draft-ietf-mmusic-ice-sip-sdp-37.txt   draft-ietf-mmusic-ice-sip-sdp-38.txt 
MMUSIC M. Petit-Huguenin MMUSIC M. Petit-Huguenin
Internet-Draft Impedance Mismatch Internet-Draft Impedance Mismatch
Obsoletes: 5245 (if approved) S. Nandakumar Obsoletes: 5245 (if approved) S. Nandakumar
Intended status: Standards Track Cisco Systems Intended status: Standards Track Cisco Systems
Expires: January 31, 2020 A. Keranen Expires: February 9, 2020 A. Keranen
Ericsson Ericsson
R. Shpount R. Shpount
TurboBridge TurboBridge
C. Holmberg C. Holmberg
Ericsson Ericsson
July 30, 2019 August 8, 2019
Session Description Protocol (SDP) Offer/Answer procedures for Session Description Protocol (SDP) Offer/Answer procedures for
Interactive Connectivity Establishment (ICE) Interactive Connectivity Establishment (ICE)
draft-ietf-mmusic-ice-sip-sdp-37 draft-ietf-mmusic-ice-sip-sdp-38
Abstract Abstract
This document describes Session Description Protocol (SDP) Offer/ This document describes Session Description Protocol (SDP) Offer/
Answer procedures for carrying out Interactive Connectivity Answer procedures for carrying out Interactive Connectivity
Establishment (ICE) between the agents. Establishment (ICE) between the agents.
This document obsoletes RFC 5245. This document obsoletes RFC 5245.
Status of This Memo Status of This Memo
skipping to change at page 1, line 42 skipping to change at page 1, line 42
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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
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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 31, 2020. This Internet-Draft will expire on February 9, 2020.
Copyright Notice Copyright Notice
Copyright (c) 2019 IETF Trust and the persons identified as the Copyright (c) 2019 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
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Without obtaining an adequate license from the person(s) controlling Without obtaining an adequate license from the person(s) controlling
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outside the IETF Standards Process, and derivative works of it may outside the IETF Standards Process, and derivative works of it may
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Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4 2. Conventions . . . . . . . . . . . . . . . . . . . . . . . . . 4
3. SDP Offer/Answer Procedures . . . . . . . . . . . . . . . . . 4 3. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4
3.1. Introduction . . . . . . . . . . . . . . . . . . . . . . 4 4. SDP Offer/Answer Procedures . . . . . . . . . . . . . . . . . 4
3.2. Generic Procedures . . . . . . . . . . . . . . . . . . . 4 4.1. Introduction . . . . . . . . . . . . . . . . . . . . . . 4
3.2.1. Encoding . . . . . . . . . . . . . . . . . . . . . . 4 4.2. Generic Procedures . . . . . . . . . . . . . . . . . . . 5
3.2.2. RTP/RTCP Considerations . . . . . . . . . . . . . . . 6 4.2.1. Encoding . . . . . . . . . . . . . . . . . . . . . . 5
3.2.3. Determining Role . . . . . . . . . . . . . . . . . . 6 4.2.2. RTP/RTCP Considerations . . . . . . . . . . . . . . . 6
3.2.4. STUN Considerations . . . . . . . . . . . . . . . . . 6 4.2.3. Determining Role . . . . . . . . . . . . . . . . . . 6
3.2.5. Verifying ICE Support Procedures . . . . . . . . . . 6 4.2.4. STUN Considerations . . . . . . . . . . . . . . . . . 6
3.2.6. SDP Example . . . . . . . . . . . . . . . . . . . . . 7 4.2.5. Verifying ICE Support Procedures . . . . . . . . . . 7
3.3. Initial Offer/Answer Exchange . . . . . . . . . . . . . . 8 4.2.6. SDP Example . . . . . . . . . . . . . . . . . . . . . 8
3.3.1. Sending the Initial Offer . . . . . . . . . . . . . . 8 4.3. Initial Offer/Answer Exchange . . . . . . . . . . . . . . 8
3.3.2. Sending the Initial Answer . . . . . . . . . . . . . 9 4.3.1. Sending the Initial Offer . . . . . . . . . . . . . . 8
3.3.3. Receiving the Initial Answer . . . . . . . . . . . . 9 4.3.2. Sending the Initial Answer . . . . . . . . . . . . . 9
3.3.4. Concluding ICE . . . . . . . . . . . . . . . . . . . 10 4.3.3. Receiving the Initial Answer . . . . . . . . . . . . 10
3.4. Subsequent Offer/Answer Exchanges . . . . . . . . . . . . 11 4.3.4. Concluding ICE . . . . . . . . . . . . . . . . . . . 10
3.4.1. Sending Subsequent Offer . . . . . . . . . . . . . . 11 4.4. Subsequent Offer/Answer Exchanges . . . . . . . . . . . . 11
3.4.2. Sending Subsequent Answer . . . . . . . . . . . . . . 13 4.4.1. Sending Subsequent Offer . . . . . . . . . . . . . . 11
3.4.3. Receiving Answer for a Subsequent Offer . . . . . . . 16 4.4.2. Sending Subsequent Answer . . . . . . . . . . . . . . 13
4. Grammar . . . . . . . . . . . . . . . . . . . . . . . . . . . 17 4.4.3. Receiving Answer for a Subsequent Offer . . . . . . . 16
4.1. "candidate" Attribute . . . . . . . . . . . . . . . . . . 17 5. Grammar . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
4.2. "remote-candidates" Attribute . . . . . . . . . . . . . . 20 5.1. "candidate" Attribute . . . . . . . . . . . . . . . . . . 18
4.3. "ice-lite" and "ice-mismatch" Attributes . . . . . . . . 20 5.2. "remote-candidates" Attribute . . . . . . . . . . . . . . 20
4.4. "ice-ufrag" and "ice-pwd" Attributes . . . . . . . . . . 21 5.3. "ice-lite" and "ice-mismatch" Attributes . . . . . . . . 20
4.5. "ice-pacing" Attribute . . . . . . . . . . . . . . . . . 22 5.4. "ice-ufrag" and "ice-pwd" Attributes . . . . . . . . . . 21
4.6. "ice-options" Attribute . . . . . . . . . . . . . . . . . 22 5.5. "ice-pacing" Attribute . . . . . . . . . . . . . . . . . 22
5. Keepalives . . . . . . . . . . . . . . . . . . . . . . . . . 22 5.6. "ice-options" Attribute . . . . . . . . . . . . . . . . . 22
6. SIP Considerations . . . . . . . . . . . . . . . . . . . . . 23 6. Keepalives . . . . . . . . . . . . . . . . . . . . . . . . . 23
6.1. Latency Guidelines . . . . . . . . . . . . . . . . . . . 23 7. SIP Considerations . . . . . . . . . . . . . . . . . . . . . 23
6.1.1. Offer in INVITE . . . . . . . . . . . . . . . . . . . 23 7.1. Latency Guidelines . . . . . . . . . . . . . . . . . . . 23
6.1.2. Offer in Response . . . . . . . . . . . . . . . . . . 24 7.1.1. Offer in INVITE . . . . . . . . . . . . . . . . . . . 23
6.2. SIP Option Tags and Media Feature Tags . . . . . . . . . 25 7.1.2. Offer in Response . . . . . . . . . . . . . . . . . . 24
6.3. Interactions with Forking . . . . . . . . . . . . . . . . 25 7.2. SIP Option Tags and Media Feature Tags . . . . . . . . . 25
6.4. Interactions with Preconditions . . . . . . . . . . . . . 25 7.3. Interactions with Forking . . . . . . . . . . . . . . . . 25
6.5. Interactions with Third Party Call Control . . . . . . . 26 7.4. Interactions with Preconditions . . . . . . . . . . . . . 25
7. Relationship with ANAT . . . . . . . . . . . . . . . . . . . 26 7.5. Interactions with Third Party Call Control . . . . . . . 26
8. Security Considerations . . . . . . . . . . . . . . . . . . . 26 8. Interactions with Application Layer Gateways and SIP . . . . 26
8.1. Attacks on the Offer/Answer Exchanges . . . . . . . . . . 26 9. Security Considerations . . . . . . . . . . . . . . . . . . . 27
8.2. Insider Attacks . . . . . . . . . . . . . . . . . . . . . 27 9.1. Attacks on the Offer/Answer Exchanges . . . . . . . . . . 27
8.2.1. The Voice Hammer Attack . . . . . . . . . . . . . . . 27 9.2. Insider Attacks . . . . . . . . . . . . . . . . . . . . . 28
8.2.2. Interactions with Application Layer Gateways and SIP 27 9.2.1. The Voice Hammer Attack . . . . . . . . . . . . . . . 28
9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 29 10. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 28
9.1. SDP Attributes . . . . . . . . . . . . . . . . . . . . . 29 10.1. SDP Attributes . . . . . . . . . . . . . . . . . . . . . 28
9.1.1. candidate Attribute . . . . . . . . . . . . . . . . . 29 10.1.1. candidate Attribute . . . . . . . . . . . . . . . . 29
9.1.2. remote-candidates Attribute . . . . . . . . . . . . . 29 10.1.2. remote-candidates Attribute . . . . . . . . . . . . 29
9.1.3. ice-lite Attribute . . . . . . . . . . . . . . . . . 30 10.1.3. ice-lite Attribute . . . . . . . . . . . . . . . . . 30
9.1.4. ice-mismatch Attribute . . . . . . . . . . . . . . . 30 10.1.4. ice-mismatch Attribute . . . . . . . . . . . . . . . 30
9.1.5. ice-pwd Attribute . . . . . . . . . . . . . . . . . . 31 10.1.5. ice-pwd Attribute . . . . . . . . . . . . . . . . . 31
9.1.6. ice-ufrag Attribute . . . . . . . . . . . . . . . . . 31 10.1.6. ice-ufrag Attribute . . . . . . . . . . . . . . . . 31
9.1.7. ice-options Attribute . . . . . . . . . . . . . . . . 32 10.1.7. ice-options Attribute . . . . . . . . . . . . . . . 32
9.1.8. ice-pacing Attribute . . . . . . . . . . . . . . . . 32 10.1.8. ice-pacing Attribute . . . . . . . . . . . . . . . . 32
9.2. Interactive Connectivity Establishment (ICE) Options 10.2. Interactive Connectivity Establishment (ICE) Options
Registry . . . . . . . . . . . . . . . . . . . . . . . . 33 Registry . . . . . . . . . . . . . . . . . . . . . . . . 33
10. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 33 11. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 33
11. References . . . . . . . . . . . . . . . . . . . . . . . . . 34 12. Changes from RFC 5245 . . . . . . . . . . . . . . . . . . . . 33
11.1. Normative References . . . . . . . . . . . . . . . . . . 34 13. References . . . . . . . . . . . . . . . . . . . . . . . . . 34
11.2. Informative References . . . . . . . . . . . . . . . . . 35 13.1. Normative References . . . . . . . . . . . . . . . . . . 34
13.2. Informative References . . . . . . . . . . . . . . . . . 36
Appendix A. Examples . . . . . . . . . . . . . . . . . . . . . . 36 Appendix A. Examples . . . . . . . . . . . . . . . . . . . . . . 36
Appendix B. The remote-candidates Attribute . . . . . . . . . . 38 Appendix B. The remote-candidates Attribute . . . . . . . . . . 38
Appendix C. Why Is the Conflict Resolution Mechanism Needed? . . 39 Appendix C. Why Is the Conflict Resolution Mechanism Needed? . . 39
Appendix D. Why Send an Updated Offer? . . . . . . . . . . . . . 40 Appendix D. Why Send an Updated Offer? . . . . . . . . . . . . . 40
Appendix E. Contributors . . . . . . . . . . . . . . . . . . . . 41 Appendix E. Contributors . . . . . . . . . . . . . . . . . . . . 41
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 41 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 41
1. Introduction 1. Introduction
This document describes how Interactive Connectivity Establishment This document describes how Interactive Connectivity Establishment
(ICE) is used with Session Description Protocol (SDP) offer/answer (ICE) is used with Session Description Protocol (SDP) offer/answer
[RFC3264]. The ICE specification [RFC8445] describes procedures that [RFC3264]. The ICE specification [RFC8445] describes procedures that
are common to all usages of ICE and this document gives the are common to all usages of ICE and this document gives the
additional details needed to use ICE with SDP offer/answer. additional details needed to use ICE with SDP offer/answer.
