draft-ietf-tsvwg-fecframe-ext-00.txt   draft-ietf-tsvwg-fecframe-ext-01.txt 
TSVWG V. Roca TSVWG V. Roca
Internet-Draft INRIA Internet-Draft INRIA
Intended status: Standards Track A. Begen Intended status: Standards Track A. Begen
Expires: January 18, 2018 Networked Media Expires: September 5, 2018 Networked Media
July 17, 2017 March 4, 2018
Forward Error Correction (FEC) Framework Extension to Sliding Window Forward Error Correction (FEC) Framework Extension to Sliding Window
Codes Codes
draft-ietf-tsvwg-fecframe-ext-00 draft-ietf-tsvwg-fecframe-ext-01
Abstract Abstract
RFC 6363 describes a framework for using Forward Error Correction RFC 6363 describes a framework for using Forward Error Correction
(FEC) codes with applications in public and private IP networks to (FEC) codes with applications in public and private IP networks to
provide protection against packet loss. The framework supports provide protection against packet loss. The framework supports
applying FEC to arbitrary packet flows over unreliable transport and applying FEC to arbitrary packet flows over unreliable transport and
is primarily intended for real-time, or streaming, media. However is primarily intended for real-time, or streaming, media. However
FECFRAME as per RFC 6363 is restricted to block FEC codes. The FECFRAME as per RFC 6363 is restricted to block FEC codes. The
present document extends FECFRAME to support FEC Codes based on a present document extends FECFRAME to support FEC Codes based on a
skipping to change at page 1, line 36 skipping to change at page 1, line 36
and lower FEC-related added latency. and lower FEC-related added latency.
Status of This Memo Status of This Memo
This Internet-Draft is submitted in full conformance with the This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79. provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet- working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/. Drafts is at https://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress." material or to cite them other than as "work in progress."
This Internet-Draft will expire on January 18, 2018. This Internet-Draft will expire on September 5, 2018.
Copyright Notice Copyright Notice
Copyright (c) 2017 IETF Trust and the persons identified as the Copyright (c) 2018 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of (https://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License. described in the Simplified BSD License.
Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
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For these use-cases, Forward Error Correction (FEC) applied within For these use-cases, Forward Error Correction (FEC) applied within
the transport or application layer, is an efficient technique to the transport or application layer, is an efficient technique to
improve packet transmission robustness in presence of packet losses improve packet transmission robustness in presence of packet losses
(or "erasures"), without going through packet retransmissions that (or "erasures"), without going through packet retransmissions that
create a delay often incompatible with real-time constraints. The create a delay often incompatible with real-time constraints. The
FEC Building Block defined in [RFC5052] provides a framework for the FEC Building Block defined in [RFC5052] provides a framework for the
definition of Content Delivery Protocols (CDPs) that make use of definition of Content Delivery Protocols (CDPs) that make use of
separately defined FEC schemes. Any CDP defined according to the separately defined FEC schemes. Any CDP defined according to the
requirements of the FEC Building Block can then easily be used with requirements of the FEC Building Block can then easily be used with
any FEC scheme that is also defined according to the requirements of any FEC Scheme that is also defined according to the requirements of
the FEC Building Block. the FEC Building Block.
Then FECFRAME [RFC6363] provides a framework to define Content Then FECFRAME [RFC6363] provides a framework to define Content
Delivery Protocols (CDPs) that provide FEC protection for arbitrary Delivery Protocols (CDPs) that provide FEC protection for arbitrary
packet flows over unreliable transports such as UDP. It is primarily packet flows over unreliable transports such as UDP. It is primarily
intended for real-time or streaming media applications, using intended for real-time or streaming media applications, using
broadcast, multicast, or on-demand delivery. broadcast, multicast, or on-demand delivery.
However [RFC6363] only considers block FEC schemes defined in However [RFC6363] only considers block FEC schemes defined in
accordance with the FEC Building Block [RFC5052] (e.g., [RFC6681], accordance with the FEC Building Block [RFC5052] (e.g., [RFC6681],
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(RLC). (RLC).
This document is fully backward compatible with [RFC6363] that it This document is fully backward compatible with [RFC6363] that it
extends but does not replace. Indeed: extends but does not replace. Indeed:
o this extension does not prevent nor compromize in any way the o this extension does not prevent nor compromize in any way the
support of block FEC codes. Both types of codes can nicely co- support of block FEC codes. Both types of codes can nicely co-
exist, just like different block FEC schemes can co-exist; exist, just like different block FEC schemes can co-exist;
o any receiver, for instance a legacy receiver that only supports o any receiver, for instance a legacy receiver that only supports
block FEC schemes, can easily identify the FEC scheme used in a block FEC schemes, can easily identify the FEC Scheme used in a
FECFRAME session thanks to the associated SDP file and its FEC FECFRAME session thanks to the associated SDP file and its FEC
Encoding ID information (i.e., the "encoding-id=" parameter of a Encoding ID information (i.e., the "encoding-id=" parameter of a
"fec-repair-flow" attribute, [RFC6364]). This mechanism is not "fec-repair-flow" attribute, [RFC6364]). This mechanism is not
specific to this extension but is the basic approach for a specific to this extension but is the basic approach for a
FECFRAME receiver to determine whether or not it supports the FEC FECFRAME receiver to determine whether or not it supports the FEC
scheme used in a given FECFRAME session; Scheme used in a given FECFRAME session;
This document leverages on [RFC6363] and re-uses its structure. It This document leverages on [RFC6363] and re-uses its structure. It
proposes new sections specific to sliding window FEC codes whenever proposes new sections specific to sliding window FEC codes whenever
required. The only exception is Section Section 3 that provides a required. The only exception is Section Section 3 that provides a
quick summary of FECFRAME in order to facilitate the understanding of quick summary of FECFRAME in order to facilitate the understanding of
this document to readers not familiar with the concepts and this document to readers not familiar with the concepts and
terminology. terminology.
