draft-ietf-mmusic-ice-sip-sdp-16.txt   draft-ietf-mmusic-ice-sip-sdp-17.txt 
MMUSIC M. Petit-Huguenin MMUSIC M. Petit-Huguenin
Internet-Draft Impedance Mismatch Internet-Draft Impedance Mismatch
Obsoletes: 5245 (if approved) A. Keranen Obsoletes: 5245 (if approved) S. Nandakumar
Intended status: Standards Track Ericsson Intended status: Standards Track Cisco Systems
Expires: May 27, 2018 S. Nandakumar Expires: September 27, 2018 A. Keranen
Cisco Systems Ericsson
November 23, 2017 March 26, 2018
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-16 draft-ietf-mmusic-ice-sip-sdp-17
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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This Internet-Draft will expire on May 27, 2018. This Internet-Draft will expire on September 27, 2018.
Copyright Notice Copyright Notice
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Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4
3. ICE Candidate Exchange and Offer/Answer Mapping . . . . . . . 4 3. SDP Offer/Answer Procedures . . . . . . . . . . . . . . . . . 4
4. SDP Offer/Answer Procedures . . . . . . . . . . . . . . . . . 4 3.1. Introduction . . . . . . . . . . . . . . . . . . . . . . 4
4.1. Initial Offer/Answer Exchange . . . . . . . . . . . . . . 4 3.2. Generic Procedures . . . . . . . . . . . . . . . . . . . 4
4.1.1. Sending the Initial Offer . . . . . . . . . . . . . . 4 3.2.1. Encoding . . . . . . . . . . . . . . . . . . . . . . 4
4.1.2. Receiving the Initial Offer . . . . . . . . . . . . . 7 3.2.2. RTP/RTCP Considerations . . . . . . . . . . . . . . . 6
4.1.3. Receipt of the Initial Answer . . . . . . . . . . . . 8 3.2.3. Determining Role . . . . . . . . . . . . . . . . . . 6
4.1.4. Performing Connectivity Checks . . . . . . . . . . . 9 3.2.4. STUN Considerations . . . . . . . . . . . . . . . . . 6
4.1.5. Concluding ICE . . . . . . . . . . . . . . . . . . . 9 3.2.5. ICE Mismatch . . . . . . . . . . . . . . . . . . . . 6
4.2. Subsequent Offer/Answer Exchanges . . . . . . . . . . . . 10 3.2.6. SDP Example . . . . . . . . . . . . . . . . . . . . . 7
4.2.1. Generating the Offer . . . . . . . . . . . . . . . . 10 3.3. Initial Offer/Answer Exchange . . . . . . . . . . . . . . 7
4.2.2. Receiving the Offer and Generating an Answer . . . . 13 3.3.1. Sending the Initial Offer . . . . . . . . . . . . . . 7
4.2.3. Receiving the Answer for a Subsequent Offer . . . . . 16 3.3.2. Sending the Initial Answer . . . . . . . . . . . . . 8
4.2.4. Updating the Check and Valid Lists . . . . . . . . . 17 3.3.3. Receiving the Initial Answer . . . . . . . . . . . . 8
5. Grammar . . . . . . . . . . . . . . . . . . . . . . . . . . . 18 3.3.4. Concluding ICE . . . . . . . . . . . . . . . . . . . 8
5.1. "candidate" Attribute . . . . . . . . . . . . . . . . . . 18 3.4. Subsequent Offer/Answer Exchanges . . . . . . . . . . . . 9
5.2. "remote-candidates" Attribute . . . . . . . . . . . . . . 21 3.4.1. Sending Subsequent Offer . . . . . . . . . . . . . . 9
5.3. "ice-lite" and "ice-mismatch" Attributes . . . . . . . . 21 3.4.2. Sending Subsequent Answer . . . . . . . . . . . . . . 11
5.4. "ice-ufrag" and "ice-pwd" Attributes . . . . . . . . . . 22 3.4.3. Receiving Answer for a Subsequent Offer . . . . . . . 13
5.5. "ice-pacing" Attribute . . . . . . . . . . . . . . . . . 22 4. Grammar . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
5.6. "ice-options" Attribute . . . . . . . . . . . . . . . . . 23 4.1. "candidate" Attribute . . . . . . . . . . . . . . . . . . 15
6. Keepalives . . . . . . . . . . . . . . . . . . . . . . . . . 23 4.2. "remote-candidates" Attribute . . . . . . . . . . . . . . 18
7. Media Handling . . . . . . . . . . . . . . . . . . . . . . . 23 4.3. "ice-lite" and "ice-mismatch" Attributes . . . . . . . . 18
7.1. Sending Media . . . . . . . . . . . . . . . . . . . . . . 23 4.4. "ice-ufrag" and "ice-pwd" Attributes . . . . . . . . . . 19
7.1.1. Procedures for All Implementations . . . . . . . . . 24 4.5. "ice-pacing" Attribute . . . . . . . . . . . . . . . . . 20
7.2. Receiving Media . . . . . . . . . . . . . . . . . . . . . 24 4.6. "ice-options" Attribute . . . . . . . . . . . . . . . . . 20
8. SIP Considerations . . . . . . . . . . . . . . . . . . . . . 24 5. Keepalives . . . . . . . . . . . . . . . . . . . . . . . . . 21
8.1. Latency Guidelines . . . . . . . . . . . . . . . . . . . 24 6. SIP Considerations . . . . . . . . . . . . . . . . . . . . . 21
8.1.1. Offer in INVITE . . . . . . . . . . . . . . . . . . . 25 6.1. Latency Guidelines . . . . . . . . . . . . . . . . . . . 21
8.1.2. Offer in Response . . . . . . . . . . . . . . . . . . 26 6.1.1. Offer in INVITE . . . . . . . . . . . . . . . . . . . 22
6.1.2. Offer in Response . . . . . . . . . . . . . . . . . . 23
8.2. SIP Option Tags and Media Feature Tags . . . . . . . . . 26 6.2. SIP Option Tags and Media Feature Tags . . . . . . . . . 23
8.3. Interactions with Forking . . . . . . . . . . . . . . . . 27 6.3. Interactions with Forking . . . . . . . . . . . . . . . . 24
8.4. Interactions with Preconditions . . . . . . . . . . . . . 27 6.4. Interactions with Preconditions . . . . . . . . . . . . . 24
8.5. Interactions with Third Party Call Control . . . . . . . 27 6.5. Interactions with Third Party Call Control . . . . . . . 24
9. Relationship with ANAT . . . . . . . . . . . . . . . . . . . 28 7. Relationship with ANAT . . . . . . . . . . . . . . . . . . . 25
10. Setting Ta and RTO for RTP Media Streams . . . . . . . . . . 28 8. Setting Ta and RTO for RTP Media Streams . . . . . . . . . . 25
11. Security Considerations . . . . . . . . . . . . . . . . . . . 28 9. Security Considerations . . . . . . . . . . . . . . . . . . . 25
11.1. Attacks on the Offer/Answer Exchanges . . . . . . . . . 28 9.1. Attacks on the Offer/Answer Exchanges . . . . . . . . . . 25
11.2. Insider Attacks . . . . . . . . . . . . . . . . . . . . 28 9.2. Insider Attacks . . . . . . . . . . . . . . . . . . . . . 26
11.2.1. The Voice Hammer Attack . . . . . . . . . . . . . . 29 9.2.1. The Voice Hammer Attack . . . . . . . . . . . . . . . 26
11.2.2. Interactions with Application Layer Gateways and SIP 29 9.2.2. Interactions with Application Layer Gateways and SIP 26
12. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 30 10. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 27
12.1. SDP Attributes . . . . . . . . . . . . . . . . . . . . . 30 10.1. SDP Attributes . . . . . . . . . . . . . . . . . . . . . 27
12.1.1. candidate Attribute . . . . . . . . . . . . . . . . 31 10.1.1. candidate Attribute . . . . . . . . . . . . . . . . 28
12.1.2. remote-candidates Attribute . . . . . . . . . . . . 31 10.1.2. remote-candidates Attribute . . . . . . . . . . . . 28
12.1.3. ice-lite Attribute . . . . . . . . . . . . . . . . . 31 10.1.3. ice-lite Attribute . . . . . . . . . . . . . . . . . 29
12.1.4. ice-mismatch Attribute . . . . . . . . . . . . . . . 32 10.1.4. ice-mismatch Attribute . . . . . . . . . . . . . . . 29
12.1.5. ice-pwd Attribute . . . . . . . . . . . . . . . . . 32 10.1.5. ice-pwd Attribute . . . . . . . . . . . . . . . . . 30
12.1.6. ice-ufrag Attribute . . . . . . . . . . . . . . . . 33 10.1.6. ice-ufrag Attribute . . . . . . . . . . . . . . . . 30
12.1.7. ice-pacing Attribute . . . . . . . . . . . . . . . . 33 10.1.7. ice-options Attribute . . . . . . . . . . . . . . . 31
12.1.8. ice-options Attribute . . . . . . . . . . . . . . . 33 10.1.8. ice-pacing Attribute . . . . . . . . . . . . . . . . 31
12.2. Interactive Connectivity Establishment (ICE) Options 10.2. Interactive Connectivity Establishment (ICE) Options
Registry . . . . . . . . . . . . . . . . . . . . . . . . 34 Registry . . . . . . . . . . . . . . . . . . . . . . . . 32
13. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 35 11. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 33
14. References . . . . . . . . . . . . . . . . . . . . . . . . . 35 12. References . . . . . . . . . . . . . . . . . . . . . . . . . 33
14.1. Normative References . . . . . . . . . . . . . . . . . . 35 12.1. Normative References . . . . . . . . . . . . . . . . . . 33
14.2. Informative References . . . . . . . . . . . . . . . . . 38 12.2. Informative References . . . . . . . . . . . . . . . . . 35
Appendix A. Examples . . . . . . . . . . . . . . . . . . . . . . 38 12.3. URIs . . . . . . . . . . . . . . . . . . . . . . . . . . 36
Appendix B. The remote-candidates Attribute . . . . . . . . . . 40 Appendix A. Examples . . . . . . . . . . . . . . . . . . . . . . 37
Appendix C. Why Is the Conflict Resolution Mechanism Needed? . . 41 Appendix B. The remote-candidates Attribute . . . . . . . . . . 38
Appendix D. Why Send an Updated Offer? . . . . . . . . . . . . . 42 Appendix C. Why Is the Conflict Resolution Mechanism Needed? . . 39
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 43 Appendix D. Why Send an Updated Offer? . . . . . . . . . . . . . 40
Appendix E. Contributors . . . . . . . . . . . . . . . . . . . . 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 [ICE-BIS] describes procedures that [RFC3264]. The ICE specification [ICE-BIS] 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.
2. Terminology 2. Terminology
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in RFC "OPTIONAL" in this document are to be interpreted as described in RFC
2119 [RFC2119]. 2119 [RFC2119].
