draft-ietf-mmusic-ice-sip-sdp-06.txt   draft-ietf-mmusic-ice-sip-sdp-07.txt 
MMUSIC M. Petit-Huguenin MMUSIC M. Petit-Huguenin
Internet-Draft Impedance Mismatch Internet-Draft Impedance Mismatch
Intended status: Standards Track A. Keranen Intended status: Standards Track A. Keranen
Expires: March 13, 2016 Ericsson Expires: April 21, 2016 Ericsson
S. Nandakumar S. Nandakumar
Cisco Systems Cisco Systems
September 10, 2015 October 19, 2015
Using Interactive Connectivity Establishment (ICE) with Using Interactive Connectivity Establishment (ICE) with
Session Description Protocol (SDP) offer/answer and Session Initiation Session Description Protocol (SDP) offer/answer and Session Initiation
Protocol (SIP) Protocol (SIP)
draft-ietf-mmusic-ice-sip-sdp-06 draft-ietf-mmusic-ice-sip-sdp-07
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
skipping to change at page 1, line 37 skipping to change at page 1, line 37
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 March 13, 2016. This Internet-Draft will expire on April 21, 2016.
Copyright Notice Copyright Notice
Copyright (c) 2015 IETF Trust and the persons identified as the Copyright (c) 2015 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
skipping to change at page 2, line 24 skipping to change at page 2, line 24
the copyright in such materials, this document may not be modified the copyright in such materials, this document may not be modified
outside the IETF Standards Process, and derivative works of it may outside the IETF Standards Process, and derivative works of it may
not be created outside the IETF Standards Process, except to format not be created outside the IETF Standards Process, except to format
it for publication as an RFC or to translate it into languages other it for publication as an RFC or to translate it into languages other
than English. than English.
Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 4 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 4
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4
3. Sending the Initial Offer . . . . . . . . . . . . . . . . . . 4 3. ICE Candidate Exchange and Offer/Answer Mapping . . . . . . . 4
3.1. Choosing Default Candidates . . . . . . . . . . . . . . . 4 4. Sending the Initial Offer . . . . . . . . . . . . . . . . . . 5
3.2. Encoding the SDP . . . . . . . . . . . . . . . . . . . . 5 4.1. Choosing Default Candidates . . . . . . . . . . . . . . . 5
4. Receiving the Initial Offer . . . . . . . . . . . . . . . . . 6 4.2. Encoding the SDP . . . . . . . . . . . . . . . . . . . . 5
4.1. Choosing Default Candidates . . . . . . . . . . . . . . . 6 5. Receiving the Initial Offer . . . . . . . . . . . . . . . . . 7
4.2. Verifying ICE Support . . . . . . . . . . . . . . . . . . 6 5.1. Choosing Default Candidates . . . . . . . . . . . . . . . 7
4.3. Determining Role . . . . . . . . . . . . . . . . . . . . 7 5.2. Verifying ICE Support . . . . . . . . . . . . . . . . . . 7
5. Receipt of the Initial Answer . . . . . . . . . . . . . . . . 7 5.3. Determining Role . . . . . . . . . . . . . . . . . . . . 8
5.1. Verifying ICE Support . . . . . . . . . . . . . . . . . . 7 6. Receipt of the Initial Answer . . . . . . . . . . . . . . . . 8
6. Performing Connectivity Checks . . . . . . . . . . . . . . . 8 6.1. Verifying ICE Support . . . . . . . . . . . . . . . . . . 8
7. Concluding ICE . . . . . . . . . . . . . . . . . . . . . . . 8 7. Performing Connectivity Checks . . . . . . . . . . . . . . . 9
7.1. Procedures for Full Implementations . . . . . . . . . . . 8 8. Concluding ICE . . . . . . . . . . . . . . . . . . . . . . . 9
7.1.1. Updating states . . . . . . . . . . . . . . . . . . . 8 8.1. Procedures for Full Implementations . . . . . . . . . . . 9
7.2. Freeing Candidates . . . . . . . . . . . . . . . . . . . 8 8.1.1. Updating states . . . . . . . . . . . . . . . . . . . 9
7.2.1. Full Implementation Procedures . . . . . . . . . . . 8 8.2. Freeing Candidates . . . . . . . . . . . . . . . . . . . 9
8. Grammar . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 8.2.1. Full Implementation Procedures . . . . . . . . . . . 9
8.1. "candidate" Attribute . . . . . . . . . . . . . . . . . . 9 9. Grammar . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
8.2. "remote-candidates" Attribute . . . . . . . . . . . . . . 11 9.1. "candidate" Attribute . . . . . . . . . . . . . . . . . . 10
8.3. "ice-lite" and "ice-mismatch" Attributes . . . . . . . . 11 9.2. "remote-candidates" Attribute . . . . . . . . . . . . . . 12
8.4. "ice-ufrag" and "ice-pwd" Attributes . . . . . . . . . . 12 9.3. "ice-lite" and "ice-mismatch" Attributes . . . . . . . . 12
8.5. "ice-pacing" Attribute . . . . . . . . . . . . . . . . . 12 9.4. "ice-ufrag" and "ice-pwd" Attributes . . . . . . . . . . 13
8.6. "ice-options" Attribute . . . . . . . . . . . . . . . . . 13 9.5. "ice-pacing" Attribute . . . . . . . . . . . . . . . . . 13
9. Subsequent Offer/Answer Exchanges . . . . . . . . . . . . . . 13 9.6. "ice-options" Attribute . . . . . . . . . . . . . . . . . 14
9.1. Generating the Offer . . . . . . . . . . . . . . . . . . 13 10. Subsequent Offer/Answer Exchanges . . . . . . . . . . . . . . 14
9.1.1. Procedures for All Implementations . . . . . . . . . 13 10.1. Generating the Offer . . . . . . . . . . . . . . . . . . 14
9.1.2. Procedures for Full Implementations . . . . . . . . . 14 10.1.1. Procedures for All Implementations . . . . . . . . . 14
9.1.3. Procedures for Lite Implementations . . . . . . . . . 16 10.1.2. Procedures for Full Implementations . . . . . . . . 15
9.2. Receiving the Offer and Generating an Answer . . . . . . 17 10.1.3. Procedures for Lite Implementations . . . . . . . . 17
9.2.1. Procedures for All Implementations . . . . . . . . . 17
9.2.2. Procedures for Full Implementations . . . . . . . . . 18 10.2. Receiving the Offer and Generating an Answer . . . . . . 17
9.2.3. Procedures for Lite Implementations . . . . . . . . . 19 10.2.1. Procedures for All Implementations . . . . . . . . . 17
9.3. Receiving the Answer for a Subsequent Offer . . . . . . . 20 10.2.2. Procedures for Full Implementations . . . . . . . . 18
9.3.1. Procedures for All Implementations . . . . . . . . . 20 10.2.3. Procedures for Lite Implementations . . . . . . . . 20
9.4. Updating the Check and Valid Lists . . . . . . . . . . . 21 10.3. Receiving the Answer for a Subsequent Offer . . . . . . 21
9.4.1. Procedures for Full Implementations . . . . . . . . . 21 10.3.1. Procedures for All Implementations . . . . . . . . . 21
9.4.2. Procedures for Lite Implementations . . . . . . . . . 22 10.4. Updating the Check and Valid Lists . . . . . . . . . . . 22
10. Keepalives . . . . . . . . . . . . . . . . . . . . . . . . . 23 10.4.1. Procedures for Full Implementations . . . . . . . . 22
11. Media Handling . . . . . . . . . . . . . . . . . . . . . . . 23 10.4.2. Procedures for Lite Implementations . . . . . . . . 23
12. Usage with SIP . . . . . . . . . . . . . . . . . . . . . . . 23 11. Keepalives . . . . . . . . . . . . . . . . . . . . . . . . . 23