This document obsoletes RFC 5245. This document obsoletes RFC 5245.
2. Terminology NOTE: Previously both the common ICE procedures, and the SDP offer/
answer specific details, were described in[RFC5245]. [RFC8445]
obsoleted [RFC5245], and the SDP offer/answer specific details were
removed from the document. Section 12 describes the changes to the
SDP offer/answer specific details specified in this document.
2. Conventions
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in "OPTIONAL" in this document are to be interpreted as described in BCP
[RFC8174]. 14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here.
3. Terminology
Readers should be familiar with the terminology defined in [RFC3264], Readers should be familiar with the terminology defined in [RFC3264],
in [RFC8445] and the following: in [RFC8445] and the following:
Default Destination/Candidate: The default destination for a Default Destination/Candidate: The default destination for a
component of a data stream is the transport address that would be component of a data 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 connection address is in the "c=" line of the SDP, and the default connection address is in the "c=" line of the SDP, and the
port and transport protocol are in the "m=" line. For the RTCP port and transport protocol are in the "m=" line. For the RTCP
component, the address and port are indicated using the "a=rtcp" component, the address and port are indicated using the "a=rtcp"
attribute defined in [RFC3605], if present; otherwise, the RTCP attribute defined in [RFC3605], if present; otherwise, the RTCP
component address is the same as the address of the RTP component, component address is the same as the address of the RTP component,
and its port is one greater than the port of the RTP component. and its port is one greater than the port of the RTP component.
3. SDP Offer/Answer Procedures 4. SDP Offer/Answer Procedures
3.1. Introduction 4.1. Introduction
[RFC8445] defines ICE candidate exchange as the process for ICE [RFC8445] 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 terms corresponds to the [RFC3264] Offer/Answer protocol and the terms
"offerer" and "answerer" correspond to the initiator and responder "offerer" and "answerer" correspond to the initiator and responder
roles from [RFC8445] respectively. roles from [RFC8445] respectively.
Once the initiating agent has gathered, pruned, and prioritized its Once the initiating agent has gathered, pruned, and prioritized its
set of candidates [RFC8445], the candidate exchange with the peer set of candidates [RFC8445], the candidate exchange with the peer
agent begins. agent begins.
3.2. Generic Procedures 4.2. Generic Procedures
3.2.1. Encoding 4.2.1. Encoding
Section 4 provides detailed rules for constructing various SDP Section 5 provides detailed rules for constructing various SDP
attributes defined in this specification. attributes defined in this specification.
3.2.1.1. Data Streams 4.2.1.1. Data Streams
Each data stream [RFC8445] is represented by an SDP media description Each data stream [RFC8445] is represented by an SDP media description
("m=" section). ("m=" section).
3.2.1.2. Candidates 4.2.1.2. Candidates
Within an "m=" section, each candidate (including the default Within an "m=" section, each candidate (including the default
candidate) associated with the data stream is represented by an SDP candidate) associated with the data stream is represented by an SDP
candidate attribute. candidate attribute.
Prior to nomination, the "c=" line associated with an "m=" section Prior to nomination, the "c=" line associated with an "m=" section
contains the connection address of the default candidate, while the contains the connection address of the default candidate, while the
"m=" line contains the port and transport protocol of the default "m=" line contains the port and transport protocol of the default
candidate for that "m=" section. candidate for that "m=" section.
After nomination, the "c=" line for a given "m=" section contains the After nomination, the "c=" line for a given "m=" section contains the
connection address of the nominated candidate (the local candidate of connection address of the nominated candidate (the local candidate of
the nominated candidate pair) and the "m=" line contains the port and the nominated candidate pair) and the "m=" line contains the port and
transport protocol corresponding to the nominated candidate for that transport protocol corresponding to the nominated candidate for that
"m=" section. "m=" section.
3.2.1.3. Username and Password 4.2.1.3. Username and Password
The ICE username is represented by an SDP ice-ufrag attribute and the The ICE username is represented by an SDP ice-ufrag attribute and the
ICE password is represented by an SDP ice-pwd attribute. ICE password is represented by an SDP ice-pwd attribute.
3.2.1.4. Lite Implementations 4.2.1.4. Lite Implementations
An ICE lite implementation [RFC8445] MUST include an SDP ice-lite An ICE lite implementation [RFC8445] MUST include an SDP ice-lite
attribute. A full implementation MUST NOT include that attribute. attribute. A full implementation MUST NOT include that attribute.
3.2.1.5. ICE Extensions 4.2.1.5. ICE Extensions
An agent uses the SDP ice-options attribute to indicate support of An agent uses the SDP ice-options attribute to indicate support of
ICE extensions. ICE extensions.
An agent compliant to this specification MUST include an SDP ice- An agent compliant to this specification MUST include an SDP ice-
options attribute with an "ice2" attribute value [RFC8445]. If an options attribute with an "ice2" attribute value [RFC8445]. If an
agent receives an SDP offer or answer that does not contain an SDP agent receives an SDP offer or answer that indicates ICE support, but
ice-options attribute with an "ice2" attribute value, the agent can that does not contain an SDP ice-options attribute with an "ice2"
assume that the peer is compliant to [RFC5245]. attribute value, the agent can assume that the peer is compliant to
[RFC5245].
3.2.1.6. Inactive and Disabled Data Streams 4.2.1.6. Inactive and Disabled Data Streams
If an "m=" section is marked as inactive [RFC4566], or has a If an "m=" section is marked as inactive [RFC4566], or has a
bandwidth value of zero [RFC4566], the agent MUST still include ICE- bandwidth value of zero [RFC4566], the agent MUST still include ICE-
related SDP attributes. related SDP attributes.
If the port value associated with an "m=" section is set to zero If the port value associated with an "m=" section is set to zero
(implying a disabled stream) as defined in section 8.2 of [RFC3264], (implying a disabled stream) as defined in section 8.2 of [RFC3264],
the agent SHOULD NOT include ICE-related SDP candidate attributes in the agent SHOULD NOT include ICE-related SDP candidate attributes in
that "m=" section, unless an SDP extension specifying otherwise is that "m=" section, unless an SDP extension specifying otherwise is
used. used.
3.2.2. RTP/RTCP Considerations 4.2.2. RTP/RTCP Considerations
If an agent utilizes both RTP and RTCP, and separate ports are used If an agent utilizes both RTP and RTCP, and separate ports are used
for RTP and RTCP, the agent MUST include SDP candidate attributes for for RTP and RTCP, the agent MUST include SDP candidate attributes for
both the RTP and RTCP components and SDP rtcp attribute SHOULD be both the RTP and RTCP components and SDP rtcp attribute SHOULD be
included in the "m=" section, as described in [RFC3605] included in the "m=" section, as described in [RFC3605]
In the cases where the port number for the RTCP is one higher than In the cases where the port number for the RTCP is one higher than
the RTP port and the RTCP component address is the same as the the RTP port and the RTCP component address is the same as the
address of the RTP component, the SDP rtcp attribute MAY be omitted. address of the RTP component, the SDP rtcp attribute MAY be omitted.
If the agent does not utilize RTCP, it indicates that by including If the agent does not utilize RTCP, it indicates that by including
b=RS:0 and b=RR:0 SDP attributes, as described in [RFC3556]. b=RS:0 and b=RR:0 SDP attributes, as described in [RFC3556].
3.2.3. Determining Role 4.2.3. Determining Role
The offerer acts as the Initiating agent. The answerer acts as the The offerer acts as the Initiating agent. The answerer acts as the
Responding agent. The ICE roles (controlling and controlled) are Responding agent. The ICE roles (controlling and controlled) are
determined using the procedures in [RFC8445]. determined using the procedures in [RFC8445].
3.2.4. STUN Considerations 4.2.4. STUN Considerations
Once an agent has provided its local candidates to its peer in an SDP Once an agent has provided its local candidates to its peer in an SDP
offer or answer, the agent MUST be prepared to receive STUN offer or answer, the agent MUST be prepared to receive STUN
connectivity check Binding requests on those candidates. connectivity check Binding requests on those candidates.
3.2.5. Verifying ICE Support Procedures 4.2.5. Verifying ICE Support Procedures
The agents will proceed with the ICE procedures defined in [RFC8445] The agents will proceed with the ICE procedures defined in [RFC8445]
and this specification if, for each data stream in the SDP it and this specification if, for each data stream in the SDP it
received, the default destination for each component of that data received, the default destination for each component of that data
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 connection address, port, and transport protocol in the "c=" RTP, the connection address, port, and transport protocol in the "c="
and "m=" lines, respectively, appear in a candidate attribute and the and "m=" lines, respectively, appear in a candidate attribute and the
value in the rtcp attribute appears in a candidate attribute. value in the rtcp attribute appears in a candidate attribute.
This specification provides no guidance on how an agent should This specification provides no guidance on how an agent should
proceed in the cases where the above condition is not met with the proceed in the cases where the above condition is not met with the
few exceptions noted below: few exceptions noted below:
1. The presence of certain application layer gateways MAY modify the 1. The presence of certain application layer gateways might modify
transport address information as described in Section 8.2.2. The the transport address information as described in Section 8. The
behavior of the responding agent in such a situation is behavior of the responding agent in such a situation is
implementation dependent. Informally, the responding agent MAY implementation dependent. Informally, the responding agent might
consider the mismatched transport address information as a consider the mismatched transport address information as a
plausible new candidate learnt from the peer and continue its ICE plausible new candidate learnt from the peer and continue its ICE
processing with that transport address included. Alternatively, processing with that transport address included. Alternatively,
the responding agent MAY include an "a=ice-mismatch" attribute in the responding agent MAY include an "a=ice-mismatch" attribute in
its answer for such data streams. If an agent chooses to include its answer for such data streams. If an agent chooses to include
an "a=ice-mismatch" attribute in its answer for a data stream, an "a=ice-mismatch" attribute in its answer for a data stream,
then it MUST also omit "a=candidate" attributes, MUST terminate then it MUST also omit "a=candidate" attributes, MUST terminate
the usage of ICE procedures and [RFC3264] procedures MUST be used the usage of ICE procedures and [RFC3264] procedures MUST be used
instead for this data stream. instead for this data stream.
2. The transport address from the peer for the default destination 2. The transport address from the peer for the default destination
correspond to IPv4/IPv6 address values "0.0.0.0"/"::" and port is set to IPv4/IPv6 address values "0.0.0.0"/"::" and port value
value of "9". This MUST NOT be considered as a ICE failure by of "9". This MUST NOT be considered as a ICE failure by the peer
the peer agent and the ICE processing MUST continue as usual. agent and the ICE processing MUST continue as usual.
