocol.

   o reason (see Section 7.5).  The crypto cryptographic handshake MUST ensure that the final negotiated key is
      distinct for every connection between two endpoints.

   o  Transport Negotiation: The crypto handshake MUST provide a
      mechanism
   responsible for providing the transport component to exchange transport
      parameters and Source Address Tokens.  To avoid downgrade attacks, client with the transport parameters sent and received MUST be verified before token.  In TLS the handshake completes successfully.

   o  Connection Establishment in 0-RTT: Since low-latency connection
      establishment
   token is a critical feature of QUIC, included in the QUIC handshake
      protocol SHOULD attempt to achieve 0-RTT connection establishment
      latency ticket that is used for repeated connections between the same endpoints.

   o  Source resumption and
   0-RTT, which is carried in a NewSessionTicket message.

7.4.3.  Address Spoofing Defense: Since QUIC handles source Validation Token Integrity

   An address
      verification, the crypto protocol SHOULD NOT impose validation token MUST be difficult to guess.  Including a separate
      source address verification mechanism.

   o  Server Config Update:
   large enough random value in the token would be sufficient, but this
   depends on the server remembering the value it sends to clients.

   A QUIC token-based scheme allows the server may refresh to offload any state
   associated with validation to the client.  For this design to work,
   the source-address token (STK) mid-connection, MUST be covered by integrity protection against
   modification or falsification by clients.  Without integrity
   protection, malicious clients could generate or guess values for
   tokens that would be accepted by the server.  Only the server
   requires access to update the information stored in integrity protection key for tokens.

   In TLS the STK at address validation token is often bundled with the client and to extend
   information that TLS requires, such as the period over which 0-RTT
      connections resumption secret.  In
   this case, adding integrity protection can be established by delegated to the client.

   o  Certificate Compression: Early QUIC experience demonstrated that
      compressing certificates exchanged during a
   cryptographic handshake protocol, avoiding redundant protection.  If
   integrity protection is valuable
      in reducing latency.  This additionally helps delegated to reduce the
      amplification attack footprint when a server sends a large set of
      certificates, which cryptographic handshake, an
   integrity failure will result in immediate cryptographic handshake
   failure.  If integrity protection is not uncommon with TLS.  The crypto protocol
      SHOULD compress certificates and any other information to minimize
      the number of packets sent during a handshake.

6.2.4.  Version Negotiation Validation

   The following information used during the performed by QUIC, QUIC handshake MUST be
   cryptographically verified by
   abort the crypto handshake protocol:

   o  Client's originally proposed version in its first packet.

   o  Server's version list in it's Version Negotiation packet, connection if one
      was sent.

6.3. the integrity check fails with a
   QUIC_ADDRESS_VALIDATION_FAILURE error code.

7.5.  Connection Migration

   QUIC connections are identified by their 64-bit Connection ID.
   QUIC's consistent connection ID allows connections to survive changes
   to the client's IP and/or port, such as those caused by client or
   server migrating to a new network.  QUIC also provides automatic
   cryptographic verification of a rebound client, since client which has changed its IP
   address because the client continues to use the same session key for
   encrypting and decrypting packets.

   DISCUSS: Simultaneous migration.  Is this reasonable?

   TODO: Perhaps move mitigation techniques from Security Considerations
   here.

6.4.

7.6.  Connection Termination

   Connections should remain open until they become idle for a pre-
   negotiated period of time.  A QUIC connection, once established, can
   be terminated in one of three ways:

   1.  Explicit Shutdown: An endpoint sends a CONNECTION_CLOSE frame to
       the peer initiating
       initiate a connection termination.  An endpoint may send a GOAWAY
       frame to the peer prior to a CONNECTION_CLOSE to indicate that
       the connection will soon be terminated.  A GOAWAY frame signals
       to the peer that any active streams will continue to be
       processed, but the sender of the GOAWAY will not initiate any
       additional streams and will not accept any new incoming streams.
       On termination of the active streams, a CONNECTION_CLOSE may be
       sent.  If an endpoint sends a CONNECTION_CLOSE frame while
       unterminated streams are active (no FIN bit or RST_STREAM frames
       have been sent or received for one or more streams), then the
       peer must assume that the streams were incomplete and were
       abnormally terminated.

   2.  Implicit Shutdown: The default idle timeout for a QUIC connection
       is 30 seconds, and is a required parameter (ICSL) in connection
       negotiation.  The maximum is 10 minutes.  If there is no network
       activity for the duration of the idle timeout, the connection is
       closed.  By default a CONNECTION_CLOSE frame will be sent.  A
       silent close option can be enabled when it is expensive to send
       an explicit close, such as mobile networks that must wake up the
       radio.

   3.  Abrupt Shutdown: An endpoint may send a Public Reset packet at
       any time during the connection to abruptly terminate an active
       connection.  A Public Reset packet SHOULD only be used as a final
       recourse.  Commonly, a public reset is expected to be sent when a
       packet on an established connection is received by an endpoint
       that is unable decrypt the packet.  For instance, if a server
       reboots mid-connection and loses any cryptographic state
       associated with open connections, and then receives a packet on
       an open connection, it should send a Public Reset packet in
       return.  (TODO: articulate rules around when a public reset
       should be sent.)

   TODO: Connections that are terminated are added to a TIME_WAIT list
   at the server, so as to absorb any straggler packets in the network.
   Discuss TIME_WAIT list.

7.

8.  Frame Types and Formats

   As described in Section 8, 6, Regular packets contain one or more
   frames.  We now describe the various QUIC frame types that can be
   present in a Regular packet.  The use of these frames and various
   frame header bits are described in subsequent sections.

7.1.

8.1.  STREAM Frame

   STREAM frames implicitly create a stream and carry stream data.  The
   type byte for a STREAM frame contains embedded flags, and is
   formatted as "1FDOOOSS".  These bits are parsed as follows:

   o  The leftmost bit must be set to 1, indicating that this is a
      STREAM frame.

   o  "F" is the FIN bit, which is used for stream termination.

   o  The "D" bit indicates whether a Data Length field is present in
      the STREAM header.  When set to 0, this field indicates that the
      Stream Data field extends to the end of the packet.  When set to
      1, this field indicates that Data Length field contains the length
      (in bytes) of the Stream Data field.  The option to omit the
      length should only be used when the packet is a "full-sized"
      packet, to avoid the risk of corruption via padding.

   o  The "OOO" bits encode the length of the Offset header field as 0,
      16, 24, 32, 40, 48, 56, or 64 bits long.

   o  The "SS" bits encode the length of the Stream ID header field as
      8, 16, 24, or 32 bits.  (DISCUSS: Consider making this 8, 16, 32,
      64.)

   A STREAM frame is shown below.

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |       [Data Length (16)]      |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                    Stream ID (8/16/24/32)                   ...
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                Offset (0/16/24/32/40/48/56/64)              ...
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                      [Data Length (16)]                       |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                        Stream Data (*)                      ...
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                       Figure 7: STREAM Frame Format

   The STREAM frame contains the following fields:

   o

   Data Length:  An optional 16-bit unsigned number specifying the
      length of the Stream Data field in this STREAM frame.  This field
      is present when the "D" bit is set to 1.

   Stream ID:  A variable-sized unsigned ID unique to this stream,
      whose size is determined by the "SS" bits in the type byte.

   o stream.

   Offset:  A variable-sized unsigned number specifying the byte offset
      in the stream for the data in this STREAM frame.  The first byte
      in the stream has an offset of 0.

   o  Data Length: An optional 16-bit unsigned number specifying  The largest offset delivered on
      a stream - the
      length sum of the Stream Data field in this STREAM frame.

   o re-constructed offset and data length -
      MUST be less than 2^64.

   Stream Data:  The bytes from the designated stream to be delivered.

   A STREAM frame MUST have either non-zero data length or the FIN bit
   set.

   Stream multiplexing is achieved by interleaving STREAM frames from
   multiple streams into one or more QUIC packets.  A single QUIC packet
   MAY bundle STREAM frames from multiple streams.

   Implementation note: One of the benefits of QUIC is avoidance of
   head-of-line blocking across multiple streams.  When a packet loss
   occurs, only streams with data in that packet are blocked waiting for
   a retransmission to be received, while other streams can continue
   making progress.  Note that when data from multiple streams is
   bundled into a single QUIC packet, loss of that packet blocks all
   those streams from making progress.  An implementation is therefore
   advised to bundle as few streams as necessary in outgoing packets
   without losing transmission efficiency to underfilled packets.

7.2.

8.2.  ACK Frame

   Receivers send ACK frames to inform senders which packets they have
   received,
   received and processed, as well as which packets are considered
   missing.  The ACK frame contains between 1 and 256 ack ACK blocks.  Ack  ACK
   blocks are ranges of acknowledged packets.

   To limit the ACK blocks to the ones those that haven't have not yet been received by the
   sender, the sender periodically sends STOP_WAITING receiver SHOULD track which ACK frames that
   signal have been
   acknowledged by its peer.  Once an ACK frame has been acknowledged,
   the receiver to stop acking packets below a specified sequence
   number, raising it acknowledges SHOULD not be acknowledged again.  To
   handle cases where the "least unacked" packet number receiver is only sending ACK frames, and hence
   will not receive acknowledgments for its packets, it MAY send a PING
   frame at most once per RTT to explicitly request acknowledgment.

   To limit receiver state or the receiver.  A
   sender size of an ACK frame thus reports only those frames, a receiver MAY
   limit the number of ACK blocks between the
   received least unacked and it sends.  A receiver can do this even
   without receiving acknowledgment of its ACK frames, with the reported largest observed packet
   numbers.  An endpoint SHOULD use
   knowledge this could cause the "Largest Acked" packet number it
   received sender to calculate the "Least Unacked Delta" value in any
   STOP_WAITING frame it might send. unnecessarily retransmit
   some data.

   Unlike TCP SACKs, QUIC ACK blocks are cumulative and therefore
   irrevocable.  Once a packet is
   acked, has been acknowledged, even if it does
   not appear in a future ACK frame, it is assumed to be acked. acknowledged.

   QUIC ACK frames contain a timestamp section with up to 255
   timestamps.  Timestamps enable better congestion control, but are not
   required for correct loss recovery, and old timestamps are less
   valuable, so it is not guaranteed every timestamp will be received by
   the sender.  A receiver SHOULD send a timestamp exactly once for each
   received packet containing retransmittable frames.  A receiver MAY
   send timestamps for non-retransmittable packets.

   A sender MAY intentionally skip packet numbers to introduce entropy
   into the connection, to avoid opportunistic ack acknowledgement attacks.
   The sender MUST close the connection if an unsent packet number is acked.
   acknowledged.  The format of the ACK frame is efficient at expressing
   blocks of missing packets; skipping packet numbers between 1 and 255
   effectively provides up to 8 bits of efficient entropy on demand,
   which should be adequate protection against most opportunistic ack
   acknowledgement attacks.

   The type byte for a ACK frame contains embedded flags, and is
   formatted as "01NULLMM".  These bits are parsed as follows:

   o  The first two bits must be set to 01 indicating that this is an
      ACK frame.

   o  The "N" bit indicates whether the frame has more than 1 ack range of
      acknowledged packets (i.e., whether the Ack ACK Block Section contains
      a Num Blocks field).

   o  The "U" bit is unused and MUST be set to zero.

   o  The two "LL" bits encode the length of the Largest Acked Acknowledged
      field as 1, 2, 4, or 6 bytes long.

   o  The two "MM" bits encode the length of the Ack ACK Block Length fields
      as 1, 2, 4, or 6 bytes long.

   An ACK frame is shown below.