12.1. Latency Guidelines . . . . . . . . . . . . . . . . . . . 23 12. Media Handling . . . . . . . . . . . . . . . . . . . . . . . 24
12.1.1. Offer in INVITE . . . . . . . . . . . . . . . . . . 24 12.1. Sending Media . . . . . . . . . . . . . . . . . . . . . 24
12.1.2. Offer in Response . . . . . . . . . . . . . . . . . 25 12.1.1. Procedures for All Implementations . . . . . . . . . 24
12.2. SIP Option Tags and Media Feature Tags . . . . . . . . . 25 12.2. Receiving Media . . . . . . . . . . . . . . . . . . . . 24
12.3. Interactions with Forking . . . . . . . . . . . . . . . 26 13. Usage with SIP . . . . . . . . . . . . . . . . . . . . . . . 24
12.4. Interactions with Preconditions . . . . . . . . . . . . 26 13.1. Latency Guidelines . . . . . . . . . . . . . . . . . . . 24
12.5. Interactions with Third Party Call Control . . . . . . . 26 13.1.1. Offer in INVITE . . . . . . . . . . . . . . . . . . 25
13. Relationship with ANAT . . . . . . . . . . . . . . . . . . . 27 13.1.2. Offer in Response . . . . . . . . . . . . . . . . . 26
14. Setting Ta and RTO for RTP Media Streams . . . . . . . . . . 27 13.2. SIP Option Tags and Media Feature Tags . . . . . . . . . 26
15. Security Considerations . . . . . . . . . . . . . . . . . . . 27 13.3. Interactions with Forking . . . . . . . . . . . . . . . 27
15.1. Attacks on the Offer/Answer Exchanges . . . . . . . . . 27 13.4. Interactions with Preconditions . . . . . . . . . . . . 27
15.2. Insider Attacks . . . . . . . . . . . . . . . . . . . . 28 13.5. Interactions with Third Party Call Control . . . . . . . 27
15.2.1. The Voice Hammer Attack . . . . . . . . . . . . . . 28 14. Relationship with ANAT . . . . . . . . . . . . . . . . . . . 28
15.2.2. Interactions with Application Layer Gateways and SIP 28 15. Setting Ta and RTO for RTP Media Streams . . . . . . . . . . 28
16. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 29 16. Security Considerations . . . . . . . . . . . . . . . . . . . 28
16.1. SDP Attributes . . . . . . . . . . . . . . . . . . . . . 29 16.1. Attacks on the Offer/Answer Exchanges . . . . . . . . . 28
16.1.1. candidate Attribute . . . . . . . . . . . . . . . . 29 16.2. Insider Attacks . . . . . . . . . . . . . . . . . . . . 29
16.1.2. remote-candidates Attribute . . . . . . . . . . . . 30 16.2.1. The Voice Hammer Attack . . . . . . . . . . . . . . 29
16.1.3. ice-lite Attribute . . . . . . . . . . . . . . . . . 30 16.2.2. Interactions with Application Layer Gateways and SIP 29
16.1.4. ice-mismatch Attribute . . . . . . . . . . . . . . . 31 17. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 30
16.1.5. ice-pwd Attribute . . . . . . . . . . . . . . . . . 31 17.1. SDP Attributes . . . . . . . . . . . . . . . . . . . . . 30
16.1.6. ice-ufrag Attribute . . . . . . . . . . . . . . . . 32 17.1.1. candidate Attribute . . . . . . . . . . . . . . . . 30
16.1.7. ice-pacing Attribute . . . . . . . . . . . . . . . . 32 17.1.2. remote-candidates Attribute . . . . . . . . . . . . 31
16.1.8. ice-options Attribute . . . . . . . . . . . . . . . 32 17.1.3. ice-lite Attribute . . . . . . . . . . . . . . . . . 31
16.2. Interactive Connectivity Establishment (ICE) Options 17.1.4. ice-mismatch Attribute . . . . . . . . . . . . . . . 32
Registry . . . . . . . . . . . . . . . . . . . . . . . . 33 17.1.5. ice-pwd Attribute . . . . . . . . . . . . . . . . . 32
17. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 34 17.1.6. ice-ufrag Attribute . . . . . . . . . . . . . . . . 33
18. References . . . . . . . . . . . . . . . . . . . . . . . . . 34 17.1.7. ice-pacing Attribute . . . . . . . . . . . . . . . . 33
18.1. Normative References . . . . . . . . . . . . . . . . . . 34 17.1.8. ice-options Attribute . . . . . . . . . . . . . . . 33
18.2. Informative References . . . . . . . . . . . . . . . . . 36 17.2. Interactive Connectivity Establishment (ICE) Options
Appendix A. Examples . . . . . . . . . . . . . . . . . . . . . . 36 Registry . . . . . . . . . . . . . . . . . . . . . . . . 34
Appendix B. The remote-candidates Attribute . . . . . . . . . . 38 18. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 35
Appendix C. Why Is the Conflict Resolution Mechanism Needed? . . 38 19. References . . . . . . . . . . . . . . . . . . . . . . . . . 35
Appendix D. Why Send an Updated Offer? . . . . . . . . . . . . . 39 19.1. Normative References . . . . . . . . . . . . . . . . . . 35
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 40 19.2. Informative References . . . . . . . . . . . . . . . . . 37
Appendix A. Examples . . . . . . . . . . . . . . . . . . . . . . 38
Appendix B. The remote-candidates Attribute . . . . . . . . . . 39
Appendix C. Why Is the Conflict Resolution Mechanism Needed? . . 40
Appendix D. Why Send an Updated Offer? . . . . . . . . . . . . . 41
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 42
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.
skipping to change at page 4, line 37 skipping to change at page 4, line 39
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, it is in the rtcp
attribute when present, and when not present, the IP address is in attribute when present, and when not present, the IP address is in
the "c=" line and 1 plus the port is in the "m=" line. the "c=" line and 1 plus the port is in the "m=" line.
3. Sending the Initial Offer 3. ICE Candidate Exchange and Offer/Answer Mapping
3.1. Choosing Default Candidates [ICE-BIS] defines ICE candidate exchange as the process for the ICE
agents (Initiator and Responder) to exchange their candidate
information required for ICE processing at the agents. For the
purposes of this specification, the candidate exchange process
corresponds to the [RFC3264] Offer/Answer protocol and the
terminologies offerer and answerer correspond to the initiator and
responder terminologies from the [ICE-BIS] respectively.
4. Sending the Initial Offer
The offerer shall follow the procedures defined in section 4 of
[ICE-BIS] to gather, prioritize and eliminate the redundant
candidates. It then chooses the default candidates and encodes them
in SDP to be sent to its peer, the answerer.
4.1. Choosing Default Candidates
A candidate is said to be default if it would be the target of media A candidate is said to be default if it would be the target of media
from a non-ICE peer; that target is called the DEFAULT DESTINATION. from a non-ICE peer; that target is called the DEFAULT DESTINATION.
If the default candidates are not selected by the ICE algorithm when If the default candidates are not selected by the ICE algorithm when
communicating with an ICE-aware peer, an updated offer/answer will be communicating with an ICE-aware peer, an updated offer/answer will be
required after ICE processing completes in order to "fix up" the SDP required after ICE processing completes in order to "fix up" the SDP
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.
skipping to change at page 5, line 14 skipping to change at page 5, line 36
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.
