draft-ietf-mmusic-ice-sip-sdp-11.txt   draft-ietf-mmusic-ice-sip-sdp-12.txt 
MMUSIC M. Petit-Huguenin MMUSIC M. Petit-Huguenin
Internet-Draft Impedance Mismatch Internet-Draft Impedance Mismatch
Intended status: Standards Track A. Keranen Obsoletes: 5245 (if approved) A. Keranen
Expires: July 24, 2017 Ericsson Intended status: Standards Track Ericsson
S. Nandakumar Expires: September 14, 2017 S. Nandakumar
Cisco Systems Cisco Systems
January 20, 2017 March 13, 2017
Using Interactive Connectivity Establishment (ICE) with Using Interactive Connectivity Establishment (ICE) with Session
Session Description Protocol (SDP) offer/answer and Session Initiation Description Protocol (SDP) offer/answer and Session Initiation Protocol
Protocol (SIP) (SIP)
draft-ietf-mmusic-ice-sip-sdp-11 draft-ietf-mmusic-ice-sip-sdp-12
Abstract Abstract
This document describes how Interactive Connectivity Establishment This document describes how Interactive Connectivity Establishment
(ICE) is used with Session Description Protocol (SDP) offer/answer (ICE) is used with Session Description Protocol (SDP) offer/answer
and Session Initiation Protocol (SIP). and Session Initiation Protocol (SIP).
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
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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 http://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 July 24, 2017. This Internet-Draft will expire on September 14, 2017.
Copyright Notice Copyright Notice
Copyright (c) 2017 IETF Trust and the persons identified as the Copyright (c) 2017 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 (http://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
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4.1.1. Sending the Initial Offer . . . . . . . . . . . . . . 4 4.1.1. Sending the Initial Offer . . . . . . . . . . . . . . 4
4.1.2. Receiving the Initial Offer . . . . . . . . . . . . . 7 4.1.2. Receiving the Initial Offer . . . . . . . . . . . . . 7
4.1.3. Receipt of the Initial Answer . . . . . . . . . . . . 8 4.1.3. Receipt of the Initial Answer . . . . . . . . . . . . 8
4.1.4. Performing Connectivity Checks . . . . . . . . . . . 9 4.1.4. Performing Connectivity Checks . . . . . . . . . . . 9
4.1.5. Concluding ICE . . . . . . . . . . . . . . . . . . . 9 4.1.5. Concluding ICE . . . . . . . . . . . . . . . . . . . 9
4.2. Subsequent Offer/Answer Exchanges . . . . . . . . . . . . 10 4.2. Subsequent Offer/Answer Exchanges . . . . . . . . . . . . 10
4.2.1. Generating the Offer . . . . . . . . . . . . . . . . 10 4.2.1. Generating the Offer . . . . . . . . . . . . . . . . 10
4.2.2. Receiving the Offer and Generating an Answer . . . . 13 4.2.2. Receiving the Offer and Generating an Answer . . . . 13
4.2.3. Receiving the Answer for a Subsequent Offer . . . . . 16 4.2.3. Receiving the Answer for a Subsequent Offer . . . . . 16
4.2.4. Updating the Check and Valid Lists . . . . . . . . . 17 4.2.4. Updating the Check and Valid Lists . . . . . . . . . 17
5. Grammar . . . . . . . . . . . . . . . . . . . . . . . . . . . 19 5. Grammar . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
5.1. "candidate" Attribute . . . . . . . . . . . . . . . . . . 19 5.1. "candidate" Attribute . . . . . . . . . . . . . . . . . . 19
5.2. "remote-candidates" Attribute . . . . . . . . . . . . . . 22 5.2. "remote-candidates" Attribute . . . . . . . . . . . . . . 21
5.3. "ice-lite" and "ice-mismatch" Attributes . . . . . . . . 22 5.3. "ice-lite" and "ice-mismatch" Attributes . . . . . . . . 22
5.4. "ice-ufrag" and "ice-pwd" Attributes . . . . . . . . . . 22 5.4. "ice-ufrag" and "ice-pwd" Attributes . . . . . . . . . . 22
5.5. "ice-pacing" Attribute . . . . . . . . . . . . . . . . . 23 5.5. "ice-pacing" Attribute . . . . . . . . . . . . . . . . . 23
5.6. "ice-options" Attribute . . . . . . . . . . . . . . . . . 23 5.6. "ice-options" Attribute . . . . . . . . . . . . . . . . . 23
6. Keepalives . . . . . . . . . . . . . . . . . . . . . . . . . 24 6. Keepalives . . . . . . . . . . . . . . . . . . . . . . . . . 23
7. Media Handling . . . . . . . . . . . . . . . . . . . . . . . 24 7. Media Handling . . . . . . . . . . . . . . . . . . . . . . . 24
7.1. Sending Media . . . . . . . . . . . . . . . . . . . . . . 24 7.1. Sending Media . . . . . . . . . . . . . . . . . . . . . . 24
7.1.1. Procedures for All Implementations . . . . . . . . . 24 7.1.1. Procedures for All Implementations . . . . . . . . . 24
7.2. Receiving Media . . . . . . . . . . . . . . . . . . . . . 24 7.2. Receiving Media . . . . . . . . . . . . . . . . . . . . . 24
8. Usage with SIP . . . . . . . . . . . . . . . . . . . . . . . 24 8. Usage with SIP . . . . . . . . . . . . . . . . . . . . . . . 24
8.1. Latency Guidelines . . . . . . . . . . . . . . . . . . . 24 8.1. Latency Guidelines . . . . . . . . . . . . . . . . . . . 24
8.1.1. Offer in INVITE . . . . . . . . . . . . . . . . . . . 25 8.1.1. Offer in INVITE . . . . . . . . . . . . . . . . . . . 25
8.1.2. Offer in Response . . . . . . . . . . . . . . . . . . 26 8.1.2. Offer in Response . . . . . . . . . . . . . . . . . . 26
8.2. SIP Option Tags and Media Feature Tags . . . . . . . . . 26 8.2. SIP Option Tags and Media Feature Tags . . . . . . . . . 26
8.3. Interactions with Forking . . . . . . . . . . . . . . . . 27 8.3. Interactions with Forking . . . . . . . . . . . . . . . . 27
8.4. Interactions with Preconditions . . . . . . . . . . . . . 27 8.4. Interactions with Preconditions . . . . . . . . . . . . . 27
8.5. Interactions with Third Party Call Control . . . . . . . 27 8.5. Interactions with Third Party Call Control . . . . . . . 27
9. Relationship with ANAT . . . . . . . . . . . . . . . . . . . 28 9. Relationship with ANAT . . . . . . . . . . . . . . . . . . . 28
10. Setting Ta and RTO for RTP Media Streams . . . . . . . . . . 28 10. Setting Ta and RTO for RTP Media Streams . . . . . . . . . . 28
11. Security Considerations . . . . . . . . . . . . . . . . . . . 28 11. Security Considerations . . . . . . . . . . . . . . . . . . . 28
11.1. Attacks on the Offer/Answer Exchanges . . . . . . . . . 28 11.1. Attacks on the Offer/Answer Exchanges . . . . . . . . . 28
11.2. Insider Attacks . . . . . . . . . . . . . . . . . . . . 29 11.2. Insider Attacks . . . . . . . . . . . . . . . . . . . . 28
11.2.1. The Voice Hammer Attack . . . . . . . . . . . . . . 29 11.2.1. The Voice Hammer Attack . . . . . . . . . . . . . . 29
11.2.2. Interactions with Application Layer Gateways and SIP 29 11.2.2. Interactions with Application Layer Gateways and SIP 29
12. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 30 12. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 30
12.1. SDP Attributes . . . . . . . . . . . . . . . . . . . . . 30 12.1. SDP Attributes . . . . . . . . . . . . . . . . . . . . . 30
12.1.1. candidate Attribute . . . . . . . . . . . . . . . . 30 12.1.1. candidate Attribute . . . . . . . . . . . . . . . . 31
12.1.2. remote-candidates Attribute . . . . . . . . . . . . 31 12.1.2. remote-candidates Attribute . . . . . . . . . . . . 31
12.1.3. ice-lite Attribute . . . . . . . . . . . . . . . . . 31 12.1.3. ice-lite Attribute . . . . . . . . . . . . . . . . . 31
12.1.4. ice-mismatch Attribute . . . . . . . . . . . . . . . 32 12.1.4. ice-mismatch Attribute . . . . . . . . . . . . . . . 32
12.1.5. ice-pwd Attribute . . . . . . . . . . . . . . . . . 32 12.1.5. ice-pwd Attribute . . . . . . . . . . . . . . . . . 32
12.1.6. ice-ufrag Attribute . . . . . . . . . . . . . . . . 33 12.1.6. ice-ufrag Attribute . . . . . . . . . . . . . . . . 33
12.1.7. ice-pacing Attribute . . . . . . . . . . . . . . . . 33 12.1.7. ice-pacing Attribute . . . . . . . . . . . . . . . . 33
12.1.8. ice-options Attribute . . . . . . . . . . . . . . . 33 12.1.8. ice-options Attribute . . . . . . . . . . . . . . . 33
12.2. Interactive Connectivity Establishment (ICE) Options 12.2. Interactive Connectivity Establishment (ICE) Options
Registry . . . . . . . . . . . . . . . . . . . . . . . . 34 Registry . . . . . . . . . . . . . . . . . . . . . . . . 34
13. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 35 13. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 35
14. References . . . . . . . . . . . . . . . . . . . . . . . . . 35 14. References . . . . . . . . . . . . . . . . . . . . . . . . . 35
14.1. Normative References . . . . . . . . . . . . . . . . . . 35 14.1. Normative References . . . . . . . . . . . . . . . . . . 35
14.2. Informative References . . . . . . . . . . . . . . . . . 37 14.2. Informative References . . . . . . . . . . . . . . . . . 38
Appendix A. Examples . . . . . . . . . . . . . . . . . . . . . . 38 Appendix A. Examples . . . . . . . . . . . . . . . . . . . . . . 38
Appendix B. The remote-candidates Attribute . . . . . . . . . . 40 Appendix B. The remote-candidates Attribute . . . . . . . . . . 40
Appendix C. Why Is the Conflict Resolution Mechanism Needed? . . 40 Appendix C. Why Is the Conflict Resolution Mechanism Needed? . . 41
Appendix D. Why Send an Updated Offer? . . . . . . . . . . . . . 41 Appendix D. Why Send an Updated Offer? . . . . . . . . . . . . . 42
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 42 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 43
1. Introduction 1. Introduction
This document describes how Interactive Connectivity Establishment This document describes how Interactive Connectivity Establishment
(ICE) is used with Session Description Protocol (SDP) offer/answer (ICE) is used with Session Description Protocol (SDP) offer/answer
[RFC3264] and Session Initiation Protocol (SIP). The ICE [RFC3264] and Session Initiation Protocol (SIP). The ICE
specification [ICE-BIS] describes procedures that are common to all specification [ICE-BIS] describes procedures that are common to all
usages of ICE and this document gives the additional details needed usages of ICE and this document gives the additional details needed
to use ICE with SDP offer/answer and SIP. to use ICE with SDP offer/answer and SIP.
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assumed to be provided via another mechanism [RFC5626]. assumed to be provided via another mechanism [RFC5626].
2. Terminology 2. Terminology
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in RFC "OPTIONAL" in this document are to be interpreted as described in RFC
2119 [RFC2119]. 2119 [RFC2119].
Readers should be familiar with the terminology defined in [RFC3264], Readers should be familiar with the terminology defined in [RFC3264],
in [ICE-BIS] and the following: in [RFC7656], in [ICE-BIS] and the following:
Default Destination/Candidate: The default destination for a Default Destination/Candidate: The default destination for a
component of a media stream is the transport address that would be component of a media stream is the transport address that would be
used by an agent that is not ICE aware. A default candidate for a used by an agent that is not ICE aware. A default candidate for a
component is one whose transport address matches the default component is one whose transport address matches the default
destination for that component. For the RTP component, the destination for that component. For the RTP component, the
default IP address is in the "c=" line of the SDP, and the port is default IP address is in the "c=" line of the SDP, and the port is
in the "m=" line.For the RTCP component, it is in the rtcp in the "m=" line. For the RTCP component, the address and port
attribute when present, and when not present, the IP address is in are indicated using the "a=rtcp" attribute defined in [RFC3605],
the "c=" line and 1 plus the port is in the "m=" line. if present; otherwise, the RTCP component address is same as the
address of the RTP component, and its port is one greater than the
port of the RTP component.
