draft-ietf-mmusic-ice-sip-sdp-09.txt   draft-ietf-mmusic-ice-sip-sdp-10.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: January 9, 2017 Ericsson Expires: January 23, 2017 Ericsson
S. Nandakumar S. Nandakumar
Cisco Systems Cisco Systems
July 8, 2016 July 22, 2016
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-09 draft-ietf-mmusic-ice-sip-sdp-10
Abstract Abstract
This document describes how Interactive Connectivity Establishment This document describes how Interactive Connectivity Establishment
(ICE) is used with Session Description Protocol (SDP) offer/answer (ICE) is used with Session Description Protocol (SDP) offer/answer
and Session Initiation Protocol (SIP). and Session Initiation Protocol (SIP).
Status of This Memo Status of This Memo
This Internet-Draft is submitted in full conformance with the This Internet-Draft is submitted in full conformance with the
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Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet- working documents as Internet-Drafts. The list of current Internet-
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Internet-Drafts are draft documents valid for a maximum of six months Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress." material or to cite them other than as "work in progress."
This Internet-Draft will expire on January 9, 2017. This Internet-Draft will expire on January 23, 2017.
Copyright Notice Copyright Notice
Copyright (c) 2016 IETF Trust and the persons identified as the Copyright (c) 2016 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of (http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents publication of this document. Please review these documents
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than English. than English.
Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4
3. ICE Candidate Exchange and Offer/Answer Mapping . . . . . . . 4 3. ICE Candidate Exchange and Offer/Answer Mapping . . . . . . . 4
4. SDP Offer/Answer Procedures . . . . . . . . . . . . . . . . . 4 4. SDP Offer/Answer Procedures . . . . . . . . . . . . . . . . . 4
4.1. Initial Offer/Answer Exchange . . . . . . . . . . . . . . 4 4.1. Initial Offer/Answer Exchange . . . . . . . . . . . . . . 4
4.1.1. Sending the Initial Offer . . . . . . . . . . . . . . 4 4.1.1. Sending the Initial Offer . . . . . . . . . . . . . . 4
4.1.2. Receiving the Initial Offer . . . . . . . . . . . . . 6 4.1.2. Receiving the Initial Offer . . . . . . . . . . . . . 7
4.1.3. Receipt of the Initial Answer . . . . . . . . . . . . 8 4.1.3. Receipt of the Initial Answer . . . . . . . . . . . . 8
4.1.4. Performing Connectivity Checks . . . . . . . . . . . 8 4.1.4. Performing Connectivity Checks . . . . . . . . . . . 9
4.1.5. Concluding ICE . . . . . . . . . . . . . . . . . . . 9 4.1.5. Concluding ICE . . . . . . . . . . . . . . . . . . . 9
4.2. Subsequent Offer/Answer Exchanges . . . . . . . . . . . . 9 4.2. Subsequent Offer/Answer Exchanges . . . . . . . . . . . . 10
4.2.1. Generating the Offer . . . . . . . . . . . . . . . . 10 4.2.1. Generating the Offer . . . . . . . . . . . . . . . . 10
4.2.2. Receiving the Offer and Generating an Answer . . . . 13 4.2.2. Receiving the Offer and Generating an Answer . . . . 13
4.2.3. Receiving the Answer for a Subsequent Offer . . . . . 16 4.2.3. Receiving the Answer for a Subsequent Offer . . . . . 16
4.2.4. Updating the Check and Valid Lists . . . . . . . . . 17 4.2.4. Updating the Check and Valid Lists . . . . . . . . . 17
5. ICE Option "ice2" Considerations . . . . . . . . . . . . . . 19 5. Grammar . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
6. Grammar . . . . . . . . . . . . . . . . . . . . . . . . . . . 19 5.1. "candidate" Attribute . . . . . . . . . . . . . . . . . . 19
6.1. "candidate" Attribute . . . . . . . . . . . . . . . . . . 19 5.2. "remote-candidates" Attribute . . . . . . . . . . . . . . 22
6.2. "remote-candidates" Attribute . . . . . . . . . . . . . . 22 5.3. "ice-lite" and "ice-mismatch" Attributes . . . . . . . . 22
6.3. "ice-lite" and "ice-mismatch" Attributes . . . . . . . . 22 5.4. "ice-ufrag" and "ice-pwd" Attributes . . . . . . . . . . 22
6.4. "ice-ufrag" and "ice-pwd" Attributes . . . . . . . . . . 22 5.5. "ice-pacing" Attribute . . . . . . . . . . . . . . . . . 23
6.5. "ice-pacing" Attribute . . . . . . . . . . . . . . . . . 23 5.6. "ice-options" Attribute . . . . . . . . . . . . . . . . . 23
6.6. "ice-options" Attribute . . . . . . . . . . . . . . . . . 23 6. Keepalives . . . . . . . . . . . . . . . . . . . . . . . . . 24
7. Keepalives . . . . . . . . . . . . . . . . . . . . . . . . . 24 7. Media Handling . . . . . . . . . . . . . . . . . . . . . . . 24
8. Media Handling . . . . . . . . . . . . . . . . . . . . . . . 24 7.1. Sending Media . . . . . . . . . . . . . . . . . . . . . . 24
8.1. Sending Media . . . . . . . . . . . . . . . . . . . . . . 24 7.1.1. Procedures for All Implementations . . . . . . . . . 24
8.1.1. Procedures for All Implementations . . . . . . . . . 24 7.2. Receiving Media . . . . . . . . . . . . . . . . . . . . . 24
8.2. Receiving Media . . . . . . . . . . . . . . . . . . . . . 24 8. Usage with SIP . . . . . . . . . . . . . . . . . . . . . . . 24
9. Usage with SIP . . . . . . . . . . . . . . . . . . . . . . . 24 8.1. Latency Guidelines . . . . . . . . . . . . . . . . . . . 24
9.1. Latency Guidelines . . . . . . . . . . . . . . . . . . . 24 8.1.1. Offer in INVITE . . . . . . . . . . . . . . . . . . . 25
9.1.1. Offer in INVITE . . . . . . . . . . . . . . . . . . . 25 8.1.2. Offer in Response . . . . . . . . . . . . . . . . . . 26
9.1.2. Offer in Response . . . . . . . . . . . . . . . . . . 26 8.2. SIP Option Tags and Media Feature Tags . . . . . . . . . 26
9.2. SIP Option Tags and Media Feature Tags . . . . . . . . . 26 8.3. Interactions with Forking . . . . . . . . . . . . . . . . 27
9.3. Interactions with Forking . . . . . . . . . . . . . . . . 27 8.4. Interactions with Preconditions . . . . . . . . . . . . . 27
9.4. Interactions with Preconditions . . . . . . . . . . . . . 27 8.5. Interactions with Third Party Call Control . . . . . . . 27
9.5. Interactions with Third Party Call Control . . . . . . . 27 9. Relationship with ANAT . . . . . . . . . . . . . . . . . . . 28
10. Relationship with ANAT . . . . . . . . . . . . . . . . . . . 28 10. Setting Ta and RTO for RTP Media Streams . . . . . . . . . . 28
11. Setting Ta and RTO for RTP Media Streams . . . . . . . . . . 28 11. Security Considerations . . . . . . . . . . . . . . . . . . . 28
12. Security Considerations . . . . . . . . . . . . . . . . . . . 28 11.1. Attacks on the Offer/Answer Exchanges . . . . . . . . . 28
12.1. Attacks on the Offer/Answer Exchanges . . . . . . . . . 28 11.2. Insider Attacks . . . . . . . . . . . . . . . . . . . . 29
12.2. Insider Attacks . . . . . . . . . . . . . . . . . . . . 29 11.2.1. The Voice Hammer Attack . . . . . . . . . . . . . . 29
12.2.1. The Voice Hammer Attack . . . . . . . . . . . . . . 29 11.2.2. Interactions with Application Layer Gateways and SIP 29