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. It is RECOMMENDED that the
default candidates are the relayed candidates (if relayed candidates default candidates are the relayed candidates (if relayed candidates
are available), server reflexive candidates (if server reflexive are available), server reflexive candidates (if server reflexive
candidates are available), and finally host candidates. candidates are available), and finally host candidates.
3.2. Encoding the SDP 4.2. 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 media stream it wishes
to use. The ordering of media streams in the SDP is relevant for to use. The ordering of media streams in the SDP is relevant for
ICE. ICE will perform its connectivity checks for the first "m=" ICE. ICE will perform its connectivity checks for the first "m="
line first, and consequently media will be able to flow for that line first, and consequently media will be able to flow for that
stream first. Agents SHOULD place their most important media stream, stream first. Agents SHOULD place their most important media stream,
if there is one, first in the SDP. 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 8 provides detailed rules for particular media stream. Section 9 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"
skipping to change at page 6, line 30 skipping to change at page 7, line 4
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 10.1 of [ICE-BIS], media packets can be sent As discussed in Section 10.1 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. Receiving the Initial Offer 5. Receiving the Initial Offer
4.1. Choosing Default Candidates 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
[ICE-BIS]), gathers candidates (section 4 of [ICE-BIS]), encodes the
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
and 5.1.4 of [ICE-BIS] to schedule the ICE connectivity checks.
The below sub-sections provide additional requirements associated
with the processing of the offerer's SDP pertaining to this
specification.
5.1. Choosing Default Candidates
The process for selecting default candidates at the answerer is The process for selecting default candidates at the answerer is
identical to the process followed by the offerer, as described in identical to the process followed by the offerer, as described in
Section 3.1 for full implementations and 4.2 of [ICE-BIS] for lite Section 4.1 for full implementations in this specification and
implementations. section 4.2 of [ICE-BIS] for lite implementations.
4.2. Verifying ICE Support 5.2. Verifying ICE Support
The agent will proceed with the ICE procedures defined in [ICE-BIS] The agent will proceed with the ICE procedures defined in [ICE-BIS]
and this specification if, for each media stream in the SDP it and this specification if, for each media stream in the SDP it
received, the default destination for each component of that media received, the default destination for each component of that media
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 10 of [ICE-BIS], which 1. The agent MUST follow the rules of section 9 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.
4.3. Determining Role 5.3. 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 7.1.2.2 of to detect and repair this case, as described in Section 6.1.2.2 of
[ICE-BIS]. [ICE-BIS].
5. Receipt of the Initial Answer 6. 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 pairs, check lists, states, and
so on. The only case in which processing of one pair impacts another so on. The only case in which processing of one pair impacts another
is freeing of candidates, discussed below in Section 7.2. is freeing of candidates, discussed below in Section 8.2.
5.1. Verifying ICE Support On receiving the SDP answer , the offerer performs steps similar to
answerer's processing of the offer. The offerer verifies the
answerer's ICE support, determines its role and processes the
answerer's candidates to schedule the connectivity checks as defined
in section 5 of [ICE-BIS].
6.1. 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 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.
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 15.2.2 for a corresponding candidate attributes. See Section 16.2.2 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.
6. Performing Connectivity Checks 7. Performing Connectivity Checks
The possibility for role conflicts described in Section 7.2.1.1 of The possibility for role conflicts described in Section 6.2.1.1 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 7.1.2.2 of [ICE-BIS]. attributes as described in Section 6.1.2.2 of [ICE-BIS].
7. Concluding ICE 8. Concluding ICE
Once all of the media streams are completed, the controlling endpoint Once all of the media streams are completed, the controlling endpoint
sends an updated offer if the transport destination in the "m=" and sends an updated offer if the transport destination in the "m=" and
"c=" lines for the media stream (called the DEFAULT CANDIDATES) don't "c=" lines for the media stream (called the DEFAULT CANDIDATES) don't
match ICE's SELECTED CANDIDATES. match ICE's SELECTED CANDIDATES.
7.1. Procedures for Full Implementations 8.1. Procedures for Full Implementations
7.1.1. Updating states 8.1.1. 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 9. updated offer as described in Section 10.
7.2. Freeing Candidates 8.2. Freeing Candidates
7.2.1. Full Implementation Procedures 8.2.1. 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
aggressive nomination is used, and the selected pairs can quickly aggressive nomination is used, and the selected pairs can quickly
change after ICE has completed. change after ICE has completed.
8. Grammar 9. 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.
8.1. "candidate" Attribute 9.1. "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 The syntax of this attribute is defined using Augmented BNF as
defined in [RFC5234]: defined in [RFC5234]:
candidate-attribute = "candidate" ":" foundation SP component-id SP candidate-attribute = "candidate" ":" foundation SP component-id SP
transport SP transport SP
skipping to change at page 10, line 42 skipping to change at page 11, line 31
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.
<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 12 in [ICE-BIS] for additional discussion on ID of 2. See section 11 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).
<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.
skipping to change at page 11, line 27 skipping to change at page 12, line 17
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.
8.2. "remote-candidates" Attribute 9.2. "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 RFC 5234 [RFC5234]. The remote-
candidates attribute is a media-level attribute only. candidates 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.
8.3. "ice-lite" and "ice-mismatch" Attributes 9.3. "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.
8.4. "ice-ufrag" and "ice-pwd" Attributes 9.4. "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
skipping to change at page 12, line 45 skipping to change at page 13, line 40
allows for 6 bits of randomness per character. The attributes MAY be allows for 6 bits of randomness per character. The attributes MAY be
longer than 4 and 22 characters, respectively, of course, up to 256 longer than 4 and 22 characters, respectively, of course, up to 256
characters. The upper limit allows for buffer sizing in 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.
8.5. "ice-pacing" Attribute 9.5. "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 13 of pacing, in milliseconds, for this agent (see Section 12 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
8.6. "ice-options" Attribute 9.6. "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.
9. Subsequent Offer/Answer Exchanges 10. 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
RFC 3264 [RFC3264]. The rules in Section 7 will cause the RFC 3264 [RFC3264]. The rules in Section 8 will cause the
controlling agent to send an updated offer at the conclusion of ICE controlling agent to send an updated offer at the conclusion of ICE
processing when ICE has selected different candidate pairs from the processing when ICE has selected different candidate pairs from the
default pairs. This section defines rules for construction of default pairs. This section defines rules for construction of
subsequent offers and answers. subsequent offers and answers.
Should a subsequent offer be rejected, ICE processing continues as if Should a subsequent offer be rejected, ICE processing continues as if
the subsequent offer had never been made. the subsequent offer had never been made.
9.1. Generating the Offer 10.1. Generating the Offer
9.1.1. Procedures for All Implementations 10.1.1. Procedures for All Implementations
9.1.1.1. ICE Restarts 10.1.1.1. ICE Restarts
An agent MAY restart ICE processing for an existing media stream. An An agent MAY restart ICE processing for an existing media stream. An
ICE restart, as the name implies, will cause all previous states of ICE restart, as the name implies, will cause all previous states of
ICE processing to be flushed and checks to start anew. The only ICE processing to be flushed and checks to start anew. The only
difference between an ICE restart and a brand new media session is difference between an ICE restart and a brand new media session is
that, during the restart, media can continue to be sent to the that, during the restart, media can continue to be sent to the
previously validated pair. previously validated pair.
An agent MUST restart ICE for a media stream if: An agent MUST restart ICE for a media stream if:
skipping to change at page 14, line 27 skipping to change at page 15, line 25
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
representation, and does not cause an ICE restart. representation, and does not cause an ICE restart.