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |[Num Blocks(8)]|   NumTS (8)   |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                Largest Acked Acknowledged (8/16/32/48)            ...
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |        Ack        ACK Delay (16)         |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |[Num Blocks(8)]|             Ack
   |                     ACK Block Section (*)                   ...
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |   NumTS (8)   |                     Timestamp Section (*)                   ...
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                        Figure 8: ACK Frame Format

   The fields in the ACK frame are as follows:

   o ACK frame are as follows:

   Num Blocks (opt):  An optional 8-bit unsigned value specifying the
      number of additional ACK blocks (besides the required First ACK
      Block) in this ACK frame.  Only present if the 'N' flag bit is 1.

   Num Timestamps:  An unsigned 8-bit number specifying the total number
      of <packet number, timestamp> pairs in the Timestamp Section.

   Largest Acked: Acknowledged:  A variable-sized unsigned value representing
      the largest packet number the peer is acking acknowledging in this packet
      (typically the largest that the peer has seen thus far.)

   o  Ack

   ACK Delay: Time  The time from when the largest acked, acknowledged packet, as
      indicated in the Largest Acked Acknowledged field, was received by this
      peer to when this ack ACK was sent.

   o  Num Blocks (opt): An optional 8-bit unsigned value specifying the
      number of additional ack blocks (besides the required First Ack
      Block) in this

   ACK frame.  Only present if the 'N' flag bit is 1.

   o  Ack Block Section:  Contains one or more blocks of packet numbers
      which have been successfully received.  See received, see Section 7.2.1.

   o  Num Timestamps: An unsigned 8-bit number specifying the total
      number of <packet number, timestamp> pairs in the Timestamp
      Section.

   o 8.2.1.

   Timestamp Section:  Contains zero or more timestamps reporting
      transit delay of received packets.  See Section 7.2.2.

7.2.1.  Ack 8.2.2.

8.2.1.  ACK Block Section

   The Ack ACK Block Section contains between one and 256 blocks of packet
   numbers which have been successfully received.  If the Num Blocks
   field is absent, only the First Ack ACK Block length is present in this
   section.  Otherwise, the Num Blocks field indicates how many
   additional blocks follow the First Ack ACK Block Length field.

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |              First Ack ACK Block Length (8/16/32/48)            ...
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |  [Gap 1 (8)]  |       [Ack       [ACK Block 1 Length (8/16/32/48)]     ...
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |  [Gap 2 (8)]  |       [Ack       [ACK Block 2 Length (8/16/32/48)]     ...
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                                ...
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |  [Gap N (8)]  |       [Ack       [ACK Block N Length (8/16/32/48)]     ...
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                        Figure 9: Ack ACK Block Section

   The fields in the Ack ACK Block Section are:

   o

   First Ack ACK Block Length:  An unsigned packet number delta that
      indicates the number of contiguous additional packets being acked
      acknowledged starting at the Largest Acked.

   o Acknowledged.

   Gap To Next Block (opt, repeated):  An unsigned number specifying the
      number of contiguous missing packets from the end of the previous ack
      ACK block to the start of the next.

   o  Ack  Repeated "Num Blocks" times.

   ACK Block Length (opt, repeated):  An unsigned packet number delta
      that indicates the number of contiguous packets being acked acknowledged
      starting after the end of the previous gap.  Along with the
      previous field, this field is repeated  Repeated "Num Blocks"
      times.

7.2.2.

8.2.2.  Timestamp Section

   The Timestamp Section contains between zero and 255 measurements of
   packet receive times relative to the beginning of the connection.

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+
   | [Delta LA (8)]|
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                    [First Timestamp (32)]                     |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |[Delta LA 1(8)]| [Time Since Previous 1 (16)]  |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |[Delta LA 2(8)]| [Time Since Previous 2 (16)]  |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                          ...
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |[Delta LA N(8)]| [Time Since Previous N (16)]  |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                       Figure 10: Timestamp Section

   The fields in the Timestamp Section are:

   o

   Delta Largest Acked Acknowledged (opt):  An optional 8-bit unsigned packet
      number delta specifying the delta between the largest acked acknowledged
      and the first packet whose timestamp is being reported.  In other
      words, this first packet number may be computed as (Largest Acked
      Acknowledged - Delta Largest Acked.)

   o Acknowledged.)

   First Timestamp (opt):  An optional 32-bit unsigned value specifying
      the time delta in microseconds, from the beginning of the
      connection to the arrival of the packet indicated by Delta Largest Acked.

   o
      Acknowledged.

   Delta Largest Acked 1..N (opt, repeated): (Same  This field has the same
      semantics and format as above.)
   o "Delta Largest Acknowledged".  Repeated
      "Num Timestamps - 1" times.

   Time Since Previous Timestamp 1..N(opt, repeated):  An optional
      16-bit unsigned value specifying time delta from the previous
      reported timestamp.  It is encoded in the same format as the Ack ACK
      Delay.  Along with the previous field, this field is repeated  Repeated "Num
      Timestamps" Timestamps - 1" times.

7.2.2.1.

   The timestamp section lists packet receipt timestamps ordered by
   timestamp.

8.2.2.1.  Time Format

   DISCUSS_AND_REPLACE: Perhaps make this format simpler.

   The time format used in the ACK frame above is a 16-bit unsigned
   float with 11 explicit bits of mantissa and 5 bits of explicit
   exponent, specifying time in microseconds.  The bit format is loosely
   modeled after IEEE 754.  For example, 1 microsecond is represented as
   0x1, which has an exponent of zero, presented in the 5 high order
   bits, and mantissa of 1, presented in the 11 low order bits.  When
   the explicit exponent is greater than zero, an implicit high-order
   12th bit of 1 is assumed in the mantissa.  For example, a floating
   value of 0x800 has an explicit exponent of 1, as well as an explicit
   mantissa of 0, but then has an effective mantissa of 4096 (12th bit
   is assumed to be 1).  Additionally, the actual exponent is one-less
   than the explicit exponent, and explicit exponent, and the value represents 4096
   microseconds.  Any values larger than the representable range are
   clamped to 0xFFFF.

8.2.3.  ACK Frames and Packet Protection

   ACK frames that acknowledge protected packets MUST be carried in a
   packet that has an equivalent or greater level of packet protection.

   Packets that are protected with 1-RTT keys MUST be acknowledged in
   packets that are also protected with 1-RTT keys.

   A packet that is not protected and claims to acknowledge a packet
   number that was sent with packet protection is not valid.  An
   unprotected packet that carries acknowledgments for protected packets
   MUST be discarded in its entirety.

   Packets that a client sends with 0-RTT packet protection MUST be
   acknowledged by the server in packets protected by 1-RTT keys.  This
   can mean that the value represents 4096
   microseconds.  Any values larger than client is unable to use these acknowledgments if
   the representable range server cryptographic handshake messages are
   clamped delayed or lost.
   Note that the same limitation applies to 0xFFFF.

7.3.  STOP_WAITING Frame

   The STOP_WAITING frame (type=0x06) is other data sent to inform by the peer
   server protected by the 1-RTT keys.

   Unprotected packets, such as those that it
   should not continue carry the initial
   cryptographic handshake messages, MAY be acknowledged in unprotected
   packets.  Unprotected packets are vulnerable to wait for falsification or
   modification.  Unprotected packets can be acknowledged along with packet numbers lower
   than
   protected packets in a specified value.  The protected packet.

   An endpoint SHOULD acknowledge packets containing cryptographic
   handshake messages in the next unprotected packet number that it sends,
   unless it is encoded able to acknowledge those packets in 1, 2, 4 or 6
   bytes, using later packets
   protected by 1-RTT keys.  At the same coding length as is specified for completion of the packet
   number for cryptographic
   handshake, both peers send unprotected packets containing
   cryptographic handshake messages followed by packets protected by
   1-RTT keys.  An endpoint SHOULD acknowledge the enclosing packet's header (specified in unprotected packets
   that complete the QUIC Frame
   packet's Flags field.)  The frame is as follows:

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |               Least Unacked Delta (8/16/32/48)              ...
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                   Figure 11: STOP_WAITING Frame Format

   The STOP_WAITING frame contains cryptographic handshake in a single field:

   o  Least Unacked Delta: A variable-length packet number delta with
      the same length as the packet header's protected packet,
   because its peer is guaranteed to have access to 1-RTT packet number.  Subtract it
      from
   protection keys.

   For instance, a server acknowledges a TLS ClientHello in the complete packet number of
   that carries the enclosing packet to
      determine TLS ServerHello; similarly, a client can acknowledge
   a TLS HelloRetryRequest in the least unacked packet number. containing a second TLS
   ClientHello.  The resulting least
      unacked packet number is the earliest packet for which the sender complete set of server handshake messages (TLS
   ServerHello through to Finished) might be acknowledged by a client in
   protected packets, because it is still awaiting an ack.  If certain that the receiver server is missing any packets
      earlier than this packet, the receiver SHOULD consider those
      packets able to be irrecoverably lost and MUST NOT report those packets
      as missing in subsequent acks.

7.4.
   decipher the packet.

8.3.  WINDOW_UPDATE Frame

   The WINDOW_UPDATE frame (type=0x04) informs the peer of an increase
   in an endpoint's flow control receive window.  The Stream ID can be
   zero, indicating this WINDOW_UPDATE applies to the connection level
   flow control window, window for either a single
   stream, or non-zero, indicating that the specified
   stream should increase its flow control window. entire connection as a whole.

   The frame is as follows:

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                        Stream ID (32)                         |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                                                               |
   +                        Byte                    Flow Control Offset (64)                   +
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   The fields in the WINDOW_UPDATE WINDOW_UPDATE frame are as follows:

   Stream ID:  ID of the stream whose flow control windows is being
      updated, or 0 to specify the connection-level flow control window.

   Flow Control Offset:  A 64-bit unsigned integer indicating the flow
      control offset for the given stream (for a stream ID other than 0)
      or the entire connection.

   The flow control offset is expressed in units of octets for
   individual streams (for stream identifiers other than 0).

   The connection-level flow control offset is expressed in units of
   1024 octets (for a stream identifier of 0).  That is, the connection-
   level flow control offset is determined by multiplying the encoded
   value by 1024.

   An endpoint accounts for the maximum offset of data that is sent or
   received on a stream.  Loss or reordering can mean that the maximum
   offset is greater than the total size of data received on a stream.
   Similarly, receiving STREAM frames might not increase the maximum
   offset on a stream.  A STREAM frame are as follows:

   o  Stream ID: ID of with a FIN bit set or RST_STREAM
   causes the final offset for a stream whose flow control windows is being
      updated, or 0 to specify be fixed.

   The maximum data offset on a stream MUST NOT exceed the connection-level stream flow
   control window.

   o  Byte offset: A 64-bit unsigned integer indicating the absolute
      byte offset of data which can be sent on advertised by the given stream.  In receiver.  The sum of the
      case maximum
   data offsets of all streams (including closed streams) MUST NOT
   exceed the connection level flow control, control offset advertised by the cumulative number receiver.
   An endpoint MUST terminate a connection with a
   QUIC_FLOW_CONTROL_RECEIVED_TOO_MUCH_DATA error if it receives more
   data than the largest flow control offset that it has sent, unless
   this is a result of
      bytes which can be sent on all currently open streams.

7.5. a change in the initial offsets (see
   Section 7.3.2).

8.4.  BLOCKED Frame

   A sender sends a BLOCKED frame (type=0x05) when it is ready to send
   data (and has data to send), but is currently flow control blocked.
   BLOCKED frames are purely informational frames, but extremely useful
   for debugging purposes.  A receiver of a BLOCKED frame should simply
   discard it (after possibly printing a helpful log message).  The
   frame is as follows:

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                        Stream ID (32)                         |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   The BLOCKED frame contains a single field:

   o

   Stream ID:  A 32-bit unsigned number indicating the stream which is
      flow control blocked.  A non-zero Stream ID field specifies the
      stream that is flow control blocked.  When zero, the Stream ID
      field indicates that the connection is flow control blocked.

