draft-ietf-mmusic-ice-sip-sdp-14.txt   draft-ietf-mmusic-ice-sip-sdp-15.txt 
MMUSIC M. Petit-Huguenin MMUSIC M. Petit-Huguenin
Internet-Draft Impedance Mismatch Internet-Draft
Obsoletes: 5245 (if approved) A. Keranen Obsoletes: 5245 (if approved) A. Keranen
Intended status: Standards Track Ericsson Intended status: Standards Track
Expires: April 5, 2018 S. Nandakumar Expires: May 27, 2018 S. Nandakumar
Cisco Systems November 23, 2017
October 2, 2017
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-14 draft-ietf-mmusic-ice-sip-sdp-15
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.
Status of This Memo Status of This Memo
This Internet-Draft is submitted in full conformance with the This Internet-Draft is submitted in full conformance with the
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Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet- working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/. Drafts is at http://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress." material or to cite them other than as "work in progress."
This Internet-Draft will expire on April 5, 2018. This Internet-Draft will expire on May 27, 2018.
Copyright Notice Copyright Notice
Copyright (c) 2017 IETF Trust and the persons identified as the Copyright (c) 2017 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of (http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents publication of this document. Please review these documents
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corresponds to the [RFC3264] Offer/Answer protocol and the corresponds to the [RFC3264] Offer/Answer protocol and the
terminologies offerer and answerer correspond to the initiator and terminologies offerer and answerer correspond to the initiator and
responder terminologies from [ICE-BIS] respectively. responder terminologies from [ICE-BIS] respectively.
4. SDP Offer/Answer Procedures 4. SDP Offer/Answer Procedures
4.1. Initial Offer/Answer Exchange 4.1. Initial Offer/Answer Exchange
4.1.1. Sending the Initial Offer 4.1.1. Sending the Initial Offer
The offerer shall follow the procedures defined in section 4 of The offerer shall follow the procedures defined in section 5 of
[ICE-BIS] to gather, prioritize and eliminate the redundant [ICE-BIS] to gather, prioritize and eliminate the redundant
candidates. It then chooses the default candidates and encodes them candidates. It then chooses the default candidates and encodes them
in the SDP to be sent to its peer, the answerer. in the SDP to be sent to its peer, the answerer.
4.1.1.1. Choosing Default Candidates 4.1.1.1. Choosing Default Candidates
A candidate is said to be default if it would be the target of media A candidate is said to be default if it would be the target of media
from a non-ICE peer; that target is called the DEFAULT DESTINATION. from a non-ICE peer; that target is called the DEFAULT DESTINATION.
An agent MUST choose a set of candidates, one for each component of An agent MUST choose a set of candidates, one for each component of
each in-use media stream, to be default. A media stream is in-use if each in-use media stream, to be default. A media stream is in-use if
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short-term credential mechanism defined for STUN [RFC5389]. This short-term credential mechanism defined for STUN [RFC5389]. This
mechanism relies on a username and password that are exchanged mechanism relies on a username and password that are exchanged
through protocol machinery between the client and server. The through protocol machinery between the client and server. The
username fragment and password are exchanged in the ice-ufrag and username fragment and password are exchanged in the ice-ufrag and
ice-pwd attributes, respectively. ice-pwd attributes, respectively.
If an agent is a lite implementation, it MUST include an "a=ice-lite" If an agent is a lite implementation, it MUST include an "a=ice-lite"
session-level attribute in its SDP to indicate this. If an agent is session-level attribute in its SDP to indicate this. If an agent is
a full implementation, it MUST NOT include this attribute. a full implementation, it MUST NOT include this attribute.
Section 9 of [ICE-BIS] defines a new ICE option, 'ice2'. This option Section 10 of [ICE-BIS] defines a new ICE option, 'ice2'. This
is used by ICE Agents to indicate their compliancy with [ICE-BIS] option is used by ICE Agents to indicate their compliancy with
specification as compared to the [RFC5245]. If the Offering agent is [ICE-BIS] specification as compared to the [RFC5245]. If the
a [ICE-BIS] compliant implementation, a session level ICE option to Offering agent is a [ICE-BIS] compliant implementation, a session
indicate the same (via the "a=ice-options:ice2" SDP line) MUST be level ICE option to indicate the same (via the "a=ice-options:ice2"
included. SDP line) MUST be included.