12.2.2. Interactions with Application Layer Gateways and SIP 29 12. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 30
13. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 30 12.1. SDP Attributes . . . . . . . . . . . . . . . . . . . . . 30
13.1. SDP Attributes . . . . . . . . . . . . . . . . . . . . . 30 12.1.1. candidate Attribute . . . . . . . . . . . . . . . . 30
13.1.1. candidate Attribute . . . . . . . . . . . . . . . . 30 12.1.2. remote-candidates Attribute . . . . . . . . . . . . 31
13.1.2. remote-candidates Attribute . . . . . . . . . . . . 31 12.1.3. ice-lite Attribute . . . . . . . . . . . . . . . . . 31
13.1.3. ice-lite Attribute . . . . . . . . . . . . . . . . . 31 12.1.4. ice-mismatch Attribute . . . . . . . . . . . . . . . 32
13.1.4. ice-mismatch Attribute . . . . . . . . . . . . . . . 32 12.1.5. ice-pwd Attribute . . . . . . . . . . . . . . . . . 32
13.1.5. ice-pwd Attribute . . . . . . . . . . . . . . . . . 32 12.1.6. ice-ufrag Attribute . . . . . . . . . . . . . . . . 33
13.1.6. ice-ufrag Attribute . . . . . . . . . . . . . . . . 33 12.1.7. ice-pacing Attribute . . . . . . . . . . . . . . . . 33
13.1.7. ice-pacing Attribute . . . . . . . . . . . . . . . . 33 12.1.8. ice-options Attribute . . . . . . . . . . . . . . . 33
13.1.8. ice-options Attribute . . . . . . . . . . . . . . . 33 12.2. Interactive Connectivity Establishment (ICE) Options
13.2. Interactive Connectivity Establishment (ICE) Options
Registry . . . . . . . . . . . . . . . . . . . . . . . . 34 Registry . . . . . . . . . . . . . . . . . . . . . . . . 34
14. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 35 13. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 35
15. References . . . . . . . . . . . . . . . . . . . . . . . . . 35 14. References . . . . . . . . . . . . . . . . . . . . . . . . . 35
15.1. Normative References . . . . . . . . . . . . . . . . . . 35 14.1. Normative References . . . . . . . . . . . . . . . . . . 35
15.2. Informative References . . . . . . . . . . . . . . . . . 37 14.2. Informative References . . . . . . . . . . . . . . . . . 37
Appendix A. Examples . . . . . . . . . . . . . . . . . . . . . . 38 Appendix A. Examples . . . . . . . . . . . . . . . . . . . . . . 38
Appendix B. The remote-candidates Attribute . . . . . . . . . . 40 Appendix B. The remote-candidates Attribute . . . . . . . . . . 40
Appendix C. Why Is the Conflict Resolution Mechanism Needed? . . 40 Appendix C. Why Is the Conflict Resolution Mechanism Needed? . . 40
Appendix D. Why Send an Updated Offer? . . . . . . . . . . . . . 41 Appendix D. Why Send an Updated Offer? . . . . . . . . . . . . . 41
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 42 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
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Readers should be familiar with the terminology defined in [RFC3264], Readers should be familiar with the terminology defined in [RFC3264],
in [ICE-BIS] and the following: in [ICE-BIS] and the following:
Default Destination/Candidate: The default destination for a Default Destination/Candidate: The default destination for a
component of a media stream is the transport address that would be component of a media stream is the transport address that would be
used by an agent that is not ICE aware. A default candidate for a used by an agent that is not ICE aware. A default candidate for a
component is one whose transport address matches the default component is one whose transport address matches the default
destination for that component. For the RTP component, the destination for that component. For the RTP component, the
default IP address is in the "c=" line of the SDP, and the port is default IP address is in the "c=" line of the SDP, and the port is
in the "m=" line. For the RTCP component, it is in the rtcp in the "m=" line.For the RTCP component, 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. ICE Candidate Exchange and Offer/Answer Mapping 3. ICE Candidate Exchange and Offer/Answer Mapping
[ICE-BIS] defines ICE candidate exchange as the process for the ICE [ICE-BIS] defines ICE candidate exchange as the process for ICE
agents (Initiator and Responder) to exchange their candidate agents (Initiator and Responder) to exchange their candidate
information required for ICE processing at the agents. For the information required for ICE processing at the agents. For the
purposes of this specification, the candidate exchange process purposes of this specification, the candidate exchange process
corresponds to the [RFC3264] Offer/Answer protocol and the corresponds to the [RFC3264] Offer/Answer protocol and the
terminologies offerer and answerer correspond to the initiator and terminologies offerer and answerer correspond to the initiator and
responder terminologies from the [ICE-BIS] respectively. responder terminologies from the [ICE-BIS] respectively.
4. SDP Offer/Answer Procedures 4. SDP Offer/Answer Procedures
4.1. Initial Offer/Answer Exchange 4.1. Initial Offer/Answer Exchange
4.1.1. Sending the Initial Offer 4.1.1. Sending the Initial Offer
The offerer shall follow the procedures defined in section 4 of The offerer shall follow the procedures defined in section 4 of
[ICE-BIS] to gather, prioritize and eliminate the redundant [ICE-BIS] to gather, prioritize and eliminate the redundant
candidates. It then chooses the default candidates and encodes them candidates. It then chooses the default candidates and encodes them
in SDP to be sent to its peer, the answerer. in the SDP to be sent to its peer, the answerer.
4.1.1.1. Choosing Default Candidates 4.1.1.1. 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
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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 6 provides detailed rules for particular media stream. Section 5 provides detailed rules for
constructing this attribute. constructing this attribute.
STUN connectivity checks between agents are authenticated using the STUN connectivity checks between agents are authenticated using the
short-term credential mechanism defined for STUN [RFC5389]. This short-term credential mechanism defined for STUN [RFC5389]. This
mechanism relies on a username and password that are exchanged mechanism relies on a username and password that are exchanged
through protocol machinery between the client and server. The through protocol machinery between the client and server. The
username fragment and password are exchanged in the ice-ufrag and username fragment and password are exchanged in the ice-ufrag and
ice-pwd attributes, respectively. ice-pwd attributes, respectively.
If an agent is a lite implementation, it MUST include an "a=ice-lite" If an agent is a lite implementation, it MUST include an "a=ice-lite"
session-level attribute in its SDP to indicate this. If an agent is session-level attribute in its SDP to indicate this. If an agent is
a full implementation, it MUST NOT include this attribute. a full implementation, it MUST NOT include this attribute.
