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<rfc category='std' ipr='trust200902' <rfc xmlns:xi="http://www.w3.org/2001/XInclude" category="std"
docName='draft-ietf-ice-trickle-21'> ipr="trust200902" number="8838" submissionType="IETF" consensus="yes"
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sortRefs="true" version="3" docName="draft-ietf-ice-trickle-21">
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<front> <front>
<title abbrev="Trickle ICE">
<title abbrev='Trickle ICE'> Trickle ICE: Incremental Provisioning of Candidates for the Interactive
Trickle ICE: Incremental Provisioning of Candidates for the Interactive Connectivity Establishment (ICE) Protocol
Connectivity Establishment (ICE) Protocol
</title> </title>
<author initials='E.' surname='Ivov' <seriesInfo name="RFC" value="8838"/>
fullname='Emil Ivov'>
<organization abbrev='Atlassian'>Atlassian</organization> <author fullname="Emil Ivov" initials="E." surname="Ivov">
<organization abbrev="8x8 / Jitsi">8x8, Inc. / Jitsi</organization>
<address> <address>
<postal> <postal>
<street>303 Colorado Street, #1600</street> <street>675 Creekside Way</street>
<city>Austin</city> <city>Campbell</city>
<region>TX</region> <region>CA</region>
<code>78701</code> <code>95008</code>
<country>USA</country> <country>United States of America</country>
</postal> </postal>
<phone>+1-512-640-3000</phone> <phone>+1 512 420 6968</phone>
<email>eivov@atlassian.com</email> <email>emcho@jitsi.org</email>
</address> </address>
</author> </author>
<author fullname="Eric Rescorla" initials="E.K." surname="Rescorla">
<organization>RTFM, Inc.</organization> <!--
<author initials="E." surname="Ivov" fullname="Emil Ivov">
<organization abbrev="Atlassian">Atlassian</organization>
<address> <address>
<postal> <postal>
<street>2064 Edgewood Drive</street> <street>303 Colorado Street, #1600</street>
<city>Palo Alto</city> <city>Austin</city>
<region>CA</region> <region>TX</region>
<code>94303</code> <code>78701</code>
<country>USA</country> <country>United States of America</country>
</postal> </postal>
<phone>+1 650 678 2350</phone> <phone>+1 512 640 3000</phone>
<email>ekr@rtfm.com</email> <email>emcho@jitsi.org</email>
</address> </address>
</author> </author>
-->
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<author fullname="Justin Uberti" initials="J." surname="Uberti"> <author fullname="Justin Uberti" initials="J." surname="Uberti">
<organization>Google</organization> <organization>Google</organization>
<address> <address>
<postal> <postal>
<street>747 6th St S</street> <street>747 6th Street S</street>
<city>Kirkland</city> <city>Kirkland</city>
<region>WA</region> <region>WA</region>
<code>98033</code> <code>98033</code>
<country>USA</country> <country>United States of America</country>
</postal> </postal>
<phone>+1 857 288 8888</phone> <phone>+1 857 288 8888</phone>
<email>justin@uberti.name</email> <email>justin@uberti.name</email>
</address> </address>
</author> </author>
<author initials="P." surname="Saint-Andre" fullname="Peter Saint-Andre"> <author initials="P." surname="Saint-Andre" fullname="Peter Saint-Andre">
<organization>Mozilla</organization> <organization>Mozilla</organization>
<address> <address>
<postal> <postal>
<street>P.O. Box 787</street> <street>P.O. Box 787</street>
<city>Parker</city> <city>Parker</city>
<region>CO</region> <region>CO</region>
<code>80134</code> <code>80134</code>
<country>USA</country> <country>United States of America</country>
</postal> </postal>
<phone>+1 720 256 6756</phone> <phone>+1 720 256 6756</phone>
<email>stpeter@mozilla.com</email> <email>stpeter@mozilla.com</email>
<uri>https://www.mozilla.com/</uri> <uri>https://www.mozilla.com/</uri>
</address> </address>
</author> </author>
<date /> <date month="May" year="2020"/>
<abstract> <abstract>
<t> <t>
This document describes "Trickle ICE", an extension to the Interactive This document describes "Trickle ICE", an extension to the Interactive
Connectivity Establishment (ICE) protocol that enables ICE agents Connectivity Establishment (ICE) protocol that enables ICE agents
to begin connectivity checks while they are still gathering to begin connectivity checks while they are still gathering
candidates, by incrementally exchanging candidates over time instead candidates, by incrementally exchanging candidates over time instead
of all at once. This method can considerably accelerate the process of all at once. This method can considerably accelerate the process
of establishing a communication session. of establishing a communication session.
</t> </t>
</abstract> </abstract>
</front> </front>
<middle> <middle>
<section title='Introduction'> <section numbered="true" toc="default">
<name>Introduction</name>
<t> <t>
The Interactive Connectivity Establishment (ICE) protocol The Interactive Connectivity Establishment (ICE) protocol
<xref target="rfc5245bis"/> describes how an ICE agent <xref target="RFC8445" format="default"/> describes how an ICE agent
gathers candidates, exchanges candidates with a peer ICE gathers candidates, exchanges candidates with a peer ICE
agent, and creates candidate pairs. Once the pairs have been agent, and creates candidate pairs. Once the pairs have been
gathered, the ICE agent will perform connectivity checks, and gathered, the ICE agent will perform connectivity checks and
eventually nominate and select pairs that will be used for eventually nominate and select pairs that will be used for
sending and receiving data within a communication session. sending and receiving data within a communication session.
</t> </t>
<!--[rfced] RFC 5766 has been obsoleted by RFC 8656. May the
reference (and the corresponding citation) be changed to RFC 8656?