3. In some cases, the controlling/initiator agent may receive the 3. In some cases, the controlling/initiator agent may receive the
SDP answer that may omit "a=candidate" attributes for the data SDP answer that may omit "a=candidate" attributes for the data
stream, and instead include a media level "a=ice-mismatch" stream, and instead include a media level "a=ice-mismatch"
attribute. This signals to the offerer that the answerer attribute. This signals to the offerer that the answerer
supports ICE, but that ICE processing was not used for this data supports ICE, but that ICE processing was not used for this data
stream. In this case, ICE processing MUST be terminated for this stream. In this case, ICE processing MUST be terminated for this
data stream and [RFC3264] procedures MUST be followed instead. data stream and [RFC3264] procedures MUST be followed instead.
4. The transport address from the peer for the default destination 4. The transport address from the peer for the default destination
is an FQDN. Regardless of the procedures used to resolve FQDN or is an FQDN. Regardless of the procedures used to resolve FQDN or
the resolution result, this MUST NOT be considered as a ICE the resolution result, this MUST NOT be considered as a ICE
failure by the peer agent and the ICE processing MUST continue as failure by the peer agent and the ICE processing MUST continue as
usual. usual.
3.2.6. SDP Example 4.2.6. SDP Example
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 203.0.113.141 o=jdoe 2890844526 2890842807 IN IP4 203.0.113.141
s= s=
c=IN IP4 192.0.2.3 c=IN IP4 192.0.2.3
t=0 0 t=0 0
a=ice-options:ice2 a=ice-options:ice2
a=ice-pacing:50
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 203.0.113.141 8998 typ host a=candidate:1 1 UDP 2130706431 203.0.113.141 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
203.0.113.141 rport 8998 203.0.113.141 rport 8998
3.3. Initial Offer/Answer Exchange 4.3. Initial Offer/Answer Exchange
3.3.1. Sending the Initial Offer 4.3.1. Sending the Initial Offer
When an offerer generates the initial offer, in each "m=" section it When an offerer generates the initial offer, in each "m=" section it
MUST include SDP candidate attributes for each available candidate MUST include SDP candidate attributes for each available candidate
associated with the "m=" section. In addition, the offerer MUST associated with the "m=" section. In addition, the offerer MUST
include an SDP ice-ufrag attribute, an SDP ice-pwd attribute and an include an SDP ice-ufrag attribute, an SDP ice-pwd attribute and an
SDP ice-options attribute with an "ice2" attribute value in the SDP ice-options attribute with an "ice2" attribute value in the
offer. If the offerer is a full ICE implementation, it SHOULD offer. If the offerer is a full ICE implementation, it SHOULD
include an ice-pacing attribute in the offer (if not included, the include an ice-pacing attribute in the offer (if not included, the
default value will apply). A lite ICE implementation MUST NOT default value will apply). A lite ICE implementation MUST NOT
included the ice-pacing attribute in the offer (as it will not included the ice-pacing attribute in the offer (as it will not
perform connectivity checks). perform connectivity checks).
It is valid for an offer "m=" line to include no SDP candidate It is valid for an offer "m=" line to include no SDP candidate
attributes and with default destination corresponding to the IP attributes and with default destination set to the IP address values
address values "0.0.0.0"/"::" and port value of "9". This implies "0.0.0.0"/"::" and port value of "9". This implies that the offering
that the offering agent is only going to use peer reflexive agent is only going to use peer reflexive candidates or that
candidates or that additional candidates would be provided in additional candidates would be provided in subsequent signaling
subsequent signaling messages. messages.
Note: Within the scope of this document, "Initial Offer" refers to Note: Within the scope of this document, "Initial Offer" refers to
the first SDP offer that is sent in order to negotiate usage of the first SDP offer that is sent in order to negotiate usage of
ICE. It might, or might not, be the initial SDP offer of the SDP ICE. It might, or might not, be the initial SDP offer of the SDP
session. session.
Note: The procedures in this document only consider "m=" sections Note: The procedures in this document only consider "m=" sections
associated with data streams where ICE is used. associated with data streams where ICE is used.
3.3.2. Sending the Initial Answer 4.3.2. Sending the Initial Answer
When an answerer receives an initial offer that indicates that the When an answerer receives an initial offer that indicates that the
offerer supports ICE, and if the answerer accepts the offer and the offerer supports ICE, and if the answerer accepts the offer and the
usage of ICE, in each "m=" section within the answer, it MUST include usage of ICE, in each "m=" section within the answer, it MUST include
SDP candidate attributes for each available candidate associated with SDP candidate attributes for each available candidate associated with
the "m=" section. In addition, the answerer MUST include an SDP ice- the "m=" section. In addition, the answerer MUST include an SDP ice-
ufrag attribute, an SDP ice-pwd attribute and an SDP ice-options ufrag attribute, an SDP ice-pwd attribute and an SDP ice-options
attribute with an "ice2" attribute value in the answer. If the attribute with an "ice2" attribute value in the answer. If the
answerer is a full ICE implementation, it SHOULD include an ice- answerer is a full ICE implementation, it SHOULD include an ice-
pacing attribute in the answerer (if not included, the default value pacing attribute in the answerer (if not included, the default value
skipping to change at page 9, line 28 skipping to change at page 9, line 31
chekcks). chekcks).
In each "m=" line, the answerer MUST use the same transport protocol In each "m=" line, the answerer MUST use the same transport protocol
as was used in the offer "m=" line. If none of the candidates in the as was used in the offer "m=" line. If none of the candidates in the
"m=" line in the answer use the same transport protocol as indicated "m=" line in the answer use the same transport protocol as indicated
in the offer "m=" line, then, in order to avoid ICE mismatch, the in the offer "m=" line, then, in order to avoid ICE mismatch, the
default destination MUST be set to IP address values "0.0.0.0"/"::" default destination MUST be set to IP address values "0.0.0.0"/"::"
and port value of "9". and port value of "9".
It is also valid for an answer "m=" line to include no SDP candidate It is also valid for an answer "m=" line to include no SDP candidate
attributes and with default destination corresponding to the IP attributes and with default destination set to the IP address values
address values "0.0.0.0"/"::" and port value of "9". This implies "0.0.0.0"/"::" and port value of "9". This implies that the
that the answering agent is only going to use peer reflexive answering agent is only going to use peer reflexive candidates or
candidates or that additional candidates would be provided in that additional candidates would be provided in subsequent signaling
subsequent signaling messages. messages.
Once the answerer has sent the answer, it can start performing Once the answerer has sent the answer, it can start performing
connectivity checks towards the peer candidates that were provided in connectivity checks towards the peer candidates that were provided in
the offer. the offer.
If the offer does not indicate support of ICE, the answerer MUST NOT If the offer does not indicate support of ICE, the answerer MUST NOT
accept the usage of ICE. If the answerer still accepts the offer, accept the usage of ICE. If the answerer still accepts the offer,
the answerer MUST NOT include any ICE-related SDP attributes in the the answerer MUST NOT include any ICE-related SDP attributes in the
answer. Instead the answerer will generate the answer according to answer. Instead the answerer will generate the answer according to
normal offer/answer procedures [RFC3264]. normal offer/answer procedures [RFC3264].
If the answerer detects a possibility of an ICE mismatch, procedures If the answerer detects a possibility of an ICE mismatch, procedures
described in (Section 3.2.5) are followed. described in Section 4.2.5 are followed.
3.3.3. Receiving the Initial Answer 4.3.3. Receiving the Initial Answer
When an offerer receives an initial answer that indicates that the When an offerer receives an initial answer that indicates that the
answerer supports ICE, it can start performing connectivity checks answerer supports ICE, it can start performing connectivity checks
towards the peer candidates that were provided in the answer. towards the peer candidates that were provided in the answer.
If the answer does not indicate that the answerer supports ICE, or if If the answer does not indicate that the answerer supports ICE, or if
the answerer included "a=ice-mismatch" attributes for all the active the answerer included "a=ice-mismatch" attributes for all the active
data streams in the answer, the offerer MUST terminate the usage of data streams in the answer, the offerer MUST terminate the usage of
ICE for the entire session and [RFC3264] procedures MUST be followed ICE for the entire session and [RFC3264] procedures MUST be followed
instead. instead.
On the other hand, if the answer indicates support for ICE but On the other hand, if the answer indicates support for ICE but
includes "a=ice-mismatch" in certain active data streams, then the includes "a=ice-mismatch" in certain active data streams, then the
offerer MUST terminate the usage of ICE procedures and [RFC3264] offerer MUST terminate the usage of ICE procedures and [RFC3264]
procedures MUST be used instead for only these data streams. Also, procedures MUST be used instead for only these data streams. Also,
ICE procedures MUST be used for data streams where an "a=ice- ICE procedures MUST be used for data streams where an "a=ice-
mismatch" attribute was not included. mismatch" attribute was not included.
If the offerer detects an ICE mismatch for one or more data streams If the offerer detects an ICE mismatch for one or more data streams
in the answer, as described in Section 3.2.5, the offerer MUST in the answer, as described in Section 4.2.5, the offerer MUST
terminate the usage of ICE for the entire session. The subsequent terminate the usage of ICE for the entire session. The subsequent
actions taken by the offerer are implementation dependent and are out actions taken by the offerer are implementation dependent and are out
of the scope of this specification. of the scope of this specification.
3.3.4. Concluding ICE 4.3.4. Concluding ICE
Once the agent has successfully nominated a pair [RFC8445], the state Once the agent has successfully nominated a pair [RFC8445], the state
of the check list associated with the pair is set to Completed. Once of the checklist associated with the pair is set to Completed. Once
the state of each check list is set to either Completed or Failed, the state of each checklist is set to either Completed or Failed, for
for each Completed check list the agent checks whether the nominated each Completed checklist the agent checks whether the nominated pair
pair matches the default candidate pair. If there are one or more matches the default candidate pair. If there are one or more pairs
pairs that do not match, and the peer did not indicate support for that do not match, and the peer did not indicate support for the
the 'ice2' ice-option, the controlling agent MUST generate a 'ice2' ice-option, the controlling agent MUST generate a subsequent
subsequent offer, in which the connection address, port and transport offer, in which the connection address, port and transport protocol
protocol in the "c=" and "m=" lines associated with each data stream in the "c=" and "m=" lines associated with each data stream match the
match the corresponding local information of the nominated pair for corresponding local information of the nominated pair for that data
that data stream (Section 3.4.1.2.2). If the peer did indicate stream (Section 4.4.1.2.2). If the peer did indicate support for the
support for the 'ice2' ice-option, the controlling agent does not 'ice2' ice-option, the controlling agent does not immediately need to
immediately need to generate an updated offer in order to align a generate an updated offer in order to align a connection address,
connection address, port and protocol with a nominated pair. port and protocol with a nominated pair. However, later in the
However, later in the session, whenever the controlling agent does session, whenever the controlling agent does sent a subsequent offer,
sent a subsequent offer, it MUST do the alignment as described above. it MUST do the alignment as described above.
If there are one or more check lists with the state set to Failed, If there are one or more checklists with the state set to Failed, the
the controlling agent MUST generate a subsequent offer in order to controlling agent MUST generate a subsequent offer in order to remove
remove the associated data streams by setting the port value of the the associated data streams by setting the port value of the data
data streams to zero (Section 3.4.1.1.2), even if the peer did streams to zero (Section 4.4.1.1.2), even if the peer did indicate
indicate support for the 'ice2' ice-option. If needed, such offer support for the 'ice2' ice-option. If needed, such offer is used to
can also be used to align the connection address, port and transport align the connection address, port and transport protocol, as
protocol, as described above. described above.