7.6.

8.5.  RST_STREAM Frame

   An endpoint may use a RST_STREAM frame (type=0x01) to abruptly
   terminate a stream.  The frame is as follows:

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                        Error Code (32)                        |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                        Stream ID (32)                         |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                                                               |
   +                        Byte                       Final Offset (64)                       +
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                        Error Code (32)                        |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   The fields are:

   o

   Error code:  A 32-bit error code which indicates why the stream is
      being closed.

   Stream ID:  The 32-bit Stream ID of the stream being terminated.

   o  Byte

   Final offset:  A 64-bit unsigned integer indicating the absolute byte
      offset of the end of data written on this stream by the RST_STREAM
      sender.

   o  Error code: A 32-bit error code which indicates why the stream is
      being closed.

7.7.

8.6.  PADDING Frame

   The PADDING frame (type=0x00) pads a packet with 0x00 bytes.  When
   this frame is encountered, has no semantic value.  PADDING frames
   can be used to increase the rest size of the packet is expected to a packet.  Padding can be
   padding bytes.  The frame contains 0x00 bytes and extends used to
   increase an initial client packet to the end minimum required size, or to
   provide protection against traffic analysis for protected packets.

   A PADDING frame has no content.  That is, a PADDING frame consists of
   the QUIC packet.  A PADDING single octet that identifies the frame has no additional fields.

7.8. as a PADDING frame.

8.7.  PING frame

   Endpoints can use PING frames (type=0x07) to verify that their peers
   are still alive or to check reachability to the peer.  The PING frame
   contains no additional fields.  The receiver of a PING frame simply
   needs to ACK acknowledge the packet containing this frame.  The PING
   frame SHOULD be used to keep a connection alive when a stream is
   open.  The default is to send a PING frame after 15 seconds of
   quiescence.  A PING frame has no additional fields.

7.9.

8.8.  CONNECTION_CLOSE frame

   An endpoint sends a CONNECTION_CLOSE frame (type=0x02) to notify its
   peer that the connection is being closed.  If there are open streams
   that haven't been explicitly closed, they are implicitly closed when
   the connection is closed.  (Ideally, a GOAWAY frame would be sent
   with enough time that all streams are torn down.)  The frame is as
   follows:

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                        Error Code (32)                        |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |   Reason Phrase Length (16)   |      [Reason Phrase (*)]    ...
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   The fields of a CONNECTION_CLOSE frame are as follows:

   o

   Error Code:  A 32-bit error code which indicates the reason for
      closing this connection.

   o

   Reason Phrase Length:  A 16-bit unsigned number specifying the length
      of the reason phrase.  This may be zero if the sender chooses to
      not give details beyond the Error Code.

   o

   Reason Phrase:  An optional human-readable explanation for why the
      connection was closed.

7.10.

8.9.  GOAWAY Frame

   An endpoint may use uses a GOAWAY frame (type=0x03) to notify its peer
   that the connection should stop being used, and will likely be closed
   in the future. initiate a graceful
   shutdown of a connection.  The endpoints will continue using to use any
   active streams, but the sender of the GOAWAY will not initiate any additional
   streams, and will not or
   accept any new streams. additional streams beyond those indicated.  The GOAWAY
   frame is as follows:

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                        Error Code                  Largest Client Stream ID (32)                |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                     Last Good                  Largest Server Stream ID (32)                |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |   Reason Phrase Length (16)   |      [Reason Phrase (*)]    ...
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   The fields of a GOAWAY frame are as follows:

   o  Frame type: An 8-bit value that must frame are:

   Largest Client Stream ID:  The highest-numbered, client-initiated
      stream on which the endpoint sending the GOAWAY frame either sent
      data, or received and delivered data.  All higher-numbered,
      client-initiated streams (that is, odd-numbered streams) are
      implicitly reset by sending or receiving the GOAWAY frame.

   Largest Server Stream ID:  The highest-numbered, server-initiated
      stream on which the endpoint sending the GOAWAY frame either sent
      data, or received and delivered data.  All higher-numbered,
      server-initiated streams (that is, even-numbered streams) are
      implicitly reset by sending or receiving the GOAWAY frame.

   A GOAWAY frame indicates that any application layer actions on
   streams with higher numbers than those indicated can be safely
   retried because no data was exchanged.  An endpoint MUST set the
   value of the Largest Client or Server Stream ID to be at least as
   high as the highest-numbered stream on which it either sent data or
   received and delivered data to the application protocol that uses
   QUIC.

   An endpoint MAY choose a larger stream identifier if it wishes to
   allow for a number of streams to be created.  This is especially
   valuable for peer-initiated streams where packets creating new
   streams could be in transit; using a larger stream number allows
   those streams to complete.

   In addition to initiating a graceful shutdown of a connection, GOAWAY
   MAY be set sent immediately prior to 0x03 specifying sending a CONNECTION_CLOSE frame
   that this is sent as a GOAWAY frame.

   o  Error Code: A 32-bit field error code which indicates the reason
      for closing this connection.

   o  Last Good Stream ID: The last Stream ID which was accepted by the
      sender result of the GOAWAY message.  If no detecting a fatal error.  Higher-numbered
   streams were replied to, this
      value must be set to 0.

   o  Reason Phrase Length: A 16-bit unsigned number specifying the
      length of than those indicated in the reason phrase.  This may GOAWAY frame can then be zero if the sender
      chooses to not give details beyond the error code.

   o  Reason Phrase: An optional human-readable explanation for why the
      connection was closed.

8. retried.

9.  Packetization and Reliability

   The maximum packet size for QUIC Path Maximum Transmission Unit (PTMU) is the maximum size of the encrypted
   entire IP header, UDP header, and UDP payload.  The UDP payload of
   includes the resulting UDP datagram. QUIC public header, encrypted payload, and any
   authentication fields.

   All QUIC packets SHOULD be sized to fit within the path's MTU estimated PMTU to
   avoid IP fragmentation.  The
   recommended default maximum fragmentation or packet size drops.  To optimize bandwidth
   efficiency, endpoints SHOULD use Packetization Layer PMTU Discovery
   ([RFC4821]) and MAY use PMTU Discovery ([RFC1191], [RFC1981]) for
   detecting the PMTU, setting the PMTU appropriately, and storing the
   result of previous PMTU determinations.

   In the absence of these mechanisms, QUIC endpoints SHOULD NOT send IP
   packets larger than 1280 octets.  Assuming the minimum IP header
   size, this results in a UDP payload length of 1232 octets for IPv6
   and 1252 octets for IPv4.

   QUIC endpoints that implement any kind of PMTU discovery SHOULD
   maintain an estimate for each combination of local and remote IP
   addresses (as each pairing could have a different maximum MTU in the
   path).

   QUIC depends on the network path supporting a MTU of at least 1280
   octets.  This is 1350 bytes for the IPv6 minimum and
   1370 bytes for IPv4.  To optimize better, endpoints MAY use PLPMTUD
   [RFC4821] for detecting the path's therefore also supported by
   most modern IPv4 networks.  An endpoint MUST NOT reduce their MTU and setting
   below this number, even if it receives signals that indicate a
   smaller limit might exist.

   Clients MUST ensure that the maximum first packet
   size appropriately.

   A sender bundles one or more frames in a Regular QUIC packet.  A
   sender MAY bundle connection, and any set
   retransmissions of frames in those octets, has a packet.  All QUIC packets
   MUST contain total size (including IP and
   UDP headers) of at least 1280 bytes.  This might require inclusion of
   PADDING frames.  It is RECOMMENDED that a packet number and MAY contain one or more frames
   (Section 5.2.2).  Packet numbers MUST be unique within padded to exactly
   1280 octets unless the client has a connection
   and MUST NOT be reused within reasonable assurance that the same connection.  Packet numbers
   MUST be assigned to packets in
   PMTU is larger.  Sending a strictly monotonically increasing
   order.  The initial packet number used, at both of this size ensures that the client
   network path supports an MTU of this size and the
   server, helps mitigate
   amplification attacks caused by server responses toward an unverified
   client address.

   Servers MUST be 0.  That is, reject the first plaintext packet received from a client
   if it its total size is less than 1280 octets, to mitigate
   amplification attacks.

   If a QUIC endpoint determines that the PMTU between any pair of local
   and remote IP addresses has fallen below 1280 octets, it MUST
   immediately cease sending QUIC packets between those IP addresses.
   This may result in both directions abrupt termination of the connection MUST have if all pairs
   are affected.  In this case, an endpoint SHOULD send a Public Reset
   packet to indicate the failure.  The application SHOULD attempt to
   use TLS over TCP instead.

   A sender bundles one or more frames in a Regular QUIC packet number of 0. (see
   Section 6).

   A sender SHOULD minimize per-packet bandwidth and computational costs
   by bundling as many frames as possible within a QUIC packet.  A
   sender MAY wait for a short period of time to bundle multiple frames
   before sending a packet that is not maximally packed, to avoid
   sending out large numbers of small packets.  An implementation may
   use heuristics about expected application sending behavior to
   determine whether and for how long to wait.  This waiting period is
   an implementation decision, and an implementation should be careful
   to delay conservatively, since any delay is likely to increase
   application-visible latency.

   Regular QUIC packets are "containers" of frames; a packet is never
   retransmitted whole, but frames in a lost packet may be rebundled and
   transmitted in a subsequent packet as necessary.

   A packet may contain whole.  How an endpoint handles the loss of the frame
   depends on the type of the frame.  Some frames and/or application data, only are simply
   retransmitted, some of
   which may require reliability. have their contents moved to new frames, and
   others are never retransmitted.

   When a packet is detected as lost, the sender re-sends any frames as
   necessary:

   o  All application data sent in STREAM frames MUST be retransmitted,
      with one exception.
      unless the endpoint has sent a RST_STREAM for that stream.  When
      an endpoint sends a RST_STREAM frame, data outstanding on that
      stream SHOULD NOT be retransmitted, since subsequent data on this
      stream is expected to not be delivered by the receiver.

   o  ACK, STOP_WAITING,  ACK and PADDING frames MUST NOT be retransmitted.
      New  ACK frames of these types may however are
      cumulative, so new frames containing updated information will be bundled with any outgoing
      packet.
      sent as described in Section 8.2.

   o  All other frames MUST be retransmitted.

   Upon detecting losses, a sender MUST take appropriate congestion
   control action.  The details of loss detection and congestion control
   are described in [QUIC-RECOVERY].

   A packet MUST NOT be acknowledged until packet protection has been
   successfully removed and all frames contained in the packet have been
   processed.  For STREAM frames, this means the data has been queued
   (but not necessarily delivered to the application).  This also means
   that any stream state transitions triggered by STREAM or RST_STREAM
   frames have occurred.  Once the packet has been fully processed, a
   receiver acknowledges receipt of a received packet by sending one or more ACK frames
   containing the packet number of the received packet.

   To avoid perpetual acking between endpoints, a receiver creating an indefinite feedback loop, an endpoint MUST NOT
   generate an ack ACK frame in response to every a packet containing only ACK or
   PADDING frames.  However, since it

   Strategies and implications of the frequency of generating
   acknowledgments are discussed in more detail in [QUIC-RECOVERY].

9.1.  Special Considerations for PMTU Discovery

   Traditional ICMP-based path MTU discovery in IPv4 ([RFC1191] is possible
   potentially vulnerable to off-path attacks that successfully guess
   the IP/port 4-tuple and reduce the MTU to a bandwidth-inefficient
   value.  TCP connections mitigate this risk by using the (at minimum)
   8 bytes of transport header echoed in the ICMP message to validate
   the TCP sequence number as valid for the current connection.
   However, as QUIC operates over UDP, in IPv4 the echoed information
   could consist only of the IP and UDP headers, which usually has
   insufficient entropy to mitigate off-path attacks.