Readers should be familiar with the terminology defined in [RFC3264], Readers should be familiar with the terminology defined in [RFC3264],
in [RFC7656], in [ICE-BIS] and the following: in [ICE-BIS] and the following:
Default Destination/Candidate: The default destination for a Default Destination/Candidate: The default destination for a
component of a media stream is the transport address that would be component of a 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 IP address is in the "c=" line of the SDP, and the port is default IP address is in the "c=" line of the SDP, and the port is
in the "m=" line. For the RTCP component, the address and port in the "m=" line. For the RTCP component, the address and port
are indicated using the "a=rtcp" attribute defined in [RFC3605], are indicated using the "a=rtcp" attribute defined in [RFC3605],
if present; otherwise, the RTCP component address is same as the if present; otherwise, the RTCP component address is same as the
address of the RTP component, and its port is one greater than the address of the RTP component, and its port is one greater than the
port of the RTP component. port of the RTP component.
3. ICE Candidate Exchange and Offer/Answer Mapping 3. SDP Offer/Answer Procedures
3.1. Introduction
[ICE-BIS] defines ICE candidate exchange as the process for ICE [ICE-BIS] defines ICE candidate exchange as the process for ICE
agents (Initiator and Responder) to exchange their candidate agents (Initiator and Responder) to exchange their candidate
information required for ICE processing at the agents. For the information required for ICE processing at the agents. For the
purposes of this specification, the candidate exchange process purposes of this specification, the candidate exchange process
corresponds to the [RFC3264] Offer/Answer protocol and the corresponds to the [RFC3264] Offer/Answer protocol and the
terminologies offerer and answerer correspond to the initiator and terminologies offerer and answerer correspond to the initiator and
responder terminologies from [ICE-BIS] respectively. responder terminologies from [ICE-BIS] respectively.
4. SDP Offer/Answer Procedures Once the initiating agent has gathered, pruned and prioritized its
set of candidates [ICE-BIS], the candidate exchange with the peer
agent begins.
4.1. Initial Offer/Answer Exchange 3.2. Generic Procedures
4.1.1. Sending the Initial Offer 3.2.1. Encoding
The offerer shall follow the procedures defined in section 5 of Section 4 provides detailed rules for constructing various SDP
[ICE-BIS] to gather, prioritize and eliminate the redundant attributes defined in this specification.
candidates. It then chooses the default candidates and encodes them
in the SDP to be sent to its peer, the answerer.
4.1.1.1. Choosing Default Candidates 3.2.1.1. Data Streams
A candidate is said to be default if it would be the target of media Each data stream [ICE-BIS] is represented by an SDP media description
from a non-ICE peer; that target is called the DEFAULT DESTINATION. ("m=" section).
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
it does not have a port of zero (which is used in RFC 3264 to reject
a media stream). Consequently, a media stream is in-use even if it
is marked as a=inactive [RFC4566] or has a bandwidth value of zero.
An agent may choose any type of the candidate as the default, if the 3.2.1.2. Candidates
chosen candidates increases the likelihood of success with the peer
that is being contacted if ICE is not being used. It is recommended
that, when multiple candidates are used, UDP based candidates SHOULD
be included wherever possible and default candidate SHOULD be chosen
from one of those UDP candidates. The proto value MUST match the
transport protocol associated with the default candidate. If UDP
transport is used for the default candidate, the 'proto' value MUST
include UDP and the 'proto' value MUST be TCP when the transport is
TCP for the default candidate.
Since it is RECOMMENDED that default candidates be chosen based on With in a "m=" section, each candidate (including the default
the likelihood of those candidates to work with the peer that is candidate) associated with the data stream is represented by an SDP
being contacted if ICE is not being used. Many factors may influence candidate attribute.
such a decision in a given agent. In scenarios where the agent is
fully aware of its peer's location and can reach the peer directly,
choosing the host candidates as the default may well be sufficient.
If the network configuration under which the agents operates is
static and known beforehand, either the host or the server reflexives
candidates can serve as the default candidates (depending on if a
given agent is behind NAT and their reachability). If the agent is
completely unaware of the peer's location or no assumptions can be
made of network characteristics and the connectivity, the relayed
candidates might be the only option as the default candidate. Having
the decision of choosing the default candidate as a configurable
option in the implementations might provide agents the flexibility to
take into account the aforementioned criteria. Barring such
configuration flexibility, it is RECOMMENDED that the default
candidates be the relayed candidates (if relayed candidates are
available), server reflexive candidates (if server reflexive
candidates are available), and finally host candidates.
4.1.1.2. Encoding the SDP Prior to nomination, the "c=" line associated with an "m=" section
contains the IP address of the default candidate, while the "m=" line
contains the port and transport of the default candidate for that
"m=" section.
The process of encoding the SDP is identical between full and lite After nomination, the "c=" line for a given "m=" section contains the
implementations. IP address of the nominated candidate (the local candidate of the
nominated candidate pair) and the "m=" line contains the port and
transport corresponding to the nominated candidate for that "m="
section.
The agent will include an "m=" line for each Source Stream [RFC7656] 3.2.1.3. Username and Password
it wishes to use. The ordering of source streams in the SDP is
relevant for ICE. ICE will perform its connectivity checks for the
first "m=" line first, and consequently media will be able to flow
for that stream first. Agents SHOULD place their most important
source stream, if there is one, first in the SDP.
There will be a candidate attribute for each candidate for a The ICE username is represented by an SDP ice-ufrag attribute and the
particular source stream. Section 5 provides detailed rules for ICE password is represented by an SDP ice-pwd attribute.
constructing this attribute.
STUN connectivity checks between agents are authenticated using the 3.2.1.4. Lite Implementations
short-term credential mechanism defined for STUN [RFC5389]. This
mechanism relies on a username and password that are exchanged
through protocol machinery between the client and server. The
username fragment and password are exchanged in the ice-ufrag and
ice-pwd attributes, respectively.
If an agent is a lite implementation, it MUST include an "a=ice-lite" An ICE lite implementation [ICE-BIS] MUST include an SDP ice-lite
session-level attribute in its SDP to indicate this. If an agent is attribute. A full implementation MUST NOT include that attribute.
a full implementation, it MUST NOT include this attribute.
Section 10 of [ICE-BIS] defines a new ICE option, 'ice2'. This 3.2.1.5. ICE Extensions
option is used by ICE Agents to indicate their compliancy with
[ICE-BIS] specification as compared to the [RFC5245]. If the
Offering agent is a [ICE-BIS] compliant implementation, a session
level ICE option to indicate the same (via the "a=ice-options:ice2"
SDP line) MUST be included.
The default candidates are added to the SDP as the default An agent uses the SDP ice-options attribute to indicate support of
destination for media. For source streams based on RTP, this is done ICE extensions.
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
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
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
b=RS:0 and b=RR:0 as defined in [RFC3556]
The transport addresses that will be the default destination for An agent compliant to this specification MUST include an SDP ice-
media when communicating with non-ICE peers MUST also be present as options attribute with an "ice2" attribute value. If an agent
candidates in one or more a=candidate lines. receives an SDP offer or answer that does not include the attribute
value, the agent assumes that the peer is compliant to [RFC5245].
ICE provides for extensibility by allowing an offer or answer to 3.2.1.6. Inactive and Disabled Data Streams
contain a series of tokens that identify the ICE extensions used by
that agent. If an agent supports an ICE extension, it MUST include
the token defined for that extension in the ice-options attribute.
The following is an example SDP message that includes ICE attributes If an "m=" section is marked as inactive [RFC4566], or has a
(lines folded for readability): bandwidth value of zero [RFC4566], the agent MUST still include ICE
related SDP attributes.
v=0 If the port value associated with an "m=" section is set to zero
o=jdoe 2890844526 2890842807 IN IP4 10.0.1.1 (implying a disabled stream), the agent SHOULD NOT include ICE
s= related SDP candidate attributes in that "m=" section, unless an SDP
c=IN IP4 192.0.2.3 extension specifying otherwise is used.
t=0 0
a=ice-options:ice2
a=ice-pwd:asd88fgpdd777uzjYhagZg
a=ice-ufrag:8hhY
m=audio 45664 RTP/AVP 0
b=RS:0
b=RR:0
a=rtpmap:0 PCMU/8000
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
10.0.1.1 rport 8998
Once an agent has sent its offer or its answer, that agent MUST be 3.2.2. RTP/RTCP Considerations
prepared to receive both STUN and media packets on each candidate.
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
media in an offer or answer.
4.1.2. Receiving the Initial Offer If an agent utilizes both RTP and RTCP, the agent MUST include SDP
candidate attributes for both the RTP and RTCP components in the "m="
section.
On receiving the offer, the answerer verifies the support for ICE If an agent uses separate ports for RTP and RTCP, the agent MUST
(section 5.4 of [ICE-BIS]), determines its role (section 6.1.1 of include an SDP rtcp attribute in the "m=" section, as described in
[ICE-BIS]), gathers candidates (section 5 of [ICE-BIS]), encodes the [RFC3605]. In the cases where the port number for the RTCP is one
candidates in an SDP answer and sends it to its peer, the offerer. higher than the RTP port and RTCP component address is same as the
The answerer shall then follow the steps defined in sections 6.1.3 address of the RTP component, the SDP rtcp attribute MUST not be
and 6.1.4 of [ICE-BIS] to schedule the ICE connectivity checks. included.
The below sub-sections provide additional requirements associated If the agent does not utilize RTCP, it indicates that by including
with the processing of the offerer's SDP pertaining to this b=RS:0 and b=RR:0 SDP attributes, as described in [RFC3556].
specification.
4.1.2.1. ICE Option "ice2" considerations 3.2.3. Determining Role
If the SDP offer contains a session level ICE option, "ice2" , and if The offerer acts as the Initiating agent. The answerer acts as the
the answering ICE Agent is also an [ICE-BIS] compliant Responding agent. The ICE roles (controlling and controlled) are
implementation, then the generated SDP answer MUST include the determined using the procedures in [ICE-BIS].
session level "a=ice-options:ice2" SDP line.
4.1.2.2. Choosing Default Candidates 3.2.4. STUN Considerations
The process for selecting default candidates at the answerer is Once an agent has provided its local candidates to its peer, within
identical to the process followed by the offerer, as described in an SDP offer or answer, the agent MUST be prepared to receive STUN
Section 4.1.1.1 for full implementations in this specification and connectivity check Binding requests on those candidates.
section 5.2 of [ICE-BIS] for lite implementations.
4.1.2.3. ICE Mismatch 3.2.5. 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 data stream in the SDP it
received, the default destination for each component of that media 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 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 [RFC3264] 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 11 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 data stream, the agent MUST include an a=ice-
mismatch attribute in its answer. mismatch attribute in its answer and may omit a=candidate
attributes for such data streams. See Section 9.2.2 for a
discussion of cases where this can happen. This specification
provides no guidance on how an agent should proceed in such a
failure case.
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 data
stream from the peer may be lost. stream from the peer may be lost.