As described in [RFC8445], once the controlling agent has nominated a As described in [RFC8445], once the controlling agent has nominated a
candidate pair for a check list, the agent MUST NOT nominate another candidate pair for a checklist, the agent MUST NOT nominate another
pair for that check list during the lifetime of the ICE session (i.e. pair for that checklist during the lifetime of the ICE session (i.e.
until ICE is restarted). until ICE is restarted).
[draft-ietf-ice-pac] provides a mechanism for allowing the ICE [draft-ietf-ice-pac] provides a mechanism for allowing the ICE
process to run long enough in order to find working candidate pairs, process to run long enough in order to find working candidate pairs,
by waiting for potential peer-reflexive candidates, even though no by waiting for potential peer-reflexive candidates, even though no
candidate pairs were received from the peer or all current candidate candidate pairs were received from the peer or all current candidate
pairs associated with a check list have either failed or been pairs associated with a checklist have either failed or been
discarded. It is OPTIONAL for an ICE agent to support the mechanism. discarded. It is OPTIONAL for an ICE agent to support the mechanism.
3.4. Subsequent Offer/Answer Exchanges 4.4. Subsequent Offer/Answer Exchanges
Either agent MAY generate a subsequent offer at any time allowed by Either agent MAY generate a subsequent offer at any time allowed by
[RFC3264]. This section defines rules for construction of subsequent [RFC3264]. This section defines rules for construction of subsequent
offers and answers. offers and answers.
Should a subsequent offer fail, ICE processing continues as if the Should a subsequent offer fail, ICE processing continues as if the
subsequent offer had never been made. subsequent offer had never been made.
3.4.1. Sending Subsequent Offer 4.4.1. Sending Subsequent Offer
3.4.1.1. Procedures for All Implementations 4.4.1.1. Procedures for All Implementations
3.4.1.1.1. ICE Restart 4.4.1.1.1. ICE Restart
An agent MAY restart ICE processing for an existing data stream An agent MAY restart ICE processing for an existing data stream
[RFC8445]. [RFC8445].
The rules governing the ICE restart imply that setting the connection The rules governing the ICE restart imply that setting the connection
address in the "c=" line to 0.0.0.0 (for IPv4)/ :: (for IPv6) will address in the "c=" line to "0.0.0.0" (for IPv4)/ "::" (for IPv6)
cause an ICE restart. Consequently, ICE implementations MUST NOT will cause an ICE restart. Consequently, ICE implementations MUST
utilize this mechanism for call hold, and instead MUST use NOT utilize this mechanism for call hold, and instead MUST use
"a=inactive" and "a=sendonly" as described in [RFC3264]. "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 data stream in an offer. However, it is permissible to ufrag for the data stream in an offer. However, it is permissible to
use a session-level attribute in one offer, but to provide the same 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 ice-pwd or ice-ufrag as a media-level attribute in a subsequent
offer. This MUST NOT be considered as ICE restart. offer. This MUST NOT be considered as ICE restart.
An agent sets the rest of the ICE-related fields in the SDP for this An agent sets the rest of the ICE-related fields in the SDP for this
data stream as it would in an initial offer of this data stream (see data stream as it would in an initial offer of this data stream
Section 3.2.1). Consequently, the set of candidates MAY include (Section 4.2.1). Consequently, the set of candidates MAY include
some, none, or all of the previous candidates for that data stream some, none, or all of the previous candidates for that data stream
and MAY include a totally new set of candidates. The agent MAY and MAY include a totally new set of candidates. The agent MAY
modify the attribute values of the SDP ice-options and SDP ice-pacing modify the attribute values of the SDP ice-options and SDP ice-pacing
attributes, and it MAY change its role using the SDP ice-lite attributes, and it MAY change its role using the SDP ice-lite
attribute. The agent MUST NOT modify the SDP ice-options, ice-pacing attribute. The agent MUST NOT modify the SDP ice-options, ice-pacing
and ice-lite attributes in a subsequent offer unless the offer is and ice-lite attributes in a subsequent offer unless the offer is
sent in order to request an ICE restart. sent in order to request an ICE restart.
3.4.1.1.2. Removing a Data Stream 4.4.1.1.2. Removing a Data Stream
If an agent removes a data stream by setting its port to zero, it If an agent removes a data stream by setting its port to zero, it
MUST NOT include any candidate attributes for that data stream and MUST NOT include any candidate attributes for that data stream and
SHOULD NOT include any other ICE-related attributes defined in SHOULD NOT include any other ICE-related attributes defined in
Section 4 for that data stream. Section 5 for that data stream.
3.4.1.1.3. Adding a Data Stream 4.4.1.1.3. Adding a Data Stream
If an agent wishes to add a new data stream, it sets the fields in If an agent wishes to add a new data stream, it sets the fields in
the SDP for this data stream as if this were an initial offer for the SDP for this data stream as if this were an initial offer for
that data stream (see Section 3.2.1). This will cause ICE processing that data stream (Section 4.2.1). This will cause ICE processing to
to begin for this data stream. begin for this data stream.
3.4.1.2. Procedures for Full Implementations 4.4.1.2. Procedures for Full Implementations
This section describes additional procedures for full This section describes additional procedures for full
implementations, covering existing data streams. implementations, covering existing data streams.
3.4.1.2.1. Before Nomination 4.4.1.2.1. Before Nomination
When an offerer sends a subsequent offer; in each "m=" section for When an offerer sends a subsequent offer; in each "m=" section for
which a candidate pair has not yet been nominated, the offer MUST which a candidate pair has not yet been nominated, the offer MUST
include the same set of ICE-related information that the offerer include the same set of ICE-related information that the offerer
included in the previous offer or answer. The agent MAY include included in the previous offer or answer. The agent MAY include
additional candidates it did not offer previously, but which it has additional candidates it did not offer previously, but which it has
gathered since the last offer/answer exchange, including peer gathered since the last offer/answer exchange, including peer
reflexive candidates. reflexive candidates.
The agent MAY change the default destination for media. As with The agent MAY change the default destination for media. As with
initial offers, there MUST be a set of candidate attributes in the initial offers, there MUST be a set of candidate attributes in the
offer matching this default destination. offer matching this default destination.
3.4.1.2.2. After Nomination 4.4.1.2.2. After Nomination
Once a candidate pair has been nominated for a data stream, the Once a candidate pair has been nominated for a data stream, the
connection address, port and transport protocol in each "c=" and "m=" connection address, port and transport protocol in each "c=" and "m="
line associated with that data stream MUST match the data associated line associated with that data stream MUST match the data associated
with the nominated pair for that data stream. In addition, the with the nominated pair for that data stream. In addition, the
offerer only includes SDP candidates representing the local offerer only includes SDP candidates (one per component) representing
candidates of the nominated candidate pair. The offerer MUST NOT the local candidates of the nominated candidate pair. The offerer
include any other SDP candidate attributes in the subsequent offer. MUST NOT include any other SDP candidate attributes in the subsequent
offer.
In addition, if the agent is controlling, it MUST include the In addition, if the agent is controlling, it MUST include the
"a=remote-candidates" attribute for each data stream whose check list "a=remote-candidates" attribute for each data stream whose checklist
is in the completed state. The attribute contains the remote is in the Completed state. The attribute contains the remote
candidates corresponding to the nominated pair in the valid list for candidates corresponding to the nominated pair in the valid list for
each component of that data stream. It is needed to avoid a race each component of that data stream. It is needed to avoid a race
condition whereby the controlling agent chooses its pairs, but the condition whereby the controlling agent chooses its pairs, but the
updated offer beats the connectivity checks to the controlled agent, updated offer beats the connectivity checks to the controlled agent,
which doesn't even know these pairs are valid, let alone selected. which doesn't even know these pairs are valid, let alone selected.
See Appendix B for elaboration on this race condition. See Appendix B for elaboration on this race condition.
3.4.1.3. Procedures for Lite Implementations 4.4.1.3. Procedures for Lite Implementations
If the ICE state is "running", a lite implementation MUST include all If the ICE state is Running, a lite implementation MUST include all
of its candidates for each component of each data stream in of its candidates for each component of each data stream in
"a=candidate" attributes in any subsequent offer. The candidates are "a=candidate" attributes in any subsequent offer. The candidates are
formed identically to the procedures for initial offers. formed identically to the procedures for initial offers.
A lite implementation MUST NOT add additional host candidates in a A lite implementation MUST NOT add additional host candidates in a
subsequent offer. If an agent needs to offer additional candidates, subsequent offer, and MUST NOT modify the username fragments and
it MUST restart ICE. Similarly, the username fragments and passwords passwords. If an agent needs to offer additional candidates, or
MUST remain the same as used previously. If an agent needs to change modify the username fragments and passwords, it MUST request an ICE
one of these, it MUST restart ICE for that data stream. restart (Section 4.4.1.1.1) for that data stream.
If ICE has completed for a data stream and if the agent is If ICE has completed for a data stream and if the agent is
controlled, the default destination for that data stream MUST be set controlled, the default destination for that data stream MUST be set
to the remote candidate of the candidate pair for that component in to the remote candidate of the candidate pair for that component in
the valid list. For a lite implementation, there is always just a the valid list. For a lite implementation, there is always just a
single candidate pair in the valid list for each component of a data single candidate pair in the valid list for each component of a data
stream. Additionally, the agent MUST include a candidate attribute stream. Additionally, the agent MUST include a candidate attribute
for each default destination. for each default destination.
If ICE state is completed and if the agent is controlling (which only If the ICE state is Completed and if the agent is controlling (which
happens when both agents are lite), the agent MUST include the only happens when both agents are lite), the agent MUST include the
"a=remote-candidates" attribute for each data stream. The attribute "a=remote-candidates" attribute for each data stream. The attribute
contains the remote candidates from the candidate pairs in the valid contains the remote candidates from the candidate pairs in the valid
list (one pair for each component of each data stream). list (one pair for each component of each data stream).
3.4.2. Sending Subsequent Answer 4.4.2. Sending Subsequent Answer
If ICE is Completed for a data stream, and the offer for that data If ICE is Completed for a data stream, and the offer for that data
stream lacked the "a=remote-candidates" attribute, the rules for stream lacked the "a=remote-candidates" attribute, the rules for
construction of the answer are identical to those for the offerer, construction of the answer are identical to those for the offerer,
except that the answerer MUST NOT include the "a=remote-candidates" except that the answerer MUST NOT include the "a=remote-candidates"
attribute in the answer. attribute in the answer.
A controlled agent will receive an offer with the "a=remote- A controlled agent will receive an offer with the "a=remote-
candidates" attribute for a data stream when its peer has concluded candidates" attribute for a data stream when its peer has concluded
ICE processing for that data stream. This attribute is present in ICE processing for that data stream. This attribute is present in
skipping to change at page 14, line 23 skipping to change at page 14, line 31
"c=" lines for RTP, and the "a=rtcp" attribute for RTCP) "c=" lines for RTP, and the "a=rtcp" attribute for RTCP)
o Setting the local candidate equal to the transport address for o Setting the local candidate equal to the transport address for
that same component in the "a=remote-candidates" attribute in the that same component in the "a=remote-candidates" attribute in the
offer. offer.
The agent then sees if each of these candidate pairs is present in The agent then sees if each of these candidate pairs is present in
the valid list. If a particular pair is not in the valid list, the the valid list. If a particular pair is not in the valid list, the
check has "lost" the race. Call such a pair a "losing pair". check has "lost" the race. Call such a pair a "losing pair".