3. ICE Candidate Exchange and Offer/Answer Mapping 3. ICE Candidate Exchange and Offer/Answer Mapping
[ICE-BIS] defines ICE candidate exchange as the process for ICE [ICE-BIS] defines ICE candidate exchange as the process for ICE
agents (Initiator and Responder) to exchange their candidate agents (Initiator and Responder) to exchange their candidate
information required for ICE processing at the agents. For the information required for ICE processing at the agents. For the
purposes of this specification, the candidate exchange process purposes of this specification, the candidate exchange process
corresponds to the [RFC3264] Offer/Answer protocol and the corresponds to the [RFC3264] Offer/Answer protocol and the
terminologies offerer and answerer correspond to the initiator and terminologies offerer and answerer correspond to the initiator and
responder terminologies from the [ICE-BIS] respectively. responder terminologies from [ICE-BIS] respectively.
4. SDP Offer/Answer Procedures 4. SDP Offer/Answer Procedures
4.1. Initial Offer/Answer Exchange 4.1. Initial Offer/Answer Exchange
4.1.1. Sending the Initial Offer 4.1.1. Sending the Initial Offer
The offerer shall follow the procedures defined in section 4 of The offerer shall follow the procedures defined in section 4 of
[ICE-BIS] to gather, prioritize and eliminate the redundant [ICE-BIS] to gather, prioritize and eliminate the redundant
candidates. It then chooses the default candidates and encodes them candidates. It then chooses the default candidates and encodes them
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so that the default destination for media matches the candidates so that the default destination for media matches the candidates
selected by ICE. If ICE happens to select the default candidates, no selected by ICE. If ICE happens to select the default candidates, no
updated offer/answer is required. updated offer/answer is required.
An agent MUST choose a set of candidates, one for each component of An agent MUST choose a set of candidates, one for each component of
each in-use media stream, to be default. A media stream is in-use if each in-use media stream, to be default. A media stream is in-use if
it does not have a port of zero (which is used in RFC 3264 to reject it does not have a port of zero (which is used in RFC 3264 to reject
a media stream). Consequently, a media stream is in-use even if it a media stream). Consequently, a media stream is in-use even if it
is marked as a=inactive [RFC4566] or has a bandwidth value of zero. is marked as a=inactive [RFC4566] or has a bandwidth value of zero.
An ageny may choose any type of the candidate as the default, if the
chosen candidates increases the likelihood of success with the peer
that is being contacted if ICE is not being used.
It is RECOMMENDED that default candidates be chosen based on the It is RECOMMENDED that default candidates be chosen based on the
likelihood of those candidates to work with the peer that is being likelihood of those candidates to work with the peer that is being
contacted if ICE is not being used. It is RECOMMENDED that the contacted if ICE is not being used. Many factors may influence such
default candidates are the relayed candidates (if relayed candidates a decision in a given agent. In scenarios where the agent is fully
are available), server reflexive candidates (if server reflexive aware of its peer's location and can reach the peer directly,
choosing the host candidates as the default may well be sufficient.
If the network configuration under which the agents operates is
static and known beforehand, either the host or the server reflexives
candidates can serve as the default candidates (depending on if a
given agent is behind NAT and their reachability). If the agent is
completely unaware of the peer's location or no assumptions can be
made of network characteristics and the connectivity, the relayed
candidates might be the only option as the default candidate. Having
the decision of choosing the default candidate as a configurable
option in the implementations might provide agents the flexibility to
take into account the aforementioned criteria. Barring such
configuration flexibility, it is RECOMMENDED that the default
candidates be the relayed candidates (if relayed candidates are
available), server reflexive candidates (if server reflexive
candidates are available), and finally host candidates. candidates are available), and finally host candidates.
4.1.1.2. Encoding the SDP 4.1.1.2. Encoding the SDP
The process of encoding the SDP is identical between full and lite The process of encoding the SDP is identical between full and lite
implementations. implementations.
The agent will include an "m=" line for each media stream it wishes The agent will include an "m=" line for each Source Stream [RFC7656]
to use. The ordering of media streams in the SDP is relevant for it wishes to use. The ordering of source streams in the SDP is
ICE. ICE will perform its connectivity checks for the first "m=" relevant for ICE. ICE will perform its connectivity checks for the
line first, and consequently media will be able to flow for that first "m=" line first, and consequently media will be able to flow
stream first. Agents SHOULD place their most important media stream, for that stream first. Agents SHOULD place their most important
if there is one, first in the SDP. source stream, if there is one, first in the SDP.
There will be a candidate attribute for each candidate for a There will be a candidate attribute for each candidate for a
particular media stream. Section 5 provides detailed rules for particular source stream. Section 5 provides detailed rules for
constructing this attribute. constructing this attribute.
STUN connectivity checks between agents are authenticated using the STUN connectivity checks between agents are authenticated using the
short-term credential mechanism defined for STUN [RFC5389]. This short-term credential mechanism defined for STUN [RFC5389]. This
mechanism relies on a username and password that are exchanged mechanism relies on a username and password that are exchanged
through protocol machinery between the client and server. The through protocol machinery between the client and server. The
username fragment and password are exchanged in the ice-ufrag and username fragment and password are exchanged in the ice-ufrag and
ice-pwd attributes, respectively. ice-pwd attributes, respectively.
If an agent is a lite implementation, it MUST include an "a=ice-lite" If an agent is a lite implementation, it MUST include an "a=ice-lite"
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a full implementation, it MUST NOT include this attribute. a full implementation, it MUST NOT include this attribute.
Section 7 of [ICE-BIS] defines a new ICE option, 'ice2'. This option Section 7 of [ICE-BIS] defines a new ICE option, 'ice2'. This option
is used by ICE Agents to indicate their compliancy with [ICE-BIS] is used by ICE Agents to indicate their compliancy with [ICE-BIS]
specification as compared to the [RFC5245]. If the Offering agent is specification as compared to the [RFC5245]. If the Offering agent is
a [ICE-BIS] compliant implementation, a session level ICE option to a [ICE-BIS] compliant implementation, a session level ICE option to
indicate the same (via the "a=ice-options:ice2" SDP line) MUST be indicate the same (via the "a=ice-options:ice2" SDP line) MUST be
included. included.
The default candidates are added to the SDP as the default The default candidates are added to the SDP as the default
destination for media. For streams based on RTP, this is done by destination for media. For source streams based on RTP, this is done
placing the IP address and port of the RTP candidate into the "c=" by placing the IP address and port of the RTP candidate into the "c="
and "m=" lines, respectively. If the agent is utilizing RTCP and if and "m=" lines, respectively. If the agent is utilizing RTCP and if
RTCP candidate is present and is not equal to the same address and RTCP candidate is present and is not equal to the same address and
the next higher port number of the RTP candidate, the agent MUST the next higher port number of the RTP candidate, the agent MUST
encode the RTCP candidate using the a=rtcp attribute as defined in encode the RTCP candidate using the a=rtcp attribute as defined in
[RFC3605]. If RTCP is not in use, the agent MUST signal that using [RFC3605]. If RTCP is not in use, the agent MUST signal that using
b=RS:0 and b=RR:0 as defined in [RFC3556] b=RS:0 and b=RR:0 as defined in [RFC3556]
The transport addresses that will be the default destination for The transport addresses that will be the default destination for
media when communicating with non-ICE peers MUST also be present as media when communicating with non-ICE peers MUST also be present as
candidates in one or more a=candidate lines. candidates in one or more a=candidate lines.
ICE provides for extensibility by allowing an offer or answer to ICE provides for extensibility by allowing an offer or answer to
contain a series of tokens that identify the ICE extensions used by contain a series of tokens that identify the ICE extensions used by
that agent. If an agent supports an ICE extension, it MUST include that agent. If an agent supports an ICE extension, it MUST include
the token defined for that extension in the ice-options attribute. the token defined for that extension in the ice-options attribute.
The following is an example SDP message that includes ICE attributes The following is an example SDP message that includes ICE attributes
(lines folded for readability): (lines folded for readability):
v=0 v=0
o=jdoe 2890844526 2890842807 IN IP4 10.0.1.1 o=jdoe 2890844526 2890842807 IN IP4 10.0.1.1
s= s=
c=IN IP4 192.0.2.3 c=IN IP4 192.0.2.3
t=0 0 t=0 0
a=ice-options:ice2 a=ice-options:ice2
a=ice-pwd:asd88fgpdd777uzjYhagZg a=ice-pwd:asd88fgpdd777uzjYhagZg
a=ice-ufrag:8hhY a=ice-ufrag:8hhY
m=audio 45664 RTP/AVP 0 m=audio 45664 RTP/AVP 0
b=RS:0 b=RS:0
b=RR:0 b=RR:0
a=rtpmap:0 PCMU/8000 a=rtpmap:0 PCMU/8000
a=candidate:1 1 UDP 2130706431 10.0.1.1 8998 typ host a=candidate:1 1 UDP 2130706431 10.0.1.1 8998 typ host
a=candidate:2 1 UDP 1694498815 192.0.2.3 45664 typ srflx raddr a=candidate:2 1 UDP 1694498815 192.0.2.3 45664 typ srflx raddr
10.0.1.1 rport 8998 10.0.1.1 rport 8998
Once an agent has sent its offer or its answer, that agent MUST be Once an agent has sent its offer or its answer, that agent MUST be
prepared to receive both STUN and media packets on each candidate. prepared to receive both STUN and media packets on each candidate.
As discussed in section 9.1 of [ICE-BIS], media packets can be sent As discussed in section 9.1 of [ICE-BIS], media packets can be sent
to a candidate prior to its appearance as the default destination for to a candidate prior to its appearance as the default destination for
media in an offer or answer. media in an offer or answer.
4.1.2. Receiving the Initial Offer 4.1.2. Receiving the Initial Offer
On receiving the offer, the answerer verifies the support for ICE On receiving the offer, the answerer verifies the support for ICE
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64-bit positive integer). This number is used in connectivity checks 64-bit positive integer). This number is used in connectivity checks
to detect and repair this case, as described in section 6.1.2.3 of to detect and repair this case, as described in section 6.1.2.3 of
[ICE-BIS]. [ICE-BIS].
4.1.3. Receipt of the Initial Answer 4.1.3. Receipt of the Initial Answer
When ICE is used with SIP, forking may result in a single offer When ICE is used with SIP, forking may result in a single offer
generating a multiplicity of answers. In that case, ICE proceeds generating a multiplicity of answers. In that case, ICE proceeds
completely in parallel and independently for each answer, treating completely in parallel and independently for each answer, treating
the combination of its offer and each answer as an independent offer/ the combination of its offer and each answer as an independent offer/
answer exchange, with its own set of pairs, check lists, states, and answer exchange, with its own set of local candidates, pairs, check
so on. The only case in which processing of one pair impacts another lists, states, and so on. The only case in which processing of one
is freeing of candidates, discussed below in Section 4.1.5.2. pair impacts another is freeing of candidates, discussed below in
Section 4.1.5.
On receiving the SDP answer , the offerer performs steps similar to On receiving the SDP answer,the offerer performs steps similar to
answerer's processing of the offer. The offerer verifies the answerer's processing of the offer. The offerer verifies the
answerer's ICE support, determines its role and processes the answerer's ICE support determines, its role, and processes the
answerer's candidates to schedule the connectivity checks (section 6 answerer's candidates to schedule the connectivity checks (section 6
of [ICE-BIS]). of [ICE-BIS]).
If the offerer had included the "ice2" ICE Option in the offer and If the offerer had included the "ice2" ICE Option in the offer and
the SDP answer also includes a similar session level ICE option, then the SDP answer also includes a similar session level ICE option, then
the peers are [ICE-BIS] complaint implementations. On the other the peers are [ICE-BIS] compliant implementations. On the other
hand, if the SDP Answer lacks such a ICE option, the offerer defaults hand, if the SDP Answer lacks such a ICE option, the offerer defaults
to the procedures that are backward compatible with the [RFC5245] to the procedures that are backward compatible with the [RFC5245]
specification. specification.
