draft-ietf-mmusic-ice-sip-sdp-12.txt   draft-ietf-mmusic-ice-sip-sdp-13.txt 
MMUSIC M. Petit-Huguenin MMUSIC M. Petit-Huguenin
Internet-Draft Impedance Mismatch Internet-Draft Impedance Mismatch
Obsoletes: 5245 (if approved) A. Keranen Obsoletes: 5245 (if approved) A. Keranen
Intended status: Standards Track Ericsson Intended status: Standards Track Ericsson
Expires: September 14, 2017 S. Nandakumar Expires: December 30, 2017 S. Nandakumar
Cisco Systems Cisco Systems
March 13, 2017 June 28, 2017
Using Interactive Connectivity Establishment (ICE) with Session Session Description Protocol (SDP) Offer/Answer procedures for
Description Protocol (SDP) offer/answer and Session Initiation Protocol Interactive Connectivity Establishment (ICE)
(SIP) draft-ietf-mmusic-ice-sip-sdp-13
draft-ietf-mmusic-ice-sip-sdp-12
Abstract Abstract
This document describes how Interactive Connectivity Establishment This document describes Session Description Protocol (SDP) Offer/
(ICE) is used with Session Description Protocol (SDP) offer/answer Answer procedures for carrying out Interactive Connectivity
and Session Initiation Protocol (SIP). Establishment (ICE) between the agents.
Status of This Memo Status of This Memo
This Internet-Draft is submitted in full conformance with the This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79. provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute Task Force (IETF). Note that other groups may also distribute
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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 September 14, 2017. This Internet-Draft will expire on December 30, 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.
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Without obtaining an adequate license from the person(s) controlling Without obtaining an adequate license from the person(s) controlling
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outside the IETF Standards Process, and derivative works of it may outside the IETF Standards Process, and derivative works of it may
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than English. than English.
Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. ICE Candidate Exchange and Offer/Answer Mapping . . . . . . . 4 3. ICE Candidate Exchange and Offer/Answer Mapping . . . . . . . 4
4. SDP Offer/Answer Procedures . . . . . . . . . . . . . . . . . 4 4. SDP Offer/Answer Procedures . . . . . . . . . . . . . . . . . 4
4.1. Initial Offer/Answer Exchange . . . . . . . . . . . . . . 4 4.1. Initial Offer/Answer Exchange . . . . . . . . . . . . . . 4
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 . . . . . . . . . . . . 9
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 . . . . 12
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 . . . . . . . . . . . . . . . . . . . . . . . . . . . 18 5. Grammar . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
5.1. "candidate" Attribute . . . . . . . . . . . . . . . . . . 19 5.1. "candidate" Attribute . . . . . . . . . . . . . . . . . . 18
5.2. "remote-candidates" Attribute . . . . . . . . . . . . . . 21 5.2. "remote-candidates" Attribute . . . . . . . . . . . . . . 21
5.3. "ice-lite" and "ice-mismatch" Attributes . . . . . . . . 22 5.3. "ice-lite" and "ice-mismatch" Attributes . . . . . . . . 21
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 . . . . . . . . . . . . . . . . . 22
5.6. "ice-options" Attribute . . . . . . . . . . . . . . . . . 23 5.6. "ice-options" Attribute . . . . . . . . . . . . . . . . . 23
6. Keepalives . . . . . . . . . . . . . . . . . . . . . . . . . 23 6. Keepalives . . . . . . . . . . . . . . . . . . . . . . . . . 23
7. Media Handling . . . . . . . . . . . . . . . . . . . . . . . 24 7. Media Handling . . . . . . . . . . . . . . . . . . . . . . . 23
7.1. Sending Media . . . . . . . . . . . . . . . . . . . . . . 24 7.1. Sending Media . . . . . . . . . . . . . . . . . . . . . . 23
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. SIP Considerations . . . . . . . . . . . . . . . . . . . . . 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 . . . . . . . . . . . . . . . . . . . . 28 11.2. Insider Attacks . . . . . . . . . . . . . . . . . . . . 28
11.2.1. The Voice Hammer Attack . . . . . . . . . . . . . . 29 11.2.1. The Voice Hammer Attack . . . . . . . . . . . . . . 29
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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? . . 41 Appendix C. Why Is the Conflict Resolution Mechanism Needed? . . 41
Appendix D. Why Send an Updated Offer? . . . . . . . . . . . . . 42 Appendix D. Why Send an Updated Offer? . . . . . . . . . . . . . 42
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 43 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]. The ICE specification [ICE-BIS] describes procedures that
specification [ICE-BIS] describes procedures that are common to all are common to all usages of ICE and this document gives the
usages of ICE and this document gives the additional details needed additional details needed to use ICE with SDP offer/answer.