The default candidates are added to the SDP as the default The default candidates are added to the SDP as the default
destination for media. For source streams based on RTP, this is done destination for media. For source streams based on RTP, this is done
by placing the IP address and port of the RTP candidate into the "c=" by placing the IP address and port of the RTP candidate into the "c="
and "m=" lines, respectively. If the agent is utilizing RTCP and if and "m=" lines, respectively. If the agent is utilizing RTCP and if
RTCP candidate is present and is not equal to the same address and RTCP candidate is present and is not equal to the same address and
the next higher port number of the RTP candidate, the agent MUST the next higher port number of the RTP candidate, the agent MUST
encode the RTCP candidate using the a=rtcp attribute as defined in encode the RTCP candidate using the a=rtcp attribute as defined in
[RFC3605]. If RTCP is not in use, the agent MUST signal that using [RFC3605]. If RTCP is not in use, the agent MUST signal that using
b=RS:0 and b=RR:0 as defined in [RFC3556] b=RS:0 and b=RR:0 as defined in [RFC3556]
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m=audio 45664 RTP/AVP 0 m=audio 45664 RTP/AVP 0
b=RS:0 b=RS:0
b=RR:0 b=RR:0
a=rtpmap:0 PCMU/8000 a=rtpmap:0 PCMU/8000
a=candidate:1 1 UDP 2130706431 10.0.1.1 8998 typ host a=candidate:1 1 UDP 2130706431 10.0.1.1 8998 typ host
a=candidate:2 1 UDP 1694498815 192.0.2.3 45664 typ srflx raddr a=candidate:2 1 UDP 1694498815 192.0.2.3 45664 typ srflx raddr
10.0.1.1 rport 8998 10.0.1.1 rport 8998
Once an agent has sent its offer or its answer, that agent MUST be Once an agent has sent its offer or its answer, that agent MUST be
prepared to receive both STUN and media packets on each candidate. prepared to receive both STUN and media packets on each candidate.
As discussed in section 11.1 of [ICE-BIS], media packets can be sent As discussed in section 12.1 of [ICE-BIS], media packets can be sent
to a candidate prior to its appearance as the default destination for to a candidate prior to its appearance as the default destination for
media in an offer or answer. media in an offer or answer.
4.1.2. Receiving the Initial Offer 4.1.2. Receiving the Initial Offer
On receiving the offer, the answerer verifies the support for ICE On receiving the offer, the answerer verifies the support for ICE
(section 4.4 of [ICE-BIS]), determines its role (section 5.1.1 of (section 5.4 of [ICE-BIS]), determines its role (section 6.1.1 of
[ICE-BIS]), gathers candidates (section 4 of [ICE-BIS]), encodes the [ICE-BIS]), gathers candidates (section 5 of [ICE-BIS]), encodes the
candidates in an SDP answer and sends it to its peer, the offerer. candidates in an SDP answer and sends it to its peer, the offerer.
The answerer shall then follow the steps defined in sections 5.1.3 The answerer shall then follow the steps defined in sections 6.1.3
and 5.1.4 of [ICE-BIS] to schedule the ICE connectivity checks. and 6.1.4 of [ICE-BIS] to schedule the ICE connectivity checks.
The below sub-sections provide additional requirements associated The below sub-sections provide additional requirements associated
with the processing of the offerer's SDP pertaining to this with the processing of the offerer's SDP pertaining to this
specification. specification.
4.1.2.1. ICE Option "ice2" considerations 4.1.2.1. ICE Option "ice2" considerations
If the SDP offer contains a session level ICE option, "ice2" , and if If the SDP offer contains a session level ICE option, "ice2" , and if
the answering ICE Agent is also an [ICE-BIS] compliant the answering ICE Agent is also an [ICE-BIS] compliant
implementation, then the generated SDP answer MUST include the implementation, then the generated SDP answer MUST include the
session level "a=ice-options:ice2" SDP line. session level "a=ice-options:ice2" SDP line.
4.1.2.2. Choosing Default Candidates 4.1.2.2. Choosing Default Candidates
The process for selecting default candidates at the answerer is The process for selecting default candidates at the answerer is
identical to the process followed by the offerer, as described in identical to the process followed by the offerer, as described in
Section 4.1.1.1 for full implementations in this specification and Section 4.1.1.1 for full implementations in this specification and
section 4.2 of [ICE-BIS] for lite implementations. section 5.2 of [ICE-BIS] for lite implementations.
4.1.2.3. Verifying ICE Support 4.1.2.3. ICE Mismatch
The agent will proceed with the ICE procedures defined in [ICE-BIS] The agent will proceed with the ICE procedures defined in [ICE-BIS]
and this specification if, for each media stream in the SDP it and this specification if, for each media stream in the SDP it
received, the default destination for each component of that media received, the default destination for each component of that media
stream appears in a candidate attribute. For example, in the case of stream appears in a candidate attribute. For example, in the case of
RTP, the IP address and port in the "c=" and "m=" lines, RTP, the IP address and port in the "c=" and "m=" lines,
respectively, appear in a candidate attribute and the value in the respectively, appear in a candidate attribute and the value in the
rtcp attribute appears in a candidate attribute. rtcp attribute appears in a candidate attribute.