2. Definitions and Abbreviations 2. Definitions and Abbreviations
The following list of definitions and abbreviations is copied from The following list of definitions and abbreviations is copied from
[RFC6363], adding only the Block/sliding window FEC Code and [RFC6363], adding only the Block/sliding window FEC Code and
Encoding/Decoding Window definitions: Encoding/Decoding Window definitions (tagged with "ADDED"):
Application Data Unit (ADU): The unit of source data provided as Application Data Unit (ADU): The unit of source data provided as
payload to the transport layer. payload to the transport layer.
ADU Flow: A sequence of ADUs associated with a transport-layer flow ADU Flow: A sequence of ADUs associated with a transport-layer flow
identifier (such as the standard 5-tuple {source IP address, identifier (such as the standard 5-tuple {source IP address,
source port, destination IP address, destination port, transport source port, destination IP address, destination port, transport
protocol}). protocol}).
AL-FEC: Application-layer Forward Error Correction. AL-FEC: Application-layer Forward Error Correction.
skipping to change at page 5, line 19 skipping to change at page 5, line 19
Content Delivery Protocol (CDP): A complete application protocol Content Delivery Protocol (CDP): A complete application protocol
specification that, through the use of the framework defined in specification that, through the use of the framework defined in
this document, is able to make use of FEC schemes to provide FEC this document, is able to make use of FEC schemes to provide FEC
capabilities. capabilities.
FEC Code: An algorithm for encoding data such that the encoded data FEC Code: An algorithm for encoding data such that the encoded data
flow is resilient to data loss. Note that, in general, FEC codes flow is resilient to data loss. Note that, in general, FEC codes
may also be used to make a data flow resilient to corruption, but may also be used to make a data flow resilient to corruption, but
that is not considered in this document. that is not considered in this document.
Block FEC Code: An FEC Code that operates in a block manner, i.e., Block FEC Code: (ADDED) An FEC Code that operates in a block manner,
for which the input flow MUST be segmented into a sequence of i.e., for which the input flow MUST be segmented into a sequence
blocks, FEC encoding and decoding being performed independently of blocks, FEC encoding and decoding being performed
on a per-block basis. independently on a per-block basis.
Sliding Window (or Convolutional) FEC Code: An FEC Code that can Sliding Window (or Convolutional) FEC Code: (ADDED) An FEC Code that
generate repair symbols on-the-fly, at any time, from the set of can generate repair symbols on-the-fly, at any time, from the set
source symbols present in the sliding encoding window at that of source symbols present in the sliding encoding window at that
time. time.
FEC Framework: A protocol framework for the definition of Content FEC Framework: A protocol framework for the definition of Content
Delivery Protocols using FEC, such as the framework defined in Delivery Protocols using FEC, such as the framework defined in
this document. this document.
FEC Framework Configuration Information: Information that controls FEC Framework Configuration Information: Information that controls
the operation of the FEC Framework. the operation of the FEC Framework.
FEC Payload ID: Information that identifies the contents of a packet FEC Payload ID: Information that identifies the contents of a packet
with respect to the FEC scheme. with respect to the FEC Scheme.
FEC Repair Packet: At a sender (respectively, at a receiver), a FEC Repair Packet: At a sender (respectively, at a receiver), a
payload submitted to (respectively, received from) the transport payload submitted to (respectively, received from) the transport
protocol containing one or more repair symbols along with a protocol containing one or more repair symbols along with a
Repair FEC Payload ID and possibly an RTP header. Repair FEC Payload ID and possibly an RTP header.
FEC Scheme: A specification that defines the additional protocol FEC Scheme: A specification that defines the additional protocol
aspects required to use a particular FEC code with the FEC aspects required to use a particular FEC code with the FEC
Framework. Framework.
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Source FEC Payload ID: A FEC Payload ID specifically for use with Source FEC Payload ID: A FEC Payload ID specifically for use with
source packets. source packets.
Source Protocol: A protocol used for the source flow being Source Protocol: A protocol used for the source flow being
protected, e.g., RTP. protected, e.g., RTP.
Transport Protocol: The protocol used for the transport of the Transport Protocol: The protocol used for the transport of the
source and repair flows, e.g., UDP and the Datagram Congestion source and repair flows, e.g., UDP and the Datagram Congestion
Control Protocol (DCCP). Control Protocol (DCCP).
Encoding Window: Set of Source Symbols available at the sender/ Encoding Window: (ADDED) Set of Source Symbols available at the
coding node that are used to generate a repair symbol, with a sender/coding node that are used to generate a repair symbol,
Sliding Window FEC Code. with a Sliding Window FEC Code.
Decoding Window: Set of received or decoded source and repair Decoding Window: (ADDED) Set of received or decoded source and
symbols available at a receiver that are used to decode erased repair symbols available at a receiver that are used to decode
source symbols, with a Sliding Window FEC Code. erased source symbols, with a Sliding Window FEC Code.