-->
<t> <t>
Following the procedures in <xref target="rfc5245bis"/> can Following the procedures in <xref target="RFC8445" format="default"/>
lead to somewhat lengthy establishment times for communication sessions, can lead to somewhat lengthy establishment times for communication
because candidate gathering often involves querying STUN servers sessions, because candidate gathering often involves querying Session
<xref target="RFC5389"/> and allocating relayed candidates using Traversal Utilities for NAT (STUN) servers <xref target="RFC5389"
TURN servers <xref target="RFC5766"/>. Although many ICE procedures format="default"/> and allocating relayed candidates on Traversal
can be completed in parallel, the pacing requirements from Using Relay NAT (TURN) servers <xref target="RFC8656"
<xref target="rfc5245bis"/> still need to be followed. format="default"/>. Although many ICE procedures can be completed in
parallel, the pacing requirements from <xref target="RFC8445"
format="default"/> still need to be followed.
</t> </t>
<t> <t>
This document defines "Trickle ICE", a supplementary mode of ICE This document defines "Trickle ICE", a supplementary mode of ICE
operation in which candidates can be exchanged operation in which candidates can be exchanged
incrementally as soon as they become available (and simultaneously incrementally as soon as they become available (and simultaneously
with the gathering of other candidates). Connectivity checks can with the gathering of other candidates). Connectivity checks can
also start as soon as candidate pairs have been created. Because also start as soon as candidate pairs have been created. Because
Trickle ICE enables candidate gathering and connectivity checks Trickle ICE enables candidate gathering and connectivity checks
to be done in parallel, the method can considerably accelerate to be done in parallel, the method can considerably accelerate
the process of establishing a communication session. the process of establishing a communication session.
</t> </t>
<t> <t>
This document also defines how to discover support for This document also defines how to discover support for
Trickle ICE, how the procedures in <xref target="rfc5245bis"/> are Trickle ICE, how the procedures in <xref target="RFC8445" format="defaul t"/> are
modified or supplemented when using Trickle ICE, and how a Trickle modified or supplemented when using Trickle ICE, and how a Trickle
ICE agent can interoperate with an ICE agent compliant to ICE agent can interoperate with an ICE agent compliant to
<xref target="rfc5245bis"/>. <xref target="RFC8445" format="default"/>.
</t> </t>
<t> <t>
This document does not define any protocol-specific usage of Trickle This document does not define any protocol-specific usage of Trickle
ICE. Instead, protocol-specific details for Trickle ICE are defined ICE. Instead, protocol-specific details for Trickle ICE are defined
in separate usage documents. Examples of such documents are in separate usage documents.
<xref target="I-D.ietf-mmusic-trickle-ice-sip"/> (which defines usage Examples of such documents are
with the Session Initiation Protocol (SIP) <xref target='RFC3261'/> <xref target="RFC8840" format="default"/> (which defines usage
and the Session Description Protocol <xref target='RFC3261'/>) and with the Session Initiation Protocol (SIP) <xref target="RFC3261" format
<xref target='XEP-0176'/> (which defines usage with XMPP ="default"/>
<xref target='RFC6120'/>). However, some of the examples in the and the Session Description Protocol (SDP) <xref target="RFC4566" format
document use SDP and the offer/answer model <xref target='RFC3264'/> ="default"/>) and
<xref target="XEP-0176" format="default"/> (which defines usage with the
Extensible Messaging and Presence Protocol (XMPP)
<xref target="RFC6120" format="default"/>). However, some of the example
s in the
document use SDP and the Offer/Answer model <xref target="RFC3264" forma
t="default"/>
to explain the underlying concepts. to explain the underlying concepts.
</t> </t>
<t> <t>
The following diagram illustrates a successful Trickle ICE exchange with a The following diagram illustrates a successful Trickle ICE exchange with a
using protocol that follows the offer/answer model: using protocol that follows the Offer/Answer model:
</t> </t>
<figure title="Flow" anchor="fig-flow"> <figure anchor="fig-flow">
<artwork> <name>Flow</name>
<![CDATA[ <artwork name="" type="" align="left" alt=""><![CDATA[
Alice Bob Alice Bob
| Offer | | Offer |
|---------------------------------------------->| |---------------------------------------------->|
| Additional Candidates | | Additional Candidates |
|---------------------------------------------->| |---------------------------------------------->|
| Answer | | Answer |
|<----------------------------------------------| |<----------------------------------------------|
| Additional Candidates | | Additional Candidates |
|<----------------------------------------------| |<----------------------------------------------|
| Additional Candidates and Connectivity Checks | | Additional Candidates and Connectivity Checks |
|<--------------------------------------------->| |<--------------------------------------------->|
|<========== CONNECTION ESTABLISHED ===========>| |<========== CONNECTION ESTABLISHED ===========>|
]]></artwork>
]]>
</artwork>
</figure> </figure>
<t> <t>
The main body of this document is structured to describe the behavior The main body of this document is structured to describe the behavior
of Trickle ICE agents in roughly the order of operations and interaction s of Trickle ICE agents in roughly the order of operations and interaction s
during an ICE session: during an ICE session:
<list style='numbers'>
<t>Determining support for trickle ICE</t>
<t>Generating the initial ICE description</t>
<t>Handling the initial ICE description and generating the initial ICE
response</t>
<t>Handling the initial ICE response</t>
<t>Forming check lists, pruning candidates, performing connectivity ch
ecks, etc.</t>
<t>Gathering and conveying candidates after the initial ICE descriptio
n and response</t>
<t>Handling inbound trickled candidates</t>
<t>Generating and handling the end-of-candidates indication</t>
<t>Handling ICE restarts</t>
</list>
</t> </t>
<ol spacing="normal" type="1">
<li>Determining support for Trickle ICE</li>
<li>Generating the initial ICE description</li>
<li>Handling the initial ICE description and generating the initial ICE
response</li>
<li>Handling the initial ICE response</li>
<li>Forming checklists, pruning candidates, performing connectivity chec
ks, etc.</li>
<li>Gathering and conveying candidates after the initial ICE description
and response</li>
<li>Handling inbound trickled candidates</li>
<li>Generating and handling the end-of-candidates indication</li>
<li>Handling ICE restarts</li>
</ol>
<t> <t>
There is quite a bit of operational experience with the technique behind There is quite a bit of operational experience with the technique behind
Trickle ICE, going back as far as 2005 (when the XMPP Jingle extension Trickle ICE, going back as far as 2005 (when the XMPP Jingle extension
defined a "dribble mode" as specified in <xref target='XEP-0176'/>); thi s defined a "dribble mode" as specified in <xref target="XEP-0176" format= "default"/>); this
document incorporates feedback from those who have implemented and document incorporates feedback from those who have implemented and
deployed the technique over the years. deployed the technique over the years.