If this condition is not met, the agent MUST process the SDP based on If this condition is not met, the agent MUST process the SDP based on
normal RFC 3264 procedures, without using any of the ICE mechanisms normal RFC 3264 procedures, without using any of the ICE mechanisms
described in the remainder of this specification with the following described in the remainder of this specification with the following
exceptions: exceptions:
1. The agent MUST follow the rules of section 10 of [ICE-BIS], which 1. The agent MUST follow the rules of section 11 of [ICE-BIS], which
describe keepalive procedures for all agents. describe keepalive procedures for all agents.
2. If the agent is not proceeding with ICE because there were 2. If the agent is not proceeding with ICE because there were
a=candidate attributes, but none that matched the default a=candidate attributes, but none that matched the default
destination of the media stream, the agent MUST include an a=ice- destination of the media stream, the agent MUST include an a=ice-
mismatch attribute in its answer. mismatch attribute in its answer.
3. If the default candidates were relayed candidates learned through 3. If the default candidates were relayed candidates learned through
a TURN server, the agent MUST create permissions in the TURN a TURN server, the agent MUST create permissions in the TURN
server for the IP addresses learned from its peer in the SDP it server for the IP addresses learned from its peer in the SDP it
just received. If this is not done, initial packets in the media just received. If this is not done, initial packets in the media
stream from the peer may be lost. stream from the peer may be lost.
4.1.2.4. Determining Role 4.1.2.4. Determining Role
In unusual cases, described in Appendix C, it is possible for both In unusual cases, described in Appendix C, it is possible for both
agents to mistakenly believe they are controlled or controlling. To agents to mistakenly believe they are controlled or controlling. To
resolve this, each agent MUST select a random number, called the tie- resolve this, each agent MUST select a random number, called the tie-
breaker, uniformly distributed between 0 and (2**64) - 1 (that is, a breaker, uniformly distributed between 0 and (2**64) - 1 (that is, a
64-bit positive integer). This number is used in connectivity checks 64-bit positive integer). This number is used in connectivity checks
to detect and repair this case, as described in section 6.1.3 of to detect and repair this case, as described in section 7.1.3 of
[ICE-BIS]. [ICE-BIS].
4.1.3. Receipt of the Initial Answer 4.1.3. Receipt of the Initial Answer
On receiving the SDP answer, the offerer performs steps similar to On receiving the SDP answer, the offerer performs steps similar to
answerer's processing of the offer. The offerer verifies the answerer's processing of the offer. The offerer verifies the
answerer's ICE support determines, its role, and processes the answerer's ICE support determines, its role, and processes the
answerer's candidates to schedule the connectivity checks (section 6 answerer's candidates to schedule the connectivity checks (section 7
of [ICE-BIS]). of [ICE-BIS]).
If the offerer had included the "ice2" ICE Option in the offer and If the offerer had included the "ice2" ICE Option in the offer and
the SDP answer also includes a similar session level ICE option, then the SDP answer also includes a similar session level ICE option, then
the peers are [ICE-BIS] compliant implementations. On the other the peers are [ICE-BIS] compliant implementations. On the other
hand, if the SDP Answer lacks such a ICE option, the offerer defaults hand, if the SDP Answer lacks such a ICE option, the offerer defaults
to the procedures that are backward compatible with the [RFC5245] to the procedures that are backward compatible with the [RFC5245]
specification. specification.
4.1.3.1. Verifying ICE Support 4.1.3.1. ICE Mismatch
The logic at the offerer is identical to that of the answerer as The logic at the offerer is identical to that of the answerer as
described in section 4.4 of [ICE-BIS], with the exception that an described in section 5.4 of [ICE-BIS], with the exception that an
offerer would not ever generate a=ice-mismatch attributes in an SDP. offerer would not ever generate a=ice-mismatch attributes in an SDP.
In some cases, the answer may omit a=candidate attributes for the In some cases, the answer may omit a=candidate attributes for the
media streams, and instead include an a=ice-mismatch attribute for media streams, and instead include an a=ice-mismatch attribute for
one or more of the media streams in the SDP. This signals to the one or more of the media streams in the SDP. This signals to the
offerer that the answerer supports ICE, but that ICE processing was offerer that the answerer supports ICE, but that ICE processing was
not used for the session because a signaling intermediary modified not used for the session because a signaling intermediary modified
the default destination for media components without modifying the the default destination for media components without modifying the
corresponding candidate attributes. See Section 11.2.2 for a corresponding candidate attributes. See Section 11.2.2 for a
discussion of cases where this can happen. This specification discussion of cases where this can happen. This specification
provides no guidance on how an agent should proceed in such a failure provides no guidance on how an agent should proceed in such a failure
case. case.