   As a result, endpoints that implement PMTUD in IPv4 SHOULD take steps
   to mitigate this risk.  For instance, an endpoint sends only
   packets containing ACK frame (or other non-retransmittable frames), application could:

   o  Set the receiving peer MAY send an ACK frame after IPv4 Don't Fragment (DF) bit on a reasonable number
   (currently 20) small proportion of such
      packets, so that most invalid ICMP messages arrive when there are
      no DF packets have been received.

   Strategies outstanding, and implications of can therefore be identified as
      spurious.

   o  Store additional information from the frequency of generating
   acknowledgments are discussed IP or UDP headers from DF
      packets (for example, the IP ID or UDP checksum) to further
      authenticate incoming Datagram Too Big messages.

   o  Any reduction in more detail PMTU due to a report contained in [QUIC-RECOVERY].

9. an ICMP packet
      is provisional until QUIC's loss detection algorithm determines
      that the packet is actually lost.

10.  Streams: QUIC's Data Structuring Abstraction

   Streams in QUIC provide a lightweight, ordered, and bidirectional
   byte-stream abstraction. abstraction modeled closely on HTTP/2 streams [RFC7540].

   Streams can be created either by the client or the server, can
   concurrently send data interleaved with other streams, and can be
   cancelled.  QUIC's stream lifetime is modeled
   closely after HTTP/2's [RFC7540].  Streams are independent of each
   other in delivery order.  That is, data

   Data that is received on a stream is delivered in order within that
   stream, but there is no particular delivery order across streams.
   Transmit ordering among streams is left to the implementation.  QUIC streams are considered lightweight
   in that the

   The creation and destruction of streams are expected to have minimal
   bandwidth and computational cost.  A single STREAM frame may create,
   carry data for, and terminate a stream, or a stream may last the
   entire duration of a connection.  Implementations

   Streams are therefore
   advised to keep these extremes in mind and individually flow controlled, allowing an endpoint to implement stream
   creation
   limit memory commitment and destruction to be as lightweight as possible. apply back pressure.

   An alternative view of QUIC streams is as an elastic "message"
   abstraction, similar to the way ephemeral streams are used in SST
   [SST], which may be a more appealing description for some
   applications.

9.1.

10.1.  Life of a Stream

   The semantics of QUIC streams is based on HTTP/2 streams, and the
   lifecycle of a QUIC stream therefore closely follows that of an
   HTTP/2 stream [RFC7540], with some differences to accommodate the
   possibility of out-of-order delivery due to the use of multiple
   streams in QUIC.  The lifecycle of a QUIC stream is shown in the
   following figure and described below.

                        app

                               +--------+
                 reserve_stream
                               |        |
                 ,--------------|
                               |  idle  |
                /
                               |        |
               /
                               +--------+
              V
                                    |
        +----------+
                                    | send data/
                                    |
        |          | recv data       | send data/
    ,---| reserved |------------.
                                    | recv data
    |   |          |             \   | higher stream
                                    |   +----------+              v
                                    v
    |               recv FIN/
                               +--------+ send FIN/
    |            app read_close |
                   recv FIN    | app write_close        |    send FIN
                     ,---------|  open  |-----------.
    |
                    /          |        |            \
    |
                   v           +--------+             v
    |
            +----------+            |             +----------+
            |        |   half   |            |             |   half   |
            |        |  closed  |            | send RST/   |  closed  |
            |        | (remote) |            | recv RST    |  (local) |
    |
            +----------+            |             +----------+
                |                   |                    |
                |
    |            | recv FIN/         | send FIN/         |
    |            | app write_close/  |    app read_close/ |          recv FIN/ |
                | send RST/         v          send RST/ |
                |            | recv RST     +--------+      recv RST  |
    | send RST/
                `------------->|        |<---------------'
                               | recv RST                  | closed |
    `-------------------------->|
                               |        |
                               +--------+

      send:   endpoint sends this frame
      recv:   endpoint receives this frame

      data: application data in a STREAM frame
      FIN: FIN flag in a STREAM frame
      RST: RST_STREAM frame

       app: application API signals to QUIC
       reserve_stream: causes a StreamID to be reserved for later use
       read_close: causes stream to be half-closed without receiving a FIN
       write_close: causes stream to be half-closed without sending a FIN frame

                     Figure 12: 11: Lifecycle of a stream

   Note that this diagram shows stream state transitions and the frames
   and flags that affect those transitions only.  For the purpose of
   state transitions, the FIN flag is processed as a separate event to
   the frame that bears it; a STREAM frame with the FIN flag set can
   cause two state transitions.  When the FIN bit flag is sent on an empty
   STREAM frame, the offset in the STREAM frame MUST be one greater than
   the last data byte sent on this stream.

   Both endpoints

   The recipient of a frame which changes stream state will have a subjective
   delayed view of the state of a stream that
   could be different when frames are while the frame is in transit.
   Endpoints do not coordinate the creation of streams; they are created
   unilaterally by either endpoint.  The negative consequences of a
   mismatch in states are limited to the "closed" state after sending
   RST_STREAM, where frames might be received for some time after
   closing.  Endpoints can use acknowledgments to understand the peer's
   subjective view of stream state at any given time.

   Streams have the following states:

9.1.1.

10.1.1.  idle

   All streams start in the "idle" state.

   The following transitions are valid from this state:

   Sending or receiving a STREAM frame causes the stream to become
   "open".  The stream identifier is selected as described in
   Section 9.2. 10.2.  The same STREAM frame can also cause a stream to
   immediately become "half-closed".

   An application

   Receiving a STREAM frame on a peer-initiated stream (that is, a
   packet sent by a server on an even-numbered stream or a client packet
   on an odd-numbered stream) also causes all lower-numbered "idle"
   streams in the same direction to become "open".  This could occur if
   a peer begins sending on streams in a different order to their
   creation, or it could happen if packets are lost or reordered in
   transit.

   Receiving any frame other than STREAM or RST_STREAM on a stream in
   this state MUST be treated as a connection error (Section 12) of type
   YYYY.

10.1.2.  open

   A stream in the "open" state may be used by both peers to send frames
   of any type.  In this state, a sending peer must observe the flow-
   control limit advertised by its receiving peer (Section 11).

   From this state, either endpoint can reserve send a frame with the FIN flag
   set, which causes the stream to transition into one of the "half-
   closed" states.  An endpoint sending an idle FIN flag causes the stream for later use.
   state to become "half-closed (local)".  An endpoint receiving a FIN
   flag causes the stream state to become "half-closed (remote)" once
   all preceding data has arrived.  The receiving endpoint MUST NOT
   consider the stream state to have changed until all data has arrived.

   Either endpoint can send a RST_STREAM frame from this state, causing
   it to transition immediately to "closed".

10.1.3.  half-closed (local)

   A stream that is in the "half-closed (local)" state MUST NOT be used
   for the reserved sending STREAM frames; WINDOW_UPDATE and RST_STREAM MAY be sent
   in this state.

   A stream transitions from this state to "reserved".

   Receiving any frame other than "closed" when a STREAM frame
   that contains a FIN flag is received and all prior data has arrived,
   or when either peer sends a RST_STREAM on frame.

   An endpoint that closes a stream in
   this state MUST be treated as a connection error (Section 11) of NOT send data beyond the final
   offset that it has chosen, see Section 10.1.5 for details.

   An endpoint can receive any type
   YYYY.

9.1.2.  reserved

   A stream of frame in this state has been reserved for later use by the
   application. state.  Providing
   flow-control credit using WINDOW_UPDATE frames is necessary to
   continue receiving flow-controlled frames.  In this state only the following transitions are
   possible:

   o  Sending or receiving state, a STREAM frame causes the stream to become
      "open".

   o  Sending or receiving receiver
   MAY ignore WINDOW_UPDATE frames for this stream, which might arrive
   for a short period after a RST_STREAM frame causes bearing the stream to
      become "closed".

9.1.3.  open FIN flag is sent.

10.1.4.  half-closed (remote)

   A stream in the "open" state may be that is "half-closed (remote)" is no longer being used by both peers
   the peer to send frames
   of any type. data.  In this state, a sending peer must observe sender is no longer
   obligated to maintain a receiver stream-level flow-control window.

   A stream that is in the flow-
   control limit advertised by its receiving peer (Section 10).

   From "half-closed (remote)" state will have a
   final offset for received data, see Section 10.1.5 for details.

   A stream in this state, either endpoint state can send a frame with the FIN flag
   set, which causes be used by the stream endpoint to transition into one send frames of
   any type.  In this state, the "half-
   closed" states.  An endpoint sending an FIN flag causes the continues to observe
   advertised stream-level and connection-level flow-control limits
   (Section 11).

   A stream can transition from this state to become "half-closed (local)".  An endpoint receiving "closed" by sending a
   frame that contains a FIN flag causes or when either peer sends a RST_STREAM
   frame.

10.1.5.  closed

   The "closed" state is the terminal state.

   An endpoint will learn the final offset of the data it receives on a
   stream state to become when it enters the "half-closed (remote)"; (remote)" or "closed" state.
   The final offset is carried explicitly in the
   receiving RST_STREAM frame;
   otherwise, the final offset is the offset of the end of the data
   carried in STREAM frame marked with a FIN flag.

   An endpoint MUST NOT process the FIN flag until all preceding send data on a stream at or beyond the final
   offset.

   Once a final offset for a stream has been received.

   Either endpoint can send is known, it cannot change.  If a
   RST_STREAM or STREAM frame from this state, causing
   it to transition immediately causes the final offset to "closed".

9.1.4.  half-closed (local) change for a
   stream, an endpoint SHOULD respond with a
   QUIC_STREAM_DATA_AFTER_TERMINATION error (see Section 12).  A stream that
   receiver SHOULD treat receipt of data at or beyond the final offset
   as a QUIC_STREAM_DATA_AFTER_TERMINATION error.  Generating these
   errors is in not mandatory, but only because requiring that an endpoint
   generate these errors also means that the "half-closed (local)" endpoint needs to maintain
   the final offset state MUST NOT be used for sending STREAM frames; WINDOW_UPDATE and RST_STREAM MAY be sent
   in this state.

   A stream transitions from this closed streams, which could mean a
   significant state to "closed" when commitment.

   An endpoint that receives a RST_STREAM frame that
   contains an (and which has not sent
   a FIN flag is received or when either peer sends a RST_STREAM) MUST immediately respond with a RST_STREAM frame.

   An endpoint can receive
   frame, and MUST NOT send any type of frame in this state.  Providing
   flow-control credit using WINDOW_UPDATE frames is necessary to more data on the stream.  This endpoint
   may continue receiving flow-controlled frames.  In this state, a receiver
   MAY ignore WINDOW_UPDATE frames for this stream, the stream on which might arrive
   for a short period after RST_STREAM is
   received.

   If this state is reached as a result of sending a RST_STREAM frame,
   the peer that receives the RST_STREAM frame bearing might have already sent -
   or enqueued for sending - frames on the FIN flag is sent.

9.1.5.  half-closed (remote)

   A stream that is "half-closed (remote)" is no longer being used by
   the peer to send any data.  In this state, cannot be
   withdrawn.  An endpoint MUST ignore frames that it receives on closed
   streams after it has sent a sender is no longer
   obligated RST_STREAM frame.  An endpoint MAY choose
   to maintain a receiver stream-level limit the period over which it ignores frames and treat frames
   that arrive after this time as being in error.