</t> </t>
</section> </section>
<section title="Terminology"> <section numbered="true" toc="default">
<t> <name>Terminology</name>
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL <t>
NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and The key words "<bcp14>MUST</bcp14>", "<bcp14>MUST NOT</bcp14>",
"OPTIONAL" in this document are to be interpreted as described "<bcp14>REQUIRED</bcp14>", "<bcp14>SHALL</bcp14>", "<bcp14>SHALL NOT</bcp14>
in <xref target="RFC2119"/>. ",
</t> "<bcp14>SHOULD</bcp14>", "<bcp14>SHOULD NOT</bcp14>",
"<bcp14>RECOMMENDED</bcp14>", "<bcp14>NOT RECOMMENDED</bcp14>",
"<bcp14>MAY</bcp14>", and "<bcp14>OPTIONAL</bcp14>" in this document are to
be
interpreted as described in BCP 14 <xref target="RFC2119"/> <xref
target="RFC8174"/> when, and only when, they appear in all capitals, as
shown here.
</t>
<t> <t>
This specification makes use of all terminology defined This specification makes use of all terminology defined
for Interactive Connectivity Establishment in for Interactive Connectivity Establishment in
<xref target="rfc5245bis"/>. In addition, it defines the following terms : <xref target="RFC8445" format="default"/>. In addition, it defines the f ollowing terms:
</t> </t>
<t> <dl newline="false" spacing="normal">
<list style="hanging"> <dt>Empty Checklist:</dt>
<t hangText="Full Trickle:"> <dd>
A checklist that initially does not contain any candidate pairs
because they will be incrementally added as they are trickled.
(This scenario does not arise with a regular ICE agent, because all
candidate pairs are known when the agent creates the checklist set.)
</dd>
<dt>Full Trickle:</dt>
<dd>
The typical mode of operation for Trickle ICE agents, in which The typical mode of operation for Trickle ICE agents, in which
the initial ICE description can include any number of candidates (ev en the initial ICE description can include any number of candidates (ev en
zero candidates) and does not need to include a full generation zero candidates) and does not need to include a full generation
of candidates as in half trickle. of candidates as in half trickle.
</t> </dd>
<t hangText="Generation:"> <dt>Generation:</dt>
All of the candidates conveyed within an ICE session. <dd>
</t> All of the candidates conveyed within an ICE session (correlated
<t hangText="Half Trickle:"> with a particular Username Fragment and Password combination).
</dd>
<dt>Half Trickle:</dt>
<dd>
A Trickle ICE mode of operation in which the initiator gathers A Trickle ICE mode of operation in which the initiator gathers
a full generation of candidates strictly before creating a full generation of candidates strictly before creating
and conveying the initial ICE description. Once conveyed, and conveying the initial ICE description. Once conveyed,
this candidate information can be this candidate information can be
processed by regular ICE agents, which do not require support processed by regular ICE agents, which do not require support
for Trickle ICE. It also allows Trickle ICE capable for Trickle ICE. It also allows Trickle-ICE-capable
responders to still gather candidates and perform responders to still gather candidates and perform
connectivity checks in a non-blocking way, thus providing roughly connectivity checks in a non-blocking way, thus providing roughly
"half" the advantages of Trickle ICE. The half trickle mechanism "half" the advantages of Trickle ICE. The half-trickle mechanism
is mostly meant for use when the responder's support for Trickle is mostly meant for use when the responder's support for Trickle
ICE cannot be confirmed prior to conveying the initial ICE descripti on. ICE cannot be confirmed prior to conveying the initial ICE descripti on.
</t> </dd>
<t hangText="ICE Description:"> <dt>ICE Description:</dt>
Any attributes related to the ICE session (not candidates) <dd>
Any attributes related to the ICE session (other than candidates)
required to configure an ICE agent. These include but are not required to configure an ICE agent. These include but are not
limited to the username fragment, password, and other attributes. limited to the Username Fragment, the Password, and other attributes
</t> .
<t hangText="Trickled Candidates:"> </dd>
Candidates that a Trickle ICE agent conveys after conveying the init <dt>Trickled Candidates:</dt>
ial <dd>
ICE description or responding to the initial ICE description, but wi Candidates that a Trickle ICE agent conveys after conveying or respo
thin nding to the initial
ICE description, but within
the same ICE session. Trickled candidates can be conveyed in the same ICE session. Trickled candidates can be conveyed in
parallel with candidate gathering and connectivity checks. parallel with candidate gathering and connectivity checks.
</t> </dd>
<t hangText="Trickling:"> <dt>Trickling:</dt>
<dd>
The act of incrementally conveying trickled candidates. The act of incrementally conveying trickled candidates.
</t> </dd>
<t hangText="Empty Check List:"> </dl>
A check list that initially does not contain any candidate pairs
because they will be incrementally added as they are trickled.
(This scenario does not arise with a regular ICE agent, because all
candidate pairs are known when the agent creates the check list set).
</t>
</list>
</t>
</section> </section>
<section title='Determining Support for Trickle ICE' anchor="support"> <section anchor="support" numbered="true" toc="default">
<name>Determining Support for Trickle ICE</name>
<t> <t>
To fully support Trickle ICE, using protocols To fully support Trickle ICE, using protocols
SHOULD incorporate one of the following mechanisms so that implementatio ns <bcp14>SHOULD</bcp14> incorporate one of the following mechanisms so tha t implementations
can determine whether Trickle ICE is supported: can determine whether Trickle ICE is supported:
</t> </t>
<t> <ol spacing="normal" type="1">
<list style='numbers'> <li>
<t>
Provide a capabilities discovery method so that agents can verify Provide a capabilities discovery method so that agents can verify
support of Trickle ICE prior to initiating a session (XMPP's support of Trickle ICE prior to initiating a session (XMPP's
<xref target="XEP-0030">Service Discovery</xref> is <xref target="XEP-0030" format="default">Service Discovery</xref> is
one such mechanism). one such mechanism).