4.1.4. Performing Connectivity Checks 4.1.4. Performing Connectivity Checks
The possibility for role conflicts described in section 6.3.1.1 of The possibility for role conflicts described in section 7.3.1.1 of
[ICE-BIS] applies to this usage and hence all full agents MUST [ICE-BIS] applies to this usage and hence all full agents MUST
implement the role conflict repairing mechanism. Also both full and implement the role conflict repairing mechanism. Also both full and
lite agents MUST utilize the ICE-CONTROLLED and ICE-CONTROLLING lite agents MUST utilize the ICE-CONTROLLED and ICE-CONTROLLING
attributes as described in section 6.1.3 of [ICE-BIS]. attributes as described in section 7.1.3 of [ICE-BIS].
4.1.5. Concluding ICE 4.1.5. Concluding ICE
Once the state of each check list is Completed, If an agent is Once the state of each check list is Completed, If an agent is
controlling, it examines the highest-priority nominated candidate controlling, it examines the highest-priority nominated candidate
pair for each component of each media stream. If any of those pair for each component of each media stream. If any of those
candidate pairs differ from the default candidate pairs in the most candidate pairs differ from the default candidate pairs in the most
recent offer/answer exchange, the controlling agent MUST generate an recent offer/answer exchange, the controlling agent MUST generate an
updated offer as described in Section 4.2. updated offer as described in Section 4.2.
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Should a subsequent offer fail, ICE processing continues as if the Should a subsequent offer fail, ICE processing continues as if the
subsequent offer had never been made. subsequent offer had never been made.
4.2.1. Generating the Offer 4.2.1. Generating the Offer
4.2.1.1. Procedures for All Implementations 4.2.1.1. Procedures for All Implementations
4.2.1.1.1. ICE Restarts 4.2.1.1.1. ICE Restarts
An agent MAY restart ICE processing for an existing media stream as An agent MAY restart ICE processing for an existing media stream as
defined in section 8 of [ICE-BIS]. defined in section 9 of [ICE-BIS].
The rules governing the ICE restart imply that setting the IP address The rules governing the ICE restart imply that setting the IP address
in the "c=" line to 0.0.0.0 will cause an ICE restart. Consequently, in the "c=" line to 0.0.0.0 will cause an ICE restart. Consequently,
ICE implementations MUST NOT utilize this mechanism for call hold, ICE implementations MUST NOT utilize this mechanism for call hold,
and instead MUST use a=inactive and a=sendonly as described in and instead MUST use a=inactive and a=sendonly as described in
[RFC3264]. [RFC3264].
To restart ICE, an agent MUST change both the ice-pwd and the ice- To restart ICE, an agent MUST change both the ice-pwd and the ice-
ufrag for the media stream in an offer. Note that it is permissible ufrag for the media stream in an offer. Note that it is permissible
to use a session-level attribute in one offer, but to provide the to use a session-level attribute in one offer, but to provide the
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4.2.1.3. Procedures for Lite Implementations 4.2.1.3. Procedures for Lite Implementations
4.2.1.3.1. Existing Media Streams with ICE Running 4.2.1.3.1. Existing Media Streams with ICE Running
This section describes procedures for lite implementations for This section describes procedures for lite implementations for
existing streams for which ICE is running. existing streams for which ICE is running.
A lite implementation MUST include all of its candidates for each A lite implementation MUST include all of its candidates for each
component of each media stream in an a=candidate attribute in any component of each media stream in an a=candidate attribute in any
subsequent offer. These candidates are formed identically to the subsequent offer. These candidates are formed identically to the
procedures for initial offers, as described in section 4.2 of procedures for initial offers, as described in section 5.2 of
[ICE-BIS]. [ICE-BIS].
A lite implementation MUST NOT add additional host candidates in a A lite implementation MUST NOT add additional host candidates in a
subsequent offer. If an agent needs to offer additional candidates, subsequent offer. If an agent needs to offer additional candidates,
it MUST restart ICE. it MUST restart ICE.
The username fragments, password, and implementation level MUST The username fragments, password, and implementation level MUST
remain the same as used previously. If an agent needs to change one remain the same as used previously. If an agent needs to change one
of these, it MUST restart ICE for that media stream. of these, it MUST restart ICE for that media stream.