4.1.3.1. Verifying ICE Support 4.1.3.1. Verifying ICE Support
The logic at the offerer is identical to that of the answerer as The logic at the offerer is identical to that of the answerer as
described in section 5.1.1 of [ICE-BIS], with the exception that an described in section 5.1.1 of [ICE-BIS], with the exception that an
offerer would not ever generate a=ice-mismatch attributes in an SDP. offerer would not ever generate a=ice-mismatch attributes in an SDP.
skipping to change at page 9, line 26 skipping to change at page 9, line 47
4.1.4. Performing Connectivity Checks 4.1.4. Performing Connectivity Checks
The possibility for role conflicts described in section 6.1.3.1.1 of The possibility for role conflicts described in section 6.1.3.1.1 of
[ICE-BIS] applies to this usage and hence all full agents MUST [ICE-BIS] applies to this usage and hence all full agents MUST
implement the role conflict repairing mechanism. Also both full and implement the role conflict repairing mechanism. Also both full and
lite agents MUST utilize the ICE-CONTROLLED and ICE-CONTROLLING lite agents MUST utilize the ICE-CONTROLLED and ICE-CONTROLLING
attributes as described in section 6.1.2.3 of [ICE-BIS]. attributes as described in section 6.1.2.3 of [ICE-BIS].
4.1.5. Concluding ICE 4.1.5. Concluding ICE
Once all of the media streams are completed, the controlling endpoint
sends an updated offer if the transport destination in the "m=" and
"c=" lines for the media stream (called the DEFAULT CANDIDATES) don't
match ICE's selected candidates.
4.1.5.1. Procedures for Full Implementations
4.1.5.1.1. Updating states
Once the state of each check list is Completed, If an agent is Once the state of each check list is Completed, If an agent is
controlling, it examines the highest-priority nominated candidate controlling, it examines the highest-priority nominated candidate
pair for each component of each media stream. If any of those pair for each component of each media stream. If any of those
candidate pairs differ from the default candidate pairs in the most candidate pairs differ from the default candidate pairs in the most
recent offer/answer exchange, the controlling agent MUST generate an recent offer/answer exchange, the controlling agent MUST generate an
updated offer as described in Section 4.2. updated offer as described in Section 4.2.
4.1.5.2. Freeing Candidates
4.1.5.2.1. Full Implementation Procedures
When ICE is used with SIP, and an offer is forked to multiple When ICE is used with SIP, and an offer is forked to multiple
recipients, ICE proceeds in parallel and independently with each recipients, ICE proceeds in parallel and independently with each
answerer, all using the same local candidates. Once ICE processing answerer, all using the same local candidates. Once ICE processing
has reached the Completed state for all peers for media streams using has reached the Completed state for all peers for media streams using
those candidates, the agent SHOULD wait an additional three seconds, those candidates, the agent SHOULD wait an additional three seconds,
and then it MAY cease responding to checks or generating triggered and then it MAY cease responding to checks or generating triggered
checks on that candidate. It MAY free the candidate at that time. checks on that candidate. It MAY free the candidate at that time.
Freeing of server reflexive candidates is never explicit; it happens Freeing of server reflexive candidates is never explicit; it happens
by lack of a keepalive. The three-second delay handles cases when by lack of a keepalive. The three-second delay handles cases when
skipping to change at page 10, line 19 skipping to change at page 10, line 29
4.2. Subsequent Offer/Answer Exchanges 4.2. Subsequent Offer/Answer Exchanges
Either agent MAY generate a subsequent offer at any time allowed by Either agent MAY generate a subsequent offer at any time allowed by
[RFC3264]. The rules in Section 4.1.5 will cause the controlling [RFC3264]. The rules in Section 4.1.5 will cause the controlling
agent to send an updated offer at the conclusion of ICE processing agent to send an updated offer at the conclusion of ICE processing
when ICE has selected different candidate pairs from the default when ICE has selected different candidate pairs from the default
pairs. This section defines rules for construction of subsequent pairs. This section defines rules for construction of subsequent
offers and answers. offers and answers.
Should a subsequent offer be rejected, ICE processing continues as if Should a subsequent offer fail, ICE processing continues as if the
the subsequent offer had never been made. subsequent offer had never been made.
4.2.1. Generating the Offer 4.2.1. Generating the Offer
4.2.1.1. Procedures for All Implementations 4.2.1.1. Procedures for All Implementations
4.2.1.1.1. ICE Restarts 4.2.1.1.1. ICE Restarts
An agent MAY restart ICE processing for an existing media stream as An agent MAY restart ICE processing for an existing media stream as
defined in section 6.3 of [ICE-BIS]. defined in section 6.3 of [ICE-BIS].
The rules govering the ICE restart imply that setting the IP address The rules governing the ICE restart imply that setting the IP address
in the "c=" line to 0.0.0.0 will cause an ICE restart. Consequently, in the "c=" line to 0.0.0.0 will cause an ICE restart. Consequently,
ICE implementations MUST NOT utilize this mechanism for call hold, ICE implementations MUST NOT utilize this mechanism for call hold,
and instead MUST use a=inactive and a=sendonly as described in and instead MUST use a=inactive and a=sendonly as described in
[RFC3264]. [RFC3264].
To restart ICE, an agent MUST change both the ice-pwd and the ice- To restart ICE, an agent MUST change both the ice-pwd and the ice-
ufrag for the media stream in an offer. Note that it is permissible ufrag for the media stream in an offer. Note that it is permissible
to use a session-level attribute in one offer, but to provide the to use a session-level attribute in one offer, but to provide the
same ice-pwd or ice-ufrag as a media-level attribute in a subsequent same ice-pwd or ice-ufrag as a media-level attribute in a subsequent
offer. This is not a change in password, just a change in its offer. This is not a change in password, just a change in its
skipping to change at page 11, line 24 skipping to change at page 11, line 32
If an agent wishes to add a new media stream, it sets the fields in If an agent wishes to add a new media stream, it sets the fields in
the SDP for this media stream as if this was an initial offer for the SDP for this media stream as if this was an initial offer for
that media stream (see Section 4.1.1.2). This will cause ICE that media stream (see Section 4.1.1.2). This will cause ICE
processing to begin for this media stream. processing to begin for this media stream.
4.2.1.2. Procedures for Full Implementations 4.2.1.2. Procedures for Full Implementations
This section describes additional procedures for full This section describes additional procedures for full
implementations, covering existing media streams. implementations, covering existing media streams.
The username fragments, password, and implementation level MUST
remain the same as used previously. If an agent needs to change one
of these, it MUST restart ICE for that media stream.
Additional behavior depends on the state ICE processing for that
media stream.
4.2.1.2.1. Existing Media Streams with ICE Running 4.2.1.2.1. Existing Media Streams with ICE Running
If an agent generates an updated offer including a media stream that If an agent generates an updated offer including a media stream that
was previously established, and for which ICE checks are in the was previously established, and for which ICE checks are in the
Running state, the agent follows the procedures defined here. Running state, the agent follows the procedures defined here.
An agent MUST include candidate attributes for all local candidates An agent MUST include candidate attributes for all local candidates
it had signaled previously for that media stream. The properties of it had signaled previously for that media stream. The properties of
that candidate as signaled in SDP -- the priority, foundation, type, that candidate as signaled in SDP -- the priority, foundation, type,
and related transport address -- SHOULD remain the same. The IP and related transport address -- SHOULD remain the same. The IP
address, port, and transport protocol, which fundamentally identify address, port, and transport protocol, which fundamentally identify
that candidate, MUST remain the same (if they change, it would be a that candidate, MUST remain the same (if they change, it would be a
new candidate). The component ID MUST remain the same. The agent new candidate). The component ID MUST remain the same. The agent
MAY include additional candidates it did not offer previously, but MAY include additional candidates it did not offer previously (see
which it has gathered since the last offer/answer exchange, including section 4.2.4.1.1), but which it has gathered since the last offer/
peer reflexive candidates. answer exchange, including peer reflexive candidates.
The agent MAY change the default destination for media. As with The agent MAY change the default destination for media. As with
initial offers, there MUST be a set of candidate attributes in the initial offers, there MUST be a set of candidate attributes in the
offer matching this default destination. offer matching this default destination.
4.2.1.2.2. Existing Media Streams with ICE Completed 4.2.1.2.2. Existing Media Streams with ICE Completed
If an agent generates an updated offer including a media stream that If an agent generates an updated offer including a media stream that
was previously established, and for which ICE checks are in the was previously established, and for which ICE checks are in the
Completed state, the agent follows the procedures defined here. Completed state, the agent follows the procedures defined here.
skipping to change at page 16, line 31 skipping to change at page 16, line 31
offer/answer exchanges will have resolved this glare condition, so offer/answer exchanges will have resolved this glare condition, so
that one agent is always the 'winner' by having its offer received that one agent is always the 'winner' by having its offer received
before its peer has sent an offer. The winner takes the role of before its peer has sent an offer. The winner takes the role of
controlling, so that the loser (the answerer under consideration in controlling, so that the loser (the answerer under consideration in
this section) MUST change its role to controlled. Consequently, if this section) MUST change its role to controlled. Consequently, if
the agent was going to send an updated offer since, based on the the agent was going to send an updated offer since, based on the
rules in section 6.2 of [ICE-BIS], it was controlling, it no longer rules in section 6.2 of [ICE-BIS], it was controlling, it no longer
needs to. needs to.
Besides the potential role change, change in the Valid list, and Besides the potential role change, change in the Valid list, and
state changes, the construction of the answer is performed i state changes, the construction of the answer is performed
dentically to the construction of an offer as described in identically to the construction of an offer as described in
Section 4.2.1.3. Section 4.2.1.3.
4.2.3. Receiving the Answer for a Subsequent Offer 4.2.3. Receiving the Answer for a Subsequent Offer
Some deployments of ICE include e.g. SDP-Modifying Signaling-only Some deployments of ICE include e.g. SDP-Modifying Signaling-only
Back-to-Back User Agents (B2BUAs) [RFC7092] that modify the SDP body Back-to-Back User Agents (B2BUAs) [RFC7092] that modify the SDP body
during the subsequent offer/answer exchange. With the B2BUA being during the subsequent offer/answer exchange. With the B2BUA being
ICE-unaware a subsequent answer might be manipulated and might not ICE-unaware, a subsequent answer might be manipulated and might not
include ICE candidates although the initial answer did. include ICE candidates although the initial answer did.
An example of a situation where such an "unexpected" answer might be An example of a situation where such an "unexpected" answer might be
experienced appears when such a B2BUA introduces a media server experienced appears when such a B2BUA introduces a media server
during call hold using 3rd party call-control procedures. Omitting during call hold using 3rd party call-control procedures. Omitting
further details how this is done this could result in an answer being further details how this is done this could result in an answer being
received at the holding UA that was constructed by the B2BUA. With received at the holding UA that was constructed by the B2BUA. With
the B2BUA being ICE-unaware that answer would not include ICE the B2BUA being ICE-unaware, that answer would not include ICE
candidates. candidates.
Receiving an answer without ICE attributes in this situation might be Receiving an answer without ICE attributes in this situation might be
unexpected, but would not necessarily impair the user experience. unexpected, but would not necessarily impair the user experience.
In addition to procedures for the expected answer, the following In addition to procedures for the expected answer, the following
sections advice on how to recover from the unexpected situation. section advices on how to recover from the unexpected situation.
4.2.3.1. Procedures for All Implementations 4.2.3.1. Procedures for All Implementations
When receiving an answer within an existing session for a subsequent When receiving an answer within an existing session for a subsequent
offer as specified in Section 4.2.1.2.2, an agent MUST verify ICE offer as specified in Section 4.2.1.2.2, an agent MUST verify ICE
support as specified in Section 4.1.3.1. support as specified in Section 4.1.3.1.
4.2.3.1.1. ICE Restarts If ICE support is indicated in the SDP answer and the offer was a
restart, the agent MUST perform ICE restart procedures as specified
If ICE support is indicated in the SDP answer, the agent MUST perform in Section 4.2.4. If ICE support is no longer indicated in the SDP
ICE restart procedures as specified in Section 4.2.4. answer, the agent MUST fall-back to [RFC3264] procedures and SHOULD
NOT drop the dialog just because of missing ICE support. If the
If ICE support is no longer indicated in the SDP answer, the agent agent sends a new offer later on, it SHOULD perform an ICE restart as
MUST fall-back to RFC 3264 procedures and SHOULD NOT drop the dialog specified in Section 4.2.1.1.1.
just because of missing ICE support. If the agent sends a new offer
later on it SHOULD perform an ICE restart as specified in
Section 4.2.1.1.1.
4.2.3.1.2. Existing Media Streams with ICE Running
If ICE support is indicated in the SDP answer, the agent MUST
continue ICE procedures as specified in Section 4.2.4.1.4.