   STREAM frames received after sending RST_STREAM are counted toward
   the connection and stream flow-control window.

   If an endpoint windows.  Even though these
   frames might be ignored, because they are sent before their sender
   receives any STREAM the RST_STREAM, the sender will consider the frames for to count
   against its flow-control windows.

   In the absence of more specific guidance elsewhere in this document,
   implementations SHOULD treat the receipt of a stream frame that is not
   expressly permitted in
   this state, it MUST close the connection with description of a
   QUIC_STREAM_DATA_AFTER_TERMINATION state as a connection
   error (Section 11).

   A stream in this state can be used 12).  Frames of unknown types are ignored.

   (TODO: QUIC_STREAM_NO_ERROR is a special case.  Write it up.)

10.2.  Stream Identifiers

   Streams are identified by the endpoint an unsigned 32-bit integer, referred to send frames of
   any type.  In this state, as
   the endpoint continues to observe
   advertised stream-level and connection-level flow-control limits
   (Section 10).

   A stream can transition from this state to "closed" StreamID.  To avoid StreamID collision, clients MUST initiate
   streams usinge odd-numbered StreamIDs; streams initiated by sending a
   frame that contains a FIN flag or when either peer sends a RST_STREAM
   frame.

9.1.6.  closed

   The "closed" state is the terminal state.
   server MUST use even-numbered StreamIDs.

   A final offset StreamID of zero (0x0) is present in both a frame bearing a FIN flag reserved and in a
   RST_STREAM frame.  Upon sending either of these frames used for connection-level
   flow control frames (Section 11); the StreamID of zero cannot be used
   to establish a stream, new stream.

   StreamID 1 (0x1) is reserved for the endpoint cryptographic handshake.
   StreamID 1 MUST NOT send a STREAM frame carrying data beyond be used for application data, and MUST be the
   final offset.

   An
   first client-initiated stream.

   A QUIC endpoint that receives cannot reuse a StreamID on a given connection.
   Streams MUST be created in sequential order.  Open streams can be
   used in any frame for this order.  Streams that are used out of order result in
   lower-numbered streams in the same direction being counted as open.

   All streams, including stream after receiving
   either 1, count toward this limit.  Thus, a FIN flag and all
   concurrent stream data preceding it, or limit of 0 will cause a RST_STREAM
   frame, MUST quietly discard the frame, with one exception. connection to be unusable.
   Application protocols that use QUIC might require a certain minimum
   number of streams to function correctly.  If a
   STREAM frame carrying data beyond the received final offset peer advertises an
   concurrent stream limit (concurrent_streams) that is
   received, too small for
   the selected application protocol to function, an endpoint MUST close
   terminate the connection with a
   QUIC_STREAM_DATA_AFTER_TERMINATION an error of type
   QUIC_TOO_MANY_OPEN_STREAMS (Section 11). 12).

10.3.  Stream Concurrency

   An endpoint limits the number of concurrently active incoming streams
   by setting the concurrent stream limit (see Section 7.3.1) in the
   transport parameters.  The maximum concurrent streams setting is
   specific to each endpoint and applies only to the peer that receives a RST_STREAM frame (and which has not sent
   a FIN or a RST_STREAM) MUST immediately respond with a RST_STREAM
   frame,
   the setting.  That is, clients specify the maximum number of
   concurrent streams the server can initiate, and MUST NOT send any more data on servers specify the stream.  This
   maximum number of concurrent streams the client can initiate.

   Streams that are in the "open" state or in either of the "half-
   closed" states count toward the maximum number of streams that an
   endpoint
   may continue receiving is permitted to open.  Streams in any of these three states
   count toward the limit advertised in the concurrent stream limit.

   A recently closed stream MUST also be considered to count toward this
   limit until packets containing all frames required to close the
   stream have been acknowledged.  For a stream which closed cleanly,
   this means all STREAM frames have been acknowledged; for the a stream on
   which a RST_STREAM is
   received.

   If closed abruptly, this state is reached as a result of sending a RST_STREAM frame,
   the peer that receives means the RST_STREAM might have already sent - or
   enqueued for sending - frames on frame has been
   acknowledged.

   Endpoints MUST NOT exceed the stream that cannot be withdrawn. limit set by their peer.  An endpoint MUST ignore frames
   that it receives on closed streams
   after it has sent a RST_STREAM frame.  An endpoint MAY choose to STREAM frame that causes its advertised concurrent
   stream limit the period over which it ignores frames and to be exceeded MUST treat frames that
   arrive after this time as being in error.

   STREAM frames received after sending RST_STREAM are counted toward
   the connection and a stream flow-control windows.  Even though these
   frames might be ignored, because they are sent before their sender
   receives the RST_STREAM, the sender will consider the frames to count
   against its flow-control windows.

   In the absence of more specific guidance elsewhere in this document,
   implementations SHOULD treat the receipt error of type
   QUIC_TOO_MANY_OPEN_STREAMS (Section 12).

10.4.  Sending and Receiving Data

   Once a frame that stream is not
   expressly permitted in created, endpoints may use the description of a state as stream to send and
   receive data.  Each endpoint may send a connection
   error (Section 11).  Frames series of unknown types are ignored.

   (TODO: QUIC_STREAM_NO_ERROR is STREAM frames
   encapsulating data on a special case.  Write it up.)

9.2.  Stream Identifiers stream until the stream is terminated in that
   direction.  Streams are identified by an unsigned 32-bit integer, referred ordered byte-stream abstraction, and they
   have no other structure within them.  STREAM frame boundaries are not
   expected to be preserved in retransmissions from the sender or during
   delivery to as the StreamID.  To avoid StreamID collision, clients MUST initiate
   streams usinge odd-numbered StreamIDs; streams initiated by application at the
   server receiver.

   When new data is to be sent on a stream, a sender MUST use even-numbered StreamIDs.

   A StreamID set the
   encapsulating STREAM frame's offset field to the stream offset of zero (0x0) is reserved and used for connection-level
   flow control frames (Section 10); the StreamID
   first byte of zero cannot be used
   to establish a this new stream.

   StreamID 1 (0x1) data.  The first byte of data that is reserved for sent on
   a stream has the crypto handshake.  StreamID 1 stream offset 0.  The largest offset delivered on a
   stream MUST NOT be used for less than 2^64.  A receiver MUST ensure that received
   stream data is delivered to the application data, and as an ordered byte-
   stream.  Data received out of order MUST be buffered for later
   delivery, as long as it is not in violation of the first client-
   initiated stream.

   Streams receiver's flow
   control limits.

   The cryptographic handshake stream, Stream 1, MUST NOT be created subject to
   congestion control or reserved in sequential order, connection-level flow control, but MAY MUST be
   used in arbitrary order.  A QUIC
   subject to stream-level flow control.  An endpoint MUST NOT reuse send data
   on any other stream without consulting the congestion controller and
   the flow controller.

   Flow control is described in detail in Section 11, and congestion
   control is described in the companion document [QUIC-RECOVERY].

10.5.  Stream Prioritization

   Stream multiplexing has a StreamID significant effect on application
   performance if resources allocated to streams are correctly
   prioritized.  Experience with other multiplexed protocols, such as
   HTTP/2 [RFC7540], shows that effective prioritization strategies have
   a significant positive impact on performance.

   QUIC does not provide frames for exchanging priotization information.
   Instead it relies on a given connection.

9.3.  Stream Concurrency

   An endpoint can limit the number of concurrently active incoming
   streams by setting the MSPC parameter (see Section 6.2.1.2) in receiving priority information from the
   transport parameters.  The maximum concurrent streams setting is
   specific
   application that uses QUIC.  Protocols that use QUIC are able to each
   define any prioritization scheme that suits their application
   semantics.  A protocol might define explicit messages for signaling
   priority, such as those defined in HTTP/2; it could define rules that
   allow an endpoint and applies only to determine priority based on context; or it could
   leave the peer that receives determination to the setting.  That is, clients specify application.

   A QUIC implementation SHOULD provide ways in which an application can
   indicate the maximum number relative priority of
   concurrent streams.  When deciding which
   streams to dedicate resources to, QUIC SHOULD use the server can initiate, and servers specify information
   provided by the
   maximum number application.  Failure to account for priority of concurrent
   streams the client can initiate.

   Streams that are in the "open" state or result in either suboptimal performance.

   Stream priority is most relevant when deciding which stream data will
   be transmitted.  Often, there will be limits on what can be
   transmitted as a result of connection flow control or the "half-
   closed" states count toward current
   congestion controller state.

   Giving preference to the maximum number transmission of streams its own management frames
   ensures that an
   endpoint is permitted the protocol functions efficiently.  That is,
   prioritizing frames other than STREAM frames ensures that loss
   recovery, congestion control, and flow control operate effectively.

   Stream 1 MUST be prioritized over other streams prior to open.  Streams in any the
   completion of these three states
   count toward the limit advertised in cryptographic handshake.  This includes the MSPC setting.

   Endpoints MUST NOT exceed
   retransmission of the limit set by their peer.  An endpoint second flight of client handshake messages,
   that receives a is, the TLS Finished and any client authentication messages.

   STREAM frame frames that causes its advertised concurrent
   stream limit are determined to be exceeded MUST treat this as a stream error of type
   QUIC_TOO_MANY_OPEN_STREAMS (Section 11).

9.4.  Sending and Receiving Data

   Once a stream is created, endpoints may use lost SHOULD be retransmitted
   before sending new data, unless application priorities indicate
   otherwise.  Retransmitting lost STREAM frames can fill in gaps, which
   allows the stream peer to send consume already received data and
   receive data.  Each endpoint may send a series free up flow
   control window.

11.  Flow Control

   It is necessary to limit the amount of STREAM frames
   encapsulating data on a stream until the stream is terminated in that
   direction.  Streams are an ordered byte-stream abstraction, and they a sender may have no other structure within them.  STREAM frame boundaries are not
   expected
   outstanding at any time, so as to be preserved in retransmissions from the prevent a fast sender from
   overwhelming a slow receiver, or during
   delivery to the application prevent a malicious sender from
   consuming significant resources at the a receiver.

   When new data  This section
   describes QUIC's flow-control mechanisms.

   QUIC employs a credit-based flow-control scheme similar to HTTP/2's
   flow control [RFC7540].  A receiver advertises the number of octets
   it is prepared to be sent receive on a stream, given stream and for the entire
   connection.  This leads to two levels of flow control in QUIC: (i)
   Connection flow control, which prevents senders from exceeding a
   receiver's buffer capacity for the connection, and (ii) Stream flow
   control, which prevents a single stream from consuming the entire
   receive buffer for a connection.

   A receiver sends WINDOW_UPDATE frames to the sender MUST set to advertise
   additional credit by sending the
   encapsulating STREAM frame's absolute byte offset field to in the stream offset of
   or in the
   first byte of this new data. connection which it is willing to receive.

   The first byte of data that initial flow control credit is sent on
   a stream has 65536 bytes for both the stream
   and connection flow controllers.

   A receiver MAY advertise a larger offset 0. at any point in the
   connection by sending a WINDOW_UPDATE frame.  A receiver MUST ensure NOT
   renege on an advertisement; that
   received stream data is delivered to the application as is, once a receiver advertises an ordered
   byte-stream.  Data received
   offset via a WINDOW_UPDATE frame, it MUST NOT subsequently advertise
   a smaller offset.  A sender may receive WINDOW_UPDATE frames out of order
   order; a sender MUST be buffered for later
   delivery, as long as it is therefore ignore any WINDOW_UPDATE that does not in violation of
   move the receiver's flow
   control limits.

   An endpoint window forward.