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Furthermore, if the agent believed it was controlling, but the offer Furthermore, if the agent believed it was controlling, but the offer
contained the remote-candidates attribute, both agents believe they contained the remote-candidates attribute, both agents believe they
are controlling. In this case, both would have sent updated offers are controlling. In this case, both would have sent updated offers
around the same time. However, the signaling protocol carrying the around the same time. However, the signaling protocol carrying the
offer/answer exchanges will have resolved this glare condition, so offer/answer exchanges will have resolved this glare condition, so
that one agent is always the 'winner' by having its offer received that one agent is always the 'winner' by having its offer received
before its peer has sent an offer. The winner takes the role of before its peer has sent an offer. The winner takes the role of
controlling, so that the loser (the answerer under consideration in controlling, so that the loser (the answerer under consideration in
this section) MUST change its role to controlled. Consequently, if this section) MUST change its role to controlled. Consequently, if
the agent was going to send an updated offer since, based on the the agent was going to send an updated offer since, based on the
rules in section 7.2 of [ICE-BIS], it was controlling, it no longer rules in section 8.2 of [ICE-BIS], it was controlling, it no longer
needs to. needs to.
Besides the potential role change, change in the Valid list, and Besides the potential role change, change in the Valid list, and
state changes, the construction of the answer is performed state changes, the construction of the answer is performed
identically to the construction of an offer as described in identically to the construction of an offer as described in
Section 4.2.1.3. Section 4.2.1.3.
4.2.3. Receiving the Answer for a Subsequent Offer 4.2.3. Receiving the Answer for a Subsequent Offer
Some deployments of ICE include e.g. SDP-Modifying Signaling-only Some deployments of ICE include e.g. SDP-Modifying Signaling-only
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4.2.4.1. Procedures for Full Implementations 4.2.4.1. Procedures for Full Implementations
4.2.4.1.1. ICE Restarts 4.2.4.1.1. ICE Restarts
The agent MUST remember the highest-priority nominated pairs in the The agent MUST remember the highest-priority nominated pairs in the
Valid list for each component of the media stream, called the Valid list for each component of the media stream, called the
previous selected pairs, prior to the restart. The agent will previous selected pairs, prior to the restart. The agent will
continue to send media using these pairs, as described in continue to send media using these pairs, as described in
Section 7.1. Once these destinations are noted, the agent MUST flush Section 7.1. Once these destinations are noted, the agent MUST flush
the valid and check lists, and then recompute the check list and its the valid and check lists, and then recompute the check list and its
states as described in section 5.1.2 of [ICE-BIS]. states as described in section 6.1.2 of [ICE-BIS].
4.2.4.1.2. New Media Stream 4.2.4.1.2. New Media Stream
If the offer/answer exchange added a new media stream, the agent MUST If the offer/answer exchange added a new media stream, the agent MUST
create a new check list for it (and an empty Valid list to start of create a new check list for it (and an empty Valid list to start of
course), as described in section 5.1.2 of [ICE-BIS]. course), as described in section 6.1.2 of [ICE-BIS].
4.2.4.1.3. Removed Media Stream 4.2.4.1.3. Removed Media Stream
If the offer/answer exchange removed a media stream, or an answer If the offer/answer exchange removed a media stream, or an answer
rejected an offered media stream, an agent MUST flush the Valid list rejected an offered media stream, an agent MUST flush the Valid list
for that media stream. It MUST terminate any STUN transactions in for that media stream. It MUST terminate any STUN transactions in
progress for that media stream. An agent MUST remove the check list progress for that media stream. An agent MUST remove the check list
for that media stream and cancel any pending ordinary checks for it. for that media stream and cancel any pending ordinary checks for it.
4.2.4.1.4. ICE Continuing for Existing Media Stream 4.2.4.1.4. ICE Continuing for Existing Media Stream
The valid list is not affected by an updated offer/answer exchange The valid list is not affected by an updated offer/answer exchange
unless ICE is restarting. unless ICE is restarting.
If an agent is in the Running state for that media stream, the check If an agent is in the Running state for that media stream, the check
list is updated (the check list is irrelevant if the state is list is updated (the check list is irrelevant if the state is
completed). To do that, the agent recomputes the check list using completed). To do that, the agent recomputes the check list using
the procedures described in section 5.1.2 of [ICE-BIS]. If a pair on the procedures described in section 6.1.2 of [ICE-BIS]. If a pair on
the new check list was also on the previous check list, and its state the new check list was also on the previous check list, and its state
was Waiting, In-Progress, Succeeded, or Failed, its state is copied was Waiting, In-Progress, Succeeded, or Failed, its state is copied
over. Otherwise, its state is set to Frozen. over. Otherwise, its state is set to Frozen.
If none of the check lists are active (meaning that the pairs in each If none of the check lists are active (meaning that the pairs in each
check list are Frozen), the full-mode agent follows steps in check list are Frozen), the full-mode agent follows steps in
Section 5.1.2.6 of [ICE-BIS] to place appropriate candidates in the Section 6.1.2.6 of [ICE-BIS] to place appropriate candidates in the
Waiting state to further continue ICE processing. Waiting state to further continue ICE processing.