If ICE support is indicated in the SDP answer and ICE is running, the
agent MUST continue ICE procedures as specified in Section 4.2.4.1.4.
If ICE support is no longer indicated in the SDP answer, the agent If ICE support is no longer indicated in the SDP answer, the agent
MUST abort the ongoing ICE processing and fall-back to RFC 3264 MUST abort the ongoing ICE processing and fall-back to [RFC3264]
procedures. The agent SHOULD NOT drop the dialog just because of procedures. The agent SHOULD NOT drop the dialog just because of
missing ICE support. If the agent sends a new offer later on, it missing ICE support. If the agent sends a new offer later on, it
SHOULD perform an ICE restart as specified in Section 4.2.1.1.1. SHOULD perform an ICE restart as specified in Section 4.2.1.1.1.
4.2.3.1.3. Existing Media Streams with ICE Completed If ICE support is indicated in the SDP answer and if ICE is completed
and the answer conforms to Section 4.2.2.2.3, the agent MUST remain
If ICE support is indicated in the SDP answer and if the answer in the ICE Completed state. If ICE support is no longer indicated in
conforms to Section 4.2.2.2.3, the agent MUST remain in the ICE the SDP answer, the agent MUST fall-back to [RFC3264] procedures and
Completed state. SHOULD NOT drop the dialog just because of this unexpected answer.
Once the agent sends a new offer later on it MUST perform an ICE
If ICE support is no longer indicated in the SDP answer, the agent restart.
MUST fall-back to RFC 3264 procedures and SHOULD NOT drop the dialog
just because of this unexpected answer. Once the agent sends a new
offer later on it MUST perform an ICE restart.
4.2.4. Updating the Check and Valid Lists 4.2.4. Updating the Check and Valid Lists
4.2.4.1. Procedures for Full Implementations 4.2.4.1. Procedures for Full Implementations
4.2.4.1.1. ICE Restarts 4.2.4.1.1. ICE Restarts
The agent MUST remember the highest-priority nominated pairs in the The agent MUST remember the highest-priority nominated pairs in the
Valid list for each component of the media stream, called the Valid list for each component of the media stream, called the
previous selected pairs, prior to the restart. The agent will previous selected pairs, prior to the restart. The agent will
continue to send media using these pairs, as described in continue to send media using these pairs, as described in
Section 7.1. Once these destinations are noted, the agent MUST flush Section 7.1. Once these destinations are noted, the agent MUST flush
the valid and check lists, and then recompute the check list and its the valid and check lists, and then recompute the check list and its
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If an agent is in the Running state for that media stream, the check If an agent is in the Running state for that media stream, the check
list is updated (the check list is irrelevant if the state is list is updated (the check list is irrelevant if the state is
completed). To do that, the agent recomputes the check list using completed). To do that, the agent recomputes the check list using
the procedures described in section 5.1.3 of [ICE-BIS]. If a pair on the procedures described in section 5.1.3 of [ICE-BIS]. If a pair on
the new check list was also on the previous check list, and its state the new check list was also on the previous check list, and its state
was Waiting, In-Progress, Succeeded, or Failed, its state is copied was Waiting, In-Progress, Succeeded, or Failed, its state is copied
over. Otherwise, its state is set to Frozen. over. Otherwise, its state is set to Frozen.
If none of the check lists are active (meaning that the pairs in each If none of the check lists are active (meaning that the pairs in each
check list are Frozen), the full-mode agent sets the first pair in check list are Frozen), the full-mode agent follows steps in
the check list for the first media stream to Waiting, and then sets Section 5.1.3.6 of [ICE-BIS] to place appropriate candidates in the
the state of all other pairs in that check list for the same Waiting state to further continue ICE processing.
component ID and with the same foundation to Waiting as well.
Next, the agent goes through each check list, starting with the
highest-priority pair. If a pair has a state of Succeeded, and it
has a component ID of 1, then all Frozen pairs in the same check list
with the same foundation whose component IDs are not 1 have their
state set to Waiting. If, for a particular check list, there are
pairs for each component of that media stream in the Succeeded state,
the agent moves the state of all Frozen pairs for the first component
of all other media streams (and thus in different check lists) with
the same foundation to Waiting.
4.2.4.2. Procedures for Lite Implementations 4.2.4.2. Procedures for Lite Implementations
If ICE is restarting for a media stream, the agent MUST start a new If ICE is restarting for a media stream, the agent MUST start a new
Valid list for that media stream. It MUST remember the pairs in the Valid list for that media stream. It MUST remember the pairs in the
previous Valid list for each component of the media stream, called previous Valid list for each component of the media stream, called
the previous selected pairs, and continue to send media there as the previous selected pairs, and continue to send media there as
described in Section 7.1. The state of ICE processing for each media described in Section 7.1. The state of ICE processing for each media
stream MUST change to Running, and the state of ICE processing MUST stream MUST change to Running, and the state of ICE processing MUST
change to Running. change to Running.
5. Grammar 5. Grammar
This specification defines eight new SDP attributes -- the This specification defines eight new SDP attributes -- the
"candidate", "remote-candidates", "ice-lite", "ice-mismatch", "ice- "candidate", "remote-candidates", "ice-lite", "ice-mismatch", "ice-
ufrag", "ice-pwd", "ice-pacing", and "ice-options" attributes. ufrag", "ice-pwd", "ice-pacing", and "ice-options" attributes. This
section also provides non-normative examples of the attributes
defined.
The syntax for the attributes follow Augmented BNF as defined in
[RFC5234].
5.1. "candidate" Attribute 5.1. "candidate" Attribute
The candidate attribute is a media-level attribute only. It contains The candidate attribute is a media-level attribute only. It contains
a transport address for a candidate that can be used for connectivity a transport address for a candidate that can be used for connectivity
checks. checks.
The syntax of this attribute is defined using Augmented BNF as
defined in [RFC5234]:
candidate-attribute = "candidate" ":" foundation SP component-id SP candidate-attribute = "candidate" ":" foundation SP component-id SP
transport SP transport SP
priority SP priority SP
connection-address SP ;from RFC 4566 connection-address SP ;from RFC 4566
port ;port from RFC 4566 port ;port from RFC 4566
SP cand-type SP cand-type
[SP rel-addr] [SP rel-addr]
[SP rel-port] [SP rel-port]
*(SP extension-att-name SP *(SP extension-att-name SP
extension-att-value) extension-att-value)
skipping to change at page 20, line 35 skipping to change at page 19, line 46
extension-att-name = token extension-att-name = token
extension-att-value = *VCHAR extension-att-value = *VCHAR
ice-char = ALPHA / DIGIT / "+" / "/" ice-char = ALPHA / DIGIT / "+" / "/"
This grammar encodes the primary information about a candidate: its This grammar encodes the primary information about a candidate: its
IP address, port and transport protocol, and its properties: the IP address, port and transport protocol, and its properties: the
foundation, component ID, priority, type, and related transport foundation, component ID, priority, type, and related transport
address: address:
<connection-address>: is taken from RFC 4566 [RFC4566]. It is the <connection-address>: is taken from RFC 4566 [RFC4566]. It is the
IP address of the candidate, allowing for IPv4 addresses, IPv6 IP address of the candidate. When parsing this field, an agent
addresses, and fully qualified domain names (FQDNs). When parsing can differentiate an IPv4 address and an IPv6 address by presence
this field, an agent can differentiate an IPv4 address and an IPv6 of a colon in its value -- the presence of a colon indicates IPv6.
address by presence of a colon in its value -- the presence of a An agent MUST ignore candidate lines that include candidates with
colon indicates IPv6. An agent MUST ignore candidate lines that IP address versions that are not supported or recognized. An IP
include candidates with IP address versions that are not supported address SHOULD be used, but an FQDN MAY be used in place of an IP
or recognized. An IP address SHOULD be used, but an FQDN MAY be address. In that case, when receiving an offer or answer
used in place of an IP address. In that case, when receiving an containing an FQDN in an a=candidate attribute, the FQDN is looked
offer or answer containing an FQDN in an a=candidate attribute, up in the DNS first using an AAAA record (assuming the agent
the FQDN is looked up in the DNS first using an AAAA record supports IPv6), and if no result is found or the agent only
(assuming the agent supports IPv6), and if no result is found or supports IPv4, using an A record. The rules from section 6 of
the agent only supports IPv4, using an A. If the DNS query [RFC6724] is followed by fixing the source address to be one from
returns more than one IP address, one is chosen, and then used for the candidate pair to be matched against destination addresses
the remainder of ICE processing. reported by FQDN, in cases where the DNS query returns more than
one IP address.
<port>: is also taken from RFC 4566 [RFC4566]. It is the port of <port>: is also taken from RFC 4566 [RFC4566]. It is the port of
the candidate. the candidate.
<transport>: indicates the transport protocol for the candidate. <transport>: indicates the transport protocol for the candidate.
This specification only defines UDP. However, extensibility is This specification only defines UDP. However, extensibility is
provided to allow for future transport protocols to be used with provided to allow for future transport protocols to be used with
ICE, such as TCP or the Datagram Congestion Control Protocol ICE, such as the Datagram Congestion Control Protocol (DCCP)
(DCCP) [RFC4340]. [RFC4340].
<foundation>: is composed of 1 to 32 <ice-char>s. It is an <foundation>: is composed of 1 to 32 <ice-char>s. It is an
identifier that is equivalent for two candidates that are of the identifier that is equivalent for two candidates that are of the
same type, share the same base, and come from the same STUN same type, share the same base, and come from the same STUN
server. The foundation is used to optimize ICE performance in the server. The foundation is used to optimize ICE performance in the
Frozen algorithm. Frozen algorithm as described in section 5.1.3 of [ICE-BIS]
<component-id>: is a positive integer between 1 and 256 that <component-id>: is a positive integer between 1 and 256 that
identifies the specific component of the media stream for which identifies the specific component of the media stream for which
this is a candidate. It MUST start at 1 and MUST increment by 1 this is a candidate. It MUST start at 1 and MUST increment by 1
for each component of a particular candidate. For media streams for each component of a particular candidate. For media streams
based on RTP, candidates for the actual RTP media MUST have a based on RTP, candidates for the actual RTP media MUST have a
component ID of 1, and candidates for RTCP MUST have a component component ID of 1, and candidates for RTCP MUST have a component
ID of 2. See section 10 in [ICE-BIS] for additional discussion on ID of 2. See section 10 in [ICE-BIS] for additional discussion on
extending ICE to new media streams. extending ICE to new media streams.
<priority>: is a positive integer between 1 and (2**31 - 1). <priority>: is a positive integer between 1 and (2**31 - 1). The
procedures for computing candidate's priority is described in
section 4.1.2 of [ICE-BIS].
<cand-type>: encodes the type of candidate. This specification <cand-type>: encodes the type of candidate. This specification
defines the values "host", "srflx", "prflx", and "relay" for host, defines the values "host", "srflx", "prflx", and "relay" for host,
server reflexive, peer reflexive, and relayed candidates, server reflexive, peer reflexive, and relayed candidates,
respectively. The set of candidate types is extensible for the respectively. The set of candidate types is extensible for the
future. future.
<rel-addr> and <rel-port>: convey transport addresses related to the <rel-addr> and <rel-port>: convey transport addresses related to the
candidate, useful for diagnostics and other purposes. <rel-addr> candidate, useful for diagnostics and other purposes. <rel-addr>
and <rel-port> MUST be present for server reflexive, peer and <rel-port> MUST be present for server reflexive, peer
reflexive, and relayed candidates. If a candidate is server or reflexive, and relayed candidates. If a candidate is server or
peer reflexive, <rel-addr> and <rel-port> are equal to the base peer reflexive, <rel-addr> and <rel-port> are equal to the base
for that server or peer reflexive candidate. If the candidate is for that server or peer reflexive candidate. If the candidate is
relayed, <rel-addr> and <rel-port> is equal to the mapped address relayed, <rel-addr> and <rel-port> are equal to the mapped address
in the Allocate response that provided the client with that in the Allocate response that provided the client with that
relayed candidate (see section Appendix B.3 of [ICE-BIS] for a relayed candidate (see section Appendix B.3 of [ICE-BIS] for a
discussion of its purpose). If the candidate is a host candidate, discussion of its purpose). If the candidate is a host candidate,
<rel-addr> and <rel-port> MUST be omitted. <rel-addr> and <rel-port> MUST be omitted.