</t> </li>
<t> <li>
Make support for Trickle ICE mandatory so that user agents Make support for Trickle ICE mandatory so that user agents
can assume support. can assume support.
</t> </li>
</list> </ol>
</t>
<t> <t>
If a using protocol does not provide a method of determining If a using protocol does not provide a method of determining
ahead of time whether Trickle ICE is supported, agents can make use of ahead of time whether Trickle ICE is supported, agents can make use of
the half trickle procedure described in <xref target="half-trickle"/>. the half-trickle procedure described in <xref target="half-trickle" form at="default"/>.
</t> </t>
<t> <t>
Prior to conveying the initial ICE description, agents that implement us ing protocols Prior to conveying the initial ICE description, agents that implement us ing protocols
that support capabilities discovery can attempt to verify whether or that support capabilities discovery can attempt to verify whether or
not the remote party supports Trickle ICE. If an agent determines not the remote party supports Trickle ICE. If an agent determines
that the remote party does not support Trickle ICE, it MUST fall back that the remote party does not support Trickle ICE, it <bcp14>MUST</bcp1 4> fall back
to using regular ICE or abandon the entire session. to using regular ICE or abandon the entire session.
</t> </t>
<t> <t>
Even if a using protocol does not include a capabilities discovery Even if a using protocol does not include a capabilities discovery
method, a user agent can provide an indication within the ICE descriptio n method, a user agent can provide an indication within the ICE descriptio n
that it supports Trickle ICE by communicating an ICE option of 'trickle' . that it supports Trickle ICE by communicating an ICE option of 'trickle' .
This token MUST be provided either at the session level or, if at the da This token <bcp14>MUST</bcp14> be provided either at the session level o
ta r, if at the data
stream level, for every data stream (an agent MUST NOT specify Trickle I stream level, for every data stream (an agent <bcp14>MUST NOT</bcp14> sp
CE ecify Trickle ICE
support for some data streams but not others). support for some data streams but not others).
Note: The encoding of the 'trickle' ICE option, and the message(s) used to Note: The encoding of the 'trickle' ICE option, and the message(s) used to
carry it to the peer, are protocol specific; for instance, the encoding for carry it to the peer, are protocol specific; for instance, the encoding for
the Session Description Protocol (SDP) <xref target='RFC4566'/> is defin SDP <xref target="RFC4566" format="default"/> is defined in
ed in <xref target="RFC8840" format="default"/>.
<xref target='I-D.ietf-mmusic-trickle-ice-sip'/>.
</t> </t>
<t> <t>
Dedicated discovery semantics and half trickle are needed only prior Dedicated discovery semantics and half trickle are needed only prior
to initiation of an ICE session. After an ICE session is established to initiation of an ICE session. After an ICE session is established
and Trickle ICE support is confirmed for both parties, either and Trickle ICE support is confirmed for both parties, either
agent can use full trickle for subsequent exchanges (see also agent can use full trickle for subsequent exchanges (see also
<xref target='subsequent'/>). <xref target="subsequent" format="default"/>).
</t> </t>
</section> </section>
<section title='Generating the Initial ICE Description' anchor="initial"> <section anchor="initial" numbered="true" toc="default">
<name>Generating the Initial ICE Description</name>
<t> <t>
An ICE agent can start gathering candidates as soon as it has an An ICE agent can start gathering candidates as soon as it has an
indication that communication is imminent (e.g., a user interface indication that communication is imminent (e.g., a user-interface
cue or an explicit request to initiate a communication session). Unlike in cue or an explicit request to initiate a communication session). Unlike in
regular ICE, in Trickle ICE implementations do not need to regular ICE, in Trickle ICE implementations do not need to
gather candidates in a blocking manner. Therefore, unless half gather candidates in a blocking manner. Therefore, unless half
trickle is being used, the user experience is improved if the trickle is being used, the user experience is improved if the
initiating agent generates and transmits its initial ICE description initiating agent generates and transmits its initial ICE description
as early as possible (thus enabling the remote party to start as early as possible (thus enabling the remote party to start
gathering and trickling candidates). gathering and trickling candidates).
</t> </t>
<t> <t>
An initiator MAY include any mix of candidates when conveying An initiator <bcp14>MAY</bcp14> include any mix of candidates when conve ying
the initial ICE description. This includes the possibility of conveying the initial ICE description. This includes the possibility of conveying
all the candidates the initiator plans to use all the candidates the initiator plans to use
(as in half trickle), conveying only a (as in half trickle), conveying only a
publicly-reachable IP address (e.g., a candidate at a data publicly reachable IP address (e.g., a candidate at a data
relay that is known to not be behind a firewall), or conveying relay that is known to not be behind a firewall), or conveying
no candidates at all (in which case the initiator can obtain the no candidates at all (in which case the initiator can obtain the
responder's initial candidate list sooner and the responder can begin responder's initial candidate list sooner, and the responder can begin
candidate gathering more quickly). candidate gathering more quickly).
</t> </t>
<t> <t>
For candidates included in the initial ICE description, the methods For candidates included in the initial ICE description, the methods
for calculating priorities and foundations, determining redundancy for calculating priorities and foundations, determining redundancy
of candidates, and the like work just as in regular ICE of candidates, and the like work just as in regular ICE
<xref target="rfc5245bis"/>. <xref target="RFC8445" format="default"/>.