4.2.4.2. Procedures for Lite Implementations 4.2.4.2. Procedures for Lite Implementations
If ICE is restarting for a media stream, the agent MUST start a new If ICE is restarting for a media stream, the agent MUST start a new
Valid list for that media stream. It MUST remember the pairs in the Valid list for that media stream. It MUST remember the pairs in the
previous Valid list for each component of the media stream, called previous Valid list for each component of the media stream, called
the previous selected pairs, and continue to send media there as the previous selected pairs, and continue to send media there as
described in Section 7.1. The state of ICE processing for each media described in Section 7.1. The state of ICE processing for each media
stream MUST change to Running, and the state of ICE processing MUST stream MUST change to Running, and the state of ICE processing MUST
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<transport>: indicates the transport protocol for the candidate. <transport>: indicates the transport protocol for the candidate.
This specification only defines UDP. However, extensibility is This specification only defines UDP. However, extensibility is
provided to allow for future transport protocols to be used with provided to allow for future transport protocols to be used with
ICE, such as the Datagram Congestion Control Protocol (DCCP) ICE, such as the Datagram Congestion Control Protocol (DCCP)
[RFC4340]. [RFC4340].
<foundation>: is composed of 1 to 32 <ice-char>s. It is an <foundation>: is composed of 1 to 32 <ice-char>s. It is an
identifier that is equivalent for two candidates that are of the identifier that is equivalent for two candidates that are of the
same type, share the same base, and come from the same STUN same type, share the same base, and come from the same STUN
server. The foundation is used to optimize ICE performance in the server. The foundation is used to optimize ICE performance in the
Frozen algorithm as described in section 5.1.2 of [ICE-BIS] Frozen algorithm as described in section 6.1.2 of [ICE-BIS]
<component-id>: is a positive integer between 1 and 256 that <component-id>: is a positive integer between 1 and 256 that
identifies the specific component of the media stream for which identifies the specific component of the media stream for which
this is a candidate. It MUST start at 1 and MUST increment by 1 this is a candidate. It MUST start at 1 and MUST increment by 1
for each component of a particular candidate. For media streams for each component of a particular candidate. For media streams
based on RTP, candidates for the actual RTP media MUST have a based on RTP, candidates for the actual RTP media MUST have a
component ID of 1, and candidates for RTCP MUST have a component component ID of 1, and candidates for RTCP MUST have a component
ID of 2. See section 12 in [ICE-BIS] for additional discussion on ID of 2. See section 14 in [ICE-BIS] for additional discussion on
extending ICE to new media streams. extending ICE to new media streams.
<priority>: is a positive integer between 1 and (2**31 - 1). The <priority>: is a positive integer between 1 and (2**31 - 1). The
procedures for computing candidate's priority is described in procedures for computing candidate's priority is described in
section 4.1.2 of [ICE-BIS]. section 5.1.2 of [ICE-BIS].
<cand-type>: encodes the type of candidate. This specification <cand-type>: encodes the type of candidate. This specification
defines the values "host", "srflx", "prflx", and "relay" for host, defines the values "host", "srflx", "prflx", and "relay" for host,
server reflexive, peer reflexive, and relayed candidates, server reflexive, peer reflexive, and relayed candidates,
respectively. The set of candidate types is extensible for the respectively. The set of candidate types is extensible for the
future. future.
<rel-addr> and <rel-port>: convey transport addresses related to the <rel-addr> and <rel-port>: convey transport addresses related to the
candidate, useful for diagnostics and other purposes. <rel-addr> candidate, useful for diagnostics and other purposes. <rel-addr>
and <rel-port> MUST be present for server reflexive, peer and <rel-port> MUST be present for server reflexive, peer
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MUST accept up to 256 characters when receiving. MUST accept up to 256 characters when receiving.
Example shows sample ice-ufrag and ice-pwd SDP lines: Example shows sample ice-ufrag and ice-pwd SDP lines:
a=ice-pwd:asd88fgpdd777uzjYhagZg a=ice-pwd:asd88fgpdd777uzjYhagZg
a=ice-ufrag:8hhY a=ice-ufrag:8hhY
5.5. "ice-pacing" Attribute 5.5. "ice-pacing" Attribute
The "ice-pacing" attribute indicates the desired connectivity check The "ice-pacing" attribute indicates the desired connectivity check
pacing, in milliseconds, for this agent (see section 13 of pacing, in milliseconds, for this agent (see section 15 of
[ICE-BIS]). The syntax is: [ICE-BIS]). The syntax is:
ice-pacing-att = "ice-pacing:" pacing-value ice-pacing-att = "ice-pacing:" pacing-value
pacing-value = 1*10DIGIT pacing-value = 1*10DIGIT
Example shows ice-pacing value of 5 ms: Example shows ice-pacing value of 5 ms:
a=ice-pacing:5 a=ice-pacing:5
5.6. "ice-options" Attribute 5.6. "ice-options" Attribute
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agents that determine how the extensions gets used in a given agents that determine how the extensions gets used in a given
session. The details of the negotiation procedures, if present, MUST session. The details of the negotiation procedures, if present, MUST
be defined by the specification defining the extension. be defined by the specification defining the extension.