In some cases, e.g., for privacy reasons, an agent may not want to In some cases, e.g., for privacy reasons, an agent may not want to
reveal the related address and port. In this case the address reveal the related address and port. In this case the address
MUST be set to "0.0.0.0" (for IPv4 candidates) or "::" (for IPv6 MUST be set to "0.0.0.0" (for IPv4 candidates) or "::" (for IPv6
candidates) and the port to zero. candidates) and the port to zero.
The candidate attribute can itself be extended. The grammar allows The candidate attribute can itself be extended. The grammar allows
for new name/value pairs to be added at the end of the attribute. An for new name/value pairs to be added at the end of the attribute. An
implementation MUST ignore any name/value pairs it doesn't implementation MUST ignore any name/value pairs it doesn't
understand. understand.
Example: SDP line for UDP server reflexive candidate attribute for the RTP component
a=candidate:2 1 UDP 1694498815 192.0.2.3 45664 typ
srflx raddr 10.0.1.1 rport 8998
5.2. "remote-candidates" Attribute 5.2. "remote-candidates" Attribute
The syntax of the "remote-candidates" attribute is defined using The syntax of the "remote-candidates" attribute is defined using
Augmented BNF as defined in RFC 5234 [RFC5234]. The remote- Augmented BNF as defined in [RFC5234]. The remote-candidates
candidates attribute is a media-level attribute only. attribute is a media-level attribute only.
remote-candidate-att = "remote-candidates" ":" remote-candidate remote-candidate-att = "remote-candidates:" remote-candidate
0*(SP remote-candidate) 0*(SP remote-candidate)
remote-candidate = component-ID SP connection-address SP port remote-candidate = component-ID SP connection-address SP port
The attribute contains a connection-address and port for each The attribute contains a connection-address and port for each
component. The ordering of components is irrelevant. However, a component. The ordering of components is irrelevant. However, a
value MUST be present for each component of a media stream. This value MUST be present for each component of a media stream. This
attribute MUST be included in an offer by a controlling agent for a attribute MUST be included in an offer by a controlling agent for a
media stream that is Completed, and MUST NOT be included in any other media stream that is Completed, and MUST NOT be included in any other
case. case.
Example: Remote candidates SDP lines for the RTP and RTCP components:
a=remote-candidates:1 192.0.2.3 45664
a=remote-candidates:2 192.0.2.3 45665
5.3. "ice-lite" and "ice-mismatch" Attributes 5.3. "ice-lite" and "ice-mismatch" Attributes
The syntax of the "ice-lite" and "ice-mismatch" attributes, both of The syntax of the "ice-lite" and "ice-mismatch" attributes, both of
which are flags, is: which are flags, is:
ice-lite = "ice-lite" ice-lite = "ice-lite"
ice-mismatch = "ice-mismatch" ice-mismatch = "ice-mismatch"
"ice-lite" is a session-level attribute only, and indicates that an "ice-lite" is a session-level attribute only, and indicates that an
agent is a lite implementation. "ice-mismatch" is a media-level agent is a lite implementation. "ice-mismatch" is a media-level
attribute only, and when present in an answer, indicates that the attribute only, and when present in an answer, indicates that the
offer arrived with a default destination for a media component that offer arrived with a default destination for a media component that
didn't have a corresponding candidate attribute. didn't have a corresponding candidate attribute.
5.4. "ice-ufrag" and "ice-pwd" Attributes 5.4. "ice-ufrag" and "ice-pwd" Attributes
The "ice-ufrag" and "ice-pwd" attributes convey the username fragment The "ice-ufrag" and "ice-pwd" attributes convey the username fragment
and password used by ICE for message integrity. Their syntax is: and password used by ICE for message integrity. Their syntax is:
ice-pwd-att = "ice-pwd" ":" password ice-pwd-att = "ice-pwd:" password
ice-ufrag-att = "ice-ufrag" ":" ufrag ice-ufrag-att = "ice-ufrag:" ufrag
password = 22*256ice-char password = 22*256ice-char
ufrag = 4*256ice-char ufrag = 4*256ice-char
The "ice-pwd" and "ice-ufrag" attributes can appear at either the The "ice-pwd" and "ice-ufrag" attributes can appear at either the
session-level or media-level. When present in both, the value in the session-level or media-level. When present in both, the value in the
media-level takes precedence. Thus, the value at the session-level media-level takes precedence. Thus, the value at the session-level
is effectively a default that applies to all media streams, unless is effectively a default that applies to all media streams, unless
overridden by a media-level value. Whether present at the session or overridden by a media-level value. Whether present at the session or
media-level, there MUST be an ice-pwd and ice-ufrag attribute for media-level, there MUST be an ice-pwd and ice-ufrag attribute for
each media stream. If two media streams have identical ice-ufrag's, each media stream. If two media streams have identical ice-ufrag's,
they MUST have identical ice-pwd's. they MUST have identical ice-pwd's.
The ice-ufrag and ice-pwd attributes MUST be chosen randomly at the The ice-ufrag and ice-pwd attributes MUST be chosen randomly at the
beginning of a session. The ice-ufrag attribute MUST contain at beginning of a session. The ice-ufrag attribute MUST contain at
least 24 bits of randomness, and the ice-pwd attribute MUST contain least 24 bits of randomness, and the ice-pwd attribute MUST contain
at least 128 bits of randomness. This means that the ice-ufrag at least 128 bits of randomness. This means that the ice-ufrag
attribute will be at least 4 characters long, and the ice-pwd at attribute will be at least 4 characters long, and the ice-pwd at
least 22 characters long, since the grammar for these attributes least 22 characters long, since the grammar for these attributes
allows for 6 bits of randomness per character. The attributes MAY be allows for 6 bits of information per character. The attributes MAY
longer than 4 and 22 characters, respectively, of course, up to 256 be longer than 4 and 22 characters, respectively, of course, up to
characters. The upper limit allows for buffer sizing in 256 characters. The upper limit allows for buffer sizing in
implementations. Its large upper limit allows for increased amounts implementations. Its large upper limit allows for increased amounts
of randomness to be added over time. For compatibility with the 512 of randomness to be added over time. For compatibility with the 512
character limitation for the STUN username attribute value and for character limitation for the STUN username attribute value and for
bandwidth conservation considerations, the ice-ufrag attribute MUST bandwidth conservation considerations, the ice-ufrag attribute MUST
NOT be longer than 32 characters when sending, but an implementation NOT be longer than 32 characters when sending, but an implementation
MUST accept up to 256 characters when receiving. MUST accept up to 256 characters when receiving.
Example shows sample ice-ufrag and ice-pwd SDP lines:
a=ice-pwd:asd88fgpdd777uzjYhagZg
a=ice-ufrag:8hhY
5.5. "ice-pacing" Attribute 5.5. "ice-pacing" Attribute
The "ice-pacing" attribute indicates the desired connectivity check The "ice-pacing" attribute indicates the desired connectivity check
pacing, in milliseconds, for this agent (see section 11 of pacing, in milliseconds, for this agent (see section 11 of
[ICE-BIS]). The syntax is: [ICE-BIS]). The syntax is:
ice-pacing-att = "ice-pacing" ":" pacing-value ice-pacing-att = "ice-pacing:" pacing-value
pacing-value = 1*10DIGIT pacing-value = 1*10DIGIT
Example shows ice-pacing value of 5 ms:
a=ice-pacing:5
5.6. "ice-options" Attribute 5.6. "ice-options" Attribute
The "ice-options" attribute is a session- and media-level attribute. The "ice-options" attribute is a session- and media-level attribute.
It contains a series of tokens that identify the options supported by It contains a series of tokens that identify the options supported by
the agent. Its grammar is: the agent. Its grammar is:
ice-options = "ice-options" ":" ice-option-tag ice-options = "ice-options:" ice-option-tag
0*(SP ice-option-tag) 0*(SP ice-option-tag)
ice-option-tag = 1*ice-char ice-option-tag = 1*ice-char
The existence of an ice-option can indicate that a certain extension The existence of an ice-option can indicate that a certain extension
is supported by the agent and will be used or that the extension is is supported by the agent and will be used or that the extension is
used only if the other agent is willing to use it too. In order to used only if the other agent is willing to use it too. In order to
avoid ambiguity, documents defining new options must indicate which avoid ambiguity, documents defining new options must indicate which
case applies to the defined extensions. case applies to the defined extensions.
Example shows 'rtp+ecn' ice-option SDP line from <<RFC6679>>:
a=ice-options:rtp+ecn
6. Keepalives 6. Keepalives
The procedures defined in section 8 of [ICE-BIS] MUST be followed. All the ICE agents MUST follow the procedures defined in section 9 of
The keepalives MUST be sent regardless of whether the media stream is [ICE-BIS] for sending keepalives. The keepalives MUST be sent
currently inactive, sendonly, recvonly, or sendrecv, and regardless regardless of whether the media stream is currently inactive,
of the presence or value of the bandwidth attribute. An agent can sendonly, recvonly, or sendrecv, and regardless of the presence or
determine that its peer supports ICE by the presence of a=candidate value of the bandwidth attribute. An agent can determine that its
attributes for each media session. peer supports ICE by the presence of a=candidate attributes for each
media session.
7. Media Handling 7. Media Handling
7.1. Sending Media 7.1. Sending Media
Note that the selected pair for a component of a media stream may not The selected pair for a component of a media stream might not equal
equal the default pair for that same component from the most recent the default pair for that same component from the most recent offer/
offer/answer exchange. When this happens, the selected pair is used answer exchange. When this happens, the selected pair is used for
for media, not the default pair. When ICE first completes, if the media, not the default pair. When ICE first completes, if the
selected pairs aren't a match for the default pairs, the controlling selected pairs aren't a match for the default pairs, the controlling
agent sends an updated offer/answer exchange to remedy this agent sends an updated offer/answer exchange to remedy this
disparity. However, until that updated offer arrives, there will not disparity. However, until that updated offer arrives, there will not
be a match. Furthermore, in very unusual cases, the default be a match. Furthermore, in very unusual cases, the default
candidates in the updated offer/answer will not be a match. candidates in the updated offer/answer will not be a match.
7.1.1. Procedures for All Implementations 7.1.1. Procedures for All Implementations
section 9.1.3 of [ICE-BIS] defines procedures for sending media section 9.1.3 of [ICE-BIS] defines procedures for sending media
common across Full and Lite implementations. common across Full and Lite implementations.
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between endpoints. These checks start from the answerer on between endpoints. These checks start from the answerer on
generation of its answer, and start from the offerer when it receives generation of its answer, and start from the offerer when it receives
the answer. These checks can take time to complete, and as such, the the answer. These checks can take time to complete, and as such, the
selection of messages to use with offers and answers can affect selection of messages to use with offers and answers can affect
perceived user latency. Two latency figures are of particular perceived user latency. Two latency figures are of particular
interest. These are the post-pickup delay and the post-dial delay. interest. These are the post-pickup delay and the post-dial delay.
The post-pickup delay refers to the time between when a user "answers The post-pickup delay refers to the time between when a user "answers
the phone" and when any speech they utter can be delivered to the the phone" and when any speech they utter can be delivered to the
caller. The post-dial delay refers to the time between when a user caller. The post-dial delay refers to the time between when a user
enters the destination address for the user and ringback begins as a enters the destination address for the user and ringback begins as a
consequence of having successfully started ringing the phone of the consequence of having successfully started alerting the called user
called party. agent.
Two cases can be considered -- one where the offer is present in the Two cases can be considered -- one where the offer is present in the
initial INVITE and one where it is in a response. initial INVITE and one where it is in a response.
8.1.1. Offer in INVITE 8.1.1. Offer in INVITE
To reduce post-dial delays, it is RECOMMENDED that the caller begin To reduce post-dial delays, it is RECOMMENDED that the caller begin
gathering candidates prior to actually sending its initial INVITE. gathering candidates prior to actually sending its initial INVITE.
This can be started upon user interface cues that a call is pending, This can be started upon user interface cues that a call is pending,
such as activity on a keypad or the phone going off-hook. such as activity on a keypad or the phone going off-hook.