to use ICE with SDP offer/answer and SIP.
Note that ICE is not intended for NAT traversal for SIP, which is
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 [RFC7656], in [ICE-BIS] and the following: in [RFC7656], in [ICE-BIS] and the following:
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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 An agent may choose any type of the candidate as the default, if the
chosen candidates increases the likelihood of success with the peer chosen candidates increases the likelihood of success with the peer
that is being contacted if ICE is not being used. 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. Many factors may influence such contacted if ICE is not being used. Many factors may influence such
a decision in a given agent. In scenarios where the agent is fully a decision in a given agent. In scenarios where the agent is fully
aware of its peer's location and can reach the peer directly, aware of its peer's location and can reach the peer directly,
choosing the host candidates as the default may well be sufficient. choosing the host candidates as the default may well be sufficient.
If the network configuration under which the agents operates is If the network configuration under which the agents operates is
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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"
session-level attribute in its SDP to indicate this. If an agent is session-level attribute in its SDP to indicate this. If an agent is
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 9 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 source streams based on RTP, this is done destination for media. For source streams based on RTP, this is done
by 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
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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 11.1 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
(section 5.1.1 of [ICE-BIS]), determines its role (section 5.1.2 of (section 4.4 of [ICE-BIS]), determines its role (section 5.1.1 of
[ICE-BIS]), gathers candidates (section 4 of [ICE-BIS]), encodes the [ICE-BIS]), gathers candidates (section 4 of [ICE-BIS]), encodes the
candidates in an SDP answer and sends it to its peer, the offerer. candidates in an SDP answer and sends it to its peer, the offerer.
The answerer shall then follow the steps defined in sections 5.1.3 The answerer shall then follow the steps defined in sections 5.1.3
and 5.1.4 of [ICE-BIS] to schedule the ICE connectivity checks. and 5.1.4 of [ICE-BIS] to schedule the ICE connectivity checks.
The below sub-sections provide additional requirements associated The below sub-sections provide additional requirements associated
with the processing of the offerer's SDP pertaining to this with the processing of the offerer's SDP pertaining to this
specification. specification.
4.1.2.1. ICE Option "ice2" considerations 4.1.2.1. ICE Option "ice2" considerations
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stream appears in a candidate attribute. For example, in the case of stream appears in a candidate attribute. For example, in the case of
RTP, the IP address and port in the "c=" and "m=" lines, RTP, the IP address and port in the "c=" and "m=" lines,
respectively, appear in a candidate attribute and the value in the respectively, appear in a candidate attribute and the value in the
rtcp attribute appears in a candidate attribute. rtcp attribute appears in a candidate attribute.
If this condition is not met, the agent MUST process the SDP based on If this condition is not met, the agent MUST process the SDP based on
normal RFC 3264 procedures, without using any of the ICE mechanisms normal RFC 3264 procedures, without using any of the ICE mechanisms
described in the remainder of this specification with the following described in the remainder of this specification with the following
exceptions: exceptions:
1. The agent MUST follow the rules of section 8 of [ICE-BIS], which 1. The agent MUST follow the rules of section 10 of [ICE-BIS], which
describe keepalive procedures for all agents. describe keepalive procedures for all agents.