Code Rate: The ratio between the number of source symbols and the Code Rate: The ratio between the number of source symbols and the
number of encoding symbols. By definition, the code rate is such number of encoding symbols. By definition, the code rate is such
that 0 < code rate <= 1. A code rate close to 1 indicates that a that 0 < code rate <= 1. A code rate close to 1 indicates that a
small number of repair symbols have been produced during the small number of repair symbols have been produced during the
encoding process. encoding process.
Encoding Symbol: Unit of data generated by the encoding process. Encoding Symbol: Unit of data generated by the encoding process.
With systematic codes, source symbols are part of the encoding With systematic codes, source symbols are part of the encoding
symbols. symbols.
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| |
| (1) Application Data Units (ADUs) | (1) Application Data Units (ADUs)
| |
v v
+----------------------+ +----------------+ +----------------------+ +----------------+
| FEC Framework | | | | FEC Framework | | |
| |-------------------------->| FEC Scheme | | |-------------------------->| FEC Scheme |
|(2) Construct source |(3) Source Block | | |(2) Construct source |(3) Source Block | |
| blocks | |(4) FEC Encoding| | blocks | |(4) FEC Encoding|
|(6) Construct FEC |<--------------------------| | |(6) Construct FEC |<--------------------------| |
| source and repair | | | | Source and Repair | | |
| packets |(5) Explicit Source FEC | | | Packets |(5) Explicit Source FEC | |
+----------------------+ Payload IDs +----------------+ +----------------------+ Payload IDs +----------------+
| Repair FEC Payload IDs | Repair FEC Payload IDs
| Repair symbols | Repair symbols
| |
|(7) FEC source and repair packets |(7) FEC Source and Repair Packets
v v
+----------------------+ +----------------------+
| Transport Layer | | Transport Layer |
| (e.g., UDP) | | (e.g., UDP) |
+----------------------+ +----------------------+
Figure 1: FECFRAME architecture at a sender. Figure 1: FECFRAME architecture at a sender.
The FECFRAME architecture is illustrated in Figure 1 from the The FECFRAME architecture is illustrated in Figure 1 from the
sender's point of view, in case of a block FEC Scheme. It shows an sender's point of view, in case of a block FEC Scheme. It shows an
skipping to change at page 8, line 26 skipping to change at page 8, line 26
FEC Source Packets (containing ADUs) and FEC Repair Packets FEC Source Packets (containing ADUs) and FEC Repair Packets
(containing one or more repair symbols each) are then generated and (containing one or more repair symbols each) are then generated and
sent using UDP (more precisely [RFC6363], Section 7, requires a sent using UDP (more precisely [RFC6363], Section 7, requires a
transport protocol providing an unreliable datagram service, like UDP transport protocol providing an unreliable datagram service, like UDP
or DCCP). In practice FEC Source Packets can be sent as soon as or DCCP). In practice FEC Source Packets can be sent as soon as
available, without having to wait for FEC encoding to take place. In available, without having to wait for FEC encoding to take place. In
that case a copy of the associated source symbols need to be kept that case a copy of the associated source symbols need to be kept
within FECFRAME for future FEC encoding purposes. within FECFRAME for future FEC encoding purposes.
At a receiver (not shown), FECFRAME processing operates in a similar At a receiver (not shown), FECFRAME processing operates in a similar
way, taking as input the incoming FEC source and repair packets way, taking as input the incoming FEC Source and Repair Packets
received. In case of FEC source packet losses, the FEC decoding of received. In case of FEC Source Packet losses, the FEC decoding of
the associated block may recover all (in case of successful decoding) the associated block may recover all (in case of successful decoding)
or a subset potentially empty (otherwise) of the missing source or a subset potentially empty (otherwise) of the missing source
symbols. After source symbol to ADU mapping, when lost ADUs are symbols. After source symbol to ADU mapping, when lost ADUs are
recovered, they are then assigned to their respective flow (see recovered, they are then assigned to their respective flow (see
below). ADUs are returned to the application(s), either in their below). ADUs are returned to the application(s), either in their
initial transmission order (in that case ADUs received after an initial transmission order (in that case ADUs received after an
erased one will be delayed until FEC decoding has taken place) or not erased one will be delayed until FEC decoding has taken place) or not
(in that case each ADU is returned as soon as it is received or (in that case each ADU is returned as soon as it is received or
recovered), depending on the application requirements. recovered), depending on the application requirements.
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one may be mapped to multiple symbols. The mapping details are one may be mapped to multiple symbols. The mapping details are
FEC Scheme dependant and must be defined in the associated FEC Scheme dependant and must be defined in the associated
document; document;
o Assignment of decoded ADUs to flows in multi-flow configurations: o Assignment of decoded ADUs to flows in multi-flow configurations:
when multiple flows are multiplexed over the same FECFRAME when multiple flows are multiplexed over the same FECFRAME
instance, a problem is to assign a decoded ADU to the right flow instance, a problem is to assign a decoded ADU to the right flow
(UDP port numbers and IP addresses traditionally used to map (UDP port numbers and IP addresses traditionally used to map
incoming ADUs to flows are not recovered during FEC decoding). To incoming ADUs to flows are not recovered during FEC decoding). To
make it possible, at the FECFRAME sending instance, each ADU is make it possible, at the FECFRAME sending instance, each ADU is
prepended with a flow identifier (1 byte) during the mapping to prepended with a flow identifier (1 byte) during the ADU to source
source symbols (see above). The flow identifiers are also shared symbols mapping (see above). The flow identifiers are also shared
between all FECFRAME instances as part of the FEC Framework between all FECFRAME instances as part of the FEC Framework
Configuration Information. This (flow identifier + length + Configuration Information. This (flow identifier + length +
application payload + padding), called ADUI, is then FEC application payload + padding), called ADUI, is then FEC
protected. Therefore a decoded ADUI contains enough information protected. Therefore a decoded ADUI contains enough information
to assign the ADU to the right flow. to assign the ADU to the right flow.