</t> </t>
</section> </section>
<section title='Handling the Initial ICE Description and Generating the Init <section numbered="true" toc="default">
ial ICE Response' > <name>Handling the Initial ICE Description and Generating the Initial ICE
Response</name>
<t> <t>
When a responder receives the initial ICE description, it will first che ck if When a responder receives the initial ICE description, it will first che ck if
the ICE description or initiator indicates support for Trickle ICE as ex plained the ICE description or initiator indicates support for Trickle ICE as ex plained
in <xref target="support"/>. If not, the responder MUST in <xref target="support" format="default"/>. If not, the responder <bcp 14>MUST</bcp14>
process the initial ICE description according to regular ICE procedures process the initial ICE description according to regular ICE procedures
<xref target="rfc5245bis"/> (or, if no ICE support is detected at all, <xref target="RFC8445" format="default"/> (or, if no ICE support is dete cted at all,
according to relevant processing rules for the using according to relevant processing rules for the using
protocol, such as offer/answer processing rules <xref target="RFC3264"/> ). protocol, such as Offer/Answer processing rules <xref target="RFC3264" f ormat="default"/>).
However, if support for Trickle ICE is confirmed, a responder will However, if support for Trickle ICE is confirmed, a responder will
automatically assume support for regular ICE as well. automatically assume support for regular ICE as well.
</t> </t>
<t> <t>
If the initial ICE description indicates support for Trickle ICE, the If the initial ICE description indicates support for Trickle ICE, the
responder will determine its role and start gathering and prioritizing responder will determine its role and start gathering and prioritizing
candidates; while doing so, it will also respond by conveying an candidates; while doing so, it will also respond by conveying an
initial ICE response, so that both the initiator initial ICE response, so that both the initiator
and the responder can form check lists and begin connectivity checks. and the responder can form checklists and begin connectivity checks.
</t> </t>
<t> <t>
A responder can respond to the initial ICE description at any point whil e A responder can respond to the initial ICE description at any point whil e
gathering candidates. The initial ICE response MAY contain any set of gathering candidates. The initial ICE response <bcp14>MAY</bcp14> contai n any set of
candidates, including all candidates or no candidates. (The benefit of candidates, including all candidates or no candidates. (The benefit of
including no candidates is to convey the initial ICE response as including no candidates is to convey the initial ICE response as
quickly as possible, so that both parties can consider the quickly as possible, so that both parties can consider the
ICE session to be under active negotiation as soon as ICE session to be under active negotiation as soon as
possible.) possible.)
</t> </t>
<t> <t>
As noted in <xref target="support"/>, in using protocols that use As noted in <xref target="support" format="default"/>, in using protocol
SDP the initial ICE response can indicate support for Trickle ICE s that use
by including a token of "trickle" in the ice-options attribute. SDP, the initial ICE response can indicate support for Trickle ICE
by including a token of 'trickle' in the ice-options attribute.
</t> </t>
</section> </section>
<section title="Handling the Initial ICE Response"> <section numbered="true" toc="default">
<name>Handling the Initial ICE Response</name>
<t> <t>
When processing the initial ICE response, the initiator follows regular ICE When processing the initial ICE response, the initiator follows regular ICE
procedures to determine its role, after which it procedures to determine its role, after which it
forms check lists (<xref target="checklists"/>) forms checklists (<xref target="checklists" format="default"/>)
and performs connectivity checks (<xref target='checks'/>). and performs connectivity checks (<xref target="checks" format="default"
/>).
</t> </t>
</section> </section>
<section title='Forming Check Lists' anchor='checklists'> <section anchor="checklists" numbered="true" toc="default">
<name>Forming Checklists</name>
<t> <t>
According to regular ICE procedures <xref target="rfc5245bis"/>, According to regular ICE procedures <xref target="RFC8445" format="defau lt"/>,
in order for candidate pairing in order for candidate pairing
to be possible and for redundant candidates to be pruned, the to be possible and for redundant candidates to be pruned, the
candidates would need to be provided in the initial ICE description candidates would need to be provided in the initial ICE description
and initial ICE response. and initial ICE response.
By contrast, under Trickle ICE check lists can be empty until By contrast, under Trickle ICE, checklists can be empty until
candidates are conveyed or received. Therefore a Trickle ICE agent candidates are conveyed or received. Therefore, a Trickle ICE agent
handles check list formation and candidate pairing in a slightly differe handles checklist formation and candidate pairing in a slightly differen
nt t
way than a regular ICE agent: the agent still forms the check lists, but way than a regular ICE agent: the agent still forms the checklists, but
it populates a given check list only after it actually has candidate it populates a given checklist only after it actually has candidate
pairs for that check list. Every check list is initially placed in the pairs for that checklist. Every checklist is initially placed in the
Running state, even if the check list is empty (this is consistent Running state, even if the checklist is empty (this is consistent
with Section 6.1.2.1 of <xref target='rfc5245bis'/>). with <xref target="RFC8445"
sectionFormat="of" section="6.1.2.1"/>).
</t> </t>
</section> </section>
<section title='Performing Connectivity Checks' anchor='checks'> <section anchor="checks" numbered="true" toc="default">
<name>Performing Connectivity Checks</name>
<t> <t>
As specified in <xref target='rfc5245bis'/>, whenever timer As specified in <xref target="RFC8445" format="default"/>, whenever time
Ta fires, only check lists in the Running state will be picked r
Ta fires, only checklists in the Running state will be picked
when scheduling connectivity checks for candidate pairs. when scheduling connectivity checks for candidate pairs.
Therefore, a Trickle ICE agent MUST keep each check list in Therefore, a Trickle ICE agent <bcp14>MUST</bcp14> keep each checklist i n
the Running state as long as it expects candidate pairs to be the Running state as long as it expects candidate pairs to be
incrementally added to the check list. After that, the check incrementally added to the checklist. After that, the checklist
list state is set according to the procedures in state is set according to the procedures in
<xref target='rfc5245bis'/>. <xref target="RFC8445" format="default"/>.