Example shows 'rtp+ecn' ice-option SDP line from <<RFC6679>>: Example shows 'rtp+ecn' ice-option SDP line from <<RFC6679>>:
a=ice-options:rtp+ecn a=ice-options:rtp+ecn
6. Keepalives 6. Keepalives
All the ICE agents MUST follow the procedures defined in section 10 All the ICE agents MUST follow the procedures defined in section 11
of [ICE-BIS] for sending keepalives. The keepalives MUST be sent of [ICE-BIS] for sending keepalives. The keepalives MUST be sent
regardless of whether the media stream is currently inactive, regardless of whether the media stream is currently inactive,
sendonly, recvonly, or sendrecv, and regardless of the presence or sendonly, recvonly, or sendrecv, and regardless of the presence or
value of the bandwidth attribute. An agent can determine that its value of the bandwidth attribute. An agent can determine that its
peer supports ICE by the presence of a=candidate attributes for each peer supports ICE by the presence of a=candidate attributes for each
media session. media session.
7. Media Handling 7. Media Handling
7.1. Sending Media 7.1. Sending Media
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answer exchange. When this happens, the selected pair is used for answer exchange. When this happens, the selected pair is used for
media, not the default pair. When ICE first completes, if the media, not the default pair. When ICE first completes, if the
selected pairs aren't a match for the default pairs, the controlling selected pairs aren't a match for the default pairs, the controlling
agent sends an updated offer/answer exchange to remedy this agent sends an updated offer/answer exchange to remedy this
disparity. However, until that updated offer arrives, there will not disparity. However, until that updated offer arrives, there will not
be a match. Furthermore, in very unusual cases, the default be a match. Furthermore, in very unusual cases, the default
candidates in the updated offer/answer will not be a match. candidates in the updated offer/answer will not be a match.
7.1.1. Procedures for All Implementations 7.1.1. Procedures for All Implementations
Section 11.1.3 of [ICE-BIS] defines procedures for sending media Section 12.1.3 of [ICE-BIS] defines procedures for sending media
common across Full and Lite implementations. common across Full and Lite implementations.
7.2. Receiving Media 7.2. Receiving Media
See section 11.2 of [ICE-BIS] for procedures on receiving media. See section 12.2 of [ICE-BIS] for procedures on receiving media.
8. SIP Considerations 8. 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, which is
assumed to be provided via another mechanism [RFC5626]. 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/
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one for v4 and one for v6. This is similar to ICE, which allows for 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 an agent to indicate multiple transport addresses using the candidate
attribute. However, ANAT relies on static selection to pick between attribute. However, ANAT relies on static selection to pick between
choices, rather than a dynamic connectivity check used by ICE. choices, rather than a dynamic connectivity check used by ICE.
It is RECOMMENDED that ICE be used in realizing the dual-stack use- It is RECOMMENDED that ICE be used in realizing the dual-stack use-
cases in agents that support ICE. cases in agents that support ICE.
10. Setting Ta and RTO for RTP Media Streams 10. Setting Ta and RTO for RTP Media Streams
During the gathering phase of ICE (section 4.1.1 [ICE-BIS]) and while During the gathering phase of ICE (section 5.1.1 [ICE-BIS]) and while
ICE is performing connectivity checks (section 6 [ICE-BIS]), an agent ICE is performing connectivity checks (section 7 [ICE-BIS]), an agent
sends STUN and TURN transactions. These transactions are paced at a sends STUN and TURN transactions. These transactions are paced at a
rate of one every Ta milliseconds, and utilize a specific RTO. See rate of one every Ta milliseconds, and utilize a specific RTO. See
Section 13 of [ICE-BIS] for details on how the values of Ta and RTO Section 15 of [ICE-BIS] for details on how the values of Ta and RTO
are computed with a real-time media stream of known maximum bandwidth are computed with a real-time media stream of known maximum bandwidth
to rate-control the ICE exchanges. to rate-control the ICE exchanges.