The agent finds all the pairs in the check list whose remote The agent finds all the pairs in the checklist whose remote
candidates equal the remote candidate in the losing pair: candidates equal the remote candidate in the losing pair:
o If none of the pairs are In-Progress, and at least one is Failed, o If none of the pairs are In-Progress, and at least one is Failed,
it is most likely that a network failure, such as a network it is most likely that a network failure, such as a network
partition or serious packet loss, has occurred. The agent SHOULD partition or serious packet loss, has occurred. The agent SHOULD
generate an answer for this data stream as if the remote- generate an answer for this data stream as if the remote-
candidates attribute had not been present, and then restart ICE candidates attribute had not been present, and then restart ICE
for this stream. for this stream.
o If at least one of the pairs is In-Progress, the agent SHOULD wait o If at least one of the pairs is In-Progress, the agent SHOULD wait
for those checks to complete, and as each completes, redo the for those checks to complete, and as each completes, redo the
processing in this section until there are no losing pairs. processing in this section until there are no losing pairs.
Once there are no losing pairs, the agent can generate the answer. Once there are no losing pairs, the agent can generate the answer.
It MUST set the default destination for media to the candidates in It MUST set the default destination for media to the candidates in
the remote-candidates attribute from the offer (each of which will the remote-candidates attribute from the offer (each of which will
now be the local candidate of a candidate pair in the valid list). now be the local candidate of a candidate pair in the valid list).
It MUST include a candidate attribute in the answer for each It MUST include a candidate attribute in the answer for each
candidate in the remote-candidates attribute in the offer. candidate in the remote-candidates attribute in the offer.
3.4.2.1. ICE Restart 4.4.2.1. ICE Restart
If the offerer in a subsequent offer requested an ICE restart If the offerer in a subsequent offer requested an ICE restart
Section 3.4.1.1.1 for a data stream, and if the answerer accepts the (Section 4.4.1.1.1) for a data stream, and if the answerer accepts
offer, the answerer follows the procedures for generating an initial the offer, the answerer follows the procedures for generating an
answer. initial answer.
For a given data stream, the answerer MAY include the same candidates For a given data stream, the answerer MAY include the same candidates
that were used in the previous ICE session, but it MUST change the that were used in the previous ICE session, but it MUST change the
SDP ice-pwd and ice-ufrag attribute values. SDP ice-pwd and ice-ufrag attribute values.
The answerer MAY modify the attribute values of the SDP ice-options The answerer MAY modify the attribute values of the SDP ice-options
and SDP ice-pacing attributes, and it MAY change its role using the and SDP ice-pacing attributes, and it MAY change its role using the
SDP ice-lite attribute. The answerer MUST NOT modify the SDP ice- SDP ice-lite attribute. The answerer MUST NOT modify the SDP ice-
options, ice-pacing and ice-lite attributes in a subsequent answer options, ice-pacing and ice-lite attributes in a subsequent answer
unless the answer is sent for an offer that was used to request an unless the answer is sent for an offer that was used to request an
ICE restart Section 3.4.1.1.1. If any of the SDP attributes have ICE restart (Section 4.4.1.1.1). If any of the SDP attributes have
been modified in a subsequent offer that is not used to request an been modified in a subsequent offer that is not used to request an
ICE restart, the answerer MUST reject the offer. ICE restart, the answerer MUST reject the offer.
3.4.2.2. Lite Implementation specific procedures 4.4.2.2. Lite Implementation specific procedures
If the received offer contains the remote-candidates attribute for a If the received offer contains the remote-candidates attribute for a
data stream, the agent forms a candidate pair for each component of data stream, the agent forms a candidate pair for each component of
the data stream by: the data 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 (i.e., the contents of the "m=" and destination for that component (i.e., the contents of the "m=" and
"c=" lines for RTP, and the "a=rtcp" attribute for RTCP). "c=" lines for RTP, and the "a=rtcp" attribute for RTCP).
o Setting the local candidate equal to the transport address for o Setting the local candidate equal to the transport address for
that same component in the "a=remote-candidates" attribute in the that same component in the "a=remote-candidates" attribute in the
offer. offer.
The state of ICE processing for that data stream is set to Completed. The state of the checklist associated with that data stream is set to
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 "a=remote-candidates" attribute, both agents believe contained the "a=remote-candidates" attribute, both agents believe
they are controlling. In this case, both would have sent updated they are controlling. In this case, both would have sent updated
offers around the same time. offers around the same time.
However, the signaling protocol carrying the offer/answer exchanges However, the signaling protocol carrying the offer/answer exchanges
will have resolved this glare condition, so that one agent is always will have resolved this glare condition, so that one agent is always
the 'winner' by having its offer received before its peer has sent an the 'winner' by having its offer received before its peer has sent an
offer. The winner takes the role of controlling, so that the loser offer. The winner takes the role of controlling, so that the loser
skipping to change at page 16, line 5 skipping to change at page 16, line 13
role to controlled. role to controlled.
Consequently, if the agent was going to send an updated offer since, Consequently, if the agent was going to send an updated offer since,
based on the rules in section 8.2 of [RFC8445], it was controlling, based on the rules in section 8.2 of [RFC8445], it was controlling,
it no longer needs to. it no longer needs to.
Besides the potential role change, change in the Valid list, and Besides the potential role change, change in the Valid list, and
state changes, the construction of the answer is performed state changes, the construction of the answer is performed
identically to the construction of an offer. identically to the construction of an offer.
3.4.3. Receiving Answer for a Subsequent Offer 4.4.3. Receiving Answer for a Subsequent Offer
3.4.3.1. Procedures for Full Implementations 4.4.3.1. Procedures for Full Implementations
There may be certain situations where the offerer receives an SDP There may be certain situations where the offerer receives an SDP
answer that lacks ICE candidates although the initial answer included answer that lacks ICE candidates although the initial answer included
them. One example of such an "unexpected" answer might be happen them. One example of such an "unexpected" answer might be happen
when an ICE-unaware Back-to-Back User Agent (B2BUA) introduces a when an ICE-unaware Back-to-Back User Agent (B2BUA) introduces a
media server during call hold using 3rd party call-control procedures media server during call hold using 3rd party call-control procedures
[RFC3725]. Omitting further details how this is done, this could [RFC3725]. Omitting further details how this is done, this could
result in an answer being received at the holding UA that was result in an answer being received at the holding UA that was
constructed by the B2BUA. With the B2BUA being ICE-unaware, that constructed by the B2BUA. With the B2BUA being ICE-unaware, that
answer would not include ICE candidates. answer would not include ICE candidates.
Receiving an answer without ICE attributes in this situation might be Receiving an answer without ICE attributes in this situation might be
unexpected, but would not necessarily impair the user experience. unexpected, but would not necessarily impair the user experience.
When the offerer receives an answer indicating support for ICE, the When the offerer receives an answer indicating support for ICE, the
offer performs one of the following actions: offer performs one of the following actions:
o If the offer was a restart, the agent MUST perform ICE restart o If the offer was a restart, the agent MUST perform ICE restart
procedures as specified in Section 3.4.3.1.1 procedures as specified in Section 4.4.3.1.1
o If the offer/answer exchange removed a data stream, or an answer o If the offer/answer exchange removed a data stream, or an answer
rejected an offered data stream, an agent MUST flush the Valid rejected an offered data stream, an agent MUST flush the Valid
list for that data stream. It MUST also terminate any STUN list for that data stream. It MUST also terminate any STUN
transactions in progress for that data stream. transactions in progress for that data stream.
o If the offer/answer exchange added a new data stream, the agent o If the offer/answer exchange added a new data stream, the agent
MUST create a new check list for it (and an empty Valid list to MUST create a new checklist for it (and an empty Valid list to
start of course) which in turn triggers the candidate processing start of course) which in turn triggers the candidate processing
procedures [RFC8445]. procedures [RFC8445].
o If ICE state is running for a given data stream, the agent o If the checklist state associated with a data stream is Running,
recomputes the check list. If a pair on the new check list was the agent recomputes the checklist. If a pair on the new
also on the previous check list, its state is copied over. checklist was also on the previous checklist, its candidate pair
Otherwise, its state is set to Frozen. If none of the check lists state is copied over. Otherwise, its candidate pair state is set
are active (meaning that the pairs in each check list are Frozen), to Frozen. If none of the checklists are active (meaning that the
appropriate procedures in [RFC8445] are performed to move candidate pair states in each checklist are Frozen), appropriate
candidate(s) to the Waiting state to further continue ICE procedures in [RFC8445] are performed to move candidate pair(s) to
processing. the Waiting state to further continue ICE processing.
o If ICE state is completed and the SDP answer conforms to o If the ICE state is Completed and the SDP answer conforms to
Section 3.4.2, the agent MUST remain in the ICE completed state. Section 4.4.2, the agent MUST remain in the Completed ICE state.
However, if the ICE support is no longer indicated in the SDP answer, However, if the ICE support is no longer indicated in the SDP answer,
the agent MUST fall-back to [RFC3264] procedures and SHOULD NOT drop the agent MUST fall-back to [RFC3264] procedures and SHOULD NOT drop
the dialog because of the missing ICE support or unexpected answer. the dialog because of the missing ICE support or unexpected answer.
Once the agent sends a new offer later on, it MUST perform an ICE Once the agent sends a new offer later on, it MUST perform an ICE
restart. restart.
3.4.3.1.1. ICE Restarts 4.4.3.1.1. ICE Restarts
The agent MUST remember the nominated pair in the Valid list for each The agent MUST remember the nominated pair in the Valid list for each
component of the data stream, called the "previous selected pair", component of the data stream, called the "previous selected pair",
prior to the restart. The agent will continue to send media using prior to the restart. The agent will continue to send media using
this pair, as described in section 12 of [RFC8445]. Once these this pair, as described in section 12 of [RFC8445]. Once these
destinations are noted, the agent MUST flush the valid and check destinations are noted, the agent MUST flush the Valid lists and
lists, and then recompute the check list and its states, thus checklists, and then recompute the checklist and its states, thus
triggering the candidate processing procedures [RFC8445] triggering the candidate processing procedures [RFC8445]
3.4.3.2. Procedures for Lite Implementations 4.4.3.2. Procedures for Lite Implementations
If ICE is restarting for a data stream, the agent MUST start a new If ICE is restarting for a data stream, the agent MUST create a new
Valid list for that data stream. It MUST remember the nominated pair Valid list for that data stream. It MUST remember the nominated pair
in the previous Valid list for each component of the data stream, in the previous Valid list for each component of the data stream,
called the "previous selected pairs", and continue to send media called the "previous selected pairs", and continue to send media
there as described in section 12 of [RFC8445]. The state of ICE there as described in section 12 of [RFC8445]. The state of each
processing for each data stream MUST change to Running, and the state checklist for each data stream MUST change to Running, and the ICE
of ICE processing MUST change to Running state MUST be set to Running.
4. Grammar 5. Grammar
This specification defines eight new SDP attributes -- the This specification defines eight new SDP attributes -- the
"candidate", "remote-candidates", "ice-lite", "ice-mismatch", "ice- "candidate", "remote-candidates", "ice-lite", "ice-mismatch", "ice-
ufrag", "ice-pwd", "ice-pacing", and "ice-options" attributes. ufrag", "ice-pwd", "ice-pacing", and "ice-options" attributes.
This section also provides non-normative examples of the attributes This section also provides non-normative examples of the attributes
defined. defined.
The syntax for the attributes follow Augmented BNF as defined in The syntax for the attributes follow Augmented BNF as defined in
[RFC5234]. [RFC5234].