2. If the agent is not proceeding with ICE because there were 2. If the agent is not proceeding with ICE because there were
a=candidate attributes, but none that matched the default a=candidate attributes, but none that matched the default
destination of the media stream, the agent MUST include an a=ice- destination of the media stream, the agent MUST include an a=ice-
mismatch attribute in its answer. mismatch attribute in its answer.
3. If the default candidates were relayed candidates learned through 3. If the default candidates were relayed candidates learned through
a TURN server, the agent MUST create permissions in the TURN a TURN server, the agent MUST create permissions in the TURN
server for the IP addresses learned from its peer in the SDP it server for the IP addresses learned from its peer in the SDP it
just received. If this is not done, initial packets in the media just received. If this is not done, initial packets in the media
stream from the peer may be lost. stream from the peer may be lost.
4.1.2.4. Determining Role 4.1.2.4. Determining Role
In unusual cases, described in Appendix C, it is possible for both In unusual cases, described in Appendix C, it is possible for both
agents to mistakenly believe they are controlled or controlling. To agents to mistakenly believe they are controlled or controlling. To
resolve this, each agent MUST select a random number, called the tie- resolve this, each agent MUST select a random number, called the tie-
breaker, uniformly distributed between 0 and (2**64) - 1 (that is, a breaker, uniformly distributed between 0 and (2**64) - 1 (that is, a
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 6.1.3 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 On receiving the SDP answer, the offerer performs steps similar to
generating a multiplicity of answers. In that case, ICE proceeds
completely in parallel and independently for each answer, treating
the combination of its offer and each answer as an independent offer/
answer exchange, with its own set of local candidates, pairs, check
lists, states, and so on. The only case in which processing of one
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
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] compliant 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 4.4 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.
In some cases, the answer may omit a=candidate attributes for the In some cases, the answer may omit a=candidate attributes for the
media streams, and instead include an a=ice-mismatch attribute for media streams, and instead include an a=ice-mismatch attribute for
one or more of the media streams in the SDP. This signals to the one or more of the media streams in the SDP. This signals to the
offerer that the answerer supports ICE, but that ICE processing was offerer that the answerer supports ICE, but that ICE processing was
not used for the session because a signaling intermediary modified not used for the session because a signaling intermediary modified
the default destination for media components without modifying the the default destination for media components without modifying the
corresponding candidate attributes. See Section 11.2.2 for a corresponding candidate attributes. See Section 11.2.2 for a
discussion of cases where this can happen. This specification discussion of cases where this can happen. This specification
provides no guidance on how an agent should proceed in such a failure provides no guidance on how an agent should proceed in such a failure
case. case.
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 6.3.1.1 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 6.1.3 of [ICE-BIS].
4.1.5. Concluding ICE 4.1.5. Concluding ICE
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.
When ICE is used with SIP, and an offer is forked to multiple
recipients, ICE proceeds in parallel and independently with each
answerer, all using the same local candidates. Once ICE processing
has reached the Completed state for all peers for media streams using
those candidates, the agent SHOULD wait an additional three seconds,
and then it MAY cease responding to checks or generating triggered
checks on that candidate. It MAY free the candidate at that time.
Freeing of server reflexive candidates is never explicit; it happens
by lack of a keepalive. The three-second delay handles cases when
aggressive nomination is used, and the selected pairs can quickly
change after ICE has completed.
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 fail, ICE processing continues as if the Should a subsequent offer fail, ICE processing continues as if 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 8 of [ICE-BIS].
The rules governing 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
skipping to change at page 16, line 27 skipping to change at page 16, line 5
Furthermore, if the agent believed it was controlling, but the offer Furthermore, if the agent believed it was controlling, but the offer
contained the remote-candidates attribute, both agents believe they contained the remote-candidates attribute, both agents believe they
are controlling. In this case, both would have sent updated offers are controlling. In this case, both would have sent updated offers
around the same time. However, the signaling protocol carrying the around the same time. However, the signaling protocol carrying the
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 7.2 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 state changes, the construction of the answer is performed
identically 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
skipping to change at page 17, line 50 skipping to change at page 17, line 29
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
states as described in section 5.1.3 of [ICE-BIS]. states as described in section 5.1.2 of [ICE-BIS].