Section 7 of [ICE-BIS] defines a new ICE option, 'ice2'. This option
is used by ICE Agents to indicate their compliancy with [ICE-BIS]
specification as compared to the [RFC5245]. If the Offering agent is
a [ICE-BIS] compliant implementation, a session level ICE option to
indicate the same (via the "a=ice-options:ice2" SDP line) MUST be
included.
The default candidates are added to the SDP as the default The default candidates are added to the SDP as the default
destination for media. For streams based on RTP, this is done by destination for media. For streams based on RTP, this is done by
placing the IP address and port of the RTP candidate into the "c=" placing the IP address and port of the RTP candidate into the "c="
and "m=" lines, respectively. If the agent is utilizing RTCP and if and "m=" lines, respectively. If the agent is utilizing RTCP and if
RTCP candidate is present and is not equal to the same address and RTCP candidate is present and is not equal to the same address and
the next higher port number of the RTP candidate, the agent MUST the next higher port number of the RTP candidate, the agent MUST
encode the RTCP candidate using the a=rtcp attribute as defined in encode the RTCP candidate using the a=rtcp attribute as defined in
RFC 3605 [RFC3605]. If RTCP is not in use, the agent MUST signal [RFC3605]. If RTCP is not in use, the agent MUST signal that using
that using b=RS:0 and b=RR:0 as defined in RFC 3556 [RFC3556]. b=RS:0 and b=RR:0 as defined in [RFC3556]
The transport addresses that will be the default destination for The transport addresses that will be the default destination for
media when communicating with non-ICE peers MUST also be present as media when communicating with non-ICE peers MUST also be present as
candidates in one or more a=candidate lines. candidates in one or more a=candidate lines.
ICE provides for extensibility by allowing an offer or answer to ICE provides for extensibility by allowing an offer or answer to
contain a series of tokens that identify the ICE extensions used by contain a series of tokens that identify the ICE extensions used by
that agent. If an agent supports an ICE extension, it MUST include that agent. If an agent supports an ICE extension, it MUST include
the token defined for that extension in the ice-options attribute. the token defined for that extension in the ice-options attribute.
The following is an example SDP message that includes ICE attributes The following is an example SDP message that includes ICE attributes
(lines folded for readability): (lines folded for readability):
v=0 v=0
o=jdoe 2890844526 2890842807 IN IP4 10.0.1.1 o=jdoe 2890844526 2890842807 IN IP4 10.0.1.1
s= s=
c=IN IP4 192.0.2.3 c=IN IP4 192.0.2.3
t=0 0 t=0 0
a=ice-options:ice2
a=ice-pwd:asd88fgpdd777uzjYhagZg a=ice-pwd:asd88fgpdd777uzjYhagZg
a=ice-ufrag:8hhY a=ice-ufrag:8hhY
m=audio 45664 RTP/AVP 0 m=audio 45664 RTP/AVP 0
b=RS:0 b=RS:0
b=RR:0 b=RR:0
a=rtpmap:0 PCMU/8000 a=rtpmap:0 PCMU/8000
a=candidate:1 1 UDP 2130706431 10.0.1.1 8998 typ host a=candidate:1 1 UDP 2130706431 10.0.1.1 8998 typ host
a=candidate:2 1 UDP 1694498815 192.0.2.3 45664 typ srflx raddr a=candidate:2 1 UDP 1694498815 192.0.2.3 45664 typ srflx raddr
10.0.1.1 rport 8998 10.0.1.1 rport 8998
Once an agent has sent its offer or its answer, that agent MUST be Once an agent has sent its offer or its answer, that agent MUST be
prepared to receive both STUN and media packets on each candidate. prepared to receive both STUN and media packets on each candidate.
As discussed in Section 10.1 of [ICE-BIS], media packets can be sent As discussed in section 9.1 of [ICE-BIS], media packets can be sent
to a candidate prior to its appearance as the default destination for to a candidate prior to its appearance as the default destination for
media in an offer or answer. media in an offer or answer.
4.1.2. Receiving the Initial Offer 4.1.2. Receiving the Initial Offer
On receiving the offer, the answerer verifies the support for ICE On receiving the offer, the answerer verifies the support for ICE
(section 5.1.1 of [ICE-BIS]), determines its role (section 5.1.2 of (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 [ICE-BIS]), gathers candidates (section 4 of [ICE-BIS]), encodes the
candidates in an SDP answer and sends it to its peer, the offerer. candidates in an SDP answer and sends it to its peer, the offerer.
The answerer shall then follow the steps defined in sections 5.1.3 The answerer shall then follow the steps defined in sections 5.1.3
and 5.1.4 of [ICE-BIS] to schedule the ICE connectivity checks. and 5.1.4 of [ICE-BIS] to schedule the ICE connectivity checks.
The below sub-sections provide additional requirements associated The below sub-sections provide additional requirements associated
with the processing of the offerer's SDP pertaining to this with the processing of the offerer's SDP pertaining to this
specification. specification.
4.1.2.1. Choosing Default Candidates 4.1.2.1. ICE Option "ice2" considerations
If the SDP offer contains a session level ICE option, "ice2" , and if
the answering ICE Agent is also an [ICE-BIS] compliant
implementation, then the generated SDP answer MUST include the
session level "a=ice-options:ice2" SDP line.
4.1.2.2. 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 4.1.1.1 for full implementations in this specification and Section 4.1.1.1 for full implementations in this specification and
section 4.2 of [ICE-BIS] for lite implementations. section 4.2 of [ICE-BIS] for lite implementations.
4.1.2.2. Verifying ICE Support 4.1.2.3. 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 9 of [ICE-BIS], which 1. The agent MUST follow the rules of section 8 of [ICE-BIS], which
describe keepalive procedures for all agents. describe keepalive procedures for all agents.
2. If the agent is not proceeding with ICE because there were 2. If the agent is not proceeding with ICE because there were
a=candidate attributes, but none that matched the default a=candidate attributes, but none that matched the default
destination of the media stream, the agent MUST include an a=ice- destination of the media stream, the agent MUST include an a=ice-
mismatch attribute in its answer. mismatch attribute in its answer.
3. If the default candidates were relayed candidates learned through 3. If the default candidates were relayed candidates learned through
a TURN server, the agent MUST create permissions in the TURN a TURN server, the agent MUST create permissions in the TURN
server for the IP addresses learned from its peer in the SDP it server for the IP addresses learned from its peer in the SDP it
just received. If this is not done, initial packets in the media just received. If this is not done, initial packets in the media
stream from the peer may be lost. stream from the peer may be lost.
4.1.2.3. Determining Role 4.1.2.4. Determining Role
In unusual cases, described in Appendix C, it is possible for both In unusual cases, described in Appendix C, it is possible for both
agents to mistakenly believe they are controlled or controlling. To agents to mistakenly believe they are controlled or controlling. To
resolve this, each agent MUST select a random number, called the tie- resolve this, each agent MUST select a random number, called the tie-
breaker, uniformly distributed between 0 and (2**64) - 1 (that is, a breaker, uniformly distributed between 0 and (2**64) - 1 (that is, a
64-bit positive integer). This number is used in connectivity checks 64-bit positive integer). This number is used in connectivity checks
to detect and repair this case, as described in Section 6.1.2.2 of to detect and repair this case, as described in section 6.1.2.3 of
[ICE-BIS]. [ICE-BIS].