</t> </t>
<t> <t>
Whenever timer Ta fires and an empty check list is picked, no action Whenever timer Ta fires and an empty checklist is picked, no action
is performed for the list. Without waiting for timer Ta to expire is performed for the list. Without waiting for timer Ta to expire
again, the agent selects the next check list in the Running state, again, the agent selects the next checklist in the Running state,
in accordance with Section 6.1.4.2 of <xref target='rfc5245bis'/>. in accordance with <xref target="RFC8445" format="default"
sectionFormat="of" section="6.1.4.2"/>.
</t> </t>
<t> <t>
Section 7.2.5.3.3 of <xref target='rfc5245bis'/> <xref target="RFC8445" format="default" sectionFormat="of" section="7.2.
requires that agents update check lists and timer states upon 5.4"/>
requires that agents update checklists and timer states upon
completing a connectivity check transaction. During such an completing a connectivity check transaction. During such an
update, regular ICE agents would set the state of a check list update, regular ICE agents would set the state of a checklist
to Failed if both of the following two conditions are satisfied: to Failed if both of the following two conditions are satisfied:
</t> </t>
<t> <ul spacing="normal">
<list style="symbols"> <li>
<t> all of the pairs in the checklist are in either the
all of the pairs in the check list are either in the Failed state or the Succeeded state; and
Failed state or Succeeded state; and </li>
</t> <li>
<t>
there is not a pair in the valid list for each component there is not a pair in the valid list for each component
of the data stream. of the data stream.
</t> </li>
</list> </ul>
</t>
<t> <t>
With Trickle ICE, the above situation would often occur when With Trickle ICE, the above situation would often occur when
candidate gathering and trickling are still in progress, even candidate gathering and trickling are still in progress, even
though it is quite possible that future checks will succeed. For though it is quite possible that future checks will succeed. For
this reason, Trickle ICE agents add the following conditions to this reason, Trickle ICE agents add the following conditions to
the above list: the above list:
</t> </t>
<t> <ul spacing="normal">
<list style="symbols"> <li>
<t> all candidate gathering has completed, and the agent
all candidate gathering has completed and the agent
is not expecting to discover any new local candidates; and is not expecting to discover any new local candidates; and
</t> </li>
<t> <li>
the remote agent has conveyed an end-of-candidates indication the remote agent has conveyed an end-of-candidates indication
for that check list as described in for that checklist as described in
<xref target="end-of-candidates.send"/>. <xref target="end-of-candidates.send" format="default"/>.
</t> </li>
</list> </ul>
</t>
</section> </section>
<section title='Gathering and Conveying Newly Gathered Local Candidates' <section anchor="trickle-send" numbered="true" toc="default">
anchor="trickle-send"> <name>Gathering and Conveying Newly Gathered Local Candidates</name>
<t> <t>
After Trickle ICE agents have conveyed initial ICE descriptions After Trickle ICE agents have conveyed initial ICE descriptions
and initial ICE responses, they will most and initial ICE responses, they will most
likely continue gathering new local candidates as STUN, TURN, likely continue gathering new local candidates as STUN, TURN,
and other non-host candidate gathering mechanisms begin to and other non-host candidate gathering mechanisms begin to
yield results. Whenever an agent discovers such a new candidate yield results. Whenever an agent discovers such a new candidate,
it will compute its priority, type, foundation, and component ID it will compute its priority, type, foundation, and component ID
according to regular ICE procedures. according to regular ICE procedures.
</t> </t>
<t> <t>
The new candidate is then checked for redundancy against the The new candidate is then checked for redundancy against the
existing list of local candidates. If its transport address and existing list of local candidates. If its transport address and
base match those of an existing candidate, it will be considered base match those of an existing candidate, it will be considered
redundant and will be ignored. This would often happen for redundant and will be ignored. This would often happen for
server reflexive candidates that match the host addresses they server-reflexive candidates that match the host addresses they
were obtained from (e.g., when the latter are public IPv4 were obtained from (e.g., when the latter are public IPv4
addresses). Contrary to regular ICE, Trickle ICE agents will addresses). Contrary to regular ICE, Trickle ICE agents will
consider the new candidate redundant regardless of its priority. consider the new candidate redundant regardless of its priority.
</t> </t>
<t> <t>
Next the agent "trickles" the newly discovered Next, the agent "trickles" the newly discovered
candidate(s) to the remote agent. The actual delivery of the new candidate(s) to the remote agent. The actual delivery of the new
candidates is handled by a using protocol such as SIP or XMPP. candidates is handled by a using protocol such as SIP or XMPP.
Trickle ICE imposes no restrictions on the way this is done Trickle ICE imposes no restrictions on the way this is done
(e.g., some using protocols might (e.g., some using protocols might
choose not to trickle updates for server reflexive choose not to trickle updates for server-reflexive
candidates and instead rely on the discovery of peer reflexive ones). candidates and instead rely on the discovery of peer-reflexive ones).
</t> </t>
<t> <t>
When candidates are trickled, the using protocol MUST deliver each When candidates are trickled, the using protocol <bcp14>MUST</bcp14> del iver each
candidate (and any end-of-candidates indication as described in candidate (and any end-of-candidates indication as described in
<xref target='end-of-candidates.send'/>) to the receiving Trickle ICE im plementation <xref target="end-of-candidates.send" format="default"/>) to the receivi ng Trickle ICE implementation
exactly once exactly once
and in the same order it was conveyed. If the using protocol and in the same order it was conveyed. If the using protocol
provides any candidate retransmissions, they need to be hidden provides any candidate retransmissions, they need to be hidden
from the ICE implementation. from the ICE implementation.