A few aspects are not covered by FECFRAME, namely: A few aspects are not covered by FECFRAME, namely:
o [RFC6363] section 8 does not detail any congestion control o [RFC6363] section 8 does not detail any congestion control
mechanism, but only provides high level normative requirements; mechanism, but only provides high level normative requirements;
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it needs to comply with the congestion control normative it needs to comply with the congestion control normative
requirements (see above). requirements (see above).
4. Procedural Overview 4. Procedural Overview
4.1. General 4.1. General
The general considerations of [RFC6363], Section 4.1, that are The general considerations of [RFC6363], Section 4.1, that are
specific to block FEC codes are not repeated here. specific to block FEC codes are not repeated here.
With a Sliding Window FEC Code, the FEC source packet MUST contain With a Sliding Window FEC Code, the FEC Source Packet MUST contain
information to identify the position occupied by the ADU within the information to identify the position occupied by the ADU within the
source flow, in terms specific to the FEC scheme. This information source flow, in terms specific to the FEC Scheme. This information
is known as the Source FEC Payload ID, and the FEC scheme is is known as the Source FEC Payload ID, and the FEC Scheme is
responsible for defining and interpreting it. responsible for defining and interpreting it.
With a Sliding Window FEC Code, the FEC repair packets MUST contain With a Sliding Window FEC Code, the FEC Repair Packets MUST contain
information that identifies the relationship between the contained information that identifies the relationship between the contained
repair payloads and the original source symbols used during encoding. repair payloads and the original source symbols used during encoding.
This information is known as the Repair FEC Payload ID, and the FEC This information is known as the Repair FEC Payload ID, and the FEC
scheme is responsible for defining and interpreting it. Scheme is responsible for defining and interpreting it.
The Sender Operation ([RFC6363], Section 4.2.) and Receiver Operation The Sender Operation ([RFC6363], Section 4.2.) and Receiver Operation
([RFC6363], Section 4.3) are both specific to block FEC codes and ([RFC6363], Section 4.3) are both specific to block FEC codes and
therefore omitted below. The following two sections detail similar therefore omitted below. The following two sections detail similar
operations for Sliding Window FEC codes. operations for Sliding Window FEC codes.
4.2. Sender Operation with Sliding Window FEC Codes 4.2. Sender Operation with Sliding Window FEC Codes
With a Sliding Window FEC scheme, the following operations, With a Sliding Window FEC Scheme, the following operations,
illustrated in Figure 2 for the case of UDP repair flows, and in illustrated in Figure 2 for the case of UDP repair flows, and in
Figure 3 for the case of RTP repair flows, describe a possible way to Figure 3 for the case of RTP repair flows, describe a possible way to
generate compliant source and repair flows: generate compliant source and repair flows:
1. A new ADU is provided by the application. 1. A new ADU is provided by the application.
2. The FEC Framework communicates this ADU to the FEC scheme. 2. The FEC Framework communicates this ADU to the FEC Scheme.
3. The sliding encoding window is updated by the FEC scheme. The 3. The sliding encoding window is updated by the FEC Scheme. The
ADU to source symbols mapping as well as the encoding window ADU to source symbols mapping as well as the encoding window
management details are both the responsibility of the FEC scheme management details are both the responsibility of the FEC Scheme
and MUST be detailed there. Appendix A provides some hints on and MUST be detailed there. Appendix A provides some hints on
the way it might be performed. the way it might be performed.
4. The Source FEC Payload ID information of the source packet is 4. The Source FEC Payload ID information of the source packet is
determined by the FEC scheme. If required by the FEC scheme, determined by the FEC Scheme. If required by the FEC Scheme,
the Source FEC Payload ID is encoded into the Explicit Source the Source FEC Payload ID is encoded into the Explicit Source
FEC Payload ID field and returned to the FEC Framework. FEC Payload ID field and returned to the FEC Framework.
5. The FEC Framework constructs the FEC source packet according to 5. The FEC Framework constructs the FEC Source Packet according to
[RFC6363] Figure 6, using the Explicit Source FEC Payload ID [RFC6363] Figure 6, using the Explicit Source FEC Payload ID
provided by the FEC scheme if applicable. provided by the FEC Scheme if applicable.
6. The FEC source packet is sent using normal transport-layer 6. The FEC Source Packet is sent using normal transport-layer
procedures. This packet is sent using the same ADU flow procedures. This packet is sent using the same ADU flow
identification information as would have been used for the identification information as would have been used for the
original source packet if the FEC Framework were not present original source packet if the FEC Framework were not present
(for example, in the UDP case, the UDP source and destination (for example, in the UDP case, the UDP source and destination
addresses and ports on the IP datagram carrying the source addresses and ports on the IP datagram carrying the source
packet will be the same whether or not the FEC Framework is packet will be the same whether or not the FEC Framework is
applied). applied).
7. When the FEC Framework needs to send one or several FEC repair 7. When the FEC Framework needs to send one or several FEC Repair
packets (e.g., according to the target Code Rate), it asks the Packets (e.g., according to the target Code Rate), it asks the
FEC scheme to create one or several repair packet payloads from FEC Scheme to create one or several repair packet payloads from
the current sliding encoding window along with their Repair FEC the current sliding encoding window along with their Repair FEC
Payload ID. Payload ID.