11. Security Considerations 11. Security Considerations
11.1. Attacks on the Offer/Answer Exchanges 11.1. Attacks on the Offer/Answer Exchanges
An attacker that can modify or disrupt the offer/answer exchanges An attacker that can modify or disrupt the offer/answer exchanges
themselves can readily launch a variety of attacks with ICE. They themselves can readily launch a variety of attacks with ICE. They
could direct media to a target of a DoS attack, they could insert could direct media to a target of a DoS attack, they could insert
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option, all new ICE options MUST also define in their specification option, all new ICE options MUST also define in their specification
how the media-level ICE option values are aggregated to generate the how the media-level ICE option values are aggregated to generate the
value of the session-level ICE option. value of the session-level ICE option.
[RFC6679] defines the "rtp+ecn" ICE option. The aggregation rule for [RFC6679] defines the "rtp+ecn" ICE option. The aggregation rule for
this ICE option is that if all aggregated media using ICE contain a this ICE option is that if all aggregated media using ICE contain a
media-level "rtp+ecn" ICE option then an "rtp+ecn" ICE option MUST be media-level "rtp+ecn" ICE option then an "rtp+ecn" ICE option MUST be
inserted at the session-level. If one of the media does not contain inserted at the session-level. If one of the media does not contain
the option, then it MUST NOT be inserted at the session-level. the option, then it MUST NOT be inserted at the session-level.
Section 9 of [ICE-BIS] defines "ice2" ICE option. Since "ice2" is a Section 10 of [ICE-BIS] defines "ice2" ICE option. Since "ice2" is a
session level ICE option, no aggregation rules apply. session level ICE option, no aggregation rules apply.
A registration request MUST include the following information: A registration request MUST include the following information:
o The ICE option identifier to be registered o The ICE option identifier to be registered
o Name, Email, and Address of a contact person for the registration o Name, Email, and Address of a contact person for the registration
o Organization or individuals having the change control o Organization or individuals having the change control
o Short description of the ICE extension to which the option relates o Short description of the ICE extension to which the option relates
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<http://www.rfc-editor.org/info/rfc5626>. <http://www.rfc-editor.org/info/rfc5626>.
[RFC5898] Andreasen, F., Camarillo, G., Oran, D., and D. Wing, [RFC5898] Andreasen, F., Camarillo, G., Oran, D., and D. Wing,
"Connectivity Preconditions for Session Description "Connectivity Preconditions for Session Description
Protocol (SDP) Media Streams", RFC 5898, Protocol (SDP) Media Streams", RFC 5898,
DOI 10.17487/RFC5898, July 2010, DOI 10.17487/RFC5898, July 2010,
<http://www.rfc-editor.org/info/rfc5898>. <http://www.rfc-editor.org/info/rfc5898>.
Appendix A. Examples Appendix A. Examples
For the example shown in section 12 of [ICE-BIS] the resulting offer For the example shown in section 16 of [ICE-BIS] the resulting offer
(message 5) encoded in SDP looks like: (message 5) encoded in SDP looks like:
v=0 v=0
o=jdoe 2890844526 2890842807 IN IP6 $L-PRIV-1.IP o=jdoe 2890844526 2890842807 IN IP6 $L-PRIV-1.IP
s= s=
c=IN IP6 $NAT-PUB-1.IP c=IN IP6 $NAT-PUB-1.IP
t=0 0 t=0 0
a=ice-pwd:asd88fgpdd777uzjYhagZg a=ice-pwd:asd88fgpdd777uzjYhagZg
a=ice-ufrag:8hhY a=ice-ufrag:8hhY
m=audio $NAT-PUB-1.PORT RTP/AVP 0 m=audio $NAT-PUB-1.PORT RTP/AVP 0
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as ALGs and Session Border Controllers (SBCs), and diagnostic tools as ALGs and Session Border Controllers (SBCs), and diagnostic tools
that passively monitor the network. For these tools to continue to that passively monitor the network. For these tools to continue to
function without change, the core property of SDP -- that the function without change, the core property of SDP -- that the
existing, pre-ICE definitions of the addresses used for media -- the existing, pre-ICE definitions of the addresses used for media -- the
"m=" and "c=" lines and the rtcp attribute -- must be retained. For "m=" and "c=" lines and the rtcp attribute -- must be retained. For
this reason, an updated offer must be sent. this reason, an updated offer must be sent.
Authors' Addresses Authors' Addresses
Marc Petit-Huguenin Marc Petit-Huguenin
Impedance Mismatch
Email: marc@petit-huguenin.org Email: marc@petit-huguenin.org
Ari Keranen Ari Keranen
Ericsson
Jorvas 02420
Finland
Email: ari.keranen@ericsson.com Email: ari.keranen@ericsson.com
Suhas Nandakumar Suhas Nandakumar
Cisco Systems
707 Tasman Dr
Milpitas, CA 95035
USA
Email: snandaku@cisco.com Email: snandaku@cisco.com
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