If an offer is received in an INVITE request, the answerer SHOULD On the receipt of the offer, the answerer SHOULD generate an answer
begin to gather its candidates on receipt of the offer and then in a provisional response once it has compelted candidate gathering.
generate an answer in a provisional response once it has completed ICE requires that a provisional response with an SDP be transmitted
that process. ICE requires that a provisional response with an SDP reliably. This can be done through the existing Provisional Response
be transmitted reliably. This can be done through the existing Acknowledgment (PRACK) mechanism [RFC3262] or through an ICE specific
Provisional Response Acknowledgment (PRACK) mechanism [RFC3262] or optimization, wherein, the agent retransmits the provisional response
through an optimization that is specific to ICE. With this with the exponential backoff timers described in [RFC3262]. Such
optimization, provisional responses containing an SDP answer that retransmissions MUST cease on receipt of a STUN Binding request for
begins ICE processing for one or more media streams can be sent one of the media streams signaled in that SDP or on transmission of
reliably without RFC 3262. To do this, the agent retransmits the the answer in a 2xx response. If no Binding request is received
provisional response with the exponential backoff timers described in prior to the last retransmit, the agent does not consider the session
RFC 3262. Retransmits MUST cease on receipt of a STUN Binding terminated. For the ICE lite peers, the agent MUST cease
request for one of the media streams signaled in that SDP (because retransmitting the 18x after sending it four times (ICE will actually
receipt of a Binding request indicates the offerer has received the work even if the peer never receives the 18x; however, experience has
answer) or on transmission of the answer in a 2xx response. If the shown that sending it is important for middleboxes and firewall
peer agent is lite, there will never be a STUN Binding request. In traversal).
such a case, the agent MUST cease retransmitting the 18x after
sending it four times (ICE will actually work even if the peer never It should be noted that the ICE specific optimization is very
receives the 18x; however, experience has shown that sending it is specific to provisional response carrying answers that start ICE
important for middleboxes and firewall traversal). If no Binding processing and it is not a general technique for 1xx reliability.
request is received prior to the last retransmit, the agent does not Also such an optimization SHOULD NOT be used if both agents support
consider the session terminated. Despite the fact that the PRACK.
provisional response will be delivered reliably, the rules for when
an agent can send an updated offer or answer do not change from those Despite the fact that the provisional response will be delivered
specified in RFC 3262. Specifically, if the INVITE contained an reliably, the rules for when an agent can send an updated offer or
offer, the same answer appears in all of the 1xx and in the 2xx answer do not change from those specified in [RFC3262].
response to the INVITE. Only after that 2xx has been sent can an Specifically, if the INVITE contained an offer, the same answer
updated offer/answer exchange occur. This optimization SHOULD NOT be appears in all of the 1xx and in the 2xx response to the INVITE.
used if both agents support PRACK. Note that the optimization is Only after that 2xx has been sent can an updated offer/answer
very specific to provisional response carrying answers that start ICE exchange occur.
processing; it is not a general technique for 1xx reliability.
Alternatively, an agent MAY delay sending an answer until the 200 OK; Alternatively, an agent MAY delay sending an answer until the 200 OK;
however, this results in a poor user experience and is NOT however, this results in a poor user experience and is NOT
RECOMMENDED. RECOMMENDED.
Once the answer has been sent, the agent SHOULD begin its Once the answer has been sent, the agent SHOULD begin its
connectivity checks. Once candidate pairs for each component of a connectivity checks. Once candidate pairs for each component of a
media stream enter the valid list, the answerer can begin sending media stream enter the valid list, the answerer can begin sending
media on that media stream. media on that media stream.
However, prior to this point, any media that needs to be sent towards However, prior to this point, any media that needs to be sent towards
the caller (such as SIP early media [RFC3960]) MUST NOT be the caller (such as SIP early media [RFC3960]) MUST NOT be
transmitted. For this reason, implementations SHOULD delay alerting transmitted. For this reason, implementations SHOULD delay alerting
the called party until candidates for each component of each media the called party until candidates for each component of each media
stream have entered the valid list. In the case of a PSTN gateway, stream have entered the valid list. In the case of a PSTN gateway,
this would mean that the setup message into the PSTN is delayed until this would mean that the setup message into the PSTN is delayed until
this point. Doing this increases the post-dial delay, but has the this point. Doing this increases the post-dial delay, but has the
effect of eliminating 'ghost rings'. Ghost rings are cases where the effect of eliminating 'ghost rings'. Ghost rings are cases where the
called party hears the phone ring, picks up, but hears nothing and called party hears the phone ring, picks up, but hears nothing and
cannot be heard. This technique works without requiring support for, cannot be heard. This technique works without requiring support for,
or usage of, preconditions [RFC3312], since it's a localized or usage of, preconditions [RFC3312]. It also has the benefit of
decision. It also has the benefit of guaranteeing that not a single guaranteeing that not a single packet of media will get clipped, so
packet of media will get clipped, so that post-pickup delay is zero. that post-pickup delay is zero. If an agent chooses to delay local
If an agent chooses to delay local alerting in this way, it SHOULD alerting in this way, it SHOULD generate a 180 response once alerting
generate a 180 response once alerting begins. begins.
8.1.2. Offer in Response 8.1.2. Offer in Response
In addition to uses where the offer is in an INVITE, and the answer In addition to uses where the offer is in an INVITE, and the answer
is in the provisional and/or 200 OK response, ICE works with cases is in the provisional and/or 200 OK response, ICE works with cases
where the offer appears in the response. In such cases, which are where the offer appears in the response. In such cases, which are
common in third party call control [RFC3725], ICE agents SHOULD common in third party call control [RFC3725], ICE agents SHOULD
generate their offers in a reliable provisional response (which MUST generate their offers in a reliable provisional response (which MUST
utilize RFC 3262), and not alert the user on receipt of the INVITE. utilize [RFC3262]), and not alert the user on receipt of the INVITE.
The answer will arrive in a PRACK. This allows for ICE processing to The answer will arrive in a PRACK. This allows for ICE processing to
take place prior to alerting, so that there is no post-pickup delay, take place prior to alerting, so that there is no post-pickup delay,
at the expense of increased call setup delays. Once ICE completes, at the expense of increased call setup delays. Once ICE completes,
the callee can alert the user and then generate a 200 OK when they the callee can alert the user and then generate a 200 OK when they
answer. The 200 OK would contain no SDP, since the offer/answer answer. The 200 OK would contain no SDP, since the offer/answer
exchange has completed. exchange has completed.
Alternatively, agents MAY place the offer in a 2xx instead (in which Alternatively, agents MAY place the offer in a 2xx instead (in which
case the answer comes in the ACK). When this happens, the callee case the answer comes in the ACK). When this happens, the callee
will alert the user on receipt of the INVITE, and the ICE exchanges will alert the user on receipt of the INVITE, and the ICE exchanges
skipping to change at page 27, line 23 skipping to change at page 27, line 21
With ICE, this problem is resolved. The connectivity checks which With ICE, this problem is resolved. The connectivity checks which
occur prior to transmission of media carry username fragments, which occur prior to transmission of media carry username fragments, which
in turn are correlated to a specific callee. Subsequent media in turn are correlated to a specific callee. Subsequent media
packets that arrive on the same candidate pair as the connectivity packets that arrive on the same candidate pair as the connectivity
check will be associated with that same callee. Thus, the caller can check will be associated with that same callee. Thus, the caller can
perform this correlation as long as it has received an answer. perform this correlation as long as it has received an answer.
8.4. Interactions with Preconditions 8.4. Interactions with Preconditions
Quality of Service (QoS) preconditions, which are defined in RFC 3312 Quality of Service (QoS) preconditions, which are defined in
[RFC3312] and RFC 4032 [RFC4032], apply only to the transport [RFC3312] and [RFC4032], apply only to the transport addresses listed
addresses listed as the default targets for media in an offer/answer. as the default targets for media in an offer/answer. If ICE changes
If ICE changes the transport address where media is received, this the transport address where media is received, this change is
change is reflected in an updated offer that changes the default reflected in an updated offer that changes the default destination
destination for media to match ICE's selection. As such, it appears for media to match ICE's selection. As such, it appears like any
like any other re-INVITE would, and is fully treated in RFCs 3312 and other re-INVITE would, and is fully treated in RFCs 3312 and 4032,
4032, which apply without regard to the fact that the destination for which apply without regard to the fact that the destination for media
media is changing due to ICE negotiations occurring "in the is changing due to ICE negotiations occurring "in the background".
background".
Indeed, an agent SHOULD NOT indicate that QoS preconditions have been Indeed, an agent SHOULD NOT indicate that QoS preconditions have been
met until the checks have completed and selected the candidate pairs met until the checks have completed and selected the candidate pairs
to be used for media. to be used for media.
ICE also has (purposeful) interactions with connectivity ICE also has (purposeful) interactions with connectivity
preconditions [RFC5898]. Those interactions are described there. preconditions [RFC5898]. Those interactions are described there.
Note that the procedures described in Section 8.1 describe their own Note that the procedures described in Section 8.1 describe their own
type of "preconditions", albeit with less functionality than those type of "preconditions", albeit with less functionality than those
provided by the explicit preconditions in [RFC5898]. provided by the explicit preconditions in [RFC5898].
8.5. Interactions with Third Party Call Control 8.5. Interactions with Third Party Call Control
ICE works with Flows I, III, and IV as described in [RFC3725]. Flow ICE works with Flows I, III, and IV as described in [RFC3725]. Flow
I works without the controller supporting or being aware of ICE. I works without the controller supporting or being aware of ICE.
Flow IV will work as long as the controller passes along the ICE Flow IV will work as long as the controller passes along the ICE
attributes without alteration. Flow II is fundamentally incompatible attributes without alteration. Flow II is fundamentally incompatible
with ICE; each agent will believe itself to be the answerer and thus with ICE; each agent will believe itself to be the answerer and thus
never generate a re-INVITE. never generate a re-INVITE.
The flows for continued operation, as described in Section 7 of RFC The flows for continued operation, as described in Section 7 of
3725, require additional behavior of ICE implementations to support. [RFC3725], require additional behavior of ICE implementations to
In particular, if an agent receives a mid-dialog re-INVITE that support. In particular, if an agent receives a mid-dialog re-INVITE
contains no offer, it MUST restart ICE for each media stream and go that contains no offer, it MUST restart ICE for each media stream and
through the process of gathering new candidates. Furthermore, that go through the process of gathering new candidates. Furthermore,
list of candidates SHOULD include the ones currently being used for that list of candidates SHOULD include the ones currently being used
media. for media.
9. Relationship with ANAT 9. Relationship with ANAT
RFC 4091 [RFC4091], the Alternative Network Address Types (ANAT) [RFC4091], the Alternative Network Address Types (ANAT) Semantics for
Semantics for the SDP grouping framework, and RFC 4092 [RFC4092], its the SDP grouping framework, and [RFC4092], its usage with SIP, define
usage with SIP, define a mechanism for indicating that an agent can a mechanism for indicating that an agent can support both IPv4 and
support both IPv4 and IPv6 for a media stream, and it does so by IPv6 for a media stream, and it does so by including two "m=" lines,
including two "m=" lines, one for v4 and one for v6. This is similar one for v4 and one for v6. This is similar to ICE, which allows for
to ICE, which allows for an agent to indicate multiple transport an agent to indicate multiple transport addresses using the candidate
addresses using the candidate attribute. However, ANAT relies on attribute. However, ANAT relies on static selection to pick between
static selection to pick between choices, rather than a dynamic choices, rather than a dynamic connectivity check used by ICE.
connectivity check used by ICE.
This specification deprecates RFC 4091 and RFC 4092. Instead, agents It is RECOMMENDED that ICE be used in realizing the dual-stack use-
wishing to support dual-stack will utilize ICE. cases in agents that support ICE.
10. Setting Ta and RTO for RTP Media Streams 10. Setting Ta and RTO for RTP Media Streams
During the gathering phase of ICE (section 4.1.1 [ICE-BIS]) and while During the gathering phase of ICE (section 4.1.1 [ICE-BIS]) and while
ICE is performing connectivity checks (section 6 [ICE-BIS]), an agent ICE is performing connectivity checks (section 6 [ICE-BIS]), an agent
sends STUN and TURN transactions. These transactions are paced at a sends STUN and TURN transactions. These transactions are paced at a
rate of one every Ta milliseconds, and utilize a specific RTO. See rate of one every Ta milliseconds, and utilize a specific RTO. See
Section 11 of [ICE-BIS] for details on how the values of Ta and RTO Section 12 of [ICE-BIS] for details on how the values of Ta and RTO
are computed with a real-time media stream of known maximum bandwidth are computed with a real-time media stream of known maximum bandwidth
to rate-control the ICE exchanges. to rate-control the ICE exchanges.