4.1.3. Receipt of the Initial Answer 4.1.3. Receipt of the Initial Answer
When ICE is used with SIP, forking may result in a single offer When ICE is used with SIP, forking may result in a single offer
generating a multiplicity of answers. In that case, ICE proceeds generating a multiplicity of answers. In that case, ICE proceeds
completely in parallel and independently for each answer, treating completely in parallel and independently for each answer, treating
the combination of its offer and each answer as an independent offer/ the combination of its offer and each answer as an independent offer/
answer exchange, with its own set of pairs, check lists, states, and answer exchange, with its own set of 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 4.1.5.2. is freeing of candidates, discussed below in Section 4.1.5.2.
On receiving the SDP answer , the offerer performs steps similar to On receiving the SDP answer , the offerer performs steps similar to
answerer's processing of the offer. The offerer verifies the answerer's processing of the offer. The offerer verifies the
answerer's ICE support, determines its role and processes the answerer's ICE support, determines its role and processes the
answerer's candidates to schedule the connectivity checks as defined answerer's candidates to schedule the connectivity checks (section 6
in section 5 of [ICE-BIS]. of [ICE-BIS]).
If the offerer had included the "ice2" ICE Option in the offer and
the SDP answer also includes a similar session level ICE option, then
the peers are [ICE-BIS] complaint implementations. On the other
hand, if the SDP Answer lacks such a ICE option, the offerer defaults
to the procedures that are backward compatible with the [RFC5245]
specification.
4.1.3.1. Verifying ICE Support 4.1.3.1. Verifying ICE Support
The logic at the offerer is identical to that of the answerer as The logic at the offerer is identical to that of the answerer as
described in section 5.1.1 of [ICE-BIS], with the exception that an described in section 5.1.1 of [ICE-BIS], with the exception that an
offerer would not ever generate a=ice-mismatch attributes in an SDP. offerer would not ever generate a=ice-mismatch attributes in an SDP.
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 12.2.2 for a corresponding candidate attributes. See Section 11.2.2 for a
discussion of cases where this can happen. This specification discussion of cases where this can happen. This specification
provides no guidance on how an agent should proceed in such a failure provides no guidance on how an agent should proceed in such a failure
case. case.
4.1.4. Performing Connectivity Checks 4.1.4. Performing Connectivity Checks
The possibility for role conflicts described in Section 6.2.1.1 of The possibility for role conflicts described in section 6.1.3.1.1 of
[ICE-BIS] applies to this usage and hence all full agents MUST [ICE-BIS] applies to this usage and hence all full agents MUST
implement the role conflict repairing mechanism. Also both full and implement the role conflict repairing mechanism. Also both full and
lite agents MUST utilize the ICE-CONTROLLED and ICE-CONTROLLING lite agents MUST utilize the ICE-CONTROLLED and ICE-CONTROLLING
attributes as described in Section 6.1.2.2 of [ICE-BIS]. attributes as described in section 6.1.2.3 of [ICE-BIS].
4.1.5. Concluding ICE 4.1.5. Concluding ICE
Once all of the media streams are completed, the controlling endpoint 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.
4.1.5.1. Procedures for Full Implementations 4.1.5.1. Procedures for Full Implementations
4.1.5.1.1. Updating states 4.1.5.1.1. Updating states
Once the state of each check list is Completed, If an agent is Once the state of each check list is Completed, If an agent is
controlling, it examines the highest-priority nominated candidate controlling, it examines the highest-priority nominated candidate
pair for each component of each media stream. If any of those pair for each component of each media stream. If any of those
candidate pairs differ from the default candidate pairs in the most candidate pairs differ from the default candidate pairs in the most
recent offer/answer exchange, the controlling agent MUST generate an recent offer/answer exchange, the controlling agent MUST generate an
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4.1.5.2.1. Full Implementation Procedures 4.1.5.2.1. Full Implementation Procedures
When ICE is used with SIP, and an offer is forked to multiple When ICE is used with SIP, and an offer is forked to multiple
recipients, ICE proceeds in parallel and independently with each recipients, ICE proceeds in parallel and independently with each
answerer, all using the same local candidates. Once ICE processing answerer, all using the same local candidates. Once ICE processing
has reached the Completed state for all peers for media streams using has reached the Completed state for all peers for media streams using
those candidates, the agent SHOULD wait an additional three seconds, those candidates, the agent SHOULD wait an additional three seconds,
and then it MAY cease responding to checks or generating triggered and then it MAY cease responding to checks or generating triggered
checks on that candidate. It MAY free the candidate at that time. checks on that candidate. It MAY free the candidate at that time.
Freeing of server reflexive candidates is never explicit; it happens Freeing of server reflexive candidates is never explicit; it happens
by lack of a keepalive. The three-second delay handles cases when by lack of a keepalive. The three-second delay handles cases when
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.
4.2. Subsequent Offer/Answer Exchanges 4.2. Subsequent Offer/Answer Exchanges
Either agent MAY generate a subsequent offer at any time allowed by Either agent MAY generate a subsequent offer at any time allowed by
RFC 3264 [RFC3264]. The rules in Section 4.1.5 will cause the [RFC3264]. The rules in Section 4.1.5 will cause the controlling
controlling agent to send an updated offer at the conclusion of ICE agent to send an updated offer at the conclusion of ICE processing
processing when ICE has selected different candidate pairs from the when ICE has selected different candidate pairs from the default
default pairs. This section defines rules for construction of pairs. This section defines rules for construction of subsequent
subsequent offers and answers. 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.
4.2.1. Generating the Offer 4.2.1. Generating the Offer
4.2.1.1. Procedures for All Implementations 4.2.1.1. Procedures for All Implementations
4.2.1.1.1. ICE Restarts 4.2.1.1.1. ICE Restarts
An agent MAY restart ICE processing for an existing media stream. An An agent MAY restart ICE processing for an existing media stream as
ICE restart, as the name implies, will cause all previous states of defined in section 6.3 of [ICE-BIS].
ICE processing to be flushed and checks to start anew. The only
difference between an ICE restart and a brand new media session is
that, during the restart, media can continue to be sent to the
previously validated pair.
An agent MUST restart ICE for a media stream if:
o The offer is being generated for the purposes of changing the
target of the media stream. In other words, if an agent wants to
generate an updated offer that, had ICE not been in use, would
result in a new value for the destination of a media component.
o An agent is changing its implementation level. This typically
only happens in third party call control use cases, where the
entity performing the signaling is not the entity receiving the
media, and it has changed the target of media mid-session to
another entity that has a different ICE implementation.
These rules imply that setting the IP address in the "c=" line to The rules govering the ICE restart imply that setting the IP address
0.0.0.0 will cause an ICE restart. Consequently, ICE implementations in the "c=" line to 0.0.0.0 will cause an ICE restart. Consequently,
MUST NOT utilize this mechanism for call hold, and instead MUST use ICE implementations MUST NOT utilize this mechanism for call hold,
a=inactive and a=sendonly as described in [RFC3264]. and instead MUST use a=inactive and a=sendonly as described in
[RFC3264].