8. The Repair FEC Payload IDs and repair packet payloads are 8. The Repair FEC Payload IDs and repair packet payloads are
provided back by the FEC scheme to the FEC Framework. provided back by the FEC Scheme to the FEC Framework.
9. The FEC Framework constructs FEC repair packets according to 9. The FEC Framework constructs FEC Repair Packets according to
[RFC6363] Figure 7, using the FEC Payload IDs and repair packet [RFC6363] Figure 7, using the FEC Payload IDs and repair packet
payloads provided by the FEC scheme. payloads provided by the FEC Scheme.
10. The FEC repair packets are sent using normal transport-layer 10. The FEC Repair Packets are sent using normal transport-layer
procedures. The port(s) and multicast group(s) to be used for procedures. The port(s) and multicast group(s) to be used for
FEC repair packets are defined in the FEC Framework FEC Repair Packets are defined in the FEC Framework
Configuration Information. Configuration Information.
+----------------------+ +----------------------+
| Application | | Application |
+----------------------+ +----------------------+
| |
| (1) New Application Data Unit (ADU) | (1) New Application Data Unit (ADU)
v v
+---------------------+ +----------------+ +---------------------+ +----------------+
| FEC Framework | | FEC Scheme | | FEC Framework | | FEC Scheme |
| |-------------------------->| | | |-------------------------->| |
| | (2) New ADU |(3) Update of | | | (2) New ADU |(3) Update of |
| | | encoding | | | | encoding |
| |<--------------------------| window | | |<--------------------------| window |
|(5) Construct FEC | (4) Explicit Source | | |(5) Construct FEC | (4) Explicit Source | |
| source packet | FEC Payload ID(s) |(7) FEC | | Source Packet | FEC Payload ID(s) |(7) FEC |
| |<--------------------------| encoding | | |<--------------------------| encoding |
|(9) Construct FEC | (8) Repair FEC Payload ID | | |(9) Construct FEC | (8) Repair FEC Payload ID | |
| repair packet(s) | + Repair symbol(s) +----------------+ | Repair Packet(s) | + Repair symbol(s) +----------------+
+---------------------+ +---------------------+
| |
| (6) FEC source packet | (6) FEC Source Packet
| (10) FEC repair packets | (10) FEC Repair Packets
v v
+----------------------+ +----------------------+
| Transport Layer | | Transport Layer |
| (e.g., UDP) | | (e.g., UDP) |
+----------------------+ +----------------------+
Figure 2: Sender Operation with Convolutional FEC Codes Figure 2: Sender Operation with Convolutional FEC Codes
+----------------------+ +----------------------+
| Application | | Application |
skipping to change at page 12, line 18 skipping to change at page 12, line 18
| |
| (1) New Application Data Unit (ADU) | (1) New Application Data Unit (ADU)
v v
+---------------------+ +----------------+ +---------------------+ +----------------+
| FEC Framework | | FEC Scheme | | FEC Framework | | FEC Scheme |
| |-------------------------->| | | |-------------------------->| |
| | (2) New ADU |(3) Update of | | | (2) New ADU |(3) Update of |
| | | encoding | | | | encoding |
| |<--------------------------| window | | |<--------------------------| window |
|(5) Construct FEC | (4) Explicit Source | | |(5) Construct FEC | (4) Explicit Source | |
| source packet | FEC Payload ID(s) |(7) FEC | | Source Packet | FEC Payload ID(s) |(7) FEC |
| |<--------------------------| encoding | | |<--------------------------| encoding |
|(9) Construct FEC | (8) Repair FEC Payload ID | | |(9) Construct FEC | (8) Repair FEC Payload ID | |
| repair packet(s) | + Repair symbol(s) +----------------+ | Repair Packet(s) | + Repair symbol(s) +----------------+
+---------------------+ +---------------------+
| | | |
|(6) Source |(10) Repair payloads |(6) Source |(10) Repair payloads
| packets | | packets |
| + -- -- -- -- -+ | + -- -- -- -- -+
| | RTP | | | RTP |
| +-- -- -- -- --+ | +-- -- -- -- --+
v v v v
+----------------------+ +----------------------+
| Transport Layer | | Transport Layer |
| (e.g., UDP) | | (e.g., UDP) |
+----------------------+ +----------------------+
Figure 3: Sender Operation with RTP Repair Flows Figure 3: Sender Operation with RTP Repair Flows
4.3. Receiver Operation with Sliding Window FEC Codes 4.3. Receiver Operation with Sliding Window FEC Codes
With a Sliding Window FEC scheme, the following operations, With a Sliding Window FEC Scheme, the following operations,
illustrated in Figure 4 for the case of UDP repair flows, and in illustrated in Figure 4 for the case of UDP repair flows, and in
Figure 5 for the case of RTP repair flows. The only differences with Figure 5 for the case of RTP repair flows. The only differences with
respect to block FEC codes lie in steps (4) and (5). Therefore this respect to block FEC codes lie in steps (4) and (5). Therefore this
section does not repeat the other steps of [RFC6363], Section 4.3, section does not repeat the other steps of [RFC6363], Section 4.3,
"Receiver Operation". The new steps (4) and (5) are: "Receiver Operation". The new steps (4) and (5) are:
4. The FEC scheme uses the received FEC Payload IDs (and derived FEC 4. The FEC Scheme uses the received FEC Payload IDs (and derived FEC
Source Payload IDs when the Explicit Source FEC Payload ID field Source Payload IDs when the Explicit Source FEC Payload ID field
is not used) to insert source and repair packets into the is not used) to insert source and repair packets into the
decoding window in the right way. If at least one source packet decoding window in the right way. If at least one source packet
is missing and at least one repair packet has been received and is missing and at least one repair packet has been received and
the rank of the associated linear system permits it, then FEC the rank of the associated linear system permits it, then FEC
decoding can be performed in order to recover missing source decoding can be performed in order to recover missing source
payloads. The FEC scheme determines whether source packets have payloads. The FEC Scheme determines whether source packets have
been lost and whether enough repair packets have been received to been lost and whether enough repair packets have been received to
decode any or all of the missing source payloads. decode any or all of the missing source payloads.