4.2.4.1.2. New Media Stream 4.2.4.1.2. New Media Stream
If the offer/answer exchange added a new media stream, the agent MUST If the offer/answer exchange added a new media stream, the agent MUST
create a new check list for it (and an empty Valid list to start of create a new check list for it (and an empty Valid list to start of
course), as described in section 5.1.3 of [ICE-BIS]. course), as described in section 5.1.2 of [ICE-BIS].
4.2.4.1.3. Removed Media Stream 4.2.4.1.3. Removed Media Stream
If the offer/answer exchange removed a media stream, or an answer If the offer/answer exchange removed a media stream, or an answer
rejected an offered media stream, an agent MUST flush the Valid list rejected an offered media stream, an agent MUST flush the Valid list
for that media stream. It MUST terminate any STUN transactions in for that media stream. It MUST terminate any STUN transactions in
progress for that media stream. An agent MUST remove the check list progress for that media stream. An agent MUST remove the check list
for that media stream and cancel any pending ordinary checks for it. for that media stream and cancel any pending ordinary checks for it.
4.2.4.1.4. ICE Continuing for Existing Media Stream 4.2.4.1.4. ICE Continuing for Existing Media Stream
The valid list is not affected by an updated offer/answer exchange The valid list is not affected by an updated offer/answer exchange
unless ICE is restarting. unless ICE is restarting.
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 5.1.2 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 follows steps in check list are Frozen), the full-mode agent follows steps in
Section 5.1.3.6 of [ICE-BIS] to place appropriate candidates in the Section 5.1.2.6 of [ICE-BIS] to place appropriate candidates in the
Waiting state to further continue ICE processing. Waiting state to further continue ICE processing.
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
skipping to change at page 20, line 27 skipping to change at page 20, line 15
<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 the Datagram Congestion Control Protocol (DCCP) ICE, such as the Datagram Congestion Control Protocol (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 as described in section 5.1.3 of [ICE-BIS] Frozen algorithm as described in section 5.1.2 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 12 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). The <priority>: is a positive integer between 1 and (2**31 - 1). The
procedures for computing candidate's priority is described in procedures for computing candidate's priority is described in
section 4.1.2 of [ICE-BIS]. 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
skipping to change at page 23, line 13 skipping to change at page 22, line 48
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: Example shows sample ice-ufrag and ice-pwd SDP lines:
a=ice-pwd:asd88fgpdd777uzjYhagZg a=ice-pwd:asd88fgpdd777uzjYhagZg
a=ice-ufrag:8hhY 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 13 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: Example shows ice-pacing value of 5 ms:
a=ice-pacing:5 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:
skipping to change at page 23, line 33 skipping to change at page 23, line 18
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 in an offer indicates that a certain
is supported by the agent and will be used or that the extension is extension is supported by the agent and is willing to use it, if the
used only if the other agent is willing to use it too. In order to peer agent also includes the same extension in the answer. There
avoid ambiguity, documents defining new options must indicate which might be further extension specific negotiations needed between the
case applies to the defined extensions. agents that determine how the extensions gets used in a given
session. The details of the negotiation procedures, if present, MUST
be defined by the specification defining the extension.
Example shows 'rtp+ecn' ice-option SDP line from <<RFC6679>>: Example shows 'rtp+ecn' ice-option SDP line from <<RFC6679>>:
a=ice-options:rtp+ecn a=ice-options:rtp+ecn
6. Keepalives 6. Keepalives
All the ICE agents MUST follow the procedures defined in section 9 of All the ICE agents MUST follow the procedures defined in section 10
[ICE-BIS] for sending keepalives. The keepalives MUST be sent of [ICE-BIS] for sending keepalives. The keepalives MUST be sent
regardless of whether the media stream is currently inactive, regardless of whether the media stream is currently inactive,
sendonly, recvonly, or sendrecv, and regardless of the presence or sendonly, recvonly, or sendrecv, and regardless of the presence or
value of the bandwidth attribute. An agent can determine that its value of the bandwidth attribute. An agent can determine that its
peer supports ICE by the presence of a=candidate attributes for each peer supports ICE by the presence of a=candidate attributes for each
media session. media session.