11. Security Considerations 11. Security Considerations
11.1. Attacks on the Offer/Answer Exchanges 11.1. Attacks on the Offer/Answer Exchanges
An attacker that can modify or disrupt the offer/answer exchanges An attacker that can modify or disrupt the offer/answer exchanges
themselves can readily launch a variety of attacks with ICE. They themselves can readily launch a variety of attacks with ICE. They
could direct media to a target of a DoS attack, they could insert could direct media to a target of a DoS attack, they could insert
themselves into the media stream, and so on. These are similar to themselves into the media stream, and so on. These are similar to
the general security considerations for offer/answer exchanges, and the general security considerations for offer/answer exchanges, and
the security considerations in RFC 3264 [RFC3264] apply. These the security considerations in [RFC3264] apply. These require
require techniques for message integrity and encryption for offers techniques for message integrity and encryption for offers and
and answers, which are satisfied by the SIPS mechanism [RFC3261] when answers, which are satisfied by the TLS mechanism [RFC3261] when SIP
SIP is used. As such, the usage of SIPS with ICE is RECOMMENDED. is used. As such, the usage of TLS with ICE is RECOMMENDED.
11.2. Insider Attacks 11.2. Insider Attacks
In addition to attacks where the attacker is a third party trying to In addition to attacks where the attacker is a third party trying to
insert fake offers, answers, or stun messages, there are several insert fake offers, answers, or STUN messages, there are several
attacks possible with ICE when the attacker is an authenticated and attacks possible with ICE when the attacker is an authenticated and
valid participant in the ICE exchange. valid participant in the ICE exchange.
11.2.1. The Voice Hammer Attack 11.2.1. The Voice Hammer Attack
The voice hammer attack is an amplification attack. In this attack, The voice hammer attack is an amplification attack. In this attack,
the attacker initiates sessions to other agents, and maliciously the attacker initiates sessions to other agents, and maliciously
includes the IP address and port of a DoS target as the destination includes the IP address and port of a DoS target as the destination
for media traffic signaled in the SDP. This causes substantial for media traffic signaled in the SDP. This causes substantial
amplification; a single offer/answer exchange can create a continuing amplification; a single offer/answer exchange can create a continuing
flood of media packets, possibly at high rates (consider video flood of media packets, possibly at high rates (consider video
sources). This attack is not specific to ICE, but ICE can help sources). This attack is not specific to ICE, but ICE can help
provide remediation. provide remediation.
Specifically, if ICE is used, the agent receiving the malicious SDP Specifically, if ICE is used, the agent receiving the malicious SDP
will first perform connectivity checks to the target of media before will first perform connectivity checks to the target of media before
sending media there. If this target is a third-party host, the sending media there. If this target is a third-party host, the
checks will not succeed, and media is never sent. checks will not succeed, and media is never sent.
Unfortunately, ICE doesn't help if its not used, in which case an Unfortunately, ICE doesn't help if it's not used, in which case an
attacker could simply send the offer without the ICE parameters. attacker could simply send the offer without the ICE parameters.
However, in environments where the set of clients is known, and is However, in environments where the set of clients is known, and is
limited to ones that support ICE, the server can reject any offers or limited to ones that support ICE, the server can reject any offers or
answers that don't indicate ICE support. answers that don't indicate ICE support.
User Agents that are not willing to receive non-ICE answers MUST
include an "ice" Option Tag in the Require Header Field in their
offer. Clients that rejects non-ICE offers SHOULD use a 421 response
code, together with an Option Tag "ice" in the Require Header Field
in the response.
11.2.2. Interactions with Application Layer Gateways and SIP 11.2.2. Interactions with Application Layer Gateways and SIP
Application Layer Gateways (ALGs) are functions present in a NAT Application Layer Gateways (ALGs) are functions present in a Network
device that inspect the contents of packets and modify them, in order Address Translation (NAT) device that inspect the contents of packets
to facilitate NAT traversal for application protocols. Session and modify them, in order to facilitate NAT traversal for application
Border Controllers (SBCs) are close cousins of ALGs, but are less protocols. Session Border Controllers (SBCs) are close cousins of
transparent since they actually exist as application layer SIP ALGs, but are less transparent since they actually exist as
intermediaries. ICE has interactions with SBCs and ALGs. application-layer SIP intermediaries. ICE has interactions with SBCs
and ALGs.
If an ALG is SIP aware but not ICE aware, ICE will work through it as If an ALG is SIP aware but not ICE aware, ICE will work through it as
long as the ALG correctly modifies the SDP. A correct ALG long as the ALG correctly modifies the SDP. A correct ALG
implementation behaves as follows: implementation behaves as follows:
o The ALG does not modify the "m=" and "c=" lines or the rtcp o The ALG does not modify the "m=" and "c=" lines or the rtcp
attribute if they contain external addresses. attribute if they contain external addresses.
o If the "m=" and "c=" lines contain internal addresses, the o If the "m=" and "c=" lines contain internal addresses, the
modification depends on the state of the ALG: modification depends on the state of the ALG:
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default destination for media (contained in the "m=" and "c=" lines default destination for media (contained in the "m=" and "c=" lines
and rtcp attribute), this will be detected as an ICE mismatch, and and rtcp attribute), this will be detected as an ICE mismatch, and
ICE processing is aborted for the call. It is outside of the scope ICE processing is aborted for the call. It is outside of the scope
of ICE for it to act as a tool for "working around" SBCs. If one is of ICE for it to act as a tool for "working around" SBCs. If one is
present, ICE will not be used and the SBC techniques take precedence. present, ICE will not be used and the SBC techniques take precedence.
12. IANA Considerations 12. IANA Considerations
12.1. SDP Attributes 12.1. SDP Attributes
Original ICE specification defined seven new SDP attributes per the The original ICE specification defined seven new SDP attributes per
procedures of Section 8.2.4 of [RFC4566]. The registration the procedures of Section 8.2.4 of [RFC4566]. The registration
information is reproduced here. information is reproduced here.
12.1.1. candidate Attribute 12.1.1. candidate Attribute
Contact Name: Jonathan Rosenberg, jdrosen@jdrosen.net. Contact Name: Jonathan Rosenberg, jdrosen@jdrosen.net.
Attribute Name: candidate Attribute Name: candidate
Long Form: candidate Long Form: candidate
Type of Attribute: media-level Type of Attribute: media-level
Charset Considerations: The attribute is not subject to the charset Charset Considerations: The attribute is not subject to the charset
attribute. attribute.
Purpose: This attribute is used with Interactive Connectivity Purpose: This attribute is used with Interactive Connectivity
Establishment (ICE), and provides one of many possible candidate Establishment (ICE), and provides one of many possible candidate
addresses for communication. These addresses are validated with addresses for communication. These addresses are validated with
skipping to change at page 34, line 24 skipping to change at page 34, line 26
IANA maintains a registry for ice-options identifiers under the IANA maintains a registry for ice-options identifiers under the
Specification Required policy as defined in "Guidelines for Writing Specification Required policy as defined in "Guidelines for Writing
an IANA Considerations Section in RFCs" [RFC5226]. an IANA Considerations Section in RFCs" [RFC5226].
ICE options are of unlimited length according to the syntax in ICE options are of unlimited length according to the syntax in
Section 5.6; however, they are RECOMMENDED to be no longer than 20 Section 5.6; however, they are RECOMMENDED to be no longer than 20
characters. This is to reduce message sizes and allow for efficient characters. This is to reduce message sizes and allow for efficient
parsing. parsing.
In RFC 5245 ICE options could only be defined at the session level. In [RFC5245] ICE options could only be defined at the session level.
ICE options can now also be defined at the media level. This can be ICE options can now also be defined at the media level. This can be
used when aggregating between different ICE agents in the same used when aggregating between different ICE agents in the same
endpoint, but future options may require to be defined at the media- endpoint, but future options may require to be defined at the media-
level. To ensure compatibility with legacy implementation, the level. To ensure compatibility with legacy implementation, the
media-level ICE options MUST be aggregated into a session-level ICE media-level ICE options MUST be aggregated into a session-level ICE
option. Because aggregation rules depend on the specifics of each option. Because aggregation rules depend on the specifics of each
option, all new ICE options MUST also define in their specification option, all new ICE options MUST also define in their specification
how the media-level ICE option values are aggregated to generate the how the media-level ICE option values are aggregated to generate the
value of the session-level ICE option. value of the session-level ICE option.
[RFC6679] defines "rtp+ecn" ICE option. The aggregation rule for [RFC6679] defines the "rtp+ecn" ICE option. The aggregation rule for
this ICE option is that if all aggregated media using ICE contain a this ICE option is that if all aggregated media using ICE contain a
media-level "rtp+ecn" ICE option then an "rtp+ecn" ICE option MUST be media-level "rtp+ecn" ICE option then an "rtp+ecn" ICE option MUST be
inserted at the session-level. If one of the media does not contain inserted at the session-level. If one of the media does not contain
the option, then it MUST NOT be inserted at the session-level. the option, then it MUST NOT be inserted at the session-level.
Section 7 of [ICE-BIS] defines "ice2" ICE option. Since "ice2" is a Section 7 of [ICE-BIS] defines "ice2" ICE option. Since "ice2" is a
session level ICE option, no aggregation rules apply. session level ICE option, no aggregation rules apply.
A registration request MUST include the following information: A registration request MUST include the following information:
skipping to change at page 34, line 49 skipping to change at page 35, line 4
the option, then it MUST NOT be inserted at the session-level. the option, then it MUST NOT be inserted at the session-level.
Section 7 of [ICE-BIS] defines "ice2" ICE option. Since "ice2" is a Section 7 of [ICE-BIS] defines "ice2" ICE option. Since "ice2" is a
session level ICE option, no aggregation rules apply. session level ICE option, no aggregation rules apply.
A registration request MUST include the following information: A registration request MUST include the following information:
o The ICE option identifier to be registered o The ICE option identifier to be registered
o Name, Email, and Address of a contact person for the registration o Name, Email, and Address of a contact person for the registration
o Organization or individuals having the change control o Organization or individuals having the change control
o Short description of the ICE extension to which the option relates o Short description of the ICE extension to which the option relates
o Reference(s) to the specification defining the ICE option and the o Reference(s) to the specification defining the ICE option and the
related extensions related extensions
13. Acknowledgments 13. Acknowledgments
A large part of the text in this document was taken from RFC 5245, A large part of the text in this document was taken from [RFC5245],
authored by Jonathan Rosenberg. authored by Jonathan Rosenberg.
Some of the text in this document was taken from RFC 6336, authored Some of the text in this document was taken from [RFC6336], authored
by Magnus Westerlund and Colin Perkins. by Magnus Westerlund and Colin Perkins.
Thanks to Thomas Stach for the text in Section 4.2.3 and Roman Thanks to Thomas Stach for the text in Section 4.2.3, Roman Shpount
Shpount for suggesting RTCP candidate handling in Section 4.1.1.2 for suggesting RTCP candidate handling in Section 4.1.1.2 and Simon
Perreault for advising on IPV6 address selection when candidate-
address includes FQDN.
Thanks to following experts for their review and constructive Thanks to following experts for their reviews and constructive
feedback: Christer Holmberg. feedback: Christer Holmberg, Adam Roach.
14. References 14. References
14.1. Normative References 14.1. Normative References
[ICE-BIS] Keranen, A. and J. Rosenberg, "Interactive Connectivity
Establishment (ICE): A Protocol for Network Address
Translator (NAT) Traversal for Offer/Answer Protocols",
draft-ietf-ice-rfc5245bis-00 (work in progress), March
2015.
[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, DOI 10.17487/ Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/
RFC2119, March 1997, RFC2119, March 1997,
<http://www.rfc-editor.org/info/rfc2119>. <http://www.rfc-editor.org/info/rfc2119>.
[RFC3261] Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston, [RFC3261] Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston,
A., Peterson, J., Sparks, R., Handley, M., and E. A., Peterson, J., Sparks, R., Handley, M., and E.
Schooler, "SIP: Session Initiation Protocol", RFC 3261, Schooler, "SIP: Session Initiation Protocol", RFC 3261,
DOI 10.17487/RFC3261, June 2002, DOI 10.17487/RFC3261, June 2002,
<http://www.rfc-editor.org/info/rfc3261>. <http://www.rfc-editor.org/info/rfc3261>.
skipping to change at page 36, line 5 skipping to change at page 36, line 15
[RFC3264] Rosenberg, J. and H. Schulzrinne, "An Offer/Answer Model [RFC3264] Rosenberg, J. and H. Schulzrinne, "An Offer/Answer Model
with Session Description Protocol (SDP)", RFC 3264, DOI with Session Description Protocol (SDP)", RFC 3264, DOI
10.17487/RFC3264, June 2002, 10.17487/RFC3264, June 2002,
<http://www.rfc-editor.org/info/rfc3264>. <http://www.rfc-editor.org/info/rfc3264>.