An agent sets the rest of the fields in the SDP for this media stream An agent sets the rest of the fields in the SDP for this media stream
as it would in an initial offer of this media stream (see as it would in an initial offer of this media stream (see
Section 3.2). Consequently, the set of candidates MAY include some, Section 4.2). Consequently, the set of candidates MAY include some,
none, or all of the previous candidates for that stream and MAY none, or all of the previous candidates for that stream and MAY
include a totally new set of candidates. include a totally new set of candidates.
9.1.1.2. Removing a Media Stream 10.1.1.2. Removing a Media Stream
If an agent removes a media stream by setting its port to zero, it If an agent removes a media stream by setting its port to zero, it
MUST NOT include any candidate attributes for that media stream and MUST NOT include any candidate attributes for that media stream and
SHOULD NOT include any other ICE-related attributes defined in SHOULD NOT include any other ICE-related attributes defined in
Section 8 for that media stream. Section 9 for that media stream.
9.1.1.3. Adding a Media Stream 10.1.1.3. Adding a Media Stream
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 3.2). This will cause ICE processing that media stream (see Section 4.2). This will cause ICE processing
to begin for this media stream. to begin for this media stream.
9.1.2. Procedures for Full Implementations 10.1.2. 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 The username fragments, password, and implementation level MUST
remain the same as used previously. If an agent needs to change one remain the same as used previously. If an agent needs to change one
of these, it MUST restart ICE for that media stream. of these, it MUST restart ICE for that media stream.
Additional behavior depends on the state ICE processing for that Additional behavior depends on the state ICE processing for that
media stream. media stream.
9.1.2.1. Existing Media Streams with ICE Running 10.1.2.1. 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, but
which it has gathered since the last offer/answer exchange, including which it has gathered since the last offer/answer exchange, including
peer reflexive candidates. 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.
9.1.2.2. Existing Media Streams with ICE Completed 10.1.2.2. 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.
The default destination for media (i.e., the values of the IP The default destination for media (i.e., the values of the IP
addresses and ports in the "m=" and "c=" lines used for that media addresses and ports in the "m=" and "c=" lines used for that media
stream) MUST be the local candidate from the highest-priority stream) MUST be the local candidate from the highest-priority
nominated pair in the valid list for each component. This "fixes" nominated pair in the valid list for each component. This "fixes"
the default destination for media to equal the destination ICE has the default destination for media to equal the destination ICE has
skipping to change at page 16, line 11 skipping to change at page 17, line 7
In addition, if the agent is controlling, it MUST include the In addition, if the agent is controlling, it MUST include the
a=remote-candidates attribute for each media stream whose check list a=remote-candidates attribute for each media stream whose check list
is in the Completed state. The attribute contains the remote is in the Completed state. The attribute contains the remote
candidates from the highest-priority nominated pair in the valid list candidates from the highest-priority nominated pair in the valid list
for each component of that media stream. It is needed to avoid a for each component of that media stream. It is needed to avoid a
race condition whereby the controlling agent chooses its pairs, but race condition whereby the controlling agent chooses its pairs, but
the updated offer beats the connectivity checks to the controlled the updated offer beats the connectivity checks to the controlled
agent, which doesn't even know these pairs are valid, let alone agent, which doesn't even know these pairs are valid, let alone
selected. See Appendix B for elaboration on this race condition. selected. See Appendix B for elaboration on this race condition.
9.1.3. Procedures for Lite Implementations 10.1.3. Procedures for Lite Implementations
9.1.3.1. Existing Media Streams with ICE Running 10.1.3.1. Existing Media Streams with ICE Running
This section describes procedures for lite implementations for This section describes procedures for lite implementations for
existing streams for which ICE is running. existing streams for which ICE is running.
A lite implementation MUST include all of its candidates for each A lite implementation MUST include all of its candidates for each
component of each media stream in an a=candidate attribute in any component of each media stream in an a=candidate attribute in any
subsequent offer. These candidates are formed identically to the subsequent offer. These candidates are formed identically to the
procedures for initial offers, as described in section 4.2 of procedures for initial offers, as described in section 4.2 of
[ICE-BIS]. [ICE-BIS].
A lite implementation MUST NOT add additional host candidates in a A lite implementation MUST NOT add additional host candidates in a
subsequent offer. If an agent needs to offer additional candidates, subsequent offer. If an agent needs to offer additional candidates,
it MUST restart ICE. it MUST restart ICE.
The username fragments, password, and implementation level MUST The username fragments, password, and implementation level MUST
remain the same as used previously. If an agent needs to change one remain the same as used previously. If an agent needs to change one
of these, it MUST restart ICE for that media stream. of these, it MUST restart ICE for that media stream.
9.1.3.2. Existing Media Streams with ICE Completed 10.1.3.2. Existing Media Streams with ICE Completed
If ICE has completed for a media stream, the default destination for If ICE has completed for a media stream, the default destination for
that media stream MUST be set to the remote candidate of the that media stream MUST be set to the remote candidate of the
candidate pair for that component in the valid list. For a lite candidate pair for that component in the valid list. For a lite
implementation, there is always just a single candidate pair in the implementation, there is always just a single candidate pair in the
valid list for each component of a media stream. Additionally, the valid list for each component of a media stream. Additionally, the
agent MUST include a candidate attribute for each default agent MUST include a candidate attribute for each default
destination. destination.
Additionally, if the agent is controlling (which only happens when Additionally, if the agent is controlling (which only happens when
both agents are lite), the agent MUST include the a=remote-candidates both agents are lite), the agent MUST include the a=remote-candidates
attribute for each media stream. The attribute contains the remote attribute for each media stream. The attribute contains the remote
candidates from the candidate pairs in the valid list (one pair for candidates from the candidate pairs in the valid list (one pair for
each component of each media stream). each component of each media stream).
9.2. Receiving the Offer and Generating an Answer 10.2. Receiving the Offer and Generating an Answer
9.2.1. Procedures for All Implementations 10.2.1. Procedures for All Implementations
When receiving a subsequent offer within an existing session, an When receiving a subsequent offer within an existing session, an
agent MUST reapply the verification procedures in Section 4.2 without agent MUST reapply the verification procedures in Section 5.2 without
regard to the results of verification from any previous offer/answer regard to the results of verification from any previous offer/answer
exchanges. Indeed, it is possible that a previous offer/answer exchanges. Indeed, it is possible that a previous offer/answer
exchange resulted in ICE not being used, but it is used as a exchange resulted in ICE not being used, but it is used as a
consequence of a subsequent exchange. consequence of a subsequent exchange.
9.2.1.1. Detecting ICE Restart 10.2.1.1. Detecting ICE Restart
If the offer contained a change in the a=ice-ufrag or a=ice-pwd If the offer contained a change in the a=ice-ufrag or a=ice-pwd
attributes compared to the previous SDP from the peer, it indicates attributes compared to the previous SDP from the peer, it indicates
that ICE is restarting for this media stream. If all media streams that ICE is restarting for this media stream. If all media streams
are restarting, then ICE is restarting overall. are restarting, then ICE is restarting overall.
If ICE is restarting for a media stream: If ICE is restarting for a media stream:
o The agent MUST change the a=ice-ufrag and a=ice-pwd attributes in o The agent MUST change the a=ice-ufrag and a=ice-pwd attributes in
the answer. the answer.
o The agent MAY change its implementation level in the answer. o The agent MAY change its implementation level in the answer.
An agent sets the rest of the fields in the SDP for this media stream An agent sets the rest of the fields in the SDP for this media stream
as it would in an initial answer to this media stream (see as it would in an initial answer to this media stream (see
Section 3.2). Consequently, the set of candidates MAY include some, Section 4.2). Consequently, the set of candidates MAY include some,
none, or all of the previous candidates for that stream and MAY none, or all of the previous candidates for that stream and MAY
include a totally new set of candidates. include a totally new set of candidates.