7. Media Handling 7. Media Handling
7.1. Sending Media 7.1. Sending Media
skipping to change at page 24, line 21 skipping to change at page 24, line 9
answer exchange. When this happens, the selected pair is used for answer exchange. When this happens, the selected pair is used 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 11.1.3 of [ICE-BIS] defines procedures for sending media
common across Full and Lite implementations. common across Full and Lite implementations.
7.2. Receiving Media 7.2. Receiving Media
See section 9.2 of [ICE-BIS] for procedures on receiving media. See section 11.2 of [ICE-BIS] for procedures on receiving media.
8. Usage with SIP 8. SIP Considerations
Note that ICE is not intended for NAT traversal for SIP, which is
assumed to be provided via another mechanism [RFC5626].
When ICE is used with SIP, forking may result in a single offer
generating a multiplicity of answers. In that case, ICE proceeds
completely in parallel and independently for each answer, treating
the combination of its offer and each answer as an independent offer/
answer exchange, with its own set of local candidates, pairs, check
lists, states, and so on.
Once ICE processing has reached the Completed state for all peers for
media streams using those candidates, the agent SHOULD wait an
additional three seconds, and then it MAY cease responding to checks
or generating triggered checks on that candidate. It MAY free the
candidate at that time. Freeing of server reflexive candidates is
never explicit; it happens by lack of a keepalive. The three-second
delay handles cases when aggressive nomination is used, and the
selected pairs can quickly change after ICE has completed.
8.1. Latency Guidelines 8.1. Latency Guidelines
ICE requires a series of STUN-based connectivity checks to take place ICE requires a series of STUN-based connectivity checks to take place
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.
skipping to change at page 28, line 29 skipping to change at page 28, line 29
It is RECOMMENDED that ICE be used in realizing the dual-stack use- It is RECOMMENDED that ICE be used in realizing the dual-stack use-
cases in agents that support 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 12 of [ICE-BIS] for details on how the values of Ta and RTO Section 13 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
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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:
If the ALG already has a binding established that maps an * If the ALG already has a binding established that maps an
external port to an internal IP address and port matching the external port to an internal IP address and port matching the
values in the "m=" and "c=" lines or rtcp attribute, the ALG values in the "m=" and "c=" lines or rtcp attribute, the ALG
uses that binding instead of creating a new one. uses that binding instead of creating a new one.
If the ALG does not already have a binding, it creates a new * If the ALG does not already have a binding, it creates a new
one and modifies the SDP, rewriting the "m=" and "c=" lines and one and modifies the SDP, rewriting the "m=" and "c=" lines and
rtcp attribute. rtcp attribute.
Unfortunately, many ALGs are known to work poorly in these corner Unfortunately, many ALGs are known to work poorly in these corner
cases. ICE does not try to work around broken ALGs, as this is cases. ICE does not try to work around broken ALGs, as this is
outside the scope of its functionality. ICE can help diagnose these outside the scope of its functionality. ICE can help diagnose these
conditions, which often show up as a mismatch between the set of conditions, which often show up as a mismatch between the set of
candidates and the "m=" and "c=" lines and rtcp attributes. The ice- candidates and the "m=" and "c=" lines and rtcp attributes. The ice-
mismatch attribute is used for this purpose. mismatch attribute is used for this purpose.
skipping to change at page 34, line 43 skipping to change at page 34, line 43
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 the "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 9 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
skipping to change at page 35, line 25 skipping to change at page 35, line 25
Some of the text in this document was taken from [RFC6336], 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, Roman Shpount Thanks to Thomas Stach for the text in Section 4.2.3, Roman Shpount
for suggesting RTCP candidate handling in Section 4.1.1.2 and Simon for suggesting RTCP candidate handling in Section 4.1.1.2 and Simon
Perreault for advising on IPV6 address selection when candidate- Perreault for advising on IPV6 address selection when candidate-
address includes FQDN. address includes FQDN.