4.1.2.4. Determining Role 3.2.6. SDP Example
In unusual cases, described in Appendix C, it is possible for both The following is an example SDP message that includes ICE attributes
agents to mistakenly believe they are controlled or controlling. To (lines folded for readability):
resolve this, each agent MUST select a random number, called the tie-
breaker, uniformly distributed between 0 and (2**64) - 1 (that is, a
64-bit positive integer). This number is used in connectivity checks
to detect and repair this case, as described in section 7.1.3 of
[ICE-BIS].
4.1.3. Receipt of the Initial Answer v=0
o=jdoe 2890844526 2890842807 IN IP4 10.0.1.1
s=
c=IN IP4 192.0.2.3
t=0 0
a=ice-options:ice2
a=ice-pwd:asd88fgpdd777uzjYhagZg
a=ice-ufrag:8hhY
m=audio 45664 RTP/AVP 0
b=RS:0
b=RR:0
a=rtpmap:0 PCMU/8000
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
10.0.1.1 rport 8998
On receiving the SDP answer, the offerer performs steps similar to 3.3. Initial Offer/Answer Exchange
answerer's processing of the offer. The offerer verifies the
answerer's ICE support determines, its role, and processes the
answerer's candidates to schedule the connectivity checks (section 7
of [ICE-BIS]).
If the offerer had included the "ice2" ICE Option in the offer and 3.3.1. Sending the Initial Offer
the SDP answer also includes a similar session level ICE option, then
the peers are [ICE-BIS] compliant implementations. On the other
hand, if the SDP Answer lacks such a ICE option, the offerer defaults
to the procedures that are backward compatible with the [RFC5245]
specification.
4.1.3.1. ICE Mismatch When an offerer generates the initial offer, in each "m=" section it
MUST include SDP candidate attributes for each available candidate
associated with the "m=" section. In addition, the offerer MUST
include an SDP ice-ufrag and an SDP ice-pwd attribute in the offer.
The logic at the offerer is identical to that of the answerer as Note: Within the scope of this document, "Initial Offer" refers to
described in section 5.4 of [ICE-BIS], with the exception that an the first SDP offer that is sent in order to negotiate usage of
offerer would not ever generate a=ice-mismatch attributes in an SDP. ICE. It might, or might not, be the initial SDP offer of the SDP
session.
In some cases, the answer may omit a=candidate attributes for the Note: The procedures in this document only consider "m=" sections
media streams, and instead include an a=ice-mismatch attribute for associated with data streams where ICE is used.
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
not used for the session because a signaling intermediary modified
the default destination for media components without modifying the
corresponding candidate attributes. See Section 11.2.2 for a
discussion of cases where this can happen. This specification
provides no guidance on how an agent should proceed in such a failure
case.
4.1.4. Performing Connectivity Checks 3.3.2. Sending the Initial Answer
The possibility for role conflicts described in section 7.3.1.1 of When an answerer receives an initial offer that indicates that the
[ICE-BIS] applies to this usage and hence all full agents MUST offerer supports ICE, and if the answerer accepts the offer and the
implement the role conflict repairing mechanism. Also both full and usage of ICE, in each "m=" section within the answer, it MUST include
lite agents MUST utilize the ICE-CONTROLLED and ICE-CONTROLLING SDP candidate attributes for each available candidate associated with
attributes as described in section 7.1.3 of [ICE-BIS]. the "m=" section. In addition, the answerer MUST include an SDP ice-
ufrag and an SDP ice-pwd attribute in the answer.
4.1.5. Concluding ICE Once the answerer has sent the answer, it can start performing
connectivity checks towards the peer candidates that were provided in
the offer.
Once the state of each check list is Completed, If an agent is If the offer does not indicate support of ICE, the answerer MUST NOT
controlling, it examines the highest-priority nominated candidate accept the usage of ICE. If the answerer still accepts the offer,
pair for each component of each media stream. If any of those the answerer MUST NOT include any ICE related SDP attributes in the
candidate pairs differ from the default candidate pairs in the most answer. Instead the answerer will generate the answer according to
recent offer/answer exchange, the controlling agent MUST generate an normal offer/answer procedures [RFC3264].
updated offer as described in Section 4.2.
However, If the support for 'ice2' ICE Option is in use, the highest- If the answerer detects a possibility of the ICE mismatch, procedures
priority nominated candidate is noted and sent in the subsequent described in (Section 3.2.5) are followed.
offer/answer exchange as the default candidate and no updated offer
is needed to fix the default candidate.
4.2. Subsequent Offer/Answer Exchanges 3.3.3. Receiving the Initial Answer
When an offerer receives an initial answer that indicates that the
answerer supports ICE, it can start performing connectivity checks
towards the peer candidates that were provided in the answer.
If the answer does not indicate that the answerer supports ICE, or if
the offerer detects an ICE mismatch in the answer, the offerer MUST
terminate the usage of ICE. The subsequent actions taken by the
offerer are implementation dependent and are out of the scope of this
specification.
3.3.4. Concluding ICE
Once the state of each check list is Completed, and if the agent is
the controlling, it nominates a candidate pair [ICE-BIS], it checks
for each data stream whether the nominated pair matches the default
candidate pair. If there are one or more data streams with a match,
the controlling agent MUST generate a subsequent offer
(Section 3.4.1), in which the IP address, port and transport in the
"c=" and "m=" lines associated with each data stream match the
corresponding local information of the nominated pair for that data
stream.
However, If the support for 'ice2' ice-option is in use, the
nominated candidate is noted and sent in the subsequent offer/answer
exchange as the default candidate and no updated offer is needed to
fix the default candidate.
Also as described in [ICE-BIS], once the controlling agent has
nominated a candidate pair for a data stream, the agent MUST NOT
nominate another pair for that data stream during the lifetime of the
ICE session.
3.4. 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.
4.2.1. Generating the Offer 3.4.1. Sending Subsequent Offer
4.2.1.1. Procedures for All Implementations 3.4.1.1. Procedures for All Implementations
4.2.1.1.1. ICE Restarts 3.4.1.1.1. ICE Restarts
An agent MAY restart ICE processing for an existing media stream as An agent MAY restart ICE processing for an existing data stream
defined in section 9 of [ICE-BIS]. [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 data stream in an offer. Note that it is permissible
to use a session-level attribute in one offer, but to provide the to use a session-level attribute in one offer, but to provide the
same ice-pwd or ice-ufrag as a media-level attribute in a subsequent same ice-pwd or ice-ufrag as a media-level attribute in a subsequent
offer. This is not a change in password, just a change in its offer. This is not a change in password, just a change in its
representation, and does not cause an ICE restart. representation, and does not cause an ICE restart.
An agent sets the rest of the fields in the SDP for this media stream An agent sets the rest of the ice related fields in the SDP for this
as it would in an initial offer of this media stream (see data stream as it would in an initial offer of this data stream (see
Section 4.1.1.2). Consequently, the set of candidates MAY include Section 3.2.1). Consequently, the set of candidates MAY include
some, none, or all of the previous candidates for that stream and MAY some, none, or all of the previous candidates for that data stream
include a totally new set of candidates. and MAY include a totally new set of candidates.
4.2.1.1.2. Removing a Media Stream 3.4.1.1.2. Removing a Data Stream
If an agent removes a media 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 media 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 5 for that media stream. Section 4 for that data stream.
4.2.1.1.3. Adding a Media Stream 3.4.1.1.3. Adding a Data Stream
If an agent wishes to add a new media 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 media stream as if this was an initial offer for the SDP for this data stream as if this was an initial offer for that
that media stream (see Section 4.1.1.2). This will cause ICE data stream (see Section 3.2.1). This will cause ICE processing to
processing to begin for this media stream. begin for this data stream.
4.2.1.2. Procedures for Full Implementations 3.4.1.2. Procedures for Full Implementations
This section describes additional procedures for full This section describes additional procedures for full
implementations, covering existing media streams. implementations, covering existing data streams.
4.2.1.2.1. Existing Media Streams with ICE Running
If an agent generates an updated offer including a media stream that 3.4.1.3. Before Nomination
was previously established, and for which ICE checks are in the
Running state, the agent follows the procedures defined here.
An agent MUST include candidate attributes for all local candidates When an offerer sends a subsequent offer, each "m=" section for which
it had signaled previously for that media stream. The properties of a candidate pair has not yet been nominated, the offer MUST include
that candidate as signaled in SDP -- the priority, foundation, type, the same set of ICE-related information that the offerer included in
and related transport address -- SHOULD remain the same. The IP the previous offer or answer. The agent MAY include additional
address, port, and transport protocol, which fundamentally identify candidates it did not offer previously, but which it has gathered
that candidate, MUST remain the same (if they change, it would be a since the last offer/ answer exchange, including peer reflexive
new candidate). The component ID MUST remain the same. The agent candidates.
MAY include additional candidates it did not offer previously (see
section 4.2.4.1.1), but which it has gathered since the last offer/
answer exchange, including peer reflexive candidates.
The agent MAY change the default destination for media. As with The agent MAY change the default destination for media. As with
initial offers, there MUST be a set of candidate attributes in the initial offers, there MUST be a set of candidate attributes in the
offer matching this default destination. offer matching this default destination.
4.2.1.2.2. Existing Media Streams with ICE Completed 3.4.1.4. After Nomination
If an agent generates an updated offer including a media stream that
was previously established, and for which ICE checks are in the
Completed state, the agent follows the procedures defined here.
The default destination for media (i.e., the values of the IP
addresses and ports in the "m=" and "c=" lines used for that media
stream) MUST be the local candidate from the highest-priority
nominated pair in the valid list for each component.
The agent MUST include candidate attributes for candidates matching Once a candidate pair has been nominated for a data stream, the IP
the default destination for each component of the media stream, and address, port and transport in each "c=" and "m=" line associated
MUST NOT include any other candidates. with that data stream MUST match the data associated with the
nominated pair for that data stream. In addition, the offerer only
includes SDP candidates representing the local candidates of the
nominated candidate pair. The offerer 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 media stream whose check list a=remote-candidates attribute for each data stream whose check list
is in the Completed state. The attribute contains the remote is in the completed state. The attribute contains the remote
candidates from the highest-priority nominated pair in the valid list candidates corresponding to the nominated pair in the valid list for
for each component of that media stream. It is needed to avoid a each component of that data stream. It is needed to avoid a race
race condition whereby the controlling agent chooses its pairs, but condition whereby the controlling agent chooses its pairs, but the
the updated offer beats the connectivity checks to the controlled updated offer beats the connectivity checks to the controlled agent,
agent, which doesn't even know these pairs are valid, let alone which doesn't even know these pairs are valid, let alone selected.
selected. See Appendix B for elaboration on this race condition. See Appendix B for elaboration on this race condition.
4.2.1.3. Procedures for Lite Implementations
4.2.1.3.1. Existing Media Streams with ICE Running
This section describes procedures for lite implementations for
existing streams for which ICE is running.
A lite implementation MUST include all of its candidates for each
component of each media stream in an a=candidate attribute in any
subsequent offer. These candidates are formed identically to the
procedures for initial offers, as described in section 5.2 of
[ICE-BIS].
A lite implementation MUST NOT add additional host candidates in a
subsequent offer. If an agent needs to offer additional candidates,
it MUST restart ICE.