To restart ICE, an agent MUST change both the ice-pwd and the ice- To restart ICE, an agent MUST change both the ice-pwd and the ice-
ufrag for the media stream in an offer. Note that it is permissible ufrag for the media stream in an offer. Note that it is permissible
to use a session-level attribute in one offer, but to provide the to use a session-level attribute in one offer, but to provide the
same ice-pwd or ice-ufrag as a media-level attribute in a subsequent same ice-pwd or ice-ufrag as a media-level attribute in a subsequent
offer. This is not a change in password, just a change in its offer. This is not a change in password, just a change in its
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 4.1.1.2). Consequently, the set of candidates MAY include Section 4.1.1.2). Consequently, the set of candidates MAY include
some, none, or all of the previous candidates for that stream and MAY some, 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.
4.2.1.1.2. Removing a Media Stream 4.2.1.1.2. 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 6 for that media stream. Section 5 for that media stream.
4.2.1.1.3. Adding a Media Stream 4.2.1.1.3. 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 4.1.1.2). This will cause ICE that media stream (see Section 4.1.1.2). This will cause ICE
processing to begin for this media stream. processing to begin for this media stream.
4.2.1.2. Procedures for Full Implementations 4.2.1.2. Procedures for Full Implementations
skipping to change at page 13, line 26 skipping to change at page 13, line 26
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).
4.2.2. Receiving the Offer and Generating an Answer 4.2.2. Receiving the Offer and Generating an Answer
4.2.2.1. Procedures for All Implementations 4.2.2.1. 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 4.1.2.2 agent MUST reapply the verification procedures in Section 4.1.2.3
without regard to the results of verification from any previous without 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 offer/answer exchange resulted in ICE not being used, but it is used
as a consequence of a subsequent exchange. as a consequence of a subsequent exchange.
4.2.2.1.1. Detecting ICE Restart 4.2.2.1.1. 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
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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 4.1.1.2). This will cause ICE processing media stream (see Section 4.1.1.2). This will cause ICE processing
to begin for this media stream. to begin for this media stream.
4.2.2.1.3. Removed Media Stream 4.2.2.1.3. 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 6 for that media stream. defined in Section 5 for that media stream.
4.2.2.2. Procedures for Full Implementations 4.2.2.2. 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
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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 4.2.1.2.2, except that the answerer MUST NOT described in Section 4.2.1.2.2, except that the answerer MUST NOT
include the a=remote-candidates attribute in the answer. include the a=remote-candidates attribute in the answer.
4.2.2.2.3. Existing Media Streams and remote-candidates 4.2.2.2.3. 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.
The agent forms a candidate pair for each component of the media The agent forms a candidate pair for each component of the media
stream by: 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)
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stream. The state of ICE processing for that media stream is set to stream. The state of ICE processing for that media stream is set to
Completed. Completed.
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 controlling, so that the loser (the answerer under consideration in
this section) MUST change its role to controlled. Consequently, if this section) MUST change its role to controlled. Consequently, if
the agent was going to send an updated offer since, based on the the agent was going to send an updated offer since, based on the
rules in section 7.2 of [ICE-BIS], it was controlling, it no longer rules in section 6.2 of [ICE-BIS], it was controlling, it no longer
needs to. needs to.
Besides the potential role change, change in the Valid list, and Besides the potential role change, change in the Valid list, and
state changes, the construction of the answer is performed state changes, the construction of the answer is performed i
identically to the construction of an offer as described in dentically to the construction of an offer as described in
Section 4.2.1.3. Section 4.2.1.3.
4.2.3. Receiving the Answer for a Subsequent Offer 4.2.3. Receiving the Answer for a Subsequent Offer
Some deployments of ICE include e.g. SDP-Modifying Signaling-only Some deployments of ICE include e.g. SDP-Modifying Signaling-only
Back-to-Back User Agents (B2BUAs) [RFC7092] that modify the SDP body Back-to-Back User Agents (B2BUAs) [RFC7092] that modify the SDP body
during the subsequent offer/answer exchange. With the B2BUA being during the subsequent offer/answer exchange. With the B2BUA being
ICE-unaware a subsequent answer might be manipulated and might not ICE-unaware a subsequent answer might be manipulated and might not
include ICE candidates although the initial answer did. include ICE candidates although the initial answer did.
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4.2.4. Updating the Check and Valid Lists 4.2.4. Updating the Check and Valid Lists
4.2.4.1. Procedures for Full Implementations 4.2.4.1. Procedures for Full Implementations
4.2.4.1.1. ICE Restarts 4.2.4.1.1. ICE Restarts
The agent MUST remember the highest-priority nominated pairs in the The agent MUST remember the highest-priority nominated pairs in the
Valid list for each component of the media stream, called the Valid list for each component of the media stream, called the
previous selected pairs, prior to the restart. The agent will previous selected pairs, prior to the restart. The agent will
continue to send media using these pairs, as described in continue to send media using these pairs, as described in
Section 8.1. Once these destinations are noted, the agent MUST flush Section 7.1. Once these destinations are noted, the agent MUST flush
the valid and check lists, and then recompute the check list and its the valid and check lists, and then recompute the check list and its
states as described in section 5.1.3 of [ICE-BIS]. states as described in section 5.1.3 of [ICE-BIS].
4.2.4.1.2. New Media Stream 4.2.4.1.2. New Media Stream
If the offer/answer exchange added a new media stream, the agent MUST If the offer/answer exchange added a new media stream, the agent MUST
create a new check list for it (and an empty Valid list to start of create a new check list for it (and an empty Valid list to start of
course), as described in section 5.1.3 of [ICE-BIS]. course), as described in section 5.1.3 of [ICE-BIS].
4.2.4.1.3. Removed Media Stream 4.2.4.1.3. Removed Media Stream
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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.
4.2.4.2. Procedures for Lite Implementations 4.2.4.2. Procedures for Lite Implementations
If ICE is restarting for a media stream, the agent MUST start a new If ICE is restarting for a media stream, the agent MUST start a new
Valid list for that media stream. It MUST remember the pairs in the Valid list for that media stream. It MUST remember the pairs in the
previous Valid list for each component of the media stream, called previous Valid list for each component of the media stream, called
the previous selected pairs, and continue to send media there as the previous selected pairs, and continue to send media there as
described in Section 8.1. The state of ICE processing for each media described in Section 7.1. The state of ICE processing for each media
stream MUST change to Running, and the state of ICE processing MUST stream MUST change to Running, and the state of ICE processing MUST
change to Running. change to Running.
5. ICE Option "ice2" Considerations 5. Grammar
Section 7 of [ICE-BIS] defines a new ICE option, 'ice2'. This option
is used by ICE Agents to indicate their compliancy with [ICE-BIS]
specification as compared to the [RFC5245].
The ICE option, 'ice2' is used with the SDP session level "a=ice-
options" attribute in an SDP offer to indicate that the initiator of
the ICE exchange is compliant to procedures from [ICE-BIS] (via
"a=ice-options: ice2"). The Responding Peer includes this same
attribute at the session level in the SDP answer if it is also an
[ICE-BIS] compliant ICE Agent.
6. 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.