Thanks to following experts for their reviews and constructive Thanks to following experts for their reviews and constructive
feedback: Christer Holmberg, Adam Roach. feedback: Christer Holmberg, Adam Roach and the MMUSIC WG.
14. References 14. References
14.1. Normative References 14.1. Normative References
[ICE-BIS] Keranen, A. and J. Rosenberg, "Interactive Connectivity [ICE-BIS] Keranen, A. and J. Rosenberg, "Interactive Connectivity
Establishment (ICE): A Protocol for Network Address Establishment (ICE): A Protocol for Network Address
Translator (NAT) Traversal for Offer/Answer Protocols", Translator (NAT) Traversal for Offer/Answer Protocols",
draft-ietf-ice-rfc5245bis-00 (work in progress), March draft-ietf-ice-rfc5245bis-00 (work in progress), March
2015. 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,
RFC2119, March 1997, DOI 10.17487/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>.
[RFC3262] Rosenberg, J. and H. Schulzrinne, "Reliability of [RFC3262] Rosenberg, J. and H. Schulzrinne, "Reliability of
Provisional Responses in Session Initiation Protocol Provisional Responses in Session Initiation Protocol
(SIP)", RFC 3262, DOI 10.17487/RFC3262, June 2002, (SIP)", RFC 3262, DOI 10.17487/RFC3262, June 2002,
<http://www.rfc-editor.org/info/rfc3262>. <http://www.rfc-editor.org/info/rfc3262>.
[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,
10.17487/RFC3264, June 2002, DOI 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>.
[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",
3556, DOI 10.17487/RFC3556, July 2003, RFC 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,
10.17487/RFC3605, October 2003, DOI 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",
4032, DOI 10.17487/RFC4032, March 2005, RFC 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, June 2005, Protocol (SDP) Grouping Framework", RFC 4091, 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
skipping to change at page 37, line 6 skipping to change at page 37, line 6
[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>.
[RFC5234] Crocker, D., Ed. and P. Overell, "Augmented BNF for Syntax [RFC5234] Crocker, D., Ed. and P. Overell, "Augmented BNF for Syntax
Specifications: ABNF", STD 68, RFC 5234, DOI 10.17487/ Specifications: ABNF", STD 68, RFC 5234,
RFC5234, January 2008, DOI 10.17487/RFC5234, January 2008,
<http://www.rfc-editor.org/info/rfc5234>. <http://www.rfc-editor.org/info/rfc5234>.
[RFC5245] Rosenberg, J., "Interactive Connectivity Establishment [RFC5245] Rosenberg, J., "Interactive Connectivity Establishment
(ICE): A Protocol for Network Address Translator (NAT) (ICE): A Protocol for Network Address Translator (NAT)
Traversal for Offer/Answer Protocols", RFC 5245, DOI Traversal for Offer/Answer Protocols", RFC 5245,
10.17487/RFC5245, April 2010, DOI 10.17487/RFC5245, April 2010,
<http://www.rfc-editor.org/info/rfc5245>. <http://www.rfc-editor.org/info/rfc5245>.