5. The FEC scheme returns the received and decoded ADUs to the FEC 5. The FEC Scheme returns the received and decoded ADUs to the FEC
Framework, along with indications of any ADUs that were missing Framework, along with indications of any ADUs that were missing
and could not be decoded. and could not be decoded.
+----------------------+ +----------------------+
| Application | | Application |
+----------------------+ +----------------------+
^ ^
|(6) ADUs |(6) ADUs
| |
+----------------------+ +----------------+ +----------------------+ +----------------+
| FEC Framework | | FEC Scheme | | FEC Framework | | FEC Scheme |
| |<--------------------------| | | |<--------------------------| |
|(2)Extract FEC Payload|(5) ADUs |(4) FEC Decoding |(2)Extract FEC Payload|(5) ADUs |(4) FEC Decoding
| IDs and pass IDs & |-------------------------->| | | IDs and pass IDs & |-------------------------->| |
| payloads to FEC |(3) Explicit Source FEC +----------------+ | payloads to FEC |(3) Explicit Source FEC +----------------+
| scheme | Payload IDs | scheme | Payload IDs
+----------------------+ Repair FEC Payload IDs +----------------------+ Repair FEC Payload IDs
^ Source payloads ^ Source payloads
| Repair payloads | Repair payloads
|(1) FEC source |(1) FEC Source
| and repair packets | and Repair Packets
+----------------------+ +----------------------+
| Transport Layer | | Transport Layer |
| (e.g., UDP) | | (e.g., UDP) |
+----------------------+ +----------------------+
Figure 4: Receiver Operation with Sliding Window FEC Codes Figure 4: Receiver Operation with Sliding Window FEC Codes
+----------------------+ +----------------------+
| Application | | Application |
+----------------------+ +----------------------+
skipping to change at page 14, line 30 skipping to change at page 14, line 30
| | Repair payloads | | Repair payloads
|Source pkts |Repair payloads |Source pkts |Repair payloads
| | | |
+-- |- -- -- -- -- -- -+ +-- |- -- -- -- -- -- -+
|RTP| | RTP Processing | |RTP| | RTP Processing |
| | +-- -- -- --|-- -+ | | +-- -- -- --|-- -+
| +-- -- -- -- -- |--+ | | +-- -- -- -- -- |--+ |
| | RTP Demux | | | | RTP Demux | |
+-- -- -- -- -- -- -- -+ +-- -- -- -- -- -- -- -+
^ ^
|(1) FEC source and repair packets |(1) FEC Source and Repair Packets
| |
+----------------------+ +----------------------+
| Transport Layer | | Transport Layer |
| (e.g., UDP) | | (e.g., UDP) |
+----------------------+ +----------------------+
Figure 5: Receiver Operation with RTP Repair Flows Figure 5: Receiver Operation with RTP Repair Flows
5. Protocol Specification 5. Protocol Specification
skipping to change at page 15, line 13 skipping to change at page 15, line 13
Window FEC codes. They are not repeated here. Window FEC codes. They are not repeated here.
5.2. FEC Framework Configuration Information 5.2. FEC Framework Configuration Information
The FEC Framework Configuration Information considerations of The FEC Framework Configuration Information considerations of
[RFC6363], Section 5.5, equally applies to this FECFRAME extension [RFC6363], Section 5.5, equally applies to this FECFRAME extension
and is not repeated here. and is not repeated here.
5.3. FEC Scheme Requirements 5.3. FEC Scheme Requirements
The FEC scheme requirements of [RFC6363], Section 5.6, mostly apply The FEC Scheme requirements of [RFC6363], Section 5.6, mostly apply
to this FECFRAME extension and are not repeated here. An exception to this FECFRAME extension and are not repeated here. An exception
though is the "full specification of the FEC code", item (4), that is though is the "full specification of the FEC code", item (4), that is
specific to block FEC codes. The following item (4) applies instead: specific to block FEC codes. The following item (4) applies instead:
4. A full specification of the Sliding Window FEC code 4. A full specification of the Sliding Window FEC code
This specification MUST precisely define the valid FEC-Scheme- This specification MUST precisely define the valid FEC-Scheme-
Specific Information values, the valid FEC Payload ID values, and Specific Information values, the valid FEC Payload ID values, and
the valid packet payload sizes (where packet payload refers to the valid packet payload sizes (where packet payload refers to
the space within a packet dedicated to carrying encoding the space within a packet dedicated to carrying encoding
symbols). symbols).
Furthermore, given valid values of the FEC-Scheme-Specific Furthermore, given valid values of the FEC-Scheme-Specific
Information, a valid Repair FEC Payload ID value, a valid packet Information, a valid Repair FEC Payload ID value, a valid packet
payload size, and a valid encoding window (i.e., a set of source payload size, and a valid encoding window (i.e., a set of source
symbols), the specification MUST uniquely define the values of symbols), the specification MUST uniquely define the values of
the encoding symbols to be included in the repair packet payload the encoding symbols to be included in the repair packet payload
with the given Repair FEC Payload ID value. with the given Repair FEC Payload ID value.