4.1. "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.
candidate-attribute = "candidate" ":" foundation SP component-id SP candidate-attribute = "candidate" ":" foundation SP component-id SP
transport SP transport SP
priority SP priority SP
connection-address SP ;from RFC 4566 connection-address SP ;from RFC 4566
port ;port from RFC 4566 port ;port from RFC 4566
SP cand-type SP cand-type
[SP rel-addr] [SP rel-addr]
[SP rel-port] [SP rel-port]
*(SP extension-att-name SP *(SP extension-att-name SP
extension-att-value) extension-att-value)
foundation = 1*32ice-char foundation = 1*32ice-char
component-id = 1*5DIGIT component-id = 1*3DIGIT
transport = "UDP" / transport-extension transport = "UDP" / transport-extension
transport-extension = token ; from RFC 3261 transport-extension = token ; from RFC 3261
priority = 1*10DIGIT priority = 1*10DIGIT
cand-type = "typ" SP candidate-types cand-type = "typ" SP candidate-types
candidate-types = "host" / "srflx" / "prflx" / "relay" / token candidate-types = "host" / "srflx" / "prflx" / "relay" / token
rel-addr = "raddr" SP connection-address rel-addr = "raddr" SP connection-address
rel-port = "rport" SP port rel-port = "rport" SP port
extension-att-name = token extension-att-name = token
extension-att-value = *VCHAR extension-att-value = *VCHAR
ice-char = ALPHA / DIGIT / "+" / "/" ice-char = ALPHA / DIGIT / "+" / "/"
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An implementation MUST ignore any name/value pairs it doesn't An implementation MUST ignore any name/value pairs it doesn't
understand. understand.
Example: SDP line for UDP server reflexive candidate attribute for Example: SDP line for UDP server reflexive candidate attribute for
the RTP component the RTP component
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
203.0.113.141 rport 8998 203.0.113.141 rport 8998
4.2. "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 [RFC5234]. The remote-candidates Augmented BNF as defined in [RFC5234]. The remote-candidates
attribute is a media-level attribute only. attribute is a media-level attribute only.
remote-candidate-att = "remote-candidates:" remote-candidate remote-candidate-att = "remote-candidates:" remote-candidate
0*(SP remote-candidate) 0*(SP remote-candidate)
remote-candidate = component-ID SP connection-address SP port remote-candidate = component-ID SP connection-address SP port
The attribute contains a connection-address and port for each The attribute contains a connection-address and port for each
skipping to change at page 20, line 40 skipping to change at page 20, line 47
value MUST be present for each component of a data stream. This value MUST be present for each component of a data 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
data stream that is Completed, and MUST NOT be included in any other data stream that is Completed, and MUST NOT be included in any other
case. case.
Example: Remote candidates SDP lines for the RTP and RTCP components: Example: Remote candidates SDP lines for the RTP and RTCP components:
a=remote-candidates:1 192.0.2.3 45664 a=remote-candidates:1 192.0.2.3 45664
a=remote-candidates:2 192.0.2.3 45665 a=remote-candidates:2 192.0.2.3 45665
4.3. "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 and only reported in the answer. It indicates that the attribute and only reported in the answer. It 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. Inclusion of didn't have a corresponding candidate attribute. Inclusion of
"a=ice-mismatch" attribute for a given data stream implies that even "a=ice-mismatch" attribute for a given data stream implies that even
though both agents support ICE, ICE procedures MUST NOT be used for though both agents support ICE, ICE procedures MUST NOT be used for
this data stream and [RFC3264] procedures MUST be used instead. this data stream and [RFC3264] procedures MUST be used instead.
4.4. "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 22, line 5 skipping to change at page 22, line 12
the STUN username attribute value and for bandwidth conservation the STUN username attribute value and for bandwidth conservation
considerations, the ice-ufrag attribute MUST NOT be longer than 32 considerations, the ice-ufrag attribute MUST NOT be longer than 32
characters when sending, but an implementation MUST accept up to 256 characters when sending, but an implementation MUST accept up to 256
characters when receiving. characters when receiving.
Example shows sample ice-ufrag and ice-pwd SDP lines: Example shows sample ice-ufrag and ice-pwd SDP lines:
a=ice-pwd:asd88fgpdd777uzjYhagZg a=ice-pwd:asd88fgpdd777uzjYhagZg
a=ice-ufrag:8hhY a=ice-ufrag:8hhY
4.5. "ice-pacing" Attribute 5.5. "ice-pacing" Attribute
The "ice-pacing" is a session level attribute that indicates the The "ice-pacing" is a session level attribute that indicates the
desired connectivity check pacing (Ta interval), in milliseconds, desired connectivity check pacing (Ta interval), in milliseconds,
that the sender wishes to use. See section 14.2 of [RFC8445] for that the sender wishes to use. See section 14.2 of [RFC8445] for
more information regarding selecting a pacing value. The syntax is: more information regarding selecting a pacing value. 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
If absent in an offer and answer the default value of the attribute If absent in an offer or answer the default value of the attribute is
is 50 ms, which is the recommended value specified in [RFC8445]. 50 ms, which is the recommended value specified in [RFC8445].
Once both agents have indicated the pacing value they with to use, Once both agents have indicated the pacing value they with to use,
both agents MUST use the larger of the indicated values. both agents MUST use the larger of the indicated values.
4.6. "ice-options" Attribute Example shows an ice-pacing SDP line with value '50':
a=ice-pacing:50
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 in an offer indicates that a certain The existence of an ice-option in an offer indicates that a certain
extension is supported by the agent and it is willing to use it, if extension is supported by the agent and it is willing to use it, if
the peer agent also includes the same extension in the answer. There the peer agent also includes the same extension in the answer. There
might be further extension specific negotiation needed between the might be further extension specific negotiation needed between the
agents that determine how the extension gets used in a given session. agents that determine how the extension gets used in a given session.
The details of the negotiation procedures, if present, MUST be The details of the negotiation procedures, if present, MUST be
defined by the specification defining the extension (see defined by the specification defining the extension (Section 10.2).
Section 9.2).
Example shows 'rtp+ecn' ice-option SDP line from [RFC6679]:
a=ice-options:rtp+ecn Example shows an ice-options SDP line with 'ice2' and 'rtp+ecn' [RFC6679] values:
5. Keepalives a=ice-options:ice2,rtp+ecn
6. Keepalives
All the ICE agents MUST follow the procedures defined in section 11 All the ICE agents MUST follow the procedures defined in section 11
of [RFC8445] for sending keepalives. The keepalives MUST be sent of [RFC8445] for sending keepalives. The keepalives MUST be sent
regardless of whether the data stream is currently inactive, regardless of whether the data stream is currently inactive,
sendonly, recvonly, or sendrecv, and regardless of the presence or sendonly, recvonly, or sendrecv, and regardless of the presence or
value of the bandwidth attribute. An agent can determine that its value of the bandwidth attribute. An agent can determine that its
peer supports ICE by the presence of "a=candidate" attributes for peer supports ICE by the presence of "a=candidate" attributes for
each media session. each media session.
6. SIP Considerations 7. SIP Considerations
Note that ICE is not intended for NAT traversal for SIP, which is Note that ICE is not intended for NAT traversal for SIP signaling,
assumed to be provided via another mechanism [RFC5626]. which is assumed to be provided via another mechanism [RFC5626].
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 local candidates, pairs, check answer exchange, with its own set of local candidates, pairs,
lists, states, and so on. checklists, states, and so on.
Once ICE processing has reached the Completed state for all peers for
media streams using those candidates, the agent SHOULD wait an
additional three seconds, and then it MAY cease responding to checks
or generating triggered checks on that candidate. It MAY free the
candidate at that time. Freeing of server reflexive candidates is
never explicit; it happens by lack of a keepalive. The three-second
delay handles cases when aggressive nomination is used, and the
selected pairs can quickly change after ICE has completed.
6.1. Latency Guidelines 7.1. 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 alerting the called user consequence of having successfully started alerting the called user
agent. agent.
Two cases can be considered -- one where the offer is present in the Two cases can be considered -- one where the offer is present in the
initial INVITE and one where it is in a response. initial INVITE and one where it is in a response.
6.1.1. Offer in INVITE 7.1.1. 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, so gathering candidates prior to actually sending its initial INVITE, so
that the candidates can be provided in the INVITE. This can be that the candidates can be provided in the INVITE. This can be
started upon user interface cues that a call is pending, such as started upon user interface cues that a call is pending, such as
activity on a keypad or the phone going off-hook. activity on a keypad or the phone going off-hook.
On the receipt of the offer, the answerer SHOULD generate an answer On the receipt of the offer, the answerer SHOULD generate an answer
in a provisional response as soon as it has completed gathering the in a provisional response as soon as it has completed gathering the
candidates. ICE requires that a provisional response with an SDP be candidates. ICE requires that a provisional response with an SDP be
transmitted reliably. This can be done through the existing transmitted reliably. This can be done through the existing
Provisional Response Acknowledgment (PRACK) mechanism [RFC3262] or Provisional Response Acknowledgment (PRACK) mechanism [RFC3262] or
through an ICE specific optimization, wherein, the agent retransmits through an ICE specific optimization, wherein, the agent retransmits
the provisional response with the exponential backoff timers the provisional response with the exponential backoff timers
described in [RFC3262]. Such retransmissions MUST cease on receipt described in [RFC3262]. Such retransmissions MUST cease on receipt
of a STUN Binding request with transport address matching candidate of a STUN Binding request with the transport address matching the
address for one of the data streams signaled in that SDP or on candidate address for one of the data streams signaled in that SDP or
transmission of the answer in a 2xx response. If no Binding request on transmission of the answer in a 2xx response. If no Binding
is received prior to the last retransmit, the agent does not consider request is received prior to the last retransmit, the agent does not
the session terminated. For the ICE lite peers, the agent MUST cease consider the session terminated. For the ICE lite peers, the agent
retransmitting the 18x after sending it four times since there will MUST cease retransmitting the 18x after sending it four times since
be no Binding request sent and the number four is arbitrarily chosen there will be no Binding request sent and the number four is
to limit the number of 18x retransmits (poor man's version of arbitrarily chosen to limit the number of 18x retransmits.
[RFC3262] basically). (ICE will actually work even if the peer never
receives the 18x; however, experience has shown that sending it is
important for middleboxes and firewall traversal).
Once the answer has been sent, the agent SHOULD begin its Once the answer has been sent, the agent SHOULD begin its
connectivity checks. Once candidate pairs for each component of a connectivity checks. Once candidate pairs for each component of a
data stream enter the valid list, the answerer can begin sending data stream enter the valid list, the answerer can begin sending
media on that data stream. media on that data stream.
However, prior to this point, any media that needs to be sent towards However, prior to this point, any media that needs to be sent towards
the caller (such as SIP early media [RFC3960]) MUST NOT be the caller (such as SIP early media [RFC3960]) MUST NOT be
transmitted. For this reason, implementations SHOULD delay alerting transmitted. For this reason, implementations SHOULD delay alerting
the called party until candidates for each component of each data the called party until candidates for each component of each data
skipping to change at page 24, line 46 skipping to change at page 24, line 43
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]. It also has the benefit of or usage of, preconditions [RFC3312]. It also has the benefit of
guaranteeing that not a single packet of media will get clipped, so guaranteeing that not a single packet of media will get clipped, so
that post-pickup delay is zero. If an agent chooses to delay local that post-pickup delay is zero. If an agent chooses to delay local
alerting in this way, it SHOULD generate a 180 response once alerting alerting in this way, it SHOULD generate a 180 response once alerting
begins. begins.
6.1.2. Offer in Response 7.1.2. 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 [RFC3262]), and not alert the user on receipt of the INVITE. utilize [RFC3262]), and not alert the user on receipt of the INVITE.