6.1. "candidate" Attribute 5.1. "candidate" Attribute
The candidate attribute is a media-level attribute only. It contains The candidate attribute is a media-level attribute only. It contains
a transport address for a candidate that can be used for connectivity a transport address for a candidate that can be used for connectivity
checks. checks.
The syntax of this attribute is defined using Augmented BNF as 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
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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 11 in [ICE-BIS] for additional discussion on ID of 2. See section 10 in [ICE-BIS] for additional discussion on
extending ICE to new media streams. extending ICE to new media streams.
<priority>: is a positive integer between 1 and (2**31 - 1). <priority>: is a positive integer between 1 and (2**31 - 1).
<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.
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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.
6.2. "remote-candidates" Attribute 5.2. "remote-candidates" Attribute
The syntax of the "remote-candidates" attribute is defined using The syntax of the "remote-candidates" attribute is defined using
Augmented BNF as defined in RFC 5234 [RFC5234]. The remote- Augmented BNF as defined in 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.
6.3. "ice-lite" and "ice-mismatch" Attributes 5.3. "ice-lite" and "ice-mismatch" Attributes
The syntax of the "ice-lite" and "ice-mismatch" attributes, both of The syntax of the "ice-lite" and "ice-mismatch" attributes, both of
which are flags, is: which are flags, is:
ice-lite = "ice-lite" ice-lite = "ice-lite"
ice-mismatch = "ice-mismatch" ice-mismatch = "ice-mismatch"
"ice-lite" is a session-level attribute only, and indicates that an "ice-lite" is a session-level attribute only, and indicates that an
agent is a lite implementation. "ice-mismatch" is a media-level agent is a lite implementation. "ice-mismatch" is a media-level
attribute only, and when present in an answer, indicates that the attribute only, and when present in an answer, indicates that the
offer arrived with a default destination for a media component that offer arrived with a default destination for a media component that
didn't have a corresponding candidate attribute. didn't have a corresponding candidate attribute.
6.4. "ice-ufrag" and "ice-pwd" Attributes 5.4. "ice-ufrag" and "ice-pwd" Attributes
The "ice-ufrag" and "ice-pwd" attributes convey the username fragment The "ice-ufrag" and "ice-pwd" attributes convey the username fragment
and password used by ICE for message integrity. Their syntax is: and password used by ICE for message integrity. Their syntax is:
ice-pwd-att = "ice-pwd" ":" password ice-pwd-att = "ice-pwd" ":" password
ice-ufrag-att = "ice-ufrag" ":" ufrag ice-ufrag-att = "ice-ufrag" ":" ufrag
password = 22*256ice-char password = 22*256ice-char
ufrag = 4*256ice-char ufrag = 4*256ice-char
The "ice-pwd" and "ice-ufrag" attributes can appear at either the The "ice-pwd" and "ice-ufrag" attributes can appear at either the
skipping to change at page 23, line 25 skipping to change at page 23, line 25
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.
6.5. "ice-pacing" Attribute 5.5. "ice-pacing" Attribute
The "ice-pacing" attribute indicates the desired connectivity check The "ice-pacing" attribute indicates the desired connectivity check
pacing, in milliseconds, for this agent (see Section 12 of pacing, in milliseconds, for this agent (see section 11 of
[ICE-BIS]). The syntax is: [ICE-BIS]). The syntax is:
ice-pacing-att = "ice-pacing" ":" pacing-value ice-pacing-att = "ice-pacing" ":" pacing-value
pacing-value = 1*10DIGIT pacing-value = 1*10DIGIT
6.6. "ice-options" Attribute 5.6. "ice-options" Attribute
The "ice-options" attribute is a session- and media-level attribute. The "ice-options" attribute is a session- and media-level attribute.
It contains a series of tokens that identify the options supported by It contains a series of tokens that identify the options supported by
the agent. Its grammar is: the agent. Its grammar is:
ice-options = "ice-options" ":" ice-option-tag ice-options = "ice-options" ":" ice-option-tag
0*(SP ice-option-tag) 0*(SP ice-option-tag)
ice-option-tag = 1*ice-char ice-option-tag = 1*ice-char
The existence of an ice-option can indicate that a certain extension The existence of an ice-option can indicate that a certain extension
is supported by the agent and will be used or that the extension is is supported by the agent and will be used or that the extension is
used only if the other agent is willing to use it too. In order to used only if the other agent is willing to use it too. In order to
avoid ambiguity, documents defining new options must indicate which avoid ambiguity, documents defining new options must indicate which
case applies to the defined extensions. case applies to the defined extensions.
7. Keepalives 6. Keepalives
The procedures defined in Section 9 of [ICE-BIS] MUST be followed. The procedures defined in section 8 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.
8. Media Handling 7. Media Handling
8.1. Sending Media 7.1. Sending Media
Note that the selected pair for a component of a media stream may not 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 equal the default pair for that same component from the most recent
offer/answer exchange. When this happens, the selected pair is used offer/answer exchange. When this happens, the selected pair is used
for media, not the default pair. When ICE first completes, if the for media, not the default pair. When ICE first completes, if the
selected pairs aren't a match for the default pairs, the controlling selected pairs aren't a match for the default pairs, the controlling
agent sends an updated offer/answer exchange to remedy this agent sends an updated offer/answer exchange to remedy this
disparity. However, until that updated offer arrives, there will not disparity. However, until that updated offer arrives, there will not
be a match. Furthermore, in very unusual cases, the default be a match. Furthermore, in very unusual cases, the default
candidates in the updated offer/answer will not be a match. candidates in the updated offer/answer will not be a match.
8.1.1. Procedures for All Implementations 7.1.1. Procedures for All Implementations
Section 10.1.3 of [ICE-BIS] defines procedures for sending media section 9.1.3 of [ICE-BIS] defines procedures for sending media
common across Full and Lite implementations. common across Full and Lite implementations.
8.2. Receiving Media 7.2. Receiving Media
See Section 10.2 of [ICE-BIS] for procedures on receiving media. See section 9.2 of [ICE-BIS] for procedures on receiving media.
9. Usage with SIP 8. Usage with SIP
9.1. Latency Guidelines 8.1. Latency Guidelines
ICE requires a series of STUN-based connectivity checks to take place ICE requires a series of STUN-based connectivity checks to take place
between endpoints. These checks start from the answerer on between endpoints. These checks start from the answerer on
generation of its answer, and start from the offerer when it receives generation of its answer, and start from the offerer when it receives
the answer. These checks can take time to complete, and as such, the the answer. These checks can take time to complete, and as such, the
selection of messages to use with offers and answers can affect selection of messages to use with offers and answers can affect
perceived user latency. Two latency figures are of particular perceived user latency. Two latency figures are of particular
interest. These are the post-pickup delay and the post-dial delay. interest. These are the post-pickup delay and the post-dial delay.
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.
9.1.1. Offer in INVITE 8.1.1. Offer in INVITE
To reduce post-dial delays, it is RECOMMENDED that the caller begin To reduce post-dial delays, it is RECOMMENDED that the caller begin
gathering candidates prior to actually sending its initial INVITE. gathering candidates prior to actually sending its initial INVITE.
This can be started upon user interface cues that a call is pending, This can be started upon user interface cues that a call is pending,
such as activity on a keypad or the phone going off-hook. such as activity on a keypad or the phone going off-hook.