Additionally, the FEC scheme associated to a Sliding Window FEC Code: Additionally, the FEC Scheme associated to a Sliding Window FEC Code:
o MUST define the relationships between ADUs and the associated o MUST define the relationships between ADUs and the associated
source symbols (mapping); source symbols (mapping);
o MUST define the management of the encoding window that slides over o MUST define the management of the encoding window that slides over
the set of ADUs. Appendix A provides a non normative example; the set of ADUs. Appendix A provides a non normative example;
o MUST define the management of the decoding window, consisting of a o MUST define the management of the decoding window, consisting of a
system of linear equations (in case of a linear FEC code); system of linear equations (in case of a linear FEC code);
skipping to change at page 16, line 44 skipping to change at page 16, line 44
o Coverage: the software implements a subset of [RFC6363], as o Coverage: the software implements a subset of [RFC6363], as
specialized by the 3GPP eMBMS standard [MBMSTS]. This software specialized by the 3GPP eMBMS standard [MBMSTS]. This software
also covers the additional features of FECFRAME extended to also covers the additional features of FECFRAME extended to
Sliding Window codes, in particular the RLC FEC Scheme. Sliding Window codes, in particular the RLC FEC Scheme.
o Lincensing: proprietary. o Lincensing: proprietary.
o Implementation experience: maximum. o Implementation experience: maximum.
o Information update date: March 2017. o Information update date: March 2018.
o Contact: vincent.roca@inria.fr o Contact: vincent.roca@inria.fr
10. Security Considerations 10. Security Considerations
This FECFRAME extension does not add any new security consideration. This FECFRAME extension does not add any new security consideration.
All the considerations of [RFC6363], Section 9, apply to this All the considerations of [RFC6363], Section 9, apply to this
document as well. document as well.
11. Operations and Management Considerations 11. Operations and Management Considerations
This FECFRAME extension does not add any new Operations and This FECFRAME extension does not add any new Operations and
Management Consideration. All the considerations of [RFC6363], Management Consideration. All the considerations of [RFC6363],
Section 10, apply to this document as well. Section 10, apply to this document as well.
12. IANA Considerations 12. IANA Considerations
A FEC scheme for use with this FEC Framework is identified via its A FEC Scheme for use with this FEC Framework is identified via its
FEC Encoding ID. It is subject to IANA registration in the "FEC FEC Encoding ID. It is subject to IANA registration in the "FEC
Framework (FECFRAME) FEC Encoding IDs" registry. All the rules of Framework (FECFRAME) FEC Encoding IDs" registry. All the rules of
[RFC6363], Section 11, apply and are not repeated here. [RFC6363], Section 11, apply and are not repeated here.
13. Acknowledgments 13. Acknowledgments
TBD TBD
14. References 14. References
14.1. Normative References 14.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997, DOI 10.17487/RFC2119, March 1997,
<http://www.rfc-editor.org/info/rfc2119>. <https://www.rfc-editor.org/info/rfc2119>.
[RFC6363] Watson, M., Begen, A., and V. Roca, "Forward Error [RFC6363] Watson, M., Begen, A., and V. Roca, "Forward Error
Correction (FEC) Framework", RFC 6363, Correction (FEC) Framework", RFC 6363,
DOI 10.17487/RFC6363, October 2011, DOI 10.17487/RFC6363, October 2011,
<http://www.rfc-editor.org/info/rfc6363>. <https://www.rfc-editor.org/info/rfc6363>.
14.2. Informative References 14.2. Informative References
[MBMSTS] 3GPP, "Multimedia Broadcast/Multicast Service (MBMS); [MBMSTS] 3GPP, "Multimedia Broadcast/Multicast Service (MBMS);
Protocols and codecs", 3GPP TS 26.346, March 2009, Protocols and codecs", 3GPP TS 26.346, March 2009,
<http://ftp.3gpp.org/specs/html-info/26346.htm>. <http://ftp.3gpp.org/specs/html-info/26346.htm>.
[RFC5052] Watson, M., Luby, M., and L. Vicisano, "Forward Error [RFC5052] Watson, M., Luby, M., and L. Vicisano, "Forward Error
Correction (FEC) Building Block", RFC 5052, Correction (FEC) Building Block", RFC 5052,
DOI 10.17487/RFC5052, August 2007, DOI 10.17487/RFC5052, August 2007,
<http://www.rfc-editor.org/info/rfc5052>. <https://www.rfc-editor.org/info/rfc5052>.
[RFC6364] Begen, A., "Session Description Protocol Elements for the [RFC6364] Begen, A., "Session Description Protocol Elements for the
Forward Error Correction (FEC) Framework", RFC 6364, Forward Error Correction (FEC) Framework", RFC 6364,
DOI 10.17487/RFC6364, October 2011, DOI 10.17487/RFC6364, October 2011,
<http://www.rfc-editor.org/info/rfc6364>. <https://www.rfc-editor.org/info/rfc6364>.
[RFC6681] Watson, M., Stockhammer, T., and M. Luby, "Raptor Forward [RFC6681] Watson, M., Stockhammer, T., and M. Luby, "Raptor Forward
Error Correction (FEC) Schemes for FECFRAME", RFC 6681, Error Correction (FEC) Schemes for FECFRAME", RFC 6681,
DOI 10.17487/RFC6681, August 2012, DOI 10.17487/RFC6681, August 2012,
<http://www.rfc-editor.org/info/rfc6681>. <https://www.rfc-editor.org/info/rfc6681>.