   A receiver MUST NOT send any stream data without consulting the
   congestion controller and close the flow controller, connection with a
   QUIC_FLOW_CONTROL_RECEIVED_TOO_MUCH_DATA error (Section 12) if the following two
   exceptions.

   o  The crypto handshake stream, Stream 1, MUST NOT be subject to
      congestion control
   peer violates the advertised stream or connection-level connection flow control, but control
   windows.

   A sender MUST be
      subject send BLOCKED frames to stream-level flow control.

   o  An application MAY exclude specific indicate it has data to write
   but is blocked by lack of connection or stream IDs from connection-
      level flow control.  If so, these streams MUST NOT control credit.
   BLOCKED frames are expected to be subject sent infrequently in common cases,
   but they are considered useful for debugging and monitoring purposes.

   A receiver advertises credit for a stream by sending a WINDOW_UPDATE
   frame with the StreamID set appropriately.  A receiver may use the
   current offset of data consumed to
      connection-level determine the flow control.

   Flow control is described offset
   to be advertised.  A receiver MAY send copies of a WINDOW_UPDATE
   frame in detail multiple packets in Section 10, and congestion order to make sure that the sender
   receives it before running out of flow control is described in credit, even if one of
   the companion document [QUIC-RECOVERY].

10.  Flow Control

   It packets is necessary to lost.

   Connection flow control is a limit to the amount total bytes of stream data that a sender may have
   outstanding at any time, so as to prevent a fast sender from
   overwhelming a slow receiver, or to prevent a malicious sender from
   consuming significant resources at a receiver.  This section
   describes QUIC's flow-control mechanisms.

   QUIC employs a credit-based flow-control scheme similar
   sent in STREAM frames on all streams contributing to HTTP/2's connection flow control [RFC7540].
   control.  A receiver advertises the number of octets
   it is prepared to receive on a given stream and credit for a connection by sending a
   WINDOW_UPDATE frame with the entire
   connection.  This leads StreamID set to two levels zero (0x00).  A receiver
   maintains a cumulative sum of flow control in QUIC: (i)
   Connection bytes received on all streams
   contributing to connection-level flow control, which prevents senders from exceeding a
   receiver's buffer capacity to check for the connection, and (ii) Stream flow
   control, which prevents a single stream from consuming the entire
   receive buffer for a connection.
   control violations.  A receiver sends WINDOW_UPDATE frames may maintain a cumulative sum of
   bytes consumed on all contributing streams to determine the sender
   connection-level flow control offset to advertise
   additional credit, for both connection be advertised.

11.1.  Edge Cases and Other Considerations

   There are some edge cases which must be considered when dealing with
   stream and connection level flow control.  A
   receiver advertises the maximum absolute byte offset in the stream or
   in the connection which  Given enough time, both
   endpoints must agree on flow control state.  If one end believes it
   can send more than the receiver other end is willing to receive.

   The initial flow control credit is 65536 bytes for both receive, the stream
   and
   connection flow controllers.

   A receiver MAY advertise will be torn down when too much data arrives.  Conversely
   if a larger offset at any point in sender believes it is blocked, while endpoint B expects more
   data can be received, then the connection by sending a WINDOW_UPDATE frame.  A receiver MUST NOT
   renege on an advertisement; that is, once a receiver advertises an
   offset via a WINDOW_UPDATE frame, it MUST NOT subsequently advertise can be in a smaller offset.  A deadlock, with
   the sender may receive waiting for a WINDOW_UPDATE frames out which will never come.

11.1.1.  Mid-stream RST_STREAM

   On receipt of
   order; a sender MUST therefore RST_STREAM frame, an endpoint will tear down state
   for the matching stream and ignore any reductions in flow control
   credit.

   A sender MUST send BLOCKED frames to indicate it has further data to write
   but is blocked by lack arriving on that
   stream.  This could result in the endpoints getting out of connection or stream flow control credit.
   BLOCKED frames are expected to sync,
   since the RST_STREAM frame may have arrived out of order and there
   may be sent infrequently further bytes in common cases, flight.  The data sender would have counted
   the data against its connection level flow control budget, but they are considered useful for debugging and monitoring purposes.

   A receiver advertises credit for a stream by sending a WINDOW_UPDATE
   frame with the StreamID set appropriately.  A
   receiver may simply use
   the current that has not received offset these bytes would not know to determine include
   them as well.  The receiver must learn the flow control offset number of bytes that were
   sent on the stream to
   be advertised.

   Connection make the same adjustment in its connection flow control is
   controller.

   To avoid this de-synchronization, a limit to RST_STREAM sender MUST include
   the total bytes of stream data final byte offset sent on the stream in STREAM frames.  A receiver advertises credit for the RST_STREAM frame.  On
   receiving a connection
   by sending RST_STREAM frame, a WINDOW_UPDATE frame with the StreamID set to zero
   (0x00).  A receiver may maintain a cumulative sum of definitively knows how many
   bytes received
   cumulatively were sent on all streams to determine that stream before the value of RST_STREAM frame, and the connection
   flow control
   receiver MUST use the final offset to be advertised in WINDOW_UPDATE frames.  A
   sender may maintain a cumulative sum of stream data account for all bytes sent to
   impose on
   the connection flow control limit.

10.1.  Edge Cases and Other Considerations

   There are some edge cases which must be considered when dealing with stream and in its connection level flow control.  Given enough time, both
   endpoints must agree controller.

11.1.2.  Response to a RST_STREAM

   Since streams are bidirectional, a sender of a RST_STREAM needs to
   know how many bytes the peer has sent on flow control state. the stream.  If one end believes an endpoint
   receives a RST_STREAM frame and has sent neither a FIN nor a
   RST_STREAM, it
   can MUST send more than a RST_STREAM in response, bearing the other end is willing to receive, offset
   of the
   connection will be torn down last byte sent on this stream as the final offset.

11.1.3.  Offset Increment

   This document leaves when too much data arrives.  Conversely
   if and how many bytes to advertise in a sender believes it is blocked, while endpoint B expects more
   data can be received, then
   WINDOW_UPDATE to the connection can be in implementation, but offers a deadlock, few considerations.
   WINDOW_UPDATE frames constitute overhead, and therefore, sending a
   WINDOW_UPDATE with small offset increments is undesirable.  At the
   same time, sending WINDOW_UPDATES with large offset increments
   requires the sender waiting for a WINDOW_UPDATE which will never come.

10.1.1.  Mid-stream RST_STREAM

   On receipt to commit to that amount of buffer.

   Implementations must find the correct tradeoff between these sides to
   determine how large an RST_STREAM frame, offset increment to send in a WINDOW_UPDATE.

   A receiver MAY use an endpoint will tear down state
   for autotuning mechanism to tune the matching stream and ignore further data arriving size of the
   offset increment to advertise based on that
   stream.  This could result in a roundtrip time estimate and
   the endpoints getting out of sync,
   since rate at which the RST_STREAM receiving application consumes data, similar to
   common TCP implementations.

11.1.4.  BLOCKED frames

   If a sender does not receive a WINDOW_UPDATE frame may have arrived when it has run
   out of order and there
   may be further bytes in flight.  The data sender would have counted
   the data against its connection level flow control budget, but credit, the sender will be blocked and MUST send
   a
   receiver that has not received these bytes would not know BLOCKED frame.  A BLOCKED frame is expected to include
   them as well.  The be useful for
   debugging at the receiver.  A receiver must learn SHOULD NOT wait for a BLOCKED
   frame before sending a WINDOW_UPDATE, since doing so will cause at
   least one roundtrip of the number quiescence.  For smooth operation of bytes that
   were sent on the stream
   congestion controller, it is generally considered best to make not let the same adjustment in its connection
   flow controller.
   sender go into quiescence if avoidable.  To avoid this de-synchronization, blocking a RST_STREAM sender MUST include
   the final byte offset sent on the stream in sender,
   and to reasonably account for the RST_STREAM frame.  On
   receiving a RST_STREAM frame, possibiity of loss, a receiver definitively knows how many
   bytes were sent on that stream
   should send a WINDOW_UPDATE frame at least two roundtrips before it
   expects the RST_STREAM frame, and the
   receiver MUST use the final offset sender to account for all bytes sent on get blocked.

12.  Error Handling

   An endpoint that detects an error SHOULD signal the stream in existence of that
   error to its peer.  Errors can affect an entire connection level flow controller.

10.1.2.  Response to a RST_STREAM

   Since streams are bidirectional, (see
   Section 12.1), or a sender of single stream (see Section 12.2).

   The most appropriate error code (Section 12.3) SHOULD be included in
   the frame that signals the error.  Where this specification
   identifies error conditions, it also identifies the error code that
   is used.

   Public Reset is not suitable for any error that can be signaled with
   a CONNECTION_CLOSE or RST_STREAM needs to
   know how many bytes the peer has frame.  Public Reset MUST NOT be
   sent on the stream.  If by an endpoint
   receives a RST_STREAM frame and that has sent neither a FIN nor a
   RST_STREAM, it MUST the state necessary to send a RST_STREAM frame on
   the connection.

12.1.  Connection Errors

   Errors that result in response, bearing the offset connection being unusable, such as an
   obvious violation of protocol semantics or corruption of state that
   affects an entire connection, MUST be signaled using a
   CONNECTION_CLOSE frame (Section 8.8).  An endpoint MAY close the last byte sent on
   connection in this stream as manner, even if the final offset.

10.1.3.  Offset Increment

   This document leaves when and how many bytes to advertise error only affects a single
   stream.

   A CONNECTION_CLOSE frame could be sent in a
   WINDOW_UPDATE packet that is lost.  An
   endpoint SHOULD be prepared to the implementation, but offers retransmit a few considerations.
   WINDOW_UPDATE frames constitute overhead, and therefore, sending packet containing a
   WINDOW_UPDATE with small offset increments is undesirable.  At the
   same time, sending WINDOW_UPDATES with large offset increments
   requires
   CONNECTION_CLOSE frame if it receives more packets on a terminated
   connection.  Limiting the sender to commit to that amount number of buffer.
   Implementations must find retransmissions and the correct tradeoff between these sides to
   determine how large an offset increment time over
   which this final packet is sent limits the effort expended on
   terminated connections.

   An endpoint that chooses not to send in retransmit packets containing
   CONNECTION_CLOSE risks a WINDOW_UPDATE.

   A receiver MAY use an autotuning peer missing the first such packet.  The
   only mechanism available to tune the size of the
   offset increment an endpoint that continues to advertise based on receive
   data for a roundtrip time estimate and
   the rate at which the receiving application consumes data, similar to
   common TCP implementations.

10.1.4.  BLOCKED frames terminated connection is to send a Public Reset packet.

12.2.  Stream Errors

   If the error affects a sender does not receive single stream, but otherwise leaves the
   connection in a WINDOW_UPDATE frame when it has run
   out of flow control credit, recoverable state, the sender will be blocked and MUST send endpoint can sent a BLOCKED frame.  A BLOCKED RST_STREAM
   frame (Section 8.5) with an appropriate error code to terminate just
   the affected stream.

   Stream 1 is expected critical to be useful for
   debugging at the receiver.  A receiver SHOULD NOT wait for functioning of the entire connection.  If
   stream 1 is closed with either a BLOCKED RST_STREAM or STREAM frame before sending with bearing
   the FIN flag, an endpoint MUST generate a WINDOW_UPDATE, since doing so will cause
   at least one roundtrip of quiescence.  For smooth operation connection error of the
   congestion controller, it is generally considered best type
   QUIC_CLOSED_CRITICAL_STREAM.

   Some application protocols make other streams critical to that
   protocol.  An application protocol does not let need to inform the
   sender go into quiescence if avoidable.  To avoid blocking
   transport that a sender,
   and stream is critical; it can instead generate
   appropriate errors in response to reasonably account for being notified that the possibiity of loss, a receiver
   should critical
   stream is closed.