If an offer is received in an INVITE request, the answerer SHOULD 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 26, line 26 skipping to change at page 26, line 26
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.
9.1.2. Offer in Response 8.1.2. Offer in Response
In addition to uses where the offer is in an INVITE, and the answer In addition to uses where the offer is in an INVITE, and the answer
is in the provisional and/or 200 OK response, ICE works with cases is in the provisional and/or 200 OK response, ICE works with cases
where the offer appears in the response. In such cases, which are where the offer appears in the response. In such cases, which are
common in third party call control [RFC3725], ICE agents SHOULD common in third party call control [RFC3725], ICE agents SHOULD
generate their offers in a reliable provisional response (which MUST generate their offers in a reliable provisional response (which MUST
utilize RFC 3262), and not alert the user on receipt of the INVITE. utilize 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 26, line 48 skipping to change at page 26, line 48
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.
9.2. SIP Option Tags and Media Feature Tags 8.2. 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.
9.3. Interactions with Forking 8.3. 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.
9.4. Interactions with Preconditions 8.4. Interactions with Preconditions
Quality of Service (QoS) preconditions, which are defined in RFC 3312 Quality of Service (QoS) preconditions, which are defined in 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 9.1 describe their own Note that the procedures described in Section 8.1 describe their own
type of "preconditions", albeit with less functionality than those type of "preconditions", albeit with less functionality than those
provided by the explicit preconditions in [RFC5898]. provided by the explicit preconditions in [RFC5898].
9.5. Interactions with Third Party Call Control 8.5. Interactions with Third Party Call Control
ICE works with Flows I, III, and IV as described in [RFC3725]. Flow ICE works with Flows I, III, and IV as described in [RFC3725]. Flow
I works without the controller supporting or being aware of ICE. I works without the controller supporting or being aware of ICE.
Flow IV will work as long as the controller passes along the ICE Flow IV will work as long as the controller passes along the ICE
attributes without alteration. Flow II is fundamentally incompatible attributes without alteration. Flow II is fundamentally incompatible
with ICE; each agent will believe itself to be the answerer and thus with ICE; each agent will believe itself to be the answerer and thus
never generate a re-INVITE. never generate a re-INVITE.
The flows for continued operation, as described in Section 7 of RFC The flows for continued operation, as described in Section 7 of 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.
10. Relationship with ANAT 9. 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.
11. Setting Ta and RTO for RTP Media Streams 10. Setting Ta and RTO for RTP Media Streams
During the gathering phase of ICE (section 4.1.1 [ICE-BIS]) and while During the gathering phase of ICE (section 4.1.1 [ICE-BIS]) and while
ICE is performing connectivity checks (section 6 [ICE-BIS]), an agent ICE is performing connectivity checks (section 6 [ICE-BIS]), an agent
sends STUN and TURN transactions. These transactions are paced at a sends STUN and TURN transactions. These transactions are paced at a
rate of one every Ta milliseconds, and utilize a specific RTO. See rate of one every Ta milliseconds, and utilize a specific RTO. See
Section 12.1 of [ICE-BIS] for details on how the values of Ta and RTO Section 11 of [ICE-BIS] for details on how the values of Ta and RTO
are computed with a real-time media stream of known maximum bandwidth are computed with a real-time media stream of known maximum bandwidth
to rate-control the ICE exchanges. to rate-control the ICE exchanges.
12. Security Considerations 11. Security Considerations
12.1. Attacks on the Offer/Answer Exchanges 11.1. Attacks on the Offer/Answer Exchanges
An attacker that can modify or disrupt the offer/answer exchanges An attacker that can modify or disrupt the offer/answer exchanges
themselves can readily launch a variety of attacks with ICE. They themselves can readily launch a variety of attacks with ICE. They
could direct media to a target of a DoS attack, they could insert could direct media to a target of a DoS attack, they could insert
themselves into the media stream, and so on. These are similar to themselves into the media stream, and so on. These are similar to
the general security considerations for offer/answer exchanges, and the general security considerations for offer/answer exchanges, and
the security considerations in RFC 3264 [RFC3264] apply. These the security considerations in 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.
12.2. Insider Attacks 11.2. Insider Attacks
In addition to attacks where the attacker is a third party trying to In addition to attacks where the attacker is a third party trying to
insert fake offers, answers, or stun messages, there are several insert fake offers, answers, or stun messages, there are several
attacks possible with ICE when the attacker is an authenticated and attacks possible with ICE when the attacker is an authenticated and
valid participant in the ICE exchange. valid participant in the ICE exchange.
12.2.1. The Voice Hammer Attack 11.2.1. The Voice Hammer Attack
The voice hammer attack is an amplification attack. In this attack, The voice hammer attack is an amplification attack. In this attack,
the attacker initiates sessions to other agents, and maliciously the attacker initiates sessions to other agents, and maliciously
includes the IP address and port of a DoS target as the destination includes the IP address and port of a DoS target as the destination
for media traffic signaled in the SDP. This causes substantial for media traffic signaled in the SDP. This causes substantial
amplification; a single offer/answer exchange can create a continuing amplification; a single offer/answer exchange can create a continuing
flood of media packets, possibly at high rates (consider video flood of media packets, possibly at high rates (consider video
sources). This attack is not specific to ICE, but ICE can help sources). This attack is not specific to ICE, but ICE can help
provide remediation. provide remediation.
skipping to change at page 29, 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.
12.2.2. Interactions with Application Layer Gateways and SIP 11.2.2. Interactions with Application Layer Gateways and SIP
Application Layer Gateways (ALGs) are functions present in a NAT Application Layer Gateways (ALGs) are functions present in a 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
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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.
13. IANA Considerations 12. IANA Considerations
13.1. SDP Attributes 12.1. 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.
13.1.1. candidate Attribute 12.1.1. candidate Attribute
Contact Name: Jonathan Rosenberg, jdrosen@jdrosen.net. Contact Name: Jonathan Rosenberg, jdrosen@jdrosen.net.
Attribute Name: candidate Attribute Name: candidate
Long Form: candidate Long Form: candidate
Type of Attribute: media-level Type of Attribute: media-level
Charset Considerations: The attribute is not subject to the charset Charset Considerations: The attribute is not subject to the charset
attribute. attribute.
Purpose: This attribute is used with Interactive Connectivity Purpose: This attribute is used with Interactive Connectivity
Establishment (ICE), and provides one of many possible candidate Establishment (ICE), and provides one of many possible candidate
addresses for communication. These addresses are validated with addresses for communication. These addresses are validated with
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 6 of RFC XXXX. Appropriate Values: See Section 5 of RFC XXXX.
13.1.2. remote-candidates Attribute 12.1.2. 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 6 of RFC XXXX. Appropriate Values: See Section 5 of RFC XXXX.
13.1.3. ice-lite Attribute 12.1.3. 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 6 of RFC XXXX. Appropriate Values: See Section 5 of RFC XXXX.
13.1.4. ice-mismatch Attribute 12.1.4. 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 6 of RFC XXXX. Appropriate Values: See Section 5 of RFC XXXX.
13.1.5. ice-pwd Attribute 12.1.5. 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 6 of RFC XXXX. Appropriate Values: See Section 5 of RFC XXXX.