9.2.1.2. New Media Stream 10.2.1.2. New Media Stream
If the offer contains a new media stream, the agent sets the fields If the offer contains a new media stream, the agent sets the fields
in the answer as if it had received an initial offer containing that in the answer as if it had received an initial offer containing that
media stream (see Section 3.2). This will cause ICE processing to media stream (see Section 4.2). This will cause ICE processing to
begin for this media stream. begin for this media stream.
9.2.1.3. Removed Media Stream 10.2.1.3. Removed Media Stream
If an offer contains a media stream whose port is zero, the agent If an offer contains a media stream whose port is zero, the agent
MUST NOT include any candidate attributes for that media stream in MUST NOT include any candidate attributes for that media stream in
its answer and SHOULD NOT include any other ICE-related attributes its answer and SHOULD NOT include any other ICE-related attributes
defined in Section 8 for that media stream. defined in Section 9 for that media stream.
9.2.2. Procedures for Full Implementations 10.2.2. Procedures for Full Implementations
Unless the agent has detected an ICE restart from the offer, the Unless the agent has detected an ICE restart from the offer, the
username fragments, password, and implementation level MUST remain username fragments, password, and implementation level MUST remain
the same as used previously. If an agent needs to change one of the same as used previously. If an agent needs to change one of
these it MUST restart ICE for that media stream by generating an these it MUST restart ICE for that media stream by generating an
offer; ICE cannot be restarted in an answer. offer; ICE cannot be restarted in an answer.
Additional behaviors depend on the state of ICE processing for that Additional behaviors depend on the state of ICE processing for that
media stream. media stream.
9.2.2.1. Existing Media Streams with ICE Running and no remote- 10.2.2.1. Existing Media Streams with ICE Running and no remote-
candidates candidates
If ICE is running for a media stream, and the offer for that media If ICE is running for a media stream, and the offer for that media
stream lacked the remote-candidates attribute, the rules for stream lacked the remote-candidates attribute, the rules for
construction of the answer are identical to those for the offerer as construction of the answer are identical to those for the offerer as
described in Section 9.1.2.1. described in Section 10.1.2.1.
9.2.2.2. Existing Media Streams with ICE Completed and no remote- 10.2.2.2. Existing Media Streams with ICE Completed and no remote-
candidates candidates
If ICE is Completed for a media stream, and the offer for that media If ICE is Completed for a media stream, and the offer for that media
stream lacked the remote-candidates attribute, the rules for stream lacked the remote-candidates attribute, the rules for
construction of the answer are identical to those for the offerer as construction of the answer are identical to those for the offerer as
described in Section 9.1.2.2, except that the answerer MUST NOT described in Section 10.1.2.2, except that the answerer MUST NOT
include the a=remote-candidates attribute in the answer. include the a=remote-candidates attribute in the answer.
9.2.2.3. Existing Media Streams and remote-candidates 10.2.2.3. Existing Media Streams and remote-candidates
A controlled agent will receive an offer with the a=remote-candidates A controlled agent will receive an offer with the a=remote-candidates
attribute for a media stream when its peer has concluded ICE attribute for a media stream when its peer has concluded ICE
processing for that media stream. This attribute is present in the processing for that media stream. This attribute is present in the
offer to deal with a race condition between the receipt of the offer, offer to deal with a race condition between the receipt of the offer,
and the receipt of the Binding response that tells the answerer the and the receipt of the Binding response that tells the answerer the
candidate that will be selected by ICE. See Appendix B for an candidate that will be selected by ICE. See Appendix B for an
explanation of this race condition. Consequently, processing of an explanation of this race condition. Consequently, processing of an
offer with this attribute depends on the winner of the race. offer with this attribute depends on the winner of the race.
skipping to change at page 19, line 34 skipping to change at page 20, line 20
for those checks to complete, and as each completes, redo the for those checks to complete, and as each completes, redo the
processing in this section until there are no losing pairs. processing in this section until there are no losing pairs.
Once there are no losing pairs, the agent can generate the answer. Once there are no losing pairs, the agent can generate the answer.
It MUST set the default destination for media to the candidates in It MUST set the default destination for media to the candidates in
the remote-candidates attribute from the offer (each of which will the remote-candidates attribute from the offer (each of which will
now be the local candidate of a candidate pair in the valid list). now be the local candidate of a candidate pair in the valid list).
It MUST include a candidate attribute in the answer for each It MUST include a candidate attribute in the answer for each
candidate in the remote-candidates attribute in the offer. candidate in the remote-candidates attribute in the offer.
9.2.3. Procedures for Lite Implementations 10.2.3. Procedures for Lite Implementations
If the received offer contains the remote-candidates attribute for a If the received offer contains the remote-candidates attribute for a
media stream, the agent forms a candidate pair for each component of media stream, the agent forms a candidate pair for each component of
the media stream by: the media stream by:
o Setting the remote candidate equal to the offerer's default o Setting the remote candidate equal to the offerer's default
destination for that component (e.g., the contents of the "m=" and destination for that component (e.g., the contents of the "m=" and
"c=" lines for RTP, and the a=rtcp attribute for RTCP). "c=" lines for RTP, and the a=rtcp attribute for RTCP).
o Setting the local candidate equal to the transport address for o Setting the local candidate equal to the transport address for
skipping to change at page 20, line 15 skipping to change at page 20, line 48
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
controlled, so that the loser (the answerer under consideration in controlled, 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 8.2 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 9.1.3. Section 10.1.3.
9.3. Receiving the Answer for a Subsequent Offer 10.3. 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
skipping to change at page 20, line 45 skipping to change at page 21, line 32
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. sections advice on how to recover from the unexpected situation.
9.3.1. Procedures for All Implementations 10.3.1. 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 9.1.2.2, an agent MUST verify ICE offer as specified in Section 10.1.2.2, an agent MUST verify ICE
support as specified in Section 5.1. support as specified in Section 6.1.
9.3.1.1. ICE Restarts 10.3.1.1. ICE Restarts
If ICE support is indicated in the SDP answer, the agent MUST perform If ICE support is indicated in the SDP answer, the agent MUST perform
ICE restart procedures as specified in Section 9.4. ICE restart procedures as specified in Section 10.4.
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 fall-back to RFC 3264 procedures and SHOULD NOT drop the dialog MUST fall-back to RFC 3264 procedures and SHOULD NOT drop the dialog
just because of missing ICE support. If the agent sends a new offer just because of missing ICE support. If the agent sends a new offer
later on it SHOULD perform an ICE restart as specified in later on it SHOULD perform an ICE restart as specified in
Section 9.1.1.1. Section 10.1.1.1.
9.3.1.2. Existing Media Streams with ICE Running 10.3.1.2. Existing Media Streams with ICE Running
If ICE support is indicated in the SDP answer, the agent MUST If ICE support is indicated in the SDP answer, the agent MUST
continue ICE procedures as specified in Section 9.4.1.4. continue ICE procedures as specified in Section 10.4.1.4.
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 RFC 3264
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 9.1.1.1. SHOULD perform an ICE restart as specified in Section 10.1.1.1.
9.3.1.3. Existing Media Streams with ICE Completed 10.3.1.3. Existing Media Streams with ICE Completed
If ICE support is indicated in the SDP answer and if the answer If ICE support is indicated in the SDP answer and if the answer
conforms to Section 9.2.2.3, the agent MUST remain in the ICE conforms to Section 10.2.2.3, the agent MUST remain in the ICE
Completed state. Completed state.