The answer will arrive in a PRACK. This allows for ICE processing to The answer will arrive in a PRACK. This allows for ICE processing to
take place prior to alerting, so that there is no post-pickup delay, take place prior to alerting, so that there is no post-pickup delay,
at the expense of increased call setup delays. Once ICE completes, at the expense of increased call setup delays. Once ICE completes,
skipping to change at page 25, line 19 skipping to change at page 25, line 16
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.
6.2. SIP Option Tags and Media Feature Tags 7.2. 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.
6.3. Interactions with Forking 7.3. 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 data streams, it cannot the caller receives multiple incoming data streams, it cannot
determine which data stream corresponds to which callee. determine which data 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.
6.4. Interactions with Preconditions 7.4. Interactions with Preconditions
Quality of Service (QoS) preconditions, which are defined in Quality of Service (QoS) preconditions, which are defined in
[RFC3312] and [RFC4032], apply only to the transport addresses listed [RFC3312] and [RFC4032], apply only to the transport addresses listed
as the default targets for media in an offer/answer. If ICE changes as the default targets for media in an offer/answer. If ICE changes
the transport address where media is received, this change is the transport address where media is received, this change is
reflected in an updated offer that changes the default destination reflected in an updated offer that changes the default destination
for media to match ICE's selection. As such, it appears like any 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 4032, other re-INVITE would, and is fully treated in RFCs 3312 and 4032,
which apply without regard to the fact that the destination for media which apply without regard to the fact that the destination for media
is changing due to ICE negotiations occurring "in the background". is changing due to ICE negotiations occurring "in the 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 6.1 describe their own Note that the procedures described in Section 7.1 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].
6.5. Interactions with Third Party Call Control 7.5. 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 The flows for continued operation, as described in Section 7 of
[RFC3725], require additional behavior of ICE implementations to [RFC3725], require additional behavior of ICE implementations to
support. In particular, if an agent receives a mid-dialog re-INVITE support. In particular, if an agent receives a mid-dialog re-INVITE
that contains no offer, it MUST restart ICE for each data stream and that contains no offer, it MUST restart ICE for each data stream and
go through the process of gathering new candidates. Furthermore, go through the process of gathering new candidates. Furthermore,
that list of candidates SHOULD include the ones currently being used that list of candidates SHOULD include the ones currently being used
for media. for media.
7. Relationship with ANAT 8. Interactions with Application Layer Gateways and SIP
[RFC4091], the Alternative Network Address Types (ANAT) Semantics for
the SDP grouping framework, and [RFC4092], its usage with SIP, define
a mechanism for indicating that an agent can support both IPv4 and
IPv6 for a data stream, and it does so by 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 addresses using the candidate
attribute. However, ANAT relies on static selection to pick between
choices, rather than a dynamic connectivity check used by ICE.
It is RECOMMENDED that ICE be used in realizing the dual-stack use-
cases in agents that support ICE.
8. Security Considerations
8.1. Attacks on 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
could direct media to a target of a DoS attack, they could insert
themselves into the data stream, and so on. These are similar to the
general security considerations for offer/answer exchanges, and the
security considerations in [RFC3264] apply. These require techniques
for message integrity and encryption for offers and answers, which
are satisfied by the TLS mechanism [RFC3261] when SIP is used. As
such, the usage of TLS with ICE is RECOMMENDED.
8.2. Insider Attacks
In addition to attacks where the attacker is a third party trying to
insert fake offers, answers, or STUN messages, there are several
attacks possible with ICE when the attacker is an authenticated and
valid participant in the ICE exchange.
8.2.1. The Voice Hammer Attack
The voice hammer attack is an amplification attack. In this attack,
the attacker initiates sessions to other agents, and maliciously
includes the connection address and port of a DoS target as the
destination for media traffic signaled in the SDP. This causes
substantial amplification; a single offer/answer exchange can create
a continuing flood of media packets, possibly at high rates (consider
video sources). This attack is not specific to ICE, but ICE can help
provide remediation.
Specifically, if ICE is used, the agent receiving the malicious SDP
will first perform connectivity checks to the target of media before
sending media there. If this target is a third-party host, the
checks will not succeed, and media is never sent.
Unfortunately, ICE doesn't help if it's not used, in which case an
attacker could simply send the offer without the ICE parameters.
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
answers that don't indicate ICE support.
SIP User Agents (UA) [RFC3261] that are not willing to receive non-
ICE answers MUST include an "ice" Option Tag [RFC5768] in the SIP
Require Header Field in their offer. UAs that reject non-ICE offers
will generally use a 421 response code, together with an Option Tag
"ice" in the Require Header Field in the response.
8.2.2. Interactions with Application Layer Gateways and SIP
Application Layer Gateways (ALGs) are functions present in a Network Application Layer Gateways (ALGs) are functions present in a Network
Address Translation (NAT) device that inspect the contents of packets Address Translation (NAT) device that inspect the contents of packets
and modify them, in order to facilitate NAT traversal for application and modify them, in order to facilitate NAT traversal for application
protocols. Session Border Controllers (SBCs) are close cousins of protocols. Session Border Controllers (SBCs) are close cousins of
ALGs, but are less transparent since they actually exist as ALGs, but are less transparent since they actually exist as
application-layer SIP intermediaries. ICE has interactions with SBCs application-layer SIP intermediaries. ICE has interactions with SBCs
and ALGs. 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
skipping to change at page 29, line 7 skipping to change at page 27, line 35
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.
9. IANA Considerations 9. Security Considerations
9.1. SDP Attributes 9.1. Attacks on 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
could direct media to a target of a DoS attack, they could insert
themselves into the data stream, and so on. These are similar to the
general security considerations for offer/answer exchanges, and the
security considerations in [RFC3264] apply. These require techniques
for message integrity and encryption for offers and answers, which
are satisfied by the TLS mechanism [RFC3261] when SIP is used. As
such, the usage of TLS with ICE is RECOMMENDED.
9.2. Insider Attacks
In addition to attacks where the attacker is a third party trying to
insert fake offers, answers, or STUN messages, there are several
attacks possible with ICE when the attacker is an authenticated and
valid participant in the ICE exchange.
9.2.1. The Voice Hammer Attack
The voice hammer attack is an amplification attack. In this attack,
the attacker initiates sessions to other agents, and maliciously
includes the connection address and port of a DoS target as the
destination for media traffic signaled in the SDP. This causes
substantial amplification; a single offer/answer exchange can create
a continuing flood of media packets, possibly at high rates (consider
video sources). This attack is not specific to ICE, but ICE can help
provide remediation.
Specifically, if ICE is used, the agent receiving the malicious SDP
will first perform connectivity checks to the target of media before
sending media there. If this target is a third-party host, the
checks will not succeed, and media is never sent.
Unfortunately, ICE doesn't help if it's not used, in which case an
attacker could simply send the offer without the ICE parameters.
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
answers that don't indicate ICE support.
SIP User Agents (UA) [RFC3261] that are not willing to receive non-
ICE answers MUST include an "ice" Option Tag [RFC5768] in the SIP
Require Header Field in their offer. UAs that reject non-ICE offers
will generally use a 421 response code, together with an Option Tag
"ice" in the Require Header Field in the response.
10. IANA Considerations
10.1. SDP Attributes
The 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 the procedures of Section 8.2.4 of [RFC4566]. The registration
information from the original specification is included here with information from the original specification is included here with
modifications to include Mux Category and also defines a new SDP modifications to include Mux Category and also defines a new SDP
attribute 'ice-pacing'. attribute 'ice-pacing'.
9.1.1. candidate Attribute 10.1.1. candidate Attribute
Attribute Name: candidate Attribute Name: candidate
Type of Attribute: media-level Type of Attribute: media-level
Subject to charset: No Subject to charset: No
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 4 of RFC XXXX. Appropriate Values: See Section 5 of RFC XXXX.
Contact Name: IESG Contact Name: IESG
Contact Email: esg@ietf.org Contact Email: iesg@ietf.org
Reference: RFCXXXX Reference: RFCXXXX
Mux Category: TRANSPORT Mux Category: TRANSPORT
9.1.2. remote-candidates Attribute 10.1.2. remote-candidates Attribute
Attribute Name: remote-candidates Attribute Name: remote-candidates
Type of Attribute: media-level Type of Attribute: media-level
Subject to charset: No Subject to charset: No
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 4 of RFC XXXX. Appropriate Values: See Section 5 of RFC XXXX.
Contact Name: IESG Contact Name: IESG
Contact Email: iesg@ietf.org Contact Email: iesg@ietf.org
Reference: RFCXXXX Reference: RFCXXXX
Mux Category: TRANSPORT Mux Category: TRANSPORT
9.1.3. ice-lite Attribute 10.1.3. ice-lite Attribute
Attribute Name: ice-lite Attribute Name: ice-lite
Type of Attribute: session-level Type of Attribute: session-level
Subject to charset: No Subject to charset: No
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 4 of RFC XXXX. Appropriate Values: See Section 5 of RFC XXXX.
Contact Name: IESG Contact Name: IESG
Contact Email: iesg@ietf.org Contact Email: iesg@ietf.org
Reference: RFCXXXX Reference: RFCXXXX
Mux Category: NORMAL Mux Category: NORMAL
9.1.4. ice-mismatch Attribute 10.1.4. ice-mismatch Attribute
Attribute Name: ice-mismatch Attribute Name: ice-mismatch
Type of Attribute: media-level Type of Attribute: media-level
Subject to charset: No Subject to charset: No
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 4 of RFC XXXX. Appropriate Values: See Section 5 of RFC XXXX.
Contact Name: IESG Contact Name: IESG
Contact e-mail: iesg@ietf.org Contact e-mail: iesg@ietf.org
Reference: RFCXXXX Reference: RFCXXXX
Mux Category: NORMAL Mux Category: NORMAL
9.1.5. ice-pwd Attribute 10.1.5. ice-pwd Attribute
Attribute Name: ice-pwd Attribute Name: ice-pwd
Type of Attribute: session- or media-level Type of Attribute: session- or media-level
Subject to charset: No Subject to charset: No
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 4 of RFC XXXX. Appropriate Values: See Section 5 of RFC XXXX.
Contact Name: IESG Contact Name: IESG
Contact e-mail: iesg@ietf.org Contact e-mail: iesg@ietf.org
Reference: RFCXXXX Reference: RFCXXXX
Mux Category: TRANSPORT Mux Category: TRANSPORT
9.1.6. ice-ufrag Attribute 10.1.6. ice-ufrag Attribute
Attribute Name: ice-ufrag Attribute Name: ice-ufrag
Type of Attribute: session- or media-level Type of Attribute: session- or media-level
Subject to charset: No Subject to charset: No
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 4 of RFC XXXX. Appropriate Values: See Section 5 of RFC XXXX.
Contact Name: IESG Contact Name: IESG
Contact e-mail: iesg@ietf.org Contact e-mail: iesg@ietf.org
Reference: RFCXXXX Reference: RFCXXXX
Mux Category: TRANSPORT Mux Category: TRANSPORT
9.1.7. ice-options Attribute 10.1.7. ice-options Attribute
Attribute Name: ice-options Attribute Name: ice-options
Long Form: ice-options Long Form: ice-options
Type of Attribute: session-level Type of Attribute: session-level
Subject to charset: No Subject to charset: No
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 4 of RFC XXXX. Appropriate Values: See Section 5 of RFC XXXX.