The username fragments, password, and implementation level MUST
remain the same as used previously. If an agent needs to change one
of these, it MUST restart ICE for that media stream.
4.2.1.3.2. Existing Media Streams with ICE Completed
If ICE has completed for a media stream, the default destination for
that media stream MUST be set to the remote candidate of the
candidate pair for that component in the valid list. For a lite
implementation, there is always just a single candidate pair in the
valid list for each component of a media stream. Additionally, the
agent MUST include a candidate attribute for each default
destination.
Additionally, if the agent is controlling (which only happens when
both agents are lite), the agent MUST include the a=remote-candidates
attribute for each media stream. The attribute contains the remote
candidates from the candidate pairs in the valid list (one pair for
each component of each media stream).
4.2.2. Receiving the Offer and Generating an Answer
4.2.2.1. Procedures for All Implementations
When receiving a subsequent offer within an existing session, an
agent MUST reapply the verification procedures in Section 4.1.2.3
without regard to the results of verification from any previous
offer/answer exchanges. Indeed, it is possible that a previous
offer/answer exchange resulted in ICE not being used, but it is used
as a consequence of a subsequent exchange.
4.2.2.1.1. Detecting ICE Restart
If the offer contained a change in the a=ice-ufrag or a=ice-pwd
attributes compared to the previous SDP from the peer, it indicates
that ICE is restarting for this media stream. If all media streams
are restarting, then ICE is restarting overall.
If ICE is restarting for a media stream:
o The agent MUST change the a=ice-ufrag and a=ice-pwd attributes in
the answer.
o The agent MAY change its implementation level in the answer.
An agent sets the rest of the fields in the SDP for this media stream
as it would in an initial answer to this media stream (see
Section 4.1.1.2). Consequently, the set of candidates MAY include
some, none, or all of the previous candidates for that stream and MAY
include a totally new set of candidates.
4.2.2.1.2. New Media Stream
If the offer contains a new media stream, the agent sets the fields
in the answer as if it had received an initial offer containing that
media stream (see Section 4.1.1.2). This will cause ICE processing
to begin for this media stream.
4.2.2.1.3. Removed Media Stream
If an offer contains a media stream whose port is zero, the agent
MUST NOT include any candidate attributes for that media stream in
its answer and SHOULD NOT include any other ICE-related attributes
defined in Section 5 for that media stream.
4.2.2.2. Procedures for Full Implementations
Unless the agent has detected an ICE restart from the offer, the 3.4.1.5. Procedures for Lite Implementations
username fragments, password, and implementation level MUST remain
the same as used previously. If an agent needs to change one of
these it MUST restart ICE for that media stream by generating an
offer; ICE cannot be restarted in an answer.
Additional behaviors depend on the state of ICE processing for that If the ICE state is running, a lite implementation MUST include all
media stream. of its candidates for each component of each data stream in
a=candidate attribute in any subsequent offer. The candidates are
formed identical to the procedures for initial offers.
4.2.2.2.1. Existing Media Streams with ICE Running and no remote- A lite implementation MUST NOT add additional host candidates or
candidates change username fragments, password in a subsequent offer.
Otherwise, it MUST restart ICE.
If ICE is running for a media stream, and the offer for that media If ICE has completed for a data stream and if the agent is
stream lacked the remote-candidates attribute, the rules for controlled, the default destination for that data stream MUST be set
construction of the answer are identical to those for the offerer as to the remote candidate of the candidate pair for that component in
described in Section 4.2.1.2.1. 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
stream. Additionally, the agent MUST include a candidate attribute
for each default destination.
4.2.2.2.2. Existing Media Streams with ICE Completed and no remote- If ICE state is completed and if the agent is controlling (which only
candidates happens when both agents are lite), the agent MUST include the
a=remote-candidates attribute for each data stream. The attribute
contains the remote candidates from the candidate pairs in the valid
list (one pair for each component of each data stream).
If ICE is Completed for a media stream, and the offer for that media 3.4.2. Sending Subsequent Answer
stream lacked the remote-candidates attribute, the rules for
construction of the answer are identical to those for the offerer as
described in Section 4.2.1.2.2, except that the answerer MUST NOT
include the a=remote-candidates attribute in the answer.
4.2.2.2.3. Existing Media Streams and remote-candidates If ICE is Completed for a data stream, and the offer for that data
stream lacked the a=remote-candidates attribute, the rules for
construction of the answer are identical to those for the offerer,
except that the answerer MUST NOT include the a=remote-candidates
attribute in the answer.
A controlled agent will receive an offer with the a=remote-candidates A controlled agent will receive an offer with the a=remote-candidates
attribute for a media stream when its peer has concluded ICE attribute for a data stream when its peer has concluded ICE
processing for that media stream. This attribute is present in the processing for that data stream. This attribute is present in the
offer to deal with a race condition between the receipt of the offer, offer to deal with a race condition between the receipt of the offer,
and the receipt of the Binding Response that tells the answerer the and the receipt of the Binding Response that tells the answerer the
candidate that will be selected by ICE. See Appendix B for an candidate that will be selected by ICE. See Appendix B for an
explanation of this race condition. Consequently, processing of an explanation of this race condition. Consequently, processing of an
offer with this attribute depends on the winner of the race. offer with this attribute depends on the winner of the race.
The agent forms a candidate pair for each component of the media The agent forms a candidate pair for each component of the data
stream by: stream by:
o Setting the remote candidate equal to the offerer's default o Setting the remote candidate equal to the offerer's default
destination for that component (e.g., the contents of the "m=" and destination for that component (e.g., the contents of the "m=" and
"c=" lines for RTP, and the a=rtcp attribute for RTCP) "c=" lines for RTP, and the a=rtcp attribute for RTCP)
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 check list 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 media 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.
4.2.2.3. Procedures for Lite Implementations 3.4.2.1. Detecting ICE Restart
If the offerer in a subsequent offer requested an ICE restart for a
data stream, and if the answerer accepts the offer, the answerer
follows the procedures for generating an initial answer.
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
SDP ice-pwd and ice-ufrag attribute values.
3.4.2.2. 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
media stream, the agent forms a candidate pair for each component of data stream, the agent forms a candidate pair for each component of
the media 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 (e.g., the contents of the "m=" and destination for that component (e.g., the contents of the "m=" and
"c=" lines for RTP, and the a=rtcp attribute for RTCP). "c=" lines for RTP, and the a=rtcp attribute for RTCP).
o Setting the local candidate equal to the transport address for o Setting the local candidate equal to the transport address for
that same component in the a=remote-candidates attribute in the that same component in the a=remote-candidates attribute in the
offer. offer.
It then places those candidates into the Valid list for the media The state of ICE processing for that data stream is set to Completed.
stream. The state of ICE processing for that media 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 remote-candidates attribute, both agents believe they contained the a=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.
offer/answer exchanges will have resolved this glare condition, so
that one agent is always the 'winner' by having its offer received However, the signaling protocol carrying the offer/answer exchanges
before its peer has sent an offer. The winner takes the role of will have resolved this glare condition, so that one agent is always
controlling, so that the loser (the answerer under consideration in the 'winner' by having its offer received before its peer has sent an
this section) MUST change its role to controlled. Consequently, if offer. The winner takes the role of controlling, so that the loser
the agent was going to send an updated offer since, based on the (the answerer under consideration in this section) MUST change its
rules in section 8.2 of [ICE-BIS], it was controlling, it no longer role to controlled.
needs to.
Consequently, if the agent was going to send an updated offer since,
based on the rules in section 8.2 of [ICE-BIS], it was controlling,
it no longer 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.
Section 4.2.1.3.
4.2.3. Receiving the Answer for a Subsequent Offer 3.4.3. Receiving Answer for a Subsequent Offer
Some deployments of ICE include e.g. SDP-Modifying Signaling-only 3.4.3.1. Procedures for Full Implementations
Back-to-Back User Agents (B2BUAs) [RFC7092] that modify the SDP body
during the subsequent offer/answer exchange. With the B2BUA being
ICE-unaware, a subsequent answer might be manipulated and might not
include ICE candidates although the initial answer did.
An example of a situation where such an "unexpected" answer might be There may be certain situations where the offerer might receive SDP
experienced appears when such a B2BUA introduces a media server answer that lacks ICE candidates although the initial answer did.
during call hold using 3rd party call-control procedures. Omitting One example of such an "unexpected" answer might be happen when a
further details how this is done this could result in an answer being ICE-unaware B2BUA introduces a media server during call hold using
received at the holding UA that was constructed by the B2BUA. With 3rd party call-control procedures. Omitting further details how this
the B2BUA being ICE-unaware, that answer would not include ICE is done, this could result in an answer being received at the holding
candidates. UA that was constructed by the B2BUA. With the B2BUA being ICE-
unaware, that 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.
In addition to procedures for the expected answer, the following When the offerer receives an answer indicating support for ICE, the
section advices on how to recover from the unexpected situation. offer performs on of the following actions:
4.2.3.1. Procedures for All Implementations
When receiving an answer within an existing session for a subsequent
offer as specified in Section 4.2.1.2.2, an agent MUST verify ICE
support as specified in Section 4.1.3.1.
If ICE support is indicated in the SDP answer and the offer was a
restart, the agent MUST perform ICE restart procedures as specified
in Section 4.2.4. If ICE support is no longer indicated in the SDP
answer, the agent MUST fall-back to [RFC3264] procedures and SHOULD
NOT drop the dialog just because of missing ICE support. If the
agent sends a new offer later on, it SHOULD perform an ICE restart as
specified in Section 4.2.1.1.1.
If ICE support is indicated in the SDP answer and ICE is running, the
agent MUST continue ICE procedures as specified in Section 4.2.4.1.4.
If ICE support is no longer indicated in the SDP answer, the agent
MUST abort the ongoing ICE processing and fall-back to [RFC3264]
procedures. The agent SHOULD NOT drop the dialog just because of
missing ICE support. If the agent sends a new offer later on, it
SHOULD perform an ICE restart as specified in Section 4.2.1.1.1.
If ICE support is indicated in the SDP answer and if ICE is completed
and the answer conforms to Section 4.2.2.2.3, the agent MUST remain
in the ICE Completed state. If ICE support is no longer indicated in
the SDP answer, the agent MUST fall-back to [RFC3264] procedures and
SHOULD NOT drop the dialog just because of this unexpected answer.
Once the agent sends a new offer later on it MUST perform an ICE
restart.
4.2.4. Updating the Check and Valid Lists
4.2.4.1. Procedures for Full Implementations
4.2.4.1.1. ICE Restarts
The agent MUST remember the highest-priority nominated pairs in the
Valid list for each component of the media stream, called the
previous selected pairs, prior to the restart. The agent will
continue to send media using these pairs, as described in
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
states as described in section 6.1.2 of [ICE-BIS].
4.2.4.1.2. New Media Stream o If the offer was a restart, the agent MUST perform ICE restart
procedures as specified in Section 3.4.3.1.1
If the offer/answer exchange added a new media stream, the agent MUST o If the offer/answer exchange removed a data stream, or an answer
create a new check list for it (and an empty Valid list to start of rejected an offered data stream, an agent MUST flush the Valid
course), as described in section 6.1.2 of [ICE-BIS]. list for that data stream. It MUST also terminate any STUN
transactions in progress for that data stream.