[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 [RFC6336] Westerlund, M. and C. Perkins, "IANA Registry for
Interactive Connectivity Establishment (ICE) Options", RFC Interactive Connectivity Establishment (ICE) Options",
6336, April 2010, RFC 6336, April 2010,
<http://www.rfc-editor.org/info/rfc6336>. <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, [RFC6724] Thaler, D., Draves, R., Matsumoto, A., and T. Chown,
"Default Address Selection for Internet Protocol Version 6 "Default Address Selection for Internet Protocol Version 6
(IPv6)", RFC 6724, September 2012, (IPv6)", RFC 6724, September 2012,
<http://www.rfc-editor.org/info/rfc6724>. <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",
7092, DOI 10.17487/RFC7092, December 2013, RFC 7092, DOI 10.17487/RFC7092, December 2013,
<http://www.rfc-editor.org/info/rfc7092>. <http://www.rfc-editor.org/info/rfc7092>.
[RFC7656] Lennox, J., Gross, K., Nandakumar, S., Salgueiro, G., and [RFC7656] Lennox, J., Gross, K., Nandakumar, S., Salgueiro, G., and
B. Burman, Ed., "A Taxonomy of Semantics and Mechanisms B. Burman, Ed., "A Taxonomy of Semantics and Mechanisms
for Real-Time Transport Protocol (RTP) Sources", RFC 7656, for Real-Time Transport Protocol (RTP) Sources", RFC 7656,
DOI 10.17487/RFC7656, November 2015, DOI 10.17487/RFC7656, November 2015,
<http://www.rfc-editor.org/info/rfc7656>. <http://www.rfc-editor.org/info/rfc7656>.
14.2. Informative References 14.2. Informative References
skipping to change at page 38, line 19 skipping to change at page 38, line 19
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
Tone Generation in the Session Initiation Protocol (SIP)", Tone Generation in the Session Initiation Protocol (SIP)",
RFC 3960, DOI 10.17487/RFC3960, December 2004, RFC 3960, DOI 10.17487/RFC3960, December 2004,
<http://www.rfc-editor.org/info/rfc3960>. <http://www.rfc-editor.org/info/rfc3960>.
[RFC4340] Kohler, E., Handley, M., and S. Floyd, "Datagram [RFC4340] Kohler, E., Handley, M., and S. Floyd, "Datagram
Congestion Control Protocol (DCCP)", RFC 4340, DOI Congestion Control Protocol (DCCP)", RFC 4340,
10.17487/RFC4340, March 2006, DOI 10.17487/RFC4340, March 2006,
<http://www.rfc-editor.org/info/rfc4340>. <http://www.rfc-editor.org/info/rfc4340>.
[RFC5626] Jennings, C., Ed., Mahy, R., Ed., and F. Audet, Ed., [RFC5626] Jennings, C., Ed., Mahy, R., Ed., and F. Audet, Ed.,
"Managing Client-Initiated Connections in the Session "Managing Client-Initiated Connections in the Session
Initiation Protocol (SIP)", RFC 5626, DOI 10.17487/ Initiation Protocol (SIP)", RFC 5626,
RFC5626, October 2009, DOI 10.17487/RFC5626, October 2009,
<http://www.rfc-editor.org/info/rfc5626>. <http://www.rfc-editor.org/info/rfc5626>.
[RFC5898] Andreasen, F., Camarillo, G., Oran, D., and D. Wing, [RFC5898] Andreasen, F., Camarillo, G., Oran, D., and D. Wing,
"Connectivity Preconditions for Session Description "Connectivity Preconditions for Session Description
Protocol (SDP) Media Streams", RFC 5898, DOI 10.17487/ Protocol (SDP) Media Streams", RFC 5898,
RFC5898, July 2010, DOI 10.17487/RFC5898, July 2010,
<http://www.rfc-editor.org/info/rfc5898>. <http://www.rfc-editor.org/info/rfc5898>.
Appendix A. Examples Appendix A. Examples
For the example shown in section 12 of [ICE-BIS] the resulting offer For the example shown in section 12 of [ICE-BIS] the resulting offer
(message 5) encoded in SDP looks like: (message 5) encoded in SDP looks like:
v=0 v=0
o=jdoe 2890844526 2890842807 IN IP6 $L-PRIV-1.IP o=jdoe 2890844526 2890842807 IN IP6 $L-PRIV-1.IP
s= s=
 End of changes. 58 change blocks. 
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