Contact Name: IESG Contact Name: IESG
Contact e-mail: iesg@ietf.org Contact e-mail: iesg@ietf.org
Reference: RFCXXXX Reference: RFCXXXX
Mux Category: NORMAL Mux Category: NORMAL
9.1.8. ice-pacing Attribute 10.1.8. ice-pacing Attribute
This specification also defines a new SDP attribute, "ice-pacing" This specification also defines a new SDP attribute, "ice-pacing"
according to the following data: according to the following data:
Attribute Name: ice-pacing Attribute Name: ice-pacing
Type of Attribute: session-level Type of Attribute: session-level
Subject to charset: No Subject to charset: No
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 4 of RFC XXXX. Appropriate Values: See Section 5 of RFC XXXX.
Contact Name: IESG Contact Name: IESG
Contact e-mail: iesg@ietf.org Contact e-mail: iesg@ietf.org
Reference: RFCXXXX Reference: RFCXXXX
Mux Category: NORMAL Mux Category: NORMAL
9.2. Interactive Connectivity Establishment (ICE) Options Registry 10.2. 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" [RFC8126]. an IANA Considerations Section in RFCs" [RFC8126].
ICE options are of unlimited length according to the syntax in ICE options are of unlimited length according to the syntax in
Section 4.6; 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. ICE options are defined at the session level. parsing. ICE options are defined at the session level.
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 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
10. Acknowledgments 11. Acknowledgments
A large part of the text in this document was taken from [RFC5245], A large part of the text in this document was taken from [RFC5245],
authored by Jonathan Rosenberg. authored by Jonathan Rosenberg.
Some of the text in this document was taken from [RFC6336], authored Some of the text in this document was taken from [RFC6336], authored
by Magnus Westerlund and Colin Perkins. by Magnus Westerlund and Colin Perkins.
Many thanks to Christer Holmberg for providing text suggestions in
Section 3 that aligns with [RFC8445]
Thanks to Thomas Stach for text help, Roman Shpount for suggesting
RTCP candidate handling and Simon Perreault for advising on IPV6
address selection when candidate-address includes FQDN.
Many thanks to Flemming Andreasen for shepherd review feedback. Many thanks to Flemming Andreasen for shepherd review feedback.
Thanks to following experts for their reviews and constructive Thanks to following experts for their reviews and constructive
feedback: Christer Holmberg, Adam Roach, Peter Saint-Andre and the feedback: Thomas Stach, Adam Roach, Peter Saint-Andre, Roman Danyliw,
MMUSIC WG. Alissa Cooper, Benjamin Kaduk, Mirja Kuhlewind, Alexey Melnikov, Eric
Vyncke for their detailed reviews.
11. References 12. Changes from RFC 5245
11.1. Normative References [RFC8445] describes the changes that were done to the common SIP
procedures, including removal of aggressive nomination, modifying the
procedures for calculating candidate pair states and scheduling
connectivity checks and the calculation of timer values.
This document defines the following SDP offer/answer specific
changes:
o SDP offer/answer realization and usage of of 'ice2' option.
o Definition and usage of SDP 'ice-pacing' attribute.
o Explicit text that an ICE agent must not generate candidates with
FQDNs, and must discard such candidates if received from the peer
agent.
o Relax requirement to include SDP 'rtcp' attribute.
o Generic clarifications of SDP offer/answer procedures.
13. References
13.1. Normative References
[draft-ietf-ice-pac]
Holmberg, C. and J. Uberti, "Interactive Connectivity
Establishment Patiently Awaiting Connectivity (ICE PAC)",
draft-ietf-ice-pac-02 (work in progress), July 2019,
<http://www.ietf.org/internet-drafts/
draft-ietf-ice-pac-02.txt>.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>.
[RFC3261] Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston, [RFC3261] Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston,
A., Peterson, J., Sparks, R., Handley, M., and E. A., Peterson, J., Sparks, R., Handley, M., and E.
Schooler, "SIP: Session Initiation Protocol", RFC 3261, Schooler, "SIP: Session Initiation Protocol", RFC 3261,
DOI 10.17487/RFC3261, June 2002, DOI 10.17487/RFC3261, June 2002,
<http://www.rfc-editor.org/info/rfc3261>. <http://www.rfc-editor.org/info/rfc3261>.
[RFC3262] Rosenberg, J. and H. Schulzrinne, "Reliability of [RFC3262] Rosenberg, J. and H. Schulzrinne, "Reliability of
Provisional Responses in Session Initiation Protocol Provisional Responses in Session Initiation Protocol
(SIP)", RFC 3262, DOI 10.17487/RFC3262, June 2002, (SIP)", RFC 3262, DOI 10.17487/RFC3262, June 2002,
skipping to change at page 35, line 35 skipping to change at page 36, line 5
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <http://www.rfc-editor.org/info/rfc8174>. May 2017, <http://www.rfc-editor.org/info/rfc8174>.
[RFC8445] Keranen, A., Holmberg, C., and J. Rosenberg, "Interactive [RFC8445] Keranen, A., Holmberg, C., and J. Rosenberg, "Interactive
Connectivity Establishment (ICE): A Protocol for Network Connectivity Establishment (ICE): A Protocol for Network
Address Translator (NAT) Traversal", RFC 8445, Address Translator (NAT) Traversal", RFC 8445,
DOI 10.17487/RFC8445, July 2018, DOI 10.17487/RFC8445, July 2018,
<http://www.rfc-editor.org/info/rfc8445>. <http://www.rfc-editor.org/info/rfc8445>.
11.2. Informative References 13.2. Informative References
[draft-ietf-ice-pac]
Holmberg, C. and J. Uberti, "Interactive Connectivity
Establishment Patiently Awaiting Connectivity (ICE PAC)",
draft-ietf-ice-pac-02 (work in progress), July 2019,
<http://www.ietf.org/internet-drafts/
draft-ietf-ice-pac-02.txt>.
[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,
<http://www.rfc-editor.org/info/rfc3960>. <http://www.rfc-editor.org/info/rfc3960>.
[RFC4091] Camarillo, G. and J. Rosenberg, "The Alternative Network
Address Types (ANAT) Semantics for the Session Description
Protocol (SDP) Grouping Framework", RFC 4091, June 2005,
<http://www.rfc-editor.org/info/rfc4091>.
[RFC4092] Camarillo, G. and J. Rosenberg, "Usage of the Session
Description Protocol (SDP) Alternative Network Address
Types (ANAT) Semantics in the Session Initiation Protocol
(SIP)", RFC 4092, June 2005,
<http://www.rfc-editor.org/info/rfc4092>.
[RFC5245] Rosenberg, J., "Interactive Connectivity Establishment [RFC5245] Rosenberg, J., "Interactive Connectivity Establishment
(ICE): A Protocol for Network Address Translator (NAT) (ICE): A Protocol for Network Address Translator (NAT)
Traversal for Offer/Answer Protocols", RFC 5245, Traversal for Offer/Answer Protocols", RFC 5245,
DOI 10.17487/RFC5245, April 2010, DOI 10.17487/RFC5245, April 2010,
<http://www.rfc-editor.org/info/rfc5245>. <http://www.rfc-editor.org/info/rfc5245>.
[RFC5626] Jennings, C., Ed., Mahy, R., Ed., and F. Audet, Ed., [RFC5626] Jennings, C., Ed., Mahy, R., Ed., and F. Audet, Ed.,
"Managing Client-Initiated Connections in the Session "Managing Client-Initiated Connections in the Session
Initiation Protocol (SIP)", RFC 5626, Initiation Protocol (SIP)", RFC 5626,
DOI 10.17487/RFC5626, October 2009, DOI 10.17487/RFC5626, October 2009,
skipping to change at page 37, line 10 skipping to change at page 37, line 10
Appendix A. Examples Appendix A. Examples
For the example shown in section 15 of [RFC8445] the resulting offer For the example shown in section 15 of [RFC8445] 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-options:ice2
a=ice-pacing:50
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
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 $L-PRIV-1.IP $L-PRIV-1.PORT typ host a=candidate:1 1 UDP 2130706431 $L-PRIV-1.IP $L-PRIV-1.PORT typ host
a=candidate:2 1 UDP 1694498815 $NAT-PUB-1.IP $NAT-PUB-1.PORT typ a=candidate:2 1 UDP 1694498815 $NAT-PUB-1.IP $NAT-PUB-1.PORT typ
srflx raddr $L-PRIV-1.IP rport $L-PRIV-1.PORT srflx raddr $L-PRIV-1.IP rport $L-PRIV-1.PORT
The offer, with the variables replaced with their values, will look The offer, with the variables replaced with their values, will look
like (lines folded for clarity): like (lines folded for clarity):
v=0 v=0
o=jdoe 2890844526 2890842807 IN IP6 fe80::6676:baff:fe9c:ee4a o=jdoe 2890844526 2890842807 IN IP6 fe80::6676:baff:fe9c:ee4a
s= s=
c=IN IP6 2001:DB8:8101:3a55:4858:a2a9:22ff:99b9 c=IN IP6 2001:db8:8101:3a55:4858:a2a9:22ff:99b9
t=0 0 t=0 0
a=ice-options:ice2
a=ice-pacing:50
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 fe80::6676:baff:fe9c:ee4a 8998 typ host a=candidate:1 1 UDP 2130706431 fe80::6676:baff:fe9c:ee4a 8998 typ host
a=candidate:2 1 UDP 1694498815 2001:DB8:8101:3a55:4858:a2a9:22ff:99b9 a=candidate:2 1 UDP 1694498815 2001:db8:8101:3a55:4858:a2a9:22ff:99b9
45664 typ srflx raddr fe80::6676:baff:fe9c:ee4a rport 8998 45664 typ srflx raddr fe80::6676:baff:fe9c:ee4a rport 8998
The resulting answer looks like: The resulting answer looks like:
v=0 v=0
o=bob 2808844564 2808844564 IN IP4 $R-PUB-1.IP o=bob 2808844564 2808844564 IN IP4 $R-PUB-1.IP
s= s=
c=IN IP4 $R-PUB-1.IP c=IN IP4 $R-PUB-1.IP
t=0 0 t=0 0
a=ice-options:ice2
a=ice-pacing:50
a=ice-pwd:YH75Fviy6338Vbrhrlp8Yh a=ice-pwd:YH75Fviy6338Vbrhrlp8Yh
a=ice-ufrag:9uB6 a=ice-ufrag:9uB6
m=audio $R-PUB-1.PORT RTP/AVP 0 m=audio $R-PUB-1.PORT 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 $R-PUB-1.IP $R-PUB-1.PORT typ host a=candidate:1 1 UDP 2130706431 $R-PUB-1.IP $R-PUB-1.PORT typ host
With the variables filled in: With the variables filled in:
v=0 v=0
o=bob 2808844564 2808844564 IN IP4 192.0.2.1 o=bob 2808844564 2808844564 IN IP4 192.0.2.1
s= s=
c=IN IP4 192.0.2.1 c=IN IP4 192.0.2.1
t=0 0 t=0 0
a=ice-options:ice2
a=ice-pacing:50
a=ice-pwd:YH75Fviy6338Vbrhrlp8Yh a=ice-pwd:YH75Fviy6338Vbrhrlp8Yh
a=ice-ufrag:9uB6 a=ice-ufrag:9uB6
m=audio 3478 RTP/AVP 0 m=audio 3478 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 192.0.2.1 3478 typ host a=candidate:1 1 UDP 2130706431 192.0.2.1 3478 typ host
Appendix B. The remote-candidates Attribute Appendix B. The remote-candidates Attribute
 End of changes. 142 change blocks. 
364 lines changed or deleted 369 lines changed or added

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