4.2.4.1.3. Removed Media Stream 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
start of course) which in turn triggers the candidate processing
procedures [ICE-BIS].
If the offer/answer exchange removed a media stream, or an answer o If ICE state is running for a given data stream, the agent
rejected an offered media stream, an agent MUST flush the Valid list recomputes the check list. If a pair on the new check list was
for that media stream. It MUST terminate any STUN transactions in also on the previous check list, and its state was Waiting, In-
progress for that media stream. An agent MUST remove the check list Progress, Succeeded, or Failed, its state is copied over.
for that media stream and cancel any pending ordinary checks for it. Otherwise, its state is set to Frozen. If none of the check lists
are active (meaning that the pairs in each check list are Frozen),
appropriate procedures in [ICE-BIS] are performed to move
candidate(s) to the Waiting state to further continue ICE
processing.
4.2.4.1.4. ICE Continuing for Existing Media Stream o If ICE state is completed and the SDP answer conforms to
Section 3.4.2, the agent MUST reman in the ICE completed state.
The valid list is not affected by an updated offer/answer exchange However, if the ICE support is no longer indicated in the SDP answer,
unless ICE is restarting. the agent MUST fall-back to [RFC3264] procedures and SHOULD NOT drop
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
restart.
If an agent is in the Running state for that media stream, the check 3.4.3.1.1. ICE Restarts
list is updated (the check list is irrelevant if the state is
completed). To do that, the agent recomputes the check list using
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
was Waiting, In-Progress, Succeeded, or Failed, its state is copied
over. Otherwise, its state is set to Frozen.
If none of the check lists are active (meaning that the pairs in each The agent MUST remember the nominated pair in the Valid list for each
check list are Frozen), the full-mode agent follows steps in component of the data stream, called the previous selected pair prior
Section 6.1.2.6 of [ICE-BIS] to place appropriate candidates in the to the restart. The agent will continue to send media using this
Waiting state to further continue ICE processing. pair, as described in section 12 of [ICE-BIS]. Once these
destinations are noted, the agent MUST flush the valid and check
lists, and then recompute the check list and its states, thus
triggering the candidate processing procedures [ICE-BIS]
4.2.4.2. Procedures for Lite Implementations 3.4.3.2. Procedures for Lite Implementations
If ICE is restarting for a media stream, the agent MUST start a new If ICE is restarting for a data stream, the agent MUST start a new
Valid list for that media stream. It MUST remember the pairs in the Valid list for that data stream. It MUST remember the nominated pair
previous Valid list for each component of the media stream, called in the previous Valid list for each component of the data stream,
the previous selected pairs, and continue to send media there as called the previous selected pairs, and continue to send media there
described in Section 7.1. The state of ICE processing for each media as described in section 12 of [ICE-BIS]. The state of ICE processing
stream MUST change to Running, and the state of ICE processing MUST for each data stream MUST change to Running, and the state of ICE
change to Running. processing MUST change to Running
5. Grammar 4. 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. This ufrag", "ice-pwd", "ice-pacing", and "ice-options" attributes.
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].
5.1. "candidate" Attribute 4.1. "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
skipping to change at page 20, line 8 skipping to change at page 17, line 8
the candidate pair to be matched against destination addresses the candidate pair to be matched against destination addresses
reported by FQDN, in cases where the DNS query returns more than reported by FQDN, in cases where the DNS query returns more than
one IP address. one IP address.
<port>: is also taken from RFC 4566 [RFC4566]. It is the port of <port>: is also taken from RFC 4566 [RFC4566]. It is the port of
the candidate. the candidate.
<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 by extending the sub-registry "ICE Transport Protocols" under
[RFC4340]. "Interactive Connectivity Establishment (ICE)" registry.
<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 6.1.2 of [ICE-BIS] Frozen algorithm as described in [ICE-BIS]
<component-id>: is a positive integer between 1 and 256 that <component-id>: is a positive integer between 1 and 256 (inclusive)
identifies the specific component of the media stream for which that identifies the specific component of the dta 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 data 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 14 in [ICE-BIS] for additional discussion on ID of 2. See section 13 in [ICE-BIS] for additional discussion on
extending ICE to new media streams. extending ICE to new data streams.
<priority>: is a positive integer between 1 and (2**31 - 1). The <priority>: is a positive integer between 1 and (2**31 - 1)
procedures for computing candidate's priority is described in inclusive. The procedures for computing candidate's priority is
section 5.1.2 of [ICE-BIS]. described in 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. Specifications for new candidate types MUST define
future. how, if at all, various steps in the ICE processing differ from
the ones defined by this specification.
<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
reflexive, and relayed candidates. If a candidate is server or reflexive, and relayed candidates. If a candidate is server or
peer reflexive, <rel-addr> and <rel-port> are equal to the base peer reflexive, <rel-addr> and <rel-port> are equal to the base
for that server or peer reflexive candidate. If the candidate is for that server or peer reflexive candidate. If the candidate is
relayed, <rel-addr> and <rel-port> are equal to the mapped address relayed, <rel-addr> and <rel-port> are equal to the mapped address
in the Allocate response that provided the client with that in the Allocate response that provided the client with that
relayed candidate (see section Appendix B.3 of [ICE-BIS] for a relayed candidate (see section Appendix B.3 of [ICE-BIS] for a
discussion of its purpose). If the candidate is a host candidate, discussion of its purpose). If the candidate is a host candidate,
<rel-addr> and <rel-port> MUST be omitted. <rel-addr> and <rel-port> MUST be omitted.
In some cases, e.g., for privacy reasons, an agent may not want to In some cases, e.g., for privacy reasons, an agent may not want to
reveal the related address and port. In this case the address reveal the related address and port. In this case the address
MUST be set to "0.0.0.0" (for IPv4 candidates) or "::" (for IPv6 MUST be set to "0.0.0.0" (for IPv4 candidates) or "::" (for IPv6
candidates) and the port to zero. candidates) and the port to zero.
The candidate attribute can itself be extended. The grammar allows The candidate attribute can itself be extended. The grammar allows
for new name/value pairs to be added at the end of the attribute. An for new name/value pairs to be added at the end of the attribute.
implementation MUST ignore any name/value pairs it doesn't Such extensions MUST be made through IETF Review or IESG Approval
[RFC5226] and the assignments MUST contain the specific extension and
a reference to the document defining the usage of the extension
An implementation MUST ignore any name/value pairs it doesn't
understand. understand.
Example: SDP line for UDP server reflexive candidate attribute for the RTP component Example: SDP line for UDP server reflexive candidate attribute for the RTP component
a=candidate:2 1 UDP 1694498815 192.0.2.3 45664 typ a=candidate:2 1 UDP 1694498815 192.0.2.3 45664 typ
srflx raddr 10.0.1.1 rport 8998 srflx raddr 10.0.1.1 rport 8998
5.2. "remote-candidates" Attribute 4.2. "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
component. The ordering of components is irrelevant. However, a component. The ordering of components is irrelevant. However, a
value MUST be present for each component of a media stream. This value MUST be present for each component of a 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
media 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
5.3. "ice-lite" and "ice-mismatch" Attributes 4.3. "ice-lite" and "ice-mismatch" Attributes
The syntax of the "ice-lite" and "ice-mismatch" attributes, both of The syntax of the "ice-lite" and "ice-mismatch" attributes, both of
which are flags, is: which are flags, is:
ice-lite = "ice-lite" ice-lite = "ice-lite"
ice-mismatch = "ice-mismatch" ice-mismatch = "ice-mismatch"
"ice-lite" is a session-level attribute only, and indicates that an "ice-lite" is a session-level attribute only, and indicates that an
agent is a lite implementation. "ice-mismatch" is a media-level agent is a lite implementation. "ice-mismatch" is a media-level
attribute only, and when present in an answer, indicates that the attribute only, and when present in an answer, indicates that the
offer arrived with a default destination for a media component that offer arrived with a default destination for a media component that
didn't have a corresponding candidate attribute. didn't have a corresponding candidate attribute.
5.4. "ice-ufrag" and "ice-pwd" Attributes 4.4. "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
session-level or media-level. When present in both, the value in the session-level or media-level. When present in both, the value in the
media-level takes precedence. Thus, the value at the session-level media-level takes precedence. Thus, the value at the session-level
is effectively a default that applies to all media streams, unless is effectively a default that applies to all data streams, unless
overridden by a media-level value. Whether present at the session or overridden by a media-level value. Whether present at the session or
media-level, there MUST be an ice-pwd and ice-ufrag attribute for media-level, there MUST be an ice-pwd and ice-ufrag attribute for
each media stream. If two media streams have identical ice-ufrag's, each data stream. If two data streams have identical ice-ufrag's,
they MUST have identical ice-pwd's. they MUST have identical ice-pwd's.
The ice-ufrag and ice-pwd attributes MUST be chosen randomly at the The ice-ufrag and ice-pwd attributes MUST be chosen randomly at the
beginning of a session. The ice-ufrag attribute MUST contain at beginning of a session (the same applies when ICE is restarting for
least 24 bits of randomness, and the ice-pwd attribute MUST contain an agent.).
at least 128 bits of randomness. This means that the ice-ufrag
attribute will be at least 4 characters long, and the ice-pwd at The ice-ufrag attribute MUST contain at least 24 bits of randomness,
least 22 characters long, since the grammar for these attributes and the ice-pwd attribute MUST contain at least 128 bits of
allows for 6 bits of information per character. The attributes MAY randomness. This means that the ice-ufrag attribute will be at least
be longer than 4 and 22 characters, respectively, of course, up to 4 characters long, and the ice-pwd at least 22 characters long, since
256 characters. The upper limit allows for buffer sizing in the grammar for these attributes allows for 6 bits of information per
implementations. Its large upper limit allows for increased amounts character. The attributes MAY be longer than 4 and 22 characters,
of randomness to be added over time. For compatibility with the 512 respectively, of course, up to 256 characters. The upper limit
character limitation for the STUN username attribute value and for allows for buffer sizing in implementations. Its large upper limit
bandwidth conservation considerations, the ice-ufrag attribute MUST allows for increased amounts of randomness to be added over time.
NOT be longer than 32 characters when sending, but an implementation For compatibility with the 512 character limitation for the STUN
MUST accept up to 256 characters when receiving. username attribute value and for bandwidth conservation
considerations, the ice-ufrag attribute MUST NOT be longer than 32
characters when sending, but an implementation 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 4.5. "ice-pacing" Attribute
The "ice-pacing" attribute indicates the desired connectivity check The "ice-pacing" is a session level attribute that indicates the
pacing, in milliseconds, for this agent (see section 15 of desired connectivity check pacing, in milliseconds, for this agent
[ICE-BIS]). The syntax is: (see section 14 of [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
Following the procedures defined in [ICE-BIS], a default value of
50ms is used for an agent when ice-pacing attribute is omitted in the
offer or the answer.