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 fall-back to RFC 3264 procedures and SHOULD NOT drop the dialog 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 just because of this unexpected answer. Once the agent sends a new
offer later on it MUST perform an ICE restart. offer later on it MUST perform an ICE restart.
9.4. Updating the Check and Valid Lists 10.4. Updating the Check and Valid Lists
9.4.1. Procedures for Full Implementations 10.4.1. Procedures for Full Implementations
9.4.1.1. ICE Restarts 10.4.1.1. 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 Section 11. continue to send media using these pairs, as described in
Once these destinations are noted, the agent MUST flush the valid and Section 12.1. Once these destinations are noted, the agent MUST
check lists, and then recompute the check list and its states as flush the valid and check lists, and then recompute the check list
described in section 6.3 of [ICE-BIS]. and its states as described in section 5.1.3 of [ICE-BIS].
9.4.1.2. New Media Stream 10.4.1.2. 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 6.3 of [ICE-BIS]. course), as described in section 5.1.3 of [ICE-BIS].
9.4.1.3. Removed Media Stream 10.4.1.3. 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.
9.4.1.4. ICE Continuing for Existing Media Stream 10.4.1.4. 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 6.3 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 sets the first pair in
the check list for the first media stream to Waiting, and then sets the check list for the first media stream to Waiting, and then sets
the state of all other pairs in that check list for the same the state of all other pairs in that check list for the same
component ID and with the same foundation to Waiting as well. component ID and with the same foundation to Waiting as well.
Next, the agent goes through each check list, starting with the Next, the agent goes through each check list, starting with the
highest-priority pair. If a pair has a state of Succeeded, and it 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 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 with the same foundation whose component IDs are not 1 have their
state set to Waiting. If, for a particular check list, there are state set to Waiting. If, for a particular check list, there are
pairs for each component of that media stream in the Succeeded state, 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 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 of all other media streams (and thus in different check lists) with
the same foundation to Waiting. the same foundation to Waiting.
9.4.2. Procedures for Lite Implementations 10.4.2. 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 11. The state of ICE processing for each media described in Section 12.1. The state of ICE processing for each
stream MUST change to Running, and the state of ICE processing MUST media stream MUST change to Running, and the state of ICE processing
change to Running. MUST change to Running.
10. Keepalives 11. Keepalives
The procedures defined in Section 10 of [ICE-BIS] MUST be followed. The procedures defined in Section 9 of [ICE-BIS] MUST be followed.
The keepalives MUST be sent regardless of whether the media stream is The keepalives MUST be sent regardless of whether the media stream is
currently inactive, sendonly, recvonly, or sendrecv, and regardless currently inactive, sendonly, recvonly, or sendrecv, and regardless
of the presence or value of the bandwidth attribute. An agent can of the presence or value of the bandwidth attribute. An agent can
determine that its peer supports ICE by the presence of a=candidate determine that its peer supports ICE by the presence of a=candidate
attributes for each media session. attributes for each media session.
11. Media Handling 12. Media Handling
Section 11.1.3 of [ICE-BIS] defines procedures common for sending 12.1. Sending Media
media across Full and Lite implementations.
Section 11.2 of [ICE-BIS] defines procedures on receiving media. Note that the selected pair for a component of a media stream may not
equal the default pair for that same component from the most recent
offer/answer exchange. When this happens, the selected pair is used
for media, not the default pair. When ICE first completes, if the
selected pairs aren't a match for the default pairs, the controlling
agent sends an updated offer/answer exchange to remedy this
disparity. However, until that updated offer arrives, there will not
be a match. Furthermore, in very unusual cases, the default
candidates in the updated offer/answer will not be a match.
When sending media, note that the selected pair for a component of a 12.1.1. Procedures for All Implementations
media stream may not equal the default pair for that same component
from the most recen offer/answer exchange. When this happens, the
selected pair is used for media, not the default pair. When ICE
first completes, if the selected pairs aren't a match for the default
pairs, the controlling agent sends an updated offer/answer exchange
to remedy this disparity. However, until that updated offer arrives,
there will not be a match. Furthermore, in very unusual cases, the
default candidates in the updated offer/answer will not be a match.
12. Usage with SIP Section 10.1.3 of [ICE-BIS] defines procedures for sending media
common across Full and Lite implementations.
12.1. Latency Guidelines 12.2. Receiving Media
See Section 10.2 of [ICE-BIS] for procedures on receiving media.
13. Usage with SIP
13.1. 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.
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 ringing the phone of the
called party. called party.
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.
12.1.1. Offer in INVITE 13.1.1. 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 If an offer is received in an INVITE request, the answerer SHOULD
begin to gather its candidates on receipt of the offer and then begin to gather its candidates on receipt of the offer and then
generate an answer in a provisional response once it has completed generate an answer in a provisional response once it has completed
that process. ICE requires that a provisional response with an SDP that process. ICE requires that a provisional response with an SDP
skipping to change at page 25, line 23 skipping to change at page 26, line 21
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], since it's a localized
decision. It also has the benefit of guaranteeing that not a single decision. It also has the benefit of guaranteeing that not a single
packet of media will get clipped, so that post-pickup delay is zero. packet of media will get clipped, so that post-pickup delay is zero.
If an agent chooses to delay local alerting in this way, it SHOULD If an agent chooses to delay local alerting in this way, it SHOULD
generate a 180 response once alerting begins. generate a 180 response once alerting begins.
12.1.2. Offer in Response 13.1.2. 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 RFC 3262), 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,
skipping to change at page 25, line 45 skipping to change at page 26, line 43
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
will take place only after the user answers. This has the effect of will take place only after the user answers. This has the effect of
reducing call setup delay, but can cause substantial post-pickup reducing call setup delay, but can cause substantial post-pickup
delays and media clipping. delays and media clipping.
12.2. SIP Option Tags and Media Feature Tags 13.2. SIP Option Tags and Media Feature Tags
[RFC5768] specifies a SIP option tag and media feature tag for usage [RFC5768] specifies a SIP option tag and media feature tag for usage
with ICE. ICE implementations using SIP SHOULD support this with ICE. ICE implementations using SIP SHOULD support this
specification, which uses a feature tag in registrations to specification, which uses a feature tag in registrations to
facilitate interoperability through signaling intermediaries. facilitate interoperability through signaling intermediaries.
12.3. Interactions with Forking 13.3. Interactions with Forking
ICE interacts very well with forking. Indeed, ICE fixes some of the ICE interacts very well with forking. Indeed, ICE fixes some of the
problems associated with forking. Without ICE, when a call forks and problems associated with forking. Without ICE, when a call forks and
the caller receives multiple incoming media streams, it cannot the caller receives multiple incoming media streams, it cannot
determine which media stream corresponds to which callee. determine which media stream corresponds to which callee.
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.
12.4. Interactions with Preconditions 13.4. Interactions with Preconditions
Quality of Service (QoS) preconditions, which are defined in RFC 3312 Quality of Service (QoS) preconditions, which are defined in RFC 3312
[RFC3312] and RFC 4032 [RFC4032], apply only to the transport [RFC3312] and RFC 4032 [RFC4032], apply only to the transport
addresses listed as the default targets for media in an offer/answer. addresses listed as the default targets for media in an offer/answer.
If ICE changes the transport address where media is received, this If ICE changes the transport address where media is received, this
change is reflected in an updated offer that changes the default change is reflected in an updated offer that changes the default
destination for media to match ICE's selection. As such, it appears destination for media to match ICE's selection. As such, it appears
like any other re-INVITE would, and is fully treated in RFCs 3312 and like any other re-INVITE would, and is fully treated in RFCs 3312 and
4032, which apply without regard to the fact that the destination for 4032, which apply without regard to the fact that the destination for
media is changing due to ICE negotiations occurring "in the media 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 12.1 describe their own Note that the procedures described in Section 13.1 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].