   An endpoint MAY send a WINDOW_UPDATE RST_STREAM frame at least two roundtrips before it
   expects in the sender to get blocked.

11. same packet as a
   CONNECTION_CLOSE frame.

12.3.  Error Codes

   Error codes are 32 bits long, with the first two bits indicating the
   source of the error code:

   0x0000-0x3FFF:

   0x00000000-0x3FFFFFFF:  Application-specific error codes.  Defined by
      each application-layer protocol.

   0x4000-0x7FFF:

   0x40000000-0x7FFFFFFF:  Reserved for host-local error codes.  These
      codes MUST NOT be sent to a peer, but MAY be used in API return
      codes and logs.

   0x8000-0xAFFF:

   0x80000000-0xBFFFFFFF:  QUIC transport error codes, including packet
      protection errors.  Applicable to all uses of QUIC.

   0xB000-0xFFFF:

   0xC0000000-0xFFFFFFFF:  Cryptographic error codes.  Defined by the crypto
      cryptographic handshake protocol in use.

   This section lists the defined QUIC transport error codes that may be
   used in a CONNECTION_CLOSE or RST_STREAM frame.  Error codes share a
   common code space.  Some error codes apply only to either streams or
   the entire connection and have no defined semantics in the other
   context.

   QUIC_INTERNAL_ERROR (0x8001): (0x80000001):  Connection has reached an invalid
      state.

   QUIC_STREAM_DATA_AFTER_TERMINATION (0x8002): (0x80000002):  There were data
      frames after the a fin or reset.

   QUIC_INVALID_PACKET_HEADER (0x8003): (0x80000003):  Control frame is malformed.

   QUIC_INVALID_FRAME_DATA (0x8004): (0x80000004):  Frame data is malformed.

   QUIC_MULTIPLE_TERMINATION_OFFSETS (0x80000005):  Multiple final
      offset values were received on the same stream

   QUIC_STREAM_CANCELLED (0x80000006):  The stream was cancelled

   QUIC_CLOSED_CRITICAL_STREAM (0x80000007):  A stream that is critical
      to the protocol was closed.

   QUIC_MISSING_PAYLOAD (0x8030): (0x80000030):  The packet contained no payload.

   QUIC_INVALID_STREAM_DATA (0x802e): (0x8000002E):  STREAM frame data is
      malformed.

   QUIC_OVERLAPPING_STREAM_DATA (0x8057):  STREAM frame data overlaps
      with buffered data.

   QUIC_UNENCRYPTED_STREAM_DATA (0x803d): (0x8000003D):  Received STREAM frame
      data is not encrypted.

   QUIC_MAYBE_CORRUPTED_MEMORY (0x8059): (0x80000059):  Received a frame which is
      likely the result of memory corruption.

   QUIC_INVALID_RST_STREAM_DATA (0x8006): (0x80000006):  RST_STREAM frame data is
      malformed.

   QUIC_INVALID_CONNECTION_CLOSE_DATA (0x8007): (0x80000007):  CONNECTION_CLOSE
      frame data is malformed.

   QUIC_INVALID_GOAWAY_DATA (0x8008): (0x80000008):  GOAWAY frame data is
      malformed.

   QUIC_INVALID_WINDOW_UPDATE_DATA (0x8039): (0x80000039):  WINDOW_UPDATE frame
      data is malformed.

   QUIC_INVALID_BLOCKED_DATA (0x803a): (0x8000003A):  BLOCKED frame data is
      malformed.

   QUIC_INVALID_STOP_WAITING_DATA (0x803c):  STOP_WAITING frame data is
      malformed.

   QUIC_INVALID_PATH_CLOSE_DATA (0x804e): (0x8000004E):  PATH_CLOSE frame data is
      malformed.

   QUIC_INVALID_ACK_DATA (0x8009): (0x80000009):  ACK frame data is malformed.

   QUIC_INVALID_VERSION_NEGOTIATION_PACKET (0x800a): (0x8000000A):  Version
      negotiation packet is malformed.

   QUIC_INVALID_PUBLIC_RST_PACKET (0x800b): (0x8000000b):  Public RST packet is
      malformed.

   QUIC_DECRYPTION_FAILURE (0x800c): (0x8000000c):  There was an error decrypting.

   QUIC_ENCRYPTION_FAILURE (0x800d): (0x8000000d):  There was an error encrypting.

   QUIC_PACKET_TOO_LARGE (0x800e): (0x8000000e):  The packet exceeded
      kMaxPacketSize.

   QUIC_PEER_GOING_AWAY (0x8010): (0x80000010):  The peer is going away.  May be a
      client or server.

   QUIC_INVALID_STREAM_ID (0x8011): (0x80000011):  A stream ID was invalid.

   QUIC_INVALID_PRIORITY (0x8031): (0x80000031):  A priority was invalid.

   QUIC_TOO_MANY_OPEN_STREAMS (0x8012): (0x80000012):  Too many streams already
      open.

   QUIC_TOO_MANY_AVAILABLE_STREAMS (0x804c): (0x8000004c):  The peer created too
      many available streams.

   QUIC_PUBLIC_RESET (0x8013): (0x80000013):  Received public reset for this
      connection.

   QUIC_INVALID_VERSION (0x8014): (0x80000014):  Invalid protocol version.

   QUIC_INVALID_HEADER_ID (0x8016): (0x80000016):  The Header ID for a stream was
      too far from the previous.

   QUIC_INVALID_NEGOTIATED_VALUE (0x8017): (0x80000017):  Negotiable parameter
      received during handshake had invalid value.

   QUIC_DECOMPRESSION_FAILURE (0x8018): (0x80000018):  There was an error
      decompressing data.

   QUIC_NETWORK_IDLE_TIMEOUT (0x8019): (0x80000019):  The connection timed out due
      to no network activity.

   QUIC_HANDSHAKE_TIMEOUT (0x8043): (0x80000043):  The connection timed out
      waiting for the handshake to complete.

   QUIC_ERROR_MIGRATING_ADDRESS (0x801a): (0x8000001a):  There was an error
      encountered migrating addresses.

   QUIC_ERROR_MIGRATING_PORT (0x8056): (0x80000056):  There was an error
      encountered migrating port only.

   QUIC_EMPTY_STREAM_FRAME_NO_FIN (0x8032): (0x80000032):  We received a
      STREAM_FRAME with no data and no fin flag set.

   QUIC_FLOW_CONTROL_RECEIVED_TOO_MUCH_DATA (0x803b): (0x8000003b):  The peer
      received too much data, violating flow control.

   QUIC_FLOW_CONTROL_SENT_TOO_MUCH_DATA (0x803f): (0x8000003f):  The peer sent too
      much data, violating flow control.

   QUIC_FLOW_CONTROL_INVALID_WINDOW (0x8040): (0x80000040):  The peer received an
      invalid flow control window.

   QUIC_CONNECTION_IP_POOLED (0x803e): (0x8000003e):  The connection has been IP
      pooled into an existing connection.

   QUIC_TOO_MANY_OUTSTANDING_SENT_PACKETS (0x8044): (0x80000044):  The connection
      has too many outstanding sent packets.

   QUIC_TOO_MANY_OUTSTANDING_RECEIVED_PACKETS (0x8045): (0x80000045):  The
      connection has too many outstanding received packets.

   QUIC_CONNECTION_CANCELLED (0x8046): (0x80000046):  The QUIC connection has been
      cancelled.

   QUIC_BAD_PACKET_LOSS_RATE (0x8047): (0x80000047):  Disabled QUIC because of
      high packet loss rate.

   QUIC_PUBLIC_RESETS_POST_HANDSHAKE (0x8049): (0x80000049):  Disabled QUIC
      because of too many PUBLIC_RESETs post handshake.

   QUIC_TIMEOUTS_WITH_OPEN_STREAMS (0x804a): (0x8000004a):  Disabled QUIC because
      of too many timeouts with streams open.

   QUIC_TOO_MANY_RTOS (0x8055): (0x80000055):  QUIC timed out after too many RTOs.

   QUIC_ENCRYPTION_LEVEL_INCORRECT (0x802c): (0x8000002c):  A packet was received
      with the wrong encryption level (i.e. it should have been
      encrypted but was not.)

   QUIC_VERSION_NEGOTIATION_MISMATCH (0x8037): (0x80000037):  This connection
      involved a version negotiation which appears to have been tampered
      with.

   QUIC_IP_ADDRESS_CHANGED (0x8050): (0x80000050):  IP address changed causing
      connection close.

   QUIC_ADDRESS_VALIDATION_FAILURE (0x80000051):  Client address
      validation failed.

   QUIC_TOO_MANY_FRAME_GAPS (0x805d): (0x8000005d):  Stream frames arrived too
      discontiguously so that stream sequencer buffer maintains too many
      gaps.

   QUIC_TOO_MANY_SESSIONS_ON_SERVER (0x8060): (0x80000060):  Connection closed
      because server hit max number of sessions allowed.

12.

13.  Security and Privacy Considerations

12.1.

13.1.  Spoofed Ack ACK Attack

   An attacker receives an STK from the server and then releases the IP
   address on which it received the STK.  The attacker may, in the
   future, spoof this same address (which now presumably addresses a
   different endpoint), and initiate a 0-RTT connection with a server on
   the victim's behalf.  The attacker then spoofs ACK frames to the
   server which cause the server to potentially drown the victim in
   data.

   There are two possible mitigations to this attack.  The simplest one
   is that a server can unilaterally create a gap in packet-number
   space.  In the non-attack scenario, the client will send an ack ACK frame
   with
   a the larger value for largest acked. acknowledged.  In the attack
   scenario, the attacker may ack could acknowledge a packet in the gap.  If the
   server sees an ack acknowledgment for a packet that was never sent, the
   connection can be aborted.

   The second mitigation is that the server can require that acks
   acknowledgments for sent packets match the encryption level of the
   sent packet.  This mitigation is useful if the connection has an
   ephemeral forward-
   secure forward-secure key that is generated and used for every new
   connection.  If a packet sent is encrypted with a forward-secure key,
   then any acks acknowledgments that are received for them must MUST also be
   forward-secure encrypted.  Since the attacker will not have the
   forward secure key, the attacker will not be able to generate
   forward-secure encrypted ack packets.

13. packets with ACK frames.

14.  IANA Considerations

   This document has no

14.1.  QUIC Transport Parameter Registry

   IANA actions yet.

14. [SHALL add/has added] a registry for "QUIC Transport Parameters"
   under a "QUIC Protocol" heading.

   The "QUIC Transport Parameters" registry governs a 16-bit space.
   This space is split into two spaces that are governed by different
   policies.  Values with the first byte in the range 0x00 to 0xfe (in
   hexadecimal) are assigned via the Specification Required policy
   [RFC5226].  Values with the first byte 0xff are reserved for Private
   Use [RFC5226].

   Registrations MUST include the following fields:

   Value:  The numeric value of the assignment (registrations will be
      between 0x0000 and 0xfeff).

   Parameter Name:  A short mnemonic for the parameter.

   Specification:  A reference to a publicly available specification for
      the value.

   The nominated expert(s) verify that a specification exists and is
   readily accessible.  The expert(s) are encouraged to be biased
   towards approving registrations unless they are abusive, frivolous,
   or actively harmful (not merely aesthetically displeasing, or
   architecturally dubious).

   The initial contents of this registry are shown in Table 4.