[RFC6816] Roca, V., Cunche, M., and J. Lacan, "Simple Low-Density [RFC6816] Roca, V., Cunche, M., and J. Lacan, "Simple Low-Density
Parity Check (LDPC) Staircase Forward Error Correction Parity Check (LDPC) Staircase Forward Error Correction
(FEC) Scheme for FECFRAME", RFC 6816, (FEC) Scheme for FECFRAME", RFC 6816,
DOI 10.17487/RFC6816, December 2012, DOI 10.17487/RFC6816, December 2012,
<http://www.rfc-editor.org/info/rfc6816>. <https://www.rfc-editor.org/info/rfc6816>.
[RFC6865] Roca, V., Cunche, M., Lacan, J., Bouabdallah, A., and K. [RFC6865] Roca, V., Cunche, M., Lacan, J., Bouabdallah, A., and K.
Matsuzono, "Simple Reed-Solomon Forward Error Correction Matsuzono, "Simple Reed-Solomon Forward Error Correction
(FEC) Scheme for FECFRAME", RFC 6865, (FEC) Scheme for FECFRAME", RFC 6865,
DOI 10.17487/RFC6865, February 2013, DOI 10.17487/RFC6865, February 2013,
<http://www.rfc-editor.org/info/rfc6865>. <https://www.rfc-editor.org/info/rfc6865>.
[RLC-ID] Roca, V., "Sliding Window Random Linear Code (RLC) Forward [RLC-ID] Roca, V., "Sliding Window Random Linear Code (RLC) Forward
Erasure Correction (FEC) Scheme for FECFRAME", Work Erasure Correction (FEC) Scheme for FECFRAME", Work
in Progress, Transport Area Working Group (TSVWG) draft- in Progress, Transport Area Working Group (TSVWG) draft-
roca-tsvwg-rlc-fec-scheme (Work in Progress), June 2017, ietf-tsvwg-rlc-fec-scheme (Work in Progress), March 2018,
<https://tools.ietf.org/html/draft-roca-tsvwg-rlc-fec- <https://tools.ietf.org/html/
scheme>. draft-ietf-tsvwg-rlc-fec-scheme>.
Appendix A. About Sliding Encoding Window Management (non Normative) Appendix A. About Sliding Encoding Window Management (non Normative)
The FEC Framework does not specify the management of the sliding The FEC Framework does not specify the management of the sliding
encoding window which is the responsibility of the FEC Scheme. This encoding window which is the responsibility of the FEC Scheme. This
annex provides a few hints with respect to the management of this annex only provides a few non normative hints.
encoding window.
Source symbols are added to the sliding encoding window each time a Source symbols are added to the sliding encoding window each time a
new ADU arrives, where the following information is provided for this new ADU is available at the sender, after the ADU to source symbol
ADU by the FEC Framework: a description of the source flow with which mapping specific to the FEC Scheme.
the ADU is associated, the ADU itself, and the length of the ADU.
This information is sufficient for the FEC scheme to map the ADU to
the corresponding source symbols.
Source symbols and the corresponding ADUs are removed from the Source symbols are removed from the sliding encoding window, for
sliding encoding window, for instance: instance:
o after a certain delay, when an "old" ADU of a real-time flow times o after a certain delay, when an "old" ADU of a real-time flow times
out. The source symbol retention delay in the sliding encoding out. The source symbol retention delay in the sliding encoding
window should therefore be initialized according to the real-time window should therefore be initialized according to the real-time
features of incoming flow(s). features of incoming flow(s);
o once the sliding encoding window has reached its maximum size o once the sliding encoding window has reached its maximum size
(there is usually an upper limit to the sliding encoding window (there is usually an upper limit to the sliding encoding window
size). In that case the oldest symbol is removed each time a new size). In that case the oldest symbol is removed each time a new
source symbol is added. source symbol is added.
Several aspects exist that can impact the sliding encoding window Several considerations can impact the management of this sliding
management: encoding:
o at the source flows level: real-time constraints can limit the o at the source flows level: real-time constraints can limit the
total time source symbols can remain in the encoding window; total time source symbols can remain in the encoding window;
o at the FEC code level: there may be theoretical or practical o at the FEC code level: theoretical or practical limitations (e.g.,
limitations (e.g., because of computational complexity) that limit because of computational complexity) can limit the number of
the number of source symbols in the encoding window. source symbols in the encoding window;
o at the FEC scheme level: signaling and window management are o at the FEC Scheme level: signaling and window management are
intrinsically related. For instance, an encoding window composed intrinsically related. For instance, an encoding window composed
of a non sequential set of source symbols requires an appropriate of a non sequential set of source symbols requires an appropriate
signaling to inform a receiver of the composition of the encoding signaling to inform a receiver of the composition of the encoding
window. On the opposite, an encoding window always composed of a window, and the associated transmission overhead can limit the
sequential set of source symbols simplifies signaling: providing maximum encoding window size. On the opposite, an encoding window
the identity of the first source symbol plus their number is always composed of a sequential set of source symbols simplifies
sufficient. signaling: providing the identity of the first source symbol plus
their number is sufficient, which creates a fixed and relatively
small transmission overhead.
Authors' Addresses Authors' Addresses
Vincent Roca Vincent Roca
INRIA INRIA
Grenoble Grenoble
France France
EMail: vincent.roca@inria.fr EMail: vincent.roca@inria.fr
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