12.5. Interactions with Third Party Call Control 13.5. 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 RFC
3725, require additional behavior of ICE implementations to support. 3725, require additional behavior of ICE implementations to support.
In particular, if an agent receives a mid-dialog re-INVITE that In particular, if an agent receives a mid-dialog re-INVITE that
contains no offer, it MUST restart ICE for each media stream and go contains no offer, it MUST restart ICE for each media stream and go
through the process of gathering new candidates. Furthermore, that through the process of gathering new candidates. Furthermore, that
list of candidates SHOULD include the ones currently being used for list of candidates SHOULD include the ones currently being used for
media. media.
13. Relationship with ANAT 14. Relationship with ANAT
RFC 4091 [RFC4091], the Alternative Network Address Types (ANAT) RFC 4091 [RFC4091], the Alternative Network Address Types (ANAT)
Semantics for the SDP grouping framework, and RFC 4092 [RFC4092], its Semantics for the SDP grouping framework, and RFC 4092 [RFC4092], its
usage with SIP, define a mechanism for indicating that an agent can usage with SIP, define a mechanism for indicating that an agent can
support both IPv4 and IPv6 for a media stream, and it does so by support both IPv4 and IPv6 for a media stream, and it does so by
including two "m=" lines, one for v4 and one for v6. This is similar including two "m=" lines, one for v4 and one for v6. This is similar
to ICE, which allows for an agent to indicate multiple transport to ICE, which allows for an agent to indicate multiple transport
addresses using the candidate attribute. However, ANAT relies on addresses using the candidate attribute. However, ANAT relies on
static selection to pick between choices, rather than a dynamic static selection to pick between 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 This specification deprecates RFC 4091 and RFC 4092. Instead, agents
wishing to support dual-stack will utilize ICE. wishing to support dual-stack will utilize ICE.
14. Setting Ta and RTO for RTP Media Streams 15. 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 7 [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 13.1 of [ICE-BIS] for details on how the valies of Ta and RTO Section 12.1 of [ICE-BIS] for details on how the values of Ta and RTO
are computed with a real-time media stream of known maximum bandwith are computed with a real-time media stream of known maximum bandwidth
to rate-control the ICE exchanges. to rate-control the ICE exchanges.
15. Security Considerations 16. Security Considerations
15.1. Attacks on the Offer/Answer Exchanges 16.1. 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 RFC 3264 [RFC3264] apply. These
require techniques for message integrity and encryption for offers require techniques for message integrity and encryption for offers
and answers, which are satisfied by the SIPS mechanism [RFC3261] when and answers, which are satisfied by the SIPS mechanism [RFC3261] when
SIP is used. As such, the usage of SIPS with ICE is RECOMMENDED. SIP is used. As such, the usage of SIPS with ICE is RECOMMENDED.
15.2. Insider Attacks 16.2. 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.
15.2.1. The Voice Hammer Attack 16.2.1. 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.
skipping to change at page 28, line 34 skipping to change at page 29, line 34
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 its 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.
15.2.2. Interactions with Application Layer Gateways and SIP 16.2.2. 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 NAT
device that inspect the contents of packets and modify them, in order device that inspect the contents of packets and modify them, in order
to facilitate NAT traversal for application protocols. Session to facilitate NAT traversal for application protocols. Session
Border Controllers (SBCs) are close cousins of ALGs, but are less Border Controllers (SBCs) are close cousins of ALGs, but are less
transparent since they actually exist as application layer SIP transparent since they actually exist as application layer SIP
intermediaries. ICE has interactions with SBCs and ALGs. 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
skipping to change at page 29, line 40 skipping to change at page 30, line 40
will appear to both endpoints as if the other side doesn't support will appear to both endpoints as if the other side doesn't support
ICE. This will result in ICE being disabled, and media flowing ICE. This will result in ICE being disabled, and media flowing
through the SBC, if the SBC has requested it. If, however, the SBC through the SBC, if the SBC has requested it. If, however, the SBC
passes the ICE attributes without modification, yet modifies the passes the ICE attributes without modification, yet modifies the
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.
16. IANA Considerations 17. IANA Considerations
16.1. SDP Attributes 17.1. SDP Attributes
Original ICE specification defined seven new SDP attributes per the Original ICE specification defined seven new SDP attributes per the
procedures of Section 8.2.4 of [RFC4566]. The registration procedures of Section 8.2.4 of [RFC4566]. The registration
information is reproduced here. information is reproduced here.
16.1.1. candidate Attribute 17.1.1. 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
an end-to-end connectivity check using Session Traversal Utilities an end-to-end connectivity check using Session Traversal Utilities
for NAT (STUN). for NAT (STUN).
Appropriate Values: See Section 8 of RFC XXXX. Appropriate Values: See Section 9 of RFC XXXX.
16.1.2. remote-candidates Attribute 17.1.2. remote-candidates Attribute
Contact Name: Jonathan Rosenberg, jdrosen@jdrosen.net. Contact Name: Jonathan Rosenberg, jdrosen@jdrosen.net.
Attribute Name: remote-candidates Attribute Name: remote-candidates
Long Form: remote-candidates Long Form: remote-candidates
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 the identity of the remote Establishment (ICE), and provides the identity of the remote
candidates that the offerer wishes the answerer to use in its candidates that the offerer wishes the answerer to use in its
answer. answer.
Appropriate Values: See Section 8 of RFC XXXX. Appropriate Values: See Section 9 of RFC XXXX.
16.1.3. ice-lite Attribute 17.1.3. ice-lite Attribute
Contact Name: Jonathan Rosenberg, jdrosen@jdrosen.net. Contact Name: Jonathan Rosenberg, jdrosen@jdrosen.net.
Attribute Name: ice-lite Attribute Name: ice-lite
Long Form: ice-lite Long Form: ice-lite
Type of Attribute: session-level Type of Attribute: session-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 indicates that an agent has the minimum Establishment (ICE), and indicates that an agent has the minimum
functionality required to support ICE inter-operation with a peer functionality required to support ICE inter-operation with a peer
that has a full implementation. that has a full implementation.
Appropriate Values: See Section 8 of RFC XXXX. Appropriate Values: See Section 9 of RFC XXXX.
16.1.4. ice-mismatch Attribute 17.1.4. ice-mismatch Attribute
Contact Name: Jonathan Rosenberg, jdrosen@jdrosen.net. Contact Name: Jonathan Rosenberg, jdrosen@jdrosen.net.
Attribute Name: ice-mismatch Attribute Name: ice-mismatch
Long Form: ice-mismatch Long Form: ice-mismatch
Type of Attribute: session-level Type of Attribute: session-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 indicates that an agent is ICE capable, Establishment (ICE), and indicates that an agent is ICE capable,
but did not proceed with ICE due to a mismatch of candidates with but did not proceed with ICE due to a mismatch of candidates with
the default destination for media signaled in the SDP. the default destination for media signaled in the SDP.
Appropriate Values: See Section 8 of RFC XXXX. Appropriate Values: See Section 9 of RFC XXXX.
16.1.5. ice-pwd Attribute 17.1.5. ice-pwd Attribute
Contact Name: Jonathan Rosenberg, jdrosen@jdrosen.net. Contact Name: Jonathan Rosenberg, jdrosen@jdrosen.net.
Attribute Name: ice-pwd Attribute Name: ice-pwd
Long Form: ice-pwd Long Form: ice-pwd
Type of Attribute: session- or media-level Type of Attribute: session- or 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 the password used to protect Establishment (ICE), and provides the password used to protect
STUN connectivity checks. STUN connectivity checks.