The same rule applies for ice-pacing attribute values lower than
50ms. This mandates that, if an agent includes the ice-pacing
attribute, its value MUST be greater than 50ms or else a value of
50ms is considered by default for that agent.
Also the larger of the ice-pacing attribute values between the offer
and the answer (determined either by the one provided in the ice-
pacing attribute or by picking the default value) MUST be considered
for a given ICE session.
The mux category [I-D.ietf-mmusic-sdp-mux-attributes] for the 'ice-
pacing' attribute is 'TRANSPORT'.
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 4.6. "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 is willing to use it, if the extension is supported by the agent and is willing to use it, if the
peer agent also includes the same extension in the answer. There peer agent also includes the same extension in the answer. There
might be further extension specific negotiations needed between the might be further extension specific negotiations needed between the
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 (see
Section 10.2).
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 5. 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 [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 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 each peer supports ICE by the presence of a=candidate attributes for each
media session. media session.
7. Media Handling 6. SIP Considerations
7.1. Sending Media
The selected pair for a component of a media stream might not equal
the default pair for that same component from the most recent offer/
answer exchange. When this happens, the selected pair is used for
media, not the default pair. When ICE first completes, if the
selected pairs aren't a match for the default pairs, the controlling
agent sends an updated offer/answer exchange to remedy this
disparity. However, until that updated offer arrives, there will not
be a match. Furthermore, in very unusual cases, the default
candidates in the updated offer/answer will not be a match.
7.1.1. Procedures for All Implementations
Section 12.1.3 of [ICE-BIS] defines procedures for sending media
common across Full and Lite implementations.
7.2. Receiving Media
See section 12.2 of [ICE-BIS] for procedures on receiving media.
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/
answer exchange, with its own set of local candidates, pairs, check answer exchange, with its own set of local candidates, pairs, check
lists, states, and so on. lists, states, and so on.
Once ICE processing has reached the Completed state for all peers for Once ICE processing has reached the Completed state for all peers for
media streams using those candidates, the agent SHOULD wait an media streams using those candidates, the agent SHOULD wait an
additional three seconds, and then it MAY cease responding to checks additional three seconds, and then it MAY cease responding to checks
or generating triggered checks on that candidate. It MAY free the or generating triggered checks on that candidate. It MAY free the
candidate at that time. Freeing of server reflexive candidates is candidate at that time. Freeing of server reflexive candidates is
never explicit; it happens by lack of a keepalive. The three-second never explicit; it happens by lack of a keepalive. The three-second
delay handles cases when aggressive nomination is used, and the delay handles cases when aggressive nomination is used, and the
selected pairs can quickly change after ICE has completed. selected pairs can quickly change after ICE has completed.
8.1. Latency Guidelines 6.1. 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.
8.1.1. Offer in INVITE 6.1.1. Offer in INVITE
To reduce post-dial delays, it is RECOMMENDED that the caller begin To reduce post-dial delays, it is RECOMMENDED that the caller begin
gathering candidates prior to actually sending its initial INVITE. gathering candidates prior to actually sending its initial INVITE.
This can be started upon user interface cues that a call is pending, This can be started upon user interface cues that a call is pending,
such as activity on a keypad or the phone going off-hook. such as activity on a keypad or the phone going off-hook.
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 once it has compelted candidate gathering. in a provisional response once it has completed candidate gathering.
ICE requires that a provisional response with an SDP be transmitted ICE requires that a provisional response with an SDP be transmitted
reliably. This can be done through the existing Provisional Response reliably. This can be done through the existing Provisional Response
Acknowledgment (PRACK) mechanism [RFC3262] or through an ICE specific Acknowledgment (PRACK) mechanism [RFC3262] or through an ICE specific
optimization, wherein, the agent retransmits the provisional response optimization, wherein, the agent retransmits the provisional response
with the exponential backoff timers described in [RFC3262]. Such with the exponential backoff timers described in [RFC3262]. Such
retransmissions MUST cease on receipt of a STUN Binding request for retransmissions MUST cease on receipt of a STUN Binding request for
one of the media streams signaled in that SDP or on transmission of one of the data streams signaled in that SDP or on transmission of
the answer in a 2xx response. If no Binding request is received the answer in a 2xx response. If no Binding request is received
prior to the last retransmit, the agent does not consider the session prior to the last retransmit, the agent does not consider the session
terminated. For the ICE lite peers, the agent MUST cease terminated. For the ICE lite peers, the agent MUST cease
retransmitting the 18x after sending it four times (ICE will actually retransmitting the 18x after sending it four times (ICE will actually
work even if the peer never receives the 18x; however, experience has work even if the peer never receives the 18x; however, experience has
shown that sending it is important for middleboxes and firewall shown that sending it is important for middleboxes and firewall
traversal). traversal).
It should be noted that the ICE specific optimization is very It should be noted that the ICE specific optimization is very
specific to provisional response carrying answers that start ICE specific to provisional response carrying answers that start ICE
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appears in all of the 1xx and in the 2xx response to the INVITE. appears in all of the 1xx and in the 2xx response to the INVITE.
Only after that 2xx has been sent can an updated offer/answer Only after that 2xx has been sent can an updated offer/answer
exchange occur. exchange occur.
Alternatively, an agent MAY delay sending an answer until the 200 OK; Alternatively, an agent MAY delay sending an answer until the 200 OK;
however, this results in a poor user experience and is NOT however, this results in a poor user experience and is NOT
RECOMMENDED. RECOMMENDED.
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
media stream enter the valid list, the answerer can begin sending data stream enter the valid list, the answerer can begin sending
media on that media 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 media the called party until candidates for each component of each data
stream have entered the valid list. In the case of a PSTN gateway, stream have entered the valid list. In the case of a PSTN gateway,
this would mean that the setup message into the PSTN is delayed until this would mean that the setup message into the PSTN is delayed until
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.
8.1.2. Offer in Response 6.1.2. 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 26, line 45 skipping to change at page 23, line 48
answer. The 200 OK would contain no SDP, since the offer/answer answer. The 200 OK would contain no SDP, since the offer/answer
exchange has completed. exchange has completed.
Alternatively, agents MAY place the offer in a 2xx instead (in which Alternatively, agents MAY place the offer in a 2xx instead (in which
case the answer comes in the ACK). When this happens, the callee case the answer comes in the ACK). When this happens, the callee
will alert the user on receipt of the INVITE, and the ICE exchanges will alert the user on receipt of the INVITE, and the ICE exchanges
will take place only after the user answers. This has the effect of will take place only after the user answers. This has the effect of
reducing call setup delay, but can cause substantial post-pickup reducing call setup delay, but can cause substantial post-pickup
delays and media clipping. delays and media clipping.
8.2. SIP Option Tags and Media Feature Tags 6.2. 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.
8.3. Interactions with Forking 6.3. Interactions with Forking
ICE interacts very well with forking. Indeed, ICE fixes some of the ICE interacts very well with forking. Indeed, ICE fixes some of the
problems associated with forking. Without ICE, when a call forks and problems associated with forking. Without ICE, when a call forks and
the caller receives multiple incoming media streams, it cannot the caller receives multiple incoming data streams, it cannot
determine which media 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.
8.4. Interactions with Preconditions 6.4. 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 8.1 describe their own Note that the procedures described in Section 6.1 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].
8.5. Interactions with Third Party Call Control 6.5. 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 media 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.
9. Relationship with ANAT 7. Relationship with ANAT
[RFC4091], the Alternative Network Address Types (ANAT) Semantics for [RFC4091], the Alternative Network Address Types (ANAT) Semantics for
the SDP grouping framework, and [RFC4092], its usage with SIP, define the SDP grouping framework, and [RFC4092], its usage with SIP, define
a mechanism for indicating that an agent can support both IPv4 and a mechanism for indicating that an agent can support both IPv4 and
IPv6 for a media stream, and it does so by including two "m=" lines, 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 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 8. Setting Ta and RTO for RTP Media Streams
During the gathering phase of ICE (section 5.1.1 [ICE-BIS]) and while During the gathering phase of ICE and while ICE is performing
ICE is performing connectivity checks (section 7 [ICE-BIS]), an agent connectivity checks, an agent sends STUN and TURN transactions.
sends STUN and TURN transactions. These transactions are paced at a These transactions are paced at a rate of one every Ta milliseconds,
rate of one every Ta milliseconds, and utilize a specific RTO. See and utilize a specific RTO. See Section 14 of [ICE-BIS] for details
Section 15 of [ICE-BIS] for details on how the values of Ta and RTO on how the values of Ta and RTO are computed with a real-time media
are computed with a real-time media stream of known maximum bandwidth stream of known maximum bandwidth to rate-control the ICE exchanges.
to rate-control the ICE exchanges.
11. Security Considerations 9. Security Considerations
11.1. Attacks on the Offer/Answer Exchanges 9.1. Attacks on the Offer/Answer Exchanges
An attacker that can modify or disrupt the offer/answer exchanges An attacker that can modify or disrupt the offer/answer exchanges
themselves can readily launch a variety of attacks with ICE. They themselves can readily launch a variety of attacks with ICE. They
could direct media to a target of a DoS attack, they could insert could direct media to a target of a DoS attack, they could insert
themselves into the media stream, and so on. These are similar to themselves into the data stream, and so on. These are similar to the
the general security considerations for offer/answer exchanges, and general security considerations for offer/answer exchanges, and the
the security considerations in [RFC3264] apply. These require security considerations in [RFC3264] apply. These require techniques
techniques for message integrity and encryption for offers and for message integrity and encryption for offers and answers, which
answers, which are satisfied by the TLS mechanism [RFC3261] when SIP are satisfied by the TLS mechanism [RFC3261] when SIP is used. As
is used. As such, the usage of TLS with ICE is RECOMMENDED. such, the usage of TLS with ICE is RECOMMENDED.
11.2. Insider Attacks 9.2. Insider Attacks
In addition to attacks where the attacker is a third party trying to In addition to attacks where the attacker is a third party trying to
insert fake offers, answers, or STUN messages, there are several insert fake offers, answers, or STUN messages, there are several
attacks possible with ICE when the attacker is an authenticated and attacks possible with ICE when the attacker is an authenticated and
valid participant in the ICE exchange. valid participant in the ICE exchange.
11.2.1. The Voice Hammer Attack 9.2.1. The Voice Hammer Attack
The voice hammer attack is an amplification attack. In this attack, The voice hammer attack is an amplification attack. In this attack,
the attacker initiates sessions to other agents, and maliciously the attacker initiates sessions to other agents, and maliciously
includes the IP address and port of a DoS target as the destination includes the IP address and port of a DoS target as the destination
for media traffic signaled in the SDP. This causes substantial for media traffic signaled in the SDP. This causes substantial
amplification; a single offer/answer exchange can create a continuing amplification; a single offer/answer exchange can create a continuing
flood of media packets, possibly at high rates (consider video flood of media packets, possibly at high rates (consider video
sources). This attack is not specific to ICE, but ICE can help sources). This attack is not specific to ICE, but ICE can help
provide remediation. provide remediation.