</t> </t>
<t> <t>
Also, candidate trickling needs to be correlated to a specific Also, candidate trickling needs to be correlated to a specific
ICE session, so that if there is an ICE restart, any ICE session, so that if there is an ICE restart, any
delayed updates for a previous session can be recognized as such delayed updates for a previous session can be recognized as such
and ignored by the receiving party. For example, using protocols and ignored by the receiving party. For example, using protocols
that signal candidates via SDP might include a Username that signal candidates via SDP might include a Username
Fragment value in the corresponding a=candidate line, such as: Fragment value in the corresponding a=candidate line, such as:
<figure> </t>
<artwork> <sourcecode type="sdp"><![CDATA[
<![CDATA[
a=candidate:1 1 UDP 2130706431 2001:db8::1 5000 typ host ufrag 8hhY a=candidate:1 1 UDP 2130706431 2001:db8::1 5000 typ host ufrag 8hhY
]]> ]]></sourcecode>
</artwork> <t>
</figure>
Or, as another example, WebRTC implementations might include a Username Or, as another example, WebRTC implementations might include a Username
Fragment in the JavaScript objects that represent candidates. Fragment in the JavaScript objects that represent candidates.
</t> </t>
<t> <t>
Note: The using protocol needs to provide a mechanism for both Note: The using protocol needs to provide a mechanism for both
parties to indicate and agree on the ICE session in force parties to indicate and agree on the ICE session in force
(as identified by the Username Fragment and Password combination) (as identified by the Username Fragment and Password combination),
so that they have a consistent view of which candidates are so that they have a consistent view of which candidates are
to be paired. This is especially important in the case of ICE to be paired. This is especially important in the case of ICE
restarts (see <xref target='subsequent'/>). restarts (see <xref target="subsequent" format="default"/>).
</t> </t>
<t> <t>
Note: A using protocol might prefer not to Note: A using protocol might prefer not to
trickle server reflexive candidates to entities that are known trickle server-reflexive candidates to entities that are known
to be publicly accessible and where sending a direct STUN to be publicly accessible and where sending a direct STUN
binding request is likely to reach the destination faster than binding request is likely to reach the destination faster than
the trickle update that travels through the signaling path. the trickle update that travels through the signaling path.
</t> </t>
</section> </section>
<section title='Pairing Newly Gathered Local Candidates' anchor="local-pairi <section anchor="local-pairing" numbered="true" toc="default">
ng"> <name>Pairing Newly Gathered Local Candidates</name>
<t> <t>
As a Trickle ICE agent gathers local candidates, it needs As a Trickle ICE agent gathers local candidates, it needs
to form candidate pairs; this works as described in to form candidate pairs; this works as described in
the ICE specification <xref target='rfc5245bis'/>, with the the ICE specification <xref target="RFC8445" format="default"/>, with th e
following provisos: following provisos:
<list style='numbers'> </t>
<t> <ol spacing="normal" type="1">
A Trickle ICE agent MUST NOT pair a local candidate until it <li>
A Trickle ICE agent <bcp14>MUST NOT</bcp14> pair a local candidate u
ntil it
has been trickled to the remote party. has been trickled to the remote party.
</t> </li>
<t> <li>
Once the agent has conveyed the local candidate to the remote Once the agent has conveyed the local candidate to the remote
party, the agent checks if any remote candidates are currently party, the agent checks if any remote candidates are currently
known for this same stream and component. If not, the agent known for this same stream and component. If not, the agent
merely adds the new candidate to the list of local candidates merely adds the new candidate to the list of local candidates
(without pairing it). (without pairing it).
</t> </li>
<t> <li>
Otherwise, if the agent has already learned of one or more Otherwise, if the agent has already learned of one or more
remote candidates for this stream and component, it attempts remote candidates for this stream and component, it attempts
to pair the new local candidate as described in the ICE to pair the new local candidate as described in the ICE
specification <xref target='rfc5245bis'/>. specification <xref target="RFC8445" format="default"/>.
</t> </li>
<t> <li>
If a newly formed pair has a local candidate whose type is server If a newly formed pair has a local candidate whose type is server
reflexive, the agent MUST replace the local candidate with its reflexive, the agent <bcp14>MUST</bcp14> replace the local candidate with its
base before completing the relevant redundancy tests. base before completing the relevant redundancy tests.
</t> </li>
<t> <li>
The agent prunes redundant pairs by following the rules The agent prunes redundant pairs by following the rules
in Section 6.1.2.4 of <xref target='rfc5245bis'/>, but checks in <xref target="RFC8445" format="default" sectionFormat="of" sectio n="6.1.2.4"/> but checks
existing pairs only if they have a state of Waiting or Frozen; existing pairs only if they have a state of Waiting or Frozen;
this avoids removal of pairs for which connectivity checks are this avoids removal of pairs for which connectivity checks are
in flight (a state of In-Progress) or for which connectivity in flight (a state of In&nbhy;Progress) or for which connectivity
checks have already yielded a definitive result (a state of checks have already yielded a definitive result (a state of
Succeeded or Failed). Succeeded or Failed).
</t> </li>
<t> <li>
If after the relevant redundancy tests the check list where the If, after completing the relevant redundancy tests, the checklist wh
ere the
pair is to be added already contains the maximum number of candidate pair is to be added already contains the maximum number of candidate
pairs (100 by default as per <xref target="rfc5245bis"/>), the agent pairs (100 by default as per <xref target="RFC8445" format="default"
SHOULD discard any pairs in the Failed state to make room for the />), the agent
new pair. If there are no such pairs, the agent SHOULD discard a <bcp14>SHOULD</bcp14> discard any pairs in the Failed state to make
room for the
new pair. If there are no such pairs, the agent <bcp14>SHOULD</bcp14
> discard a
pair with a lower priority than the new pair in order to make room pair with a lower priority than the new pair in order to make room
for the new pair, until the number of pairs is equal to the maximum for the new pair, until the number of pairs is equal to the maximum
number of pairs. This processing is consistent with Section 6.1.2.5 number of pairs. This processing is consistent with
of <xref target='rfc5245bis'/>. <xref target="RFC8445" format="default" sectionFormat="of" section="
</t> 6.1.2.5"/>.