Appropriate Values: See Section 8 of RFC XXXX. Appropriate Values: See Section 9 of RFC XXXX.
16.1.6. ice-ufrag Attribute 17.1.6. ice-ufrag Attribute
Contact Name: Jonathan Rosenberg, jdrosen@jdrosen.net. Contact Name: Jonathan Rosenberg, jdrosen@jdrosen.net.
Attribute Name: ice-ufrag Attribute Name: ice-ufrag
Long Form: ice-ufrag Long Form: ice-ufrag
Type of Attribute: session- or media-level Type of Attribute: session- or 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 the fragments used to construct Establishment (ICE), and provides the fragments used to construct
the username in STUN connectivity checks. the username in STUN connectivity checks.
Appropriate Values: See Section 8 of RFC XXXX. Appropriate Values: See Section 9 of RFC XXXX.
16.1.7. ice-pacing Attribute 17.1.7. ice-pacing Attribute
Contact Name: Jonathan Rosenberg, jdrosen@jdrosen.net. Contact Name: Jonathan Rosenberg, jdrosen@jdrosen.net.
Attribute Name: ice-pacing Attribute Name: ice-pacing
Long Form: ice-pacing Long Form: ice-pacing
Type of Attribute: session-level Type of Attribute: session-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) to indicate desired connectivity check pacing Establishment (ICE) to indicate desired connectivity check pacing
values. values.
Appropriate Values: See Section 8 of RFC XXXX. Appropriate Values: See Section 9 of RFC XXXX.
16.1.8. ice-options Attribute 17.1.8. ice-options Attribute
Contact Name: Jonathan Rosenberg, jdrosen@jdrosen.net. Contact Name: Jonathan Rosenberg, jdrosen@jdrosen.net.
Attribute Name: ice-options Attribute Name: ice-options
Long Form: ice-options Long Form: ice-options
Type of Attribute: session- or media-level Type of Attribute: session- or 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 indicates the ICE options or extensions Establishment (ICE), and indicates the ICE options or extensions
used by the agent. used by the agent.
Appropriate Values: See Section 8 of RFC XXXX. Appropriate Values: See Section 9 of RFC XXXX.
16.2. Interactive Connectivity Establishment (ICE) Options Registry 17.2. Interactive Connectivity Establishment (ICE) Options Registry
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 8.6; however, they are RECOMMENDED to be no longer than 20 Section 9.6; 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 RFC 5245 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
skipping to change at page 34, line 7 skipping to change at page 35, line 7
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
17. Acknowledgments 18. 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 RFC 5245,
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 RFC 6336, authored
by Magnus Westerlund and Colin Perkins. by Magnus Westerlund and Colin Perkins.
Thanks to Thomas Stach for the text in Section 9.3 Thanks to Thomas Stach for the text in Section 10.3
18. References 19. References
18.1. Normative References 19.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997. Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<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,
June 2002. DOI 10.17487/RFC3261, June 2002,
<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, June 2002. (SIP)", RFC 3262, DOI 10.17487/RFC3262, June 2002,
<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, June with Session Description Protocol (SDP)", RFC 3264,
2002. DOI 10.17487/RFC3264, June 2002,
<http://www.rfc-editor.org/info/rfc3264>.
[RFC3312] Camarillo, G., Marshall, W., 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, October 2002. Protocol (SIP)", RFC 3312, DOI 10.17487/RFC3312, October
2002, <http://www.rfc-editor.org/info/rfc3312>.
[RFC3550] Schulzrinne, H., Casner, S., Frederick, R., and V. [RFC3550] Schulzrinne, H., Casner, S., Frederick, R., and V.
Jacobson, "RTP: A Transport Protocol for Real-Time Jacobson, "RTP: A Transport Protocol for Real-Time
Applications", STD 64, RFC 3550, July 2003. 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",
3556, July 2003. RFC 3556, DOI 10.17487/RFC3556, July 2003,
<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, October in Session Description Protocol (SDP)", RFC 3605,
2003. DOI 10.17487/RFC3605, October 2003,
<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, March 2005. RFC 4032, DOI 10.17487/RFC4032, March 2005,
<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,
DOI 10.17487/RFC4091, June 2005,
<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, June 2005. (SIP)", RFC 4092, DOI 10.17487/RFC4092, June 2005,
<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, July 2006. Description Protocol", RFC 4566, DOI 10.17487/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,
May 2008. DOI 10.17487/RFC5226, May 2008,
<http://www.rfc-editor.org/info/rfc5226>.
[RFC5234] Crocker, D. and P. Overell, "Augmented BNF for Syntax [RFC5234] Crocker, D., Ed. and P. Overell, "Augmented BNF for Syntax
Specifications: ABNF", STD 68, RFC 5234, January 2008. Specifications: ABNF", STD 68, RFC 5234,
DOI 10.17487/RFC5234, January 2008,
<http://www.rfc-editor.org/info/rfc5234>.
[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,
October 2008. DOI 10.17487/RFC5389, October 2008,
<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, April 2010. Protocol (SIP)", RFC 5768, DOI 10.17487/RFC5768, April
2010, <http://www.rfc-editor.org/info/rfc5768>.
[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, August 2012. for RTP over UDP", RFC 6679, DOI 10.17487/RFC6679, August
2012, <http://www.rfc-editor.org/info/rfc6679>.
[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, December 2013. RFC 7092, DOI 10.17487/RFC7092, December 2013,
<http://www.rfc-editor.org/info/rfc7092>.
[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-mmusic-rfc5245bis-04 (work in progress), March draft-ietf-ice-rfc5245bis-00 (work in progress), March
2015. 2015.
18.2. Informative References 19.2. 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, April 2004. BCP 85, RFC 3725, DOI 10.17487/RFC3725, April 2004,
<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, December 2004. RFC 3960, DOI 10.17487/RFC3960, December 2004,
<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, March 2006. Congestion Control Protocol (DCCP)", RFC 4340,
DOI 10.17487/RFC4340, March 2006,
<http://www.rfc-editor.org/info/rfc4340>.
[RFC5626] Jennings, C., Mahy, R., and F. Audet, "Managing Client- [RFC5626] Jennings, C., Ed., Mahy, R., Ed., and F. Audet, Ed.,
Initiated Connections in the Session Initiation Protocol "Managing Client-Initiated Connections in the Session
(SIP)", RFC 5626, October 2009. Initiation Protocol (SIP)", RFC 5626,
DOI 10.17487/RFC5626, October 2009,
<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, July 2010. Protocol (SDP) Media Streams", RFC 5898,
DOI 10.17487/RFC5898, July 2010,
<http://www.rfc-editor.org/info/rfc5898>.
Appendix A. Examples Appendix A. Examples
For the example shown in Section 14 of [ICE-BIS] the resulting offer For the example shown in Section 13 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 IP4 $L-PRIV-1.IP o=jdoe 2890844526 2890842807 IN IP4 $L-PRIV-1.IP
s= s=
c=IN IP4 $NAT-PUB-1.IP c=IN IP4 $NAT-PUB-1.IP
t=0 0 t=0 0
a=ice-pwd:asd88fgpdd777uzjYhagZg a=ice-pwd:asd88fgpdd777uzjYhagZg
a=ice-ufrag:8hhY a=ice-ufrag:8hhY
m=audio $NAT-PUB-1.PORT RTP/AVP 0 m=audio $NAT-PUB-1.PORT RTP/AVP 0
 End of changes. 172 change blocks. 
270 lines changed or deleted 344 lines changed or added

This html diff was produced by rfcdiff 1.42. The latest version is available from http://tools.ietf.org/tools/rfcdiff/