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However, in environments where the set of clients is known, and is However, in environments where the set of clients is known, and is
limited to ones that support ICE, the server can reject any offers or limited to ones that support ICE, the server can reject any offers or
answers that don't indicate ICE support. answers that don't indicate ICE support.
User Agents that are not willing to receive non-ICE answers MUST User Agents that are not willing to receive non-ICE answers MUST
include an "ice" Option Tag in the Require Header Field in their include an "ice" Option Tag in the Require Header Field in their
offer. Clients that rejects non-ICE offers SHOULD use a 421 response offer. Clients that rejects non-ICE offers SHOULD use a 421 response
code, together with an Option Tag "ice" in the Require Header Field code, together with an Option Tag "ice" in the Require Header Field
in the response. in the response.
11.2.2. Interactions with Application Layer Gateways and SIP 9.2.2. 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
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will appear to both endpoints as if the other side doesn't support will appear to both endpoints as if the other side doesn't support
ICE. This will result in ICE being disabled, and media flowing ICE. This will result in ICE being disabled, and media flowing
through the SBC, if the SBC has requested it. If, however, the SBC through the SBC, if the SBC has requested it. If, however, the SBC
passes the ICE attributes without modification, yet modifies the passes the ICE attributes without modification, yet modifies the
default destination for media (contained in the "m=" and "c=" lines default destination for media (contained in the "m=" and "c=" lines
and rtcp attribute), this will be detected as an ICE mismatch, and and rtcp attribute), this will be detected as an ICE mismatch, and
ICE processing is aborted for the call. It is outside of the scope ICE processing is aborted for the call. It is outside of the scope
of ICE for it to act as a tool for "working around" SBCs. If one is of ICE for it to act as a tool for "working around" SBCs. If one is
present, ICE will not be used and the SBC techniques take precedence. present, ICE will not be used and the SBC techniques take precedence.
12. IANA Considerations 10. IANA Considerations
12.1. SDP Attributes 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 is reproduced here. information from the original specification is included here with
modifications to include Mux Category and to align with the recent
12.1.1. candidate Attribute recommendations for populating Contact information.
Contact Name: Jonathan Rosenberg, jdrosen@jdrosen.net. 10.1.1. candidate Attribute
Attribute Name: candidate Attribute Name: candidate
Long Form: candidate
Type of Attribute: media-level Type of Attribute: media-level
Charset Considerations: The attribute is not subject to the charset Subject to charset: No
attribute.
Purpose: This attribute is used with Interactive Connectivity Purpose: This attribute is used with Interactive Connectivity
Establishment (ICE), and provides one of many possible candidate Establishment (ICE), and provides one of many possible candidate
addresses for communication. These addresses are validated with addresses for communication. These addresses are validated with
an end-to-end connectivity check using Session Traversal Utilities an end-to-end connectivity check using Session Traversal Utilities
for NAT (STUN). for NAT (STUN).
Appropriate Values: See Section 5 of RFC XXXX. Appropriate Values: See Section 4 of RFC XXXX.
12.1.2. remote-candidates Attribute Contact Name: IESG
Contact Name: Jonathan Rosenberg, jdrosen@jdrosen.net. Contact e-mail: iesg@ietf.org [1]
Attribute Name: remote-candidates Reference: RFCXXXX
Long Form: remote-candidates Mux Category: TRANSPORT
10.1.2. remote-candidates Attribute
Attribute Name: remote-candidates
Type of Attribute: media-level Type of Attribute: media-level
Charset Considerations: The attribute is not subject to the charset Subject to charset: No
attribute.
Purpose: This attribute is used with Interactive Connectivity Purpose: This attribute is used with Interactive Connectivity
Establishment (ICE), and provides the identity of the remote Establishment (ICE), and provides the identity of the remote
candidates that the offerer wishes the answerer to use in its candidates that the offerer wishes the answerer to use in its
answer. answer.
Appropriate Values: See Section 5 of RFC XXXX. Appropriate Values: See Section 4 of RFC XXXX.
12.1.3. ice-lite Attribute Contact Name: IESG
Contact Name: Jonathan Rosenberg, jdrosen@jdrosen.net. Contact e-mail: iesg@ietf.org [2]
Reference: RFCXXXX
Mux Category: TRANSPORT
10.1.3. ice-lite Attribute
Attribute Name: ice-lite Attribute Name: ice-lite
Long Form: ice-lite
Type of Attribute: session-level Type of Attribute: session-level
Charset Considerations: The attribute is not subject to the charset Subject to charset: No
attribute.
Purpose: This attribute is used with Interactive Connectivity Purpose: This attribute is used with Interactive Connectivity
Establishment (ICE), and indicates that an agent has the minimum Establishment (ICE), and indicates that an agent has the minimum
functionality required to support ICE inter-operation with a peer functionality required to support ICE inter-operation with a peer
that has a full implementation. that has a full implementation.
Appropriate Values: See Section 5 of RFC XXXX. Appropriate Values: See Section 4 of RFC XXXX.
12.1.4. ice-mismatch Attribute Contact Name: IESG
Contact Name: Jonathan Rosenberg, jdrosen@jdrosen.net. Contact e-mail: iesg@ietf.org [3]
Attribute Name: ice-mismatch Reference: RFCXXXX
Long Form: ice-mismatch Mux Category: NORMAL
Type of Attribute: session-level 10.1.4. ice-mismatch Attribute
Charset Considerations: The attribute is not subject to the charset Attribute Name: ice-mismatch
attribute.
Type of Attribute: media-level
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 5 of RFC XXXX. Appropriate Values: See Section 4 of RFC XXXX.
12.1.5. ice-pwd Attribute Contact Name: IESG
Contact Name: Jonathan Rosenberg, jdrosen@jdrosen.net. Contact e-mail: iesg@ietf.org [4]
Attribute Name: ice-pwd Reference: RFCXXXX
Long Form: ice-pwd Mux Category: NORMAL
10.1.5. ice-pwd Attribute
Attribute Name: ice-pwd
Type of Attribute: session- or media-level Type of Attribute: session- or media-level
Charset Considerations: The attribute is not subject to the charset Subject to charset: No
attribute.
Purpose: This attribute is used with Interactive Connectivity Purpose: This attribute is used with Interactive Connectivity
Establishment (ICE), and provides the password used to protect Establishment (ICE), and provides the password used to protect
STUN connectivity checks. STUN connectivity checks.
Appropriate Values: See Section 5 of RFC XXXX. Appropriate Values: See Section 4 of RFC XXXX.
12.1.6. ice-ufrag Attribute Contact Name: IESG
Contact Name: Jonathan Rosenberg, jdrosen@jdrosen.net. Contact e-mail: iesg@ietf.org [5]
Attribute Name: ice-ufrag Reference: RFCXXXX
Long Form: ice-ufrag Mux Category: TRANSPORT
10.1.6. ice-ufrag Attribute
Attribute Name: ice-ufrag
Type of Attribute: session- or media-level Type of Attribute: session- or media-level
Charset Considerations: The attribute is not subject to the charset Subject to charset: No
attribute.
Purpose: This attribute is used with Interactive Connectivity Purpose: This attribute is used with Interactive Connectivity
Establishment (ICE), and provides the fragments used to construct Establishment (ICE), and provides the fragments used to construct
the username in STUN connectivity checks. the username in STUN connectivity checks.
Appropriate Values: See Section 5 of RFC XXXX. Appropriate Values: See Section 4 of RFC XXXX.
12.1.7. ice-pacing Attribute Contact Name: IESG
Contact Name: Jonathan Rosenberg, jdrosen@jdrosen.net. Contact e-mail: iesg@ietf.org [6]
Attribute Name: ice-pacing Reference: RFCXXXX
Long Form: ice-pacing Mux Category: TRANSPORT
Type of Attribute: session-level 10.1.7. ice-options Attribute
Charset Considerations: The attribute is not subject to the charset Attribute Name: ice-options
attribute.
Long Form: ice-options
Type of Attribute: session- or media-level
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), and indicates the ICE options or extensions
values. used by the agent.
Appropriate Values: See Section 5 of RFC XXXX. Appropriate Values: See Section 4 of RFC XXXX.
12.1.8. ice-options Attribute Contact Name: IESG
Contact Name: Jonathan Rosenberg, jdrosen@jdrosen.net. Contact e-mail: iesg@ietf.org [7]
Attribute Name: ice-options Reference: RFCXXXX
Long Form: ice-options Mux Category: NORMAL
Type of Attribute: session- or media-level
Charset Considerations: The attribute is not subject to the charset 10.1.8. ice-pacing Attribute
attribute.
This specification also defines a new SDP attribute, "ice-pacing"
according to the following data:
Attribute Name: ice-pacing
Type of Attribute: session-level
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) to indicate desired connectivity check pacing
used by the agent. values.
Appropriate Values: See Section 5 of RFC XXXX. Appropriate Values: See Section 4 of RFC XXXX.
12.2. Interactive Connectivity Establishment (ICE) Options Registry Contact Name: IESG
Contact e-mail: iesg@ietf.org [8]
Reference: RFCXXXX
Mux Category: TRANSPORT
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" [RFC5226]. an IANA Considerations Section in RFCs" [RFC5226].
ICE options are of unlimited length according to the syntax in ICE options are of unlimited length according to the syntax in
Section 5.6; however, they are RECOMMENDED to be no longer than 20 Section 4.6; however, they are RECOMMENDED to be no longer than 20
characters. This is to reduce message sizes and allow for efficient characters. This is to reduce message sizes and allow for efficient
parsing. parsing.
In [RFC5245] ICE options could only be defined at the session level. In [RFC5245] ICE options could only be defined at the session level.
ICE options can now also be defined at the media level. This can be ICE options can now also be defined at the media level. This can be
used when aggregating between different ICE agents in the same used when aggregating between different ICE agents in the same
endpoint, but future options may require to be defined at the media- endpoint, but future options may require to be defined at the media-
level. To ensure compatibility with legacy implementation, the level. To ensure compatibility with legacy implementation, the
media-level ICE options MUST be aggregated into a session-level ICE media-level ICE options MUST be aggregated into a session-level ICE
option. Because aggregation rules depend on the specifics of each option. Because aggregation rules depend on the specifics of each
skipping to change at page 35, line 4 skipping to change at page 32, line 41
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 10 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
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
13. 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.
Thanks to Thomas Stach for the text in Section 4.2.3, Roman Shpount Many thanks to Christer Holmberg for providing text suggestions in
for suggesting RTCP candidate handling in Section 4.1.1.2 and Simon Section 4 that aligns with [ICE-BIS]
Perreault for advising on IPV6 address selection when candidate-
address includes FQDN. 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.
Thanks to following experts for their reviews and constructive Thanks to following experts for their reviews and constructive
feedback: Christer Holmberg, Adam Roach and the MMUSIC WG. feedback: Christer Holmberg, Adam Roach and the MMUSIC WG.
14. References 12. References
14.1. Normative References 12.1. Normative References
[I-D.ietf-mmusic-sdp-mux-attributes]
Nandakumar, S., "A Framework for SDP Attributes when
Multiplexing", draft-ietf-mmusic-sdp-mux-attributes-17
(work in progress), February 2018,
<http://www.rfc-editor.org/info/rfc7656>.