            +--------+------------------------+---------------+
            | Value  | Parameter Name         | Specification |
            +--------+------------------------+---------------+
            | 0x0000 | stream_fc_offset       | Section 7.3.1 |
            |        |                        |               |
            | 0x0001 | connection_fc_offset   | Section 7.3.1 |
            |        |                        |               |
            | 0x0002 | concurrent_streams     | Section 7.3.1 |
            |        |                        |               |
            | 0x0003 | idle_timeout           | Section 7.3.1 |
            |        |                        |               |
            | 0x0004 | truncate_connection_id | Section 7.3.1 |
            +--------+------------------------+---------------+

            Table 4: Initial QUIC Transport Parameters Entries

15.  References

14.1.

15.1.  Normative References

   [I-D.ietf-tls-tls13]
              Rescorla, E., "The Transport Layer Security (TLS) Protocol
              Version 1.3", draft-ietf-tls-tls13-19 (work in progress),
              March 2017.

   [QUIC-RECOVERY]
              Iyengar, J., Ed. and I. Swett, Ed., "QUIC Loss Detection
              and Congestion Control".

   [QUIC-TLS]
              Thomson, M., Ed. and S. Turner, Ed, Ed., "Using Transport
              Layer Security (TLS) to Secure QUIC".

   [RFC1191]  Mogul, J. and S. Deering, "Path MTU discovery", RFC 1191,
              DOI 10.17487/RFC1191, November 1990,
              <http://www.rfc-editor.org/info/rfc1191>.

   [RFC1981]  McCann, J., Deering, S., and J. Mogul, "Path MTU Discovery
              for IP version 6", RFC 1981, DOI 10.17487/RFC1981, August
              1996, <http://www.rfc-editor.org/info/rfc1981>.

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,
              <http://www.rfc-editor.org/info/rfc2119>.

   [RFC4821]  Mathis, M. and J. Heffner, "Packetization Layer Path MTU
              Discovery", RFC 4821, DOI 10.17487/RFC4821, March 2007,
              <http://www.rfc-editor.org/info/rfc4821>.

   [RFC5226]  Narten, T. and H. Alvestrand, "Guidelines for Writing an
              IANA Considerations Section in RFCs", BCP 26, RFC 5226,
              DOI 10.17487/RFC5226, May 2008,
              <http://www.rfc-editor.org/info/rfc5226>.

15.2.  Informative References

   [EARLY-DESIGN]
              Roskind, J., "QUIC: Multiplexed Transport Over UDP",
              December 2013, <https://goo.gl/dMVtFi>.

   [RFC2360]  Scott, G., "Guide for Internet Standards Writers", BCP 22,
              RFC 2360, DOI 10.17487/RFC2360, June 1998,
              <http://www.rfc-editor.org/info/rfc2360>.

   [RFC4086]  Eastlake 3rd, D., Schiller, J., and S. Crocker,
              "Randomness Requirements for Security", BCP 106, RFC 2119, 4086,
              DOI 10.17487/RFC2119, March 1997,
              <http://www.rfc-editor.org/info/rfc2119>.

   [RFC4821]  Mathis, M. 10.17487/RFC4086, June 2005,
              <http://www.rfc-editor.org/info/rfc4086>.

   [RFC6824]  Ford, A., Raiciu, C., Handley, M., and J. Heffner, "Packetization O. Bonaventure,
              "TCP Extensions for Multipath Operation with Multiple
              Addresses", RFC 6824, DOI 10.17487/RFC6824, January 2013,
              <http://www.rfc-editor.org/info/rfc6824>.

   [RFC7301]  Friedl, S., Popov, A., Langley, A., and E. Stephan,
              "Transport Layer Path MTU
              Discovery", Security (TLS) Application-Layer Protocol
              Negotiation Extension", RFC 4821, 7301, DOI 10.17487/RFC4821, March 2007,
              <http://www.rfc-editor.org/info/rfc4821>. 10.17487/RFC7301,
              July 2014, <http://www.rfc-editor.org/info/rfc7301>.

   [RFC7540]  Belshe, M., Peon, R., and M. Thomson, Ed., "Hypertext
              Transfer Protocol Version 2 (HTTP/2)", RFC 7540,
              DOI 10.17487/RFC7540, May 2015,
              <http://www.rfc-editor.org/info/rfc7540>.

14.2.  Informative References

   [EARLY-DESIGN]
              Roskind, J., "QUIC: Multiplexed Transport Over UDP",
              December 2013, <https://goo.gl/dMVtFi>.

   [QUIC-HTTP]
              Bishop, M., Ed., "Hypertext Transfer Protocol (HTTP) over
              QUIC".

   [QUICCrypto]
              Langley, A. M. Thomson, Ed., "Hypertext
              Transfer Protocol Version 2 (HTTP/2)", RFC 7540,
              DOI 10.17487/RFC7540, May 2015,
              <http://www.rfc-editor.org/info/rfc7540>.

   [SST]      Ford, B., "Structured Streams: A New Transport
              Abstraction", DOI 10.1145/1282427.1282421, ACM
              SIGCOMM Computer Communication Review Volume 37 Issue 4,
              October 2007.

15.3.  URIs

   [1] https://github.com/quicwg/base-drafts/wiki/QUIC-Versions

Appendix A.  Contributors

   The original authors of this specification were Ryan Hamilton, Jana
   Iyengar, Ian Swett, and Alyssa Wilk.

   The original design and rationale behind this protocol draw
   significantly from work by Jim Roskind [EARLY-DESIGN].  In
   alphabetical order, the contributors to the pre-IETF QUIC project at
   Google are: Britt Cyr, Jeremy Dorfman, Ryan Hamilton, Jana Iyengar,
   Fedor Kouranov, Charles Krasic, Jo Kulik, Adam Langley, Jim Roskind,
   Robbie Shade, Satyam Shekhar, Cherie Shi, Ian Swett, Raman Tenneti,
   Victor Vasiliev, Antonio Vicente, Patrik Westin, Alyssa Wilk, Dale
   Worley, Fan Yang, Dan Zhang, Daniel Ziegler.

Appendix B.  Acknowledgments

   Special thanks are due to the following for helping shape pre-IETF
   QUIC and its deployment: Chris Bentzel, Misha Efimov, Roberto Peon,
   Alistair Riddoch, Siddharth Vijayakrishnan, and Assar Westerlund.

   This document has benefited immensely from various private
   discussions and public ones on the quic@ietf.org and proto-
   quic@chromium.org mailing lists.  Our thanks to all.

Appendix C.  Change Log

      *RFC Editor's Note:* Please remove this section prior to
      publication of a final version of this document.

   Issue and pull request numbers are listed with a leading octothorp.

C.1.  Since draft-ietf-quic-transport-01:

   o  Defined short and long packet headers (#40, #148, #361)

   o  Defined a versioning scheme and W. Chang, "QUIC Crypto", May 2016,
              <http://goo.gl/OuVSxa>.

   [RFC2360]  Scott, G., "Guide stable fields (#51, #361)

   o  Define reserved version values for Internet Standards Writers", BCP 22,
              RFC 2360, DOI 10.17487/RFC2360, June 1998,
              <http://www.rfc-editor.org/info/rfc2360>.

   [SST]      Ford, B., "Structured Streams: A New Transport
              Abstraction", ACM SIGCOMM 2007 , August 2007.

14.3.  URIs

   [1] https://github.com/quicwg/base-drafts/wiki/QUIC-Versions

Appendix A.  Contributors "greasing" negotiation (#112,
      #278)

   o  The original authors of this specification were Ryan Hamilton, Jana
   Iyengar, Ian Swett, initial packet number is randomized (#35, #283)

   o  Narrow the packet number encoding range requirement (#67, #286,
      #299, #323, #356)

   o  Defined client address validation (#52, #118, #120, #275)

   o  Define transport parameters as a TLS extension (#122)

   o  SCUP and Alyssa Wilk. COPT parameters are no longer valid (#116, #117)

   o  Transport parameters for 0-RTT are either remembered from before,
      or assume default values (#126)

   o  The original design server chooses connection IDs in its final flight (#119, #349,
      #361)

   o  The server echoes the Connection ID and rationale behind this protocol draw
   significantly packet number fields when
      sending a Version Negotiation packet (#133, #295, #244)

   o  Definied a minimum packet size for the initial handshake packet
      from work by Jim Roskind [EARLY-DESIGN].  In
   alphabetical order, the contributors to client (#69, #136, #139, #164)

   o  Path MTU Discovery (#64, #106)

   o  The initial handshake packet from the client needs to fit in a
      single packet (#338)

   o  Forbid acknowledgment of packets containing only ACK and PADDING
      (#291)

   o  Require that frames are processed when packets are acknowledged
      (#381, #341)

   o  Removed the STOP_WAITING frame (#66)

   o  Don't require retransmission of old timestamps for lost ACK frames
      (#308)

   o  Clarified that frames are not retransmitted, but the information
      in them can be (#157, #298)

   o  Error handling definitions (#335)

   o  Split error codes into four sections (#74)

   o  Forbid the use of Public Reset where CONNECTION_CLOSE is possible
      (#289)

   o  Define packet protection rules (#336)
   o  Require that stream be entirely delivered or reset, including
      acknowledgment of all STREAM frames or the pre-IETF QUIC project at
   Google are: Britt Cyr, Jeremy Dorfman, Ryan Hamilton, Jana Iyengar,
   Fedor Kouranov, Charles Krasic, Jo Kulik, Adam Langley, Jim Roskind,
   Robbie Shade, Satyam Shekhar, Cherie Shi, Ian Swett, Raman Tenneti,
   Victor Vasiliev, Antonio Vicente, Patrik Westin, Alyssa Wilk, Dale
   Worley, Fan Yang, Dan Zhang, Daniel Ziegler.

Appendix B.  Acknowledgments

   Special thanks are due RST_STREAM, before it
      closes (#381)

   o  Remove stream reservation from state machine (#174, #280)

   o  Only stream 0 does not contributing to connection-level flow
      control (#204)

   o  Stream 1 counts towards the following maximum concurrent stream limit (#201,
      #282)

   o  Remove connection-level flow control exclusion for helping shape pre-IETF
   QUIC and its deployment: Chris Bentzel, Misha Efimov, Roberto Peon,
   Alistair Riddoch, Siddharth Vijayakrishnan, and Assar Westerlund.

   This document has benefited immensely from various private
   discussions and public ones some streams
      (except 1) (#246)

   o  RST_STREAM affects connection-level flow control (#162, #163)

   o  Flow control accounting uses the maximum data offset on each
      stream, rather than bytes received (#378)

   o  Moved length-determining fields to the quic@ietf.org start of STREAM and proto-
   quic@chromium.org mailing lists.  Our thanks to all.

Appendix C.  Change Log

      *RFC Editor's Note:* Please remove this section prior ACK
      (#168, #277)

   o  Added the ability to
      publication of pad between frames (#158, #276)

   o  Remove error code and reason phrase from GOAWAY (#352, #355)

   o  GOAWAY includes a final version stream number for both directions (#347)

   o  Error codes for RST_STREAM and CONNECTION_CLOSE are now at a
      consistent offset (#249)

   o  Defined priority as the responsibility of this document.

C.1. the application protocol
      (#104, #303)

C.2.  Since draft-ietf-quic-transport-00:

   o  Replaced DIVERSIFICATION_NONCE flag with KEY_PHASE flag

   o  Defined versioning

   o  Reworked description of packet and frame layout

   o  Error code space is divided into regions for each component

C.2.

   o  Use big endian for all numeric values

C.3.  Since draft-hamilton-quic-transport-protocol-01:

   o  Adopted as base for draft-ietf-quic-tls.

   o  Updated authors/editors list.

   o  Added IANA Considerations section.

   o  Moved Contributors and Acknowledgments to appendices.

Authors' Addresses

   Jana Iyengar (editor)
   Google

   Email: jri@google.com

   Martin Thomson (editor)
   Mozilla

   Email: martin.thomson@gmail.com