</list> </li>
</t> </ol>
</section> </section>
<section title='Receiving Trickled Candidates' anchor="trickle-recv"> <section anchor="trickle-recv" numbered="true" toc="default">
<name>Receiving Trickled Candidates</name>
<t> <t>
At any time during an ICE session, a Trickle ICE agent might receive At any time during an ICE session, a Trickle ICE agent might receive
new candidates from the remote agent, from which it will attempt to new candidates from the remote agent, from which it will attempt to
form a candidate pair; this works as described in the ICE specification form a candidate pair; this works as described in the ICE specification
<xref target='rfc5245bis'/>, with the following provisos: <xref target="RFC8445" format="default"/>, with the following provisos:
<list style='numbers'> </t>
<t> <ol spacing="normal" type="1">
<li>
The agent checks if any local candidates are currently known for The agent checks if any local candidates are currently known for
this same stream and component. If not, the agent merely adds the this same stream and component. If not, the agent merely adds the
new candidate to the list of remote candidates (without pairing it). new candidate to the list of remote candidates (without pairing it).
</t> </li>
<t> <li>
Otherwise, if the agent has already gathered one or more Otherwise, if the agent has already gathered one or more
local candidates for this stream and component, it attempts local candidates for this stream and component, it attempts
to pair the new remote candidate as described in the ICE to pair the new remote candidate as described in the ICE
specification <xref target='rfc5245bis'/>. specification <xref target="RFC8445" format="default"/>.
</t> </li>
<t> <li>
If a newly formed pair has a local candidate whose type is server If a newly formed pair has a local candidate whose type is server
reflexive, the agent MUST replace the local candidate with its reflexive, the agent <bcp14>MUST</bcp14> replace the local candidate with its
base before completing the redundancy check in the next step. base before completing the redundancy check in the next step.
</t> </li>
<li>
<t> <t>
The agent prunes redundant pairs as described below, but checks The agent prunes redundant pairs as described below but checks
existing pairs only if they have a state of Waiting or Frozen; existing pairs only if they have a state of Waiting or Frozen;
this avoids removal of pairs for which connectivity checks are this avoids removal of pairs for which connectivity checks are
in flight (a state of In-Progress) or for which connectivity in flight (a state of In-Progress) or for which connectivity
checks have already yielded a definitive result (a state of checks have already yielded a definitive result (a state of
Succeeded or Failed). Succeeded or Failed).
<list style='letters'> </t>
<t> <ol spacing="normal" type="A">
<li>
If the agent finds a redundancy between two pairs and one of If the agent finds a redundancy between two pairs and one of
those pairs contains a newly received remote candidate whose those pairs contains a newly received remote candidate whose
type is peer reflexive, the agent SHOULD discard the type is peer reflexive, the agent <bcp14>SHOULD</bcp14> discard the
pair containing that candidate, set the priority of the pair containing that candidate, set the priority of the
existing pair to the priority of the discarded pair, and existing pair to the priority of the discarded pair, and
re-sort the check list. (This policy helps to eliminate re-sort the checklist.
problems with remote peer reflexive candidates for which (This policy helps to eliminate
a STUN binding request is received before signaling of the problems with remote peer-reflexive candidates for which
a STUN Binding request is received before signaling of the
candidate is trickled to the receiving agent, such as a candidate is trickled to the receiving agent, such as a
different view of pair priorities between the local agent different view of pair priorities between the local agent
and the remote agent, since the same candidate could be and the remote agent, because the same candidate could be
perceived as peer reflexive by one agent and as server perceived as peer reflexive by one agent and as server
reflexive by the other agent.) reflexive by the other agent.)
</t>
<t> </li>
<li>
The agent then applies the rules defined in The agent then applies the rules defined in
Section 6.1.2.4 of <xref target='rfc5245bis'/>. <xref target="RFC8445" format="default" sectionFormat="of" sect
</t> ion="6.1.2.4"/>.
</list> </li>
</t> </ol>
<t> </li>
If after the relevant redundancy tests the check list where the <li>
If, after completing the relevant redundancy tests, the checklist wh
ere the
pair is to be added already contains the maximum number of candidate pair is to be added already contains the maximum number of candidate
pairs (100 by default as per <xref target="rfc5245bis"/>), the agent pairs (100 by default as per <xref target="RFC8445" format="default"
SHOULD discard any pairs in the Failed state to make room for the />), the agent
new pair. If there are no such pairs, the agent SHOULD discard a <bcp14>SHOULD</bcp14> discard any pairs in the Failed state to make
room for the
new pair. If there are no such pairs, the agent <bcp14>SHOULD</bcp14
> discard a
pair with a lower priority than the new pair in order to make room pair with a lower priority than the new pair in order to make room
for the new pair, until the number of pairs is equal to the maximum for the new pair, until the number of pairs is equal to the maximum
number of pairs. This processing is consistent with Section 6.1.2.5 number of pairs. This processing is consistent with
of <xref target='rfc5245bis'/>. <xref target="RFC8445" format="default" sectionFormat="of" section="
</t> 6.1.2.5"/>.
</list> </li>
</t> </ol>
</section> </section>
<section title='Inserting Trickled Candidate Pairs into a Check List' <section anchor="trickle-insert" numbered="true" toc="default">
anchor="trickle-insert"> <name>Inserting Trickled Candidate Pairs into a Checklist</name>
<t> <t>
After a local agent has trickled a candidate and formed a candidate After a local agent has trickled a candidate and formed a candidate
pair from that local candidate (<xref target='trickle-send'/>), or after pair from that local candidate (<xref target="trickle-send" format="defa ult"/>), or after
a remote agent has received a trickled candidate and formed a candidate a remote agent has received a trickled candidate and formed a candidate
pair from that remote candidate (<xref target='trickle-recv'/>), a Trick pair from that remote candidate (<xref target="trickle-recv" format="def
le ault"/>), a Trickle
ICE agent adds the new candidate pair to a check list as defined in ICE agent adds the new candidate pair to a checklist as defined in
this section. this section.
</t> </t>
<t> <t>
As an aid to understanding the procedures defined in this section, As an aid to understanding the procedures defined in this section,
consider the following tabular representation of all check lists in consider the following tabular representation of all checklists