13.1.6. ice-ufrag Attribute 12.1.6. 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 6 of RFC XXXX. Appropriate Values: See Section 5 of RFC XXXX.
13.1.7. ice-pacing Attribute 12.1.7. 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 6 of RFC XXXX. Appropriate Values: See Section 5 of RFC XXXX.
13.1.8. ice-options Attribute 12.1.8. 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 6 of RFC XXXX. Appropriate Values: See Section 5 of RFC XXXX.
13.2. Interactive Connectivity Establishment (ICE) Options Registry 12.2. 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 6.6; however, they are RECOMMENDED to be no longer than 20 Section 5.6; however, they are RECOMMENDED to be no longer than 20
characters. This is to reduce message sizes and allow for efficient characters. This is to reduce message sizes and allow for efficient
parsing. parsing.
In RFC 5245 ICE options could only be defined at the session level. In 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
option, all new ICE options MUST also define in their specification option, all new ICE options MUST also define in their specification
how the media-level ICE option values are aggregated to generate the how the media-level ICE option values are aggregated to generate the
value of the session-level ICE option. value of the session-level ICE option.
[RFC6679] defines "rtp+ecn" ICE option. The aggregation rule for [RFC6679] defines "rtp+ecn" ICE option. The aggregation rule for
this ICE option is that if all aggregated media using ICE contain a this ICE option is that if all aggregated media using ICE contain a
media-level "rtp+ecn" ICE option then an "rtp+ecn" ICE option MUST be media-level "rtp+ecn" ICE option then an "rtp+ecn" ICE option MUST be
inserted at the session-level. If one of the media does not contain inserted at the session-level. If one of the media does not contain
the option, then it MUST NOT be inserted at the session-level. the option, then it MUST NOT be inserted at the session-level.
[ICE-BIS] defines "ice2" ICE option. Since "ice2" is a session level Section 7 of [ICE-BIS] defines "ice2" ICE option. Since "ice2" is a
ICE option, no aggregation rules apply. session level ICE option, no aggregation rules apply.
A registration request MUST include the following information: A registration request MUST include the following information:
o The ICE option identifier to be registered o The ICE option identifier to be registered
o Name, Email, and Address of a contact person for the registration o Name, Email, and Address of a contact person for the registration
o Organization or individuals having the change control o Organization or individuals having the change control
o Short description of the ICE extension to which the option relates o Short description of the ICE extension to which the option relates
o Reference(s) to the specification defining the ICE option and the o Reference(s) to the specification defining the ICE option and the
related extensions related extensions
14. Acknowledgments 13. Acknowledgments
A large part of the text in this document was taken from RFC 5245, A large part of the text in this document was taken from 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 4.2.3 and Roman Thanks to Thomas Stach for the text in Section 4.2.3 and Roman
Shpount for suggesting RTCP candidate handling in Section 4.1.1.2 Shpount for suggesting RTCP candidate handling in Section 4.1.1.2
Thanks to following experts for their review and constructive Thanks to following experts for their review and constructive
feedback: Christer Holmberg. feedback: Christer Holmberg.
15. References 14. References
15.1. Normative References 14.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/ Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/
RFC2119, March 1997, RFC2119, March 1997,
<http://www.rfc-editor.org/info/rfc2119>. <http://www.rfc-editor.org/info/rfc2119>.
[RFC3261] Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston, [RFC3261] Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston,
A., Peterson, J., Sparks, R., Handley, M., and E. A., Peterson, J., Sparks, R., Handley, M., and E.
Schooler, "SIP: Session Initiation Protocol", RFC 3261, Schooler, "SIP: Session Initiation Protocol", RFC 3261,
DOI 10.17487/RFC3261, June 2002, DOI 10.17487/RFC3261, June 2002,
skipping to change at page 37, line 37 skipping to change at page 37, line 37
Initiation Protocol (SIP) Back-to-Back User Agents", RFC Initiation Protocol (SIP) Back-to-Back User Agents", RFC
7092, DOI 10.17487/RFC7092, December 2013, 7092, DOI 10.17487/RFC7092, December 2013,
<http://www.rfc-editor.org/info/rfc7092>. <http://www.rfc-editor.org/info/rfc7092>.
[ICE-BIS] Keranen, A. and J. Rosenberg, "Interactive Connectivity [ICE-BIS] Keranen, A. and J. Rosenberg, "Interactive Connectivity
Establishment (ICE): A Protocol for Network Address Establishment (ICE): A Protocol for Network Address
Translator (NAT) Traversal for Offer/Answer Protocols", Translator (NAT) Traversal for Offer/Answer Protocols",
draft-ietf-ice-rfc5245bis-00 (work in progress), March draft-ietf-ice-rfc5245bis-00 (work in progress), March
2015. 2015.
15.2. Informative References 14.2. Informative References
[RFC3725] Rosenberg, J., Peterson, J., Schulzrinne, H., and G. [RFC3725] Rosenberg, J., Peterson, J., Schulzrinne, H., and G.
Camarillo, "Best Current Practices for Third Party Call Camarillo, "Best Current Practices for Third Party Call
Control (3pcc) in the Session Initiation Protocol (SIP)", Control (3pcc) in the Session Initiation Protocol (SIP)",
BCP 85, RFC 3725, DOI 10.17487/RFC3725, April 2004, BCP 85, RFC 3725, DOI 10.17487/RFC3725, April 2004,
<http://www.rfc-editor.org/info/rfc3725>. <http://www.rfc-editor.org/info/rfc3725>.
[RFC3960] Camarillo, G. and H. Schulzrinne, "Early Media and Ringing [RFC3960] Camarillo, G. and H. Schulzrinne, "Early Media and Ringing
Tone Generation in the Session Initiation Protocol (SIP)", Tone Generation in the Session Initiation Protocol (SIP)",
RFC 3960, DOI 10.17487/RFC3960, December 2004, RFC 3960, DOI 10.17487/RFC3960, December 2004,
skipping to change at page 38, line 24 skipping to change at page 38, line 24
<http://www.rfc-editor.org/info/rfc5626>. <http://www.rfc-editor.org/info/rfc5626>.
[RFC5898] Andreasen, F., Camarillo, G., Oran, D., and D. Wing, [RFC5898] Andreasen, F., Camarillo, G., Oran, D., and D. Wing,
"Connectivity Preconditions for Session Description "Connectivity Preconditions for Session Description
Protocol (SDP) Media Streams", RFC 5898, DOI 10.17487/ Protocol (SDP) Media Streams", RFC 5898, DOI 10.17487/
RFC5898, July 2010, RFC5898, July 2010,
<http://www.rfc-editor.org/info/rfc5898>. <http://www.rfc-editor.org/info/rfc5898>.
Appendix A. Examples Appendix A. Examples
For the example shown in Section 12 of [ICE-BIS] the resulting offer For the example shown in section 12 of [ICE-BIS] the resulting offer
(message 5) encoded in SDP looks like: (message 5) encoded in SDP looks like:
v=0 v=0
o=jdoe 2890844526 2890842807 IN IP6 $L-PRIV-1.IP o=jdoe 2890844526 2890842807 IN IP6 $L-PRIV-1.IP
s= s=
c=IN IP6 $NAT-PUB-1.IP c=IN IP6 $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
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