[ICE-BIS] Keranen, A. and J. Rosenberg, "Interactive Connectivity [ICE-BIS] Keranen, A. and J. Rosenberg, "Interactive Connectivity
Establishment (ICE): A Protocol for Network Address Establishment (ICE): A Protocol for Network Address
Translator (NAT) Traversal for Offer/Answer Protocols", Translator (NAT) Traversal for Offer/Answer Protocols",
draft-ietf-ice-rfc5245bis-00 (work in progress), March draft-ietf-ice-rfc5245bis-00 (work in progress), March
2015. 2015.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997, DOI 10.17487/RFC2119, March 1997,
skipping to change at page 37, line 16 skipping to change at page 35, line 21
Specifications: ABNF", STD 68, RFC 5234, Specifications: ABNF", STD 68, RFC 5234,
DOI 10.17487/RFC5234, January 2008, DOI 10.17487/RFC5234, January 2008,
<http://www.rfc-editor.org/info/rfc5234>. <http://www.rfc-editor.org/info/rfc5234>.
[RFC5245] Rosenberg, J., "Interactive Connectivity Establishment [RFC5245] Rosenberg, J., "Interactive Connectivity Establishment
(ICE): A Protocol for Network Address Translator (NAT) (ICE): A Protocol for Network Address Translator (NAT)
Traversal for Offer/Answer Protocols", RFC 5245, 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>.
[RFC5389] Rosenberg, J., Mahy, R., Matthews, P., and D. Wing,
"Session Traversal Utilities for NAT (STUN)", RFC 5389,
DOI 10.17487/RFC5389, October 2008,
<http://www.rfc-editor.org/info/rfc5389>.
[RFC5768] Rosenberg, J., "Indicating Support for Interactive [RFC5768] Rosenberg, J., "Indicating Support for Interactive
Connectivity Establishment (ICE) in the Session Initiation Connectivity Establishment (ICE) in the Session Initiation
Protocol (SIP)", RFC 5768, DOI 10.17487/RFC5768, April Protocol (SIP)", RFC 5768, DOI 10.17487/RFC5768, April
2010, <http://www.rfc-editor.org/info/rfc5768>. 2010, <http://www.rfc-editor.org/info/rfc5768>.
[RFC6336] Westerlund, M. and C. Perkins, "IANA Registry for [RFC6336] Westerlund, M. and C. Perkins, "IANA Registry for
Interactive Connectivity Establishment (ICE) Options", Interactive Connectivity Establishment (ICE) Options",
RFC 6336, April 2010, RFC 6336, April 2010,
<http://www.rfc-editor.org/info/rfc6336>. <http://www.rfc-editor.org/info/rfc6336>.
[RFC6679] Westerlund, M., Johansson, I., Perkins, C., O'Hanlon, P., [RFC6679] Westerlund, M., Johansson, I., Perkins, C., O'Hanlon, P.,
and K. Carlberg, "Explicit Congestion Notification (ECN) and K. Carlberg, "Explicit Congestion Notification (ECN)
for RTP over UDP", RFC 6679, DOI 10.17487/RFC6679, August for RTP over UDP", RFC 6679, DOI 10.17487/RFC6679, August
2012, <http://www.rfc-editor.org/info/rfc6679>. 2012, <http://www.rfc-editor.org/info/rfc6679>.
[RFC6724] Thaler, D., Draves, R., Matsumoto, A., and T. Chown, [RFC6724] Thaler, D., Draves, R., Matsumoto, A., and T. Chown,
"Default Address Selection for Internet Protocol Version 6 "Default Address Selection for Internet Protocol Version 6
(IPv6)", RFC 6724, September 2012, (IPv6)", RFC 6724, September 2012,
<http://www.rfc-editor.org/info/rfc6724>. <http://www.rfc-editor.org/info/rfc6724>.
[RFC7092] Kaplan, H. and V. Pascual, "A Taxonomy of Session
Initiation Protocol (SIP) Back-to-Back User Agents",
RFC 7092, DOI 10.17487/RFC7092, December 2013,
<http://www.rfc-editor.org/info/rfc7092>.
[RFC7656] Lennox, J., Gross, K., Nandakumar, S., Salgueiro, G., and [RFC7656] Lennox, J., Gross, K., Nandakumar, S., Salgueiro, G., and
B. Burman, Ed., "A Taxonomy of Semantics and Mechanisms B. Burman, Ed., "A Taxonomy of Semantics and Mechanisms
for Real-Time Transport Protocol (RTP) Sources", RFC 7656, for Real-Time Transport Protocol (RTP) Sources", RFC 7656,
DOI 10.17487/RFC7656, November 2015, DOI 10.17487/RFC7656, November 2015,
<http://www.rfc-editor.org/info/rfc7656>. <http://www.rfc-editor.org/info/rfc7656>.
14.2. Informative References 12.2. Informative References
[RFC3725] Rosenberg, J., Peterson, J., Schulzrinne, H., and G. [RFC3725] Rosenberg, J., Peterson, J., Schulzrinne, H., and G.
Camarillo, "Best Current Practices for Third Party Call Camarillo, "Best Current Practices for Third Party Call
Control (3pcc) in the Session Initiation Protocol (SIP)", Control (3pcc) in the Session Initiation Protocol (SIP)",
BCP 85, RFC 3725, DOI 10.17487/RFC3725, April 2004, BCP 85, RFC 3725, DOI 10.17487/RFC3725, April 2004,
<http://www.rfc-editor.org/info/rfc3725>. <http://www.rfc-editor.org/info/rfc3725>.
[RFC3960] Camarillo, G. and H. Schulzrinne, "Early Media and Ringing [RFC3960] Camarillo, G. and H. Schulzrinne, "Early Media and Ringing
Tone Generation in the Session Initiation Protocol (SIP)", Tone Generation in the Session Initiation Protocol (SIP)",
RFC 3960, DOI 10.17487/RFC3960, December 2004, RFC 3960, DOI 10.17487/RFC3960, December 2004,
<http://www.rfc-editor.org/info/rfc3960>. <http://www.rfc-editor.org/info/rfc3960>.
[RFC4340] Kohler, E., Handley, M., and S. Floyd, "Datagram
Congestion Control Protocol (DCCP)", RFC 4340,
DOI 10.17487/RFC4340, March 2006,
<http://www.rfc-editor.org/info/rfc4340>.
[RFC5626] Jennings, C., Ed., Mahy, R., Ed., and F. Audet, Ed., [RFC5626] Jennings, C., Ed., Mahy, R., Ed., and F. Audet, Ed.,
"Managing Client-Initiated Connections in the Session "Managing Client-Initiated Connections in the Session
Initiation Protocol (SIP)", RFC 5626, Initiation Protocol (SIP)", RFC 5626,
DOI 10.17487/RFC5626, October 2009, DOI 10.17487/RFC5626, October 2009,
<http://www.rfc-editor.org/info/rfc5626>. <http://www.rfc-editor.org/info/rfc5626>.
[RFC5898] Andreasen, F., Camarillo, G., Oran, D., and D. Wing, [RFC5898] Andreasen, F., Camarillo, G., Oran, D., and D. Wing,
"Connectivity Preconditions for Session Description "Connectivity Preconditions for Session Description
Protocol (SDP) Media Streams", RFC 5898, 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>.
12.3. URIs
[1] mailto:iesg@ietf.org
[2] mailto:iesg@ietf.org
[3] mailto:iesg@ietf.org
[4] mailto:iesg@ietf.org
[5] mailto:iesg@ietf.org
[6] mailto:iesg@ietf.org
[7] mailto:iesg@ietf.org
[8] mailto:iesg@ietf.org
[9] mailto:christer.holmberg@ericsson.com
[10] mailto:rshpount@turbobridge.com
[11] mailto:thomass.stach@gmail.com
Appendix A. Examples Appendix A. Examples
For the example shown in section 16 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
skipping to change at page 40, line 26 skipping to change at page 38, line 40
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
The a=remote-candidates attribute exists to eliminate a race The a=remote-candidates attribute exists to eliminate a race
condition between the updated offer and the response to the STUN condition between the updated offer and the response to the STUN
Binding request that moved a candidate into the Valid list. This Binding request that moved a candidate into the Valid list. This
race condition is shown in Figure 1. On receipt of message 4, agent race condition is shown in Figure 1. On receipt of message 4, agent
L adds a candidate pair to the valid list. If there was only a L adds a candidate pair to the valid list. If there was only a
single media stream with a single component, agent L could now send single data stream with a single component, agent L could now send an
an updated offer. However, the check from agent R has not yet updated offer. However, the check from agent R has not yet generated
generated a response, and agent R receives the updated offer (message a response, and agent R receives the updated offer (message 7) before
7) before getting the response (message 9). Thus, it does not yet getting the response (message 9). Thus, it does not yet know that
know that this particular pair is valid. To eliminate this this particular pair is valid. To eliminate this condition, the
condition, the actual candidates at R that were selected by the actual candidates at R that were selected by the offerer (the remote
offerer (the remote candidates) are included in the offer itself, and candidates) are included in the offer itself, and the answerer delays
the answerer delays its answer until those pairs validate. its answer until those pairs validate.
Agent L Network Agent R Agent L Network Agent R
|(1) Offer | | |(1) Offer | |
|------------------------------------------>| |------------------------------------------>|
|(2) Answer | | |(2) Answer | |
|<------------------------------------------| |<------------------------------------------|
|(3) STUN Req. | | |(3) STUN Req. | |
|------------------------------------------>| |------------------------------------------>|
|(4) STUN Res. | | |(4) STUN Res. | |
|<------------------------------------------| |<------------------------------------------|
skipping to change at page 43, line 12 skipping to change at page 41, line 12
information. However, in practice, numerous components along the information. However, in practice, numerous components along the
signaling path look at the SDP information. These include entities signaling path look at the SDP information. These include entities
performing off-path QoS reservations, NAT traversal components such performing off-path QoS reservations, NAT traversal components such
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.
Appendix E. Contributors
o Christer Holmberg Ericsson Email: christer.holmberg@ericsson.com
[9]
o Roman Shpount TurboBridge rshpount@turbobridge.com [10]
o Thomas Stach thomass.stach@gmail.com [11]
Authors' Addresses Authors' Addresses
Marc Petit-Huguenin Marc Petit-Huguenin
Impedance Mismatch Impedance Mismatch
Email: marc@petit-huguenin.org Email: marc@petit-huguenin.org
Ari Keranen
Ericsson
Jorvas 02420
Finland
Email: ari.keranen@ericsson.com
Suhas Nandakumar Suhas Nandakumar
Cisco Systems Cisco Systems
707 Tasman Dr 707 Tasman Dr
Milpitas, CA 95035 Milpitas, CA 95035
USA USA
Email: snandaku@cisco.com Email: snandaku@cisco.com
Ari Keranen
Ericsson
Jorvas 02420
Finland
Email: ari.keranen@ericsson.com
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