[RFC3312] Camarillo, G., Ed., Marshall, W., Ed., and J. Rosenberg, [RFC3312] Camarillo, G., Ed., Marshall, W., Ed., and J. Rosenberg,
"Integration of Resource Management and Session Initiation "Integration of Resource Management and Session Initiation
Protocol (SIP)", RFC 3312, DOI 10.17487/RFC3312, October Protocol (SIP)", RFC 3312, DOI 10.17487/RFC3312, October
2002, <http://www.rfc-editor.org/info/rfc3312>. 2002, <http://www.rfc-editor.org/info/rfc3312>.
[RFC3550] Schulzrinne, H., Casner, S., Frederick, R., and V.
Jacobson, "RTP: A Transport Protocol for Real-Time
Applications", STD 64, RFC 3550, DOI 10.17487/RFC3550,
July 2003, <http://www.rfc-editor.org/info/rfc3550>.
[RFC3556] Casner, S., "Session Description Protocol (SDP) Bandwidth [RFC3556] Casner, S., "Session Description Protocol (SDP) Bandwidth
Modifiers for RTP Control Protocol (RTCP) Bandwidth", RFC Modifiers for RTP Control Protocol (RTCP) Bandwidth", RFC
3556, DOI 10.17487/RFC3556, July 2003, 3556, DOI 10.17487/RFC3556, July 2003,
<http://www.rfc-editor.org/info/rfc3556>. <http://www.rfc-editor.org/info/rfc3556>.
[RFC3605] Huitema, C., "Real Time Control Protocol (RTCP) attribute [RFC3605] Huitema, C., "Real Time Control Protocol (RTCP) attribute
in Session Description Protocol (SDP)", RFC 3605, DOI in Session Description Protocol (SDP)", RFC 3605, DOI
10.17487/RFC3605, October 2003, 10.17487/RFC3605, October 2003,
<http://www.rfc-editor.org/info/rfc3605>. <http://www.rfc-editor.org/info/rfc3605>.
[RFC4032] Camarillo, G. and P. Kyzivat, "Update to the Session [RFC4032] Camarillo, G. and P. Kyzivat, "Update to the Session
Initiation Protocol (SIP) Preconditions Framework", RFC Initiation Protocol (SIP) Preconditions Framework", RFC
4032, DOI 10.17487/RFC4032, March 2005, 4032, DOI 10.17487/RFC4032, March 2005,
<http://www.rfc-editor.org/info/rfc4032>. <http://www.rfc-editor.org/info/rfc4032>.
[RFC4091] Camarillo, G. and J. Rosenberg, "The Alternative Network [RFC4091] Camarillo, G. and J. Rosenberg, "The Alternative Network
Address Types (ANAT) Semantics for the Session Description Address Types (ANAT) Semantics for the Session Description
Protocol (SDP) Grouping Framework", RFC 4091, DOI Protocol (SDP) Grouping Framework", RFC 4091, June 2005,
10.17487/RFC4091, June 2005,
<http://www.rfc-editor.org/info/rfc4091>. <http://www.rfc-editor.org/info/rfc4091>.
[RFC4092] Camarillo, G. and J. Rosenberg, "Usage of the Session [RFC4092] Camarillo, G. and J. Rosenberg, "Usage of the Session
Description Protocol (SDP) Alternative Network Address Description Protocol (SDP) Alternative Network Address
Types (ANAT) Semantics in the Session Initiation Protocol Types (ANAT) Semantics in the Session Initiation Protocol
(SIP)", RFC 4092, DOI 10.17487/RFC4092, June 2005, (SIP)", RFC 4092, June 2005,
<http://www.rfc-editor.org/info/rfc4092>. <http://www.rfc-editor.org/info/rfc4092>.
[RFC4566] Handley, M., Jacobson, V., and C. Perkins, "SDP: Session [RFC4566] Handley, M., Jacobson, V., and C. Perkins, "SDP: Session
Description Protocol", RFC 4566, DOI 10.17487/RFC4566, Description Protocol", RFC 4566, DOI 10.17487/RFC4566,
July 2006, <http://www.rfc-editor.org/info/rfc4566>. July 2006, <http://www.rfc-editor.org/info/rfc4566>.
[RFC5226] Narten, T. and H. Alvestrand, "Guidelines for Writing an [RFC5226] Narten, T. and H. Alvestrand, "Guidelines for Writing an
IANA Considerations Section in RFCs", BCP 26, RFC 5226, IANA Considerations Section in RFCs", BCP 26, RFC 5226,
DOI 10.17487/RFC5226, May 2008, DOI 10.17487/RFC5226, May 2008,
<http://www.rfc-editor.org/info/rfc5226>. <http://www.rfc-editor.org/info/rfc5226>.
skipping to change at page 37, line 21 skipping to change at page 37, line 26
[RFC5389] Rosenberg, J., Mahy, R., Matthews, P., and D. Wing, [RFC5389] Rosenberg, J., Mahy, R., Matthews, P., and D. Wing,
"Session Traversal Utilities for NAT (STUN)", RFC 5389, "Session Traversal Utilities for NAT (STUN)", RFC 5389,
DOI 10.17487/RFC5389, October 2008, DOI 10.17487/RFC5389, October 2008,
<http://www.rfc-editor.org/info/rfc5389>. <http://www.rfc-editor.org/info/rfc5389>.
[RFC5768] Rosenberg, J., "Indicating Support for Interactive [RFC5768] Rosenberg, J., "Indicating Support for Interactive
Connectivity Establishment (ICE) in the Session Initiation Connectivity Establishment (ICE) in the Session Initiation
Protocol (SIP)", RFC 5768, DOI 10.17487/RFC5768, April Protocol (SIP)", RFC 5768, DOI 10.17487/RFC5768, April
2010, <http://www.rfc-editor.org/info/rfc5768>. 2010, <http://www.rfc-editor.org/info/rfc5768>.
[RFC6336] Westerlund, M. and C. Perkins, "IANA Registry for
Interactive Connectivity Establishment (ICE) Options", RFC
6336, April 2010,
<http://www.rfc-editor.org/info/rfc6336>.
[RFC6679] Westerlund, M., Johansson, I., Perkins, C., O'Hanlon, P., [RFC6679] Westerlund, M., Johansson, I., Perkins, C., O'Hanlon, P.,
and K. Carlberg, "Explicit Congestion Notification (ECN) and K. Carlberg, "Explicit Congestion Notification (ECN)
for RTP over UDP", RFC 6679, DOI 10.17487/RFC6679, August for RTP over UDP", RFC 6679, DOI 10.17487/RFC6679, August
2012, <http://www.rfc-editor.org/info/rfc6679>. 2012, <http://www.rfc-editor.org/info/rfc6679>.
[RFC6724] Thaler, D., Draves, R., Matsumoto, A., and T. Chown,
"Default Address Selection for Internet Protocol Version 6
(IPv6)", RFC 6724, September 2012,
<http://www.rfc-editor.org/info/rfc6724>.
[RFC7092] Kaplan, H. and V. Pascual, "A Taxonomy of Session [RFC7092] Kaplan, H. and V. Pascual, "A Taxonomy of Session
Initiation Protocol (SIP) Back-to-Back User Agents", RFC Initiation Protocol (SIP) Back-to-Back User Agents", RFC
7092, DOI 10.17487/RFC7092, December 2013, 7092, DOI 10.17487/RFC7092, December 2013,
<http://www.rfc-editor.org/info/rfc7092>. <http://www.rfc-editor.org/info/rfc7092>.
[ICE-BIS] Keranen, A. and J. Rosenberg, "Interactive Connectivity [RFC7656] Lennox, J., Gross, K., Nandakumar, S., Salgueiro, G., and
Establishment (ICE): A Protocol for Network Address B. Burman, Ed., "A Taxonomy of Semantics and Mechanisms
Translator (NAT) Traversal for Offer/Answer Protocols", for Real-Time Transport Protocol (RTP) Sources", RFC 7656,
draft-ietf-ice-rfc5245bis-00 (work in progress), March DOI 10.17487/RFC7656, November 2015,
2015. <http://www.rfc-editor.org/info/rfc7656>.
14.2. Informative References 14.2. Informative References
[RFC3725] Rosenberg, J., Peterson, J., Schulzrinne, H., and G. [RFC3725] Rosenberg, J., Peterson, J., Schulzrinne, H., and G.
Camarillo, "Best Current Practices for Third Party Call Camarillo, "Best Current Practices for Third Party Call
Control (3pcc) in the Session Initiation Protocol (SIP)", Control (3pcc) in the Session Initiation Protocol (SIP)",
BCP 85, RFC 3725, DOI 10.17487/RFC3725, April 2004, BCP 85, RFC 3725, DOI 10.17487/RFC3725, April 2004,
<http://www.rfc-editor.org/info/rfc3725>. <http://www.rfc-editor.org/info/rfc3725>.
[RFC3960] Camarillo, G. and H. Schulzrinne, "Early Media and Ringing [RFC3960] Camarillo, G. and H. Schulzrinne, "Early Media and Ringing
skipping to change at page 40, line 21 skipping to change at page 41, line 5
L adds a candidate pair to the valid list. If there was only a L adds a candidate pair to the valid list. If there was only a
single media stream with a single component, agent L could now send single media stream with a single component, agent L could now send
an updated offer. However, the check from agent R has not yet an updated offer. However, the check from agent R has not yet
generated a response, and agent R receives the updated offer (message generated a response, and agent R receives the updated offer (message
7) before getting the response (message 9). Thus, it does not yet 7) before getting the response (message 9). Thus, it does not yet
know that this particular pair is valid. To eliminate this know that this particular pair is valid. To eliminate this
condition, the actual candidates at R that were selected by the condition, the actual candidates at R that were selected by the
offerer (the remote candidates) are included in the offer itself, and offerer (the remote candidates) are included in the offer itself, and
the answerer delays its answer until those pairs validate. the answerer delays its answer until those pairs validate.
Agent L Network Agent R Agent L Network Agent R
|(1) Offer | | |(1) Offer | |
|------------------------------------------>| |------------------------------------------>|
|(2) Answer | | |(2) Answer | |
|<------------------------------------------| |<------------------------------------------|
|(3) STUN Req. | | |(3) STUN Req. | |
|------------------------------------------>| |------------------------------------------>|
|(4) STUN Res. | | |(4) STUN Res. | |
|<------------------------------------------| |<------------------------------------------|
|(5) STUN Req. | | |(5) STUN Req. | |
|<------------------------------------------| |<------------------------------------------|
|(6) STUN Res. | | |(6) STUN Res. | |
|-------------------->| | |-------------------->| |
| |Lost | | |Lost |
|(7) Offer | | |(7) Offer | |
|------------------------------------------>| |------------------------------------------>|
|(8) STUN Req. | | |(8) STUN Req. | |
|<------------------------------------------| |<------------------------------------------|
|(9) STUN Res. | | |(9) STUN Res. | |
|------------------------------------------>| |------------------------------------------>|
|(10) Answer | | |(10) Answer | |
|<------------------------------------------| |<------------------------------------------|
Figure 1: Race Condition Flow Figure 1: Race Condition Flow
Appendix C. Why Is the Conflict Resolution Mechanism Needed? Appendix C. Why Is the Conflict Resolution Mechanism Needed?
When ICE runs between two peers, one agent acts as controlled, and When ICE runs between two peers, one agent acts as controlled, and
the other as controlling. Rules are defined as a function of the other as controlling. Rules are defined as a function of
implementation type and offerer/answerer to determine who is implementation type and offerer/answerer to determine who is
controlling and who is controlled. However, the specification controlling and who is controlled. However, the specification
mentions that, in some cases, both sides might believe they are mentions that, in some cases, both sides might believe they are
skipping to change at page 42, line 37 skipping to change at page 43, line 29
Ari Keranen Ari Keranen
Ericsson Ericsson
Jorvas 02420 Jorvas 02420
Finland Finland
Email: ari.keranen@ericsson.com Email: ari.keranen@ericsson.com
Suhas Nandakumar Suhas Nandakumar
Cisco Systems Cisco Systems
707 Tasman Dr 707 Tasman Dr
Milpitas 95035 Milpitas, CA 95035
USA USA
Email: snandaku@cisco.com Email: snandaku@cisco.com
 End of changes. 94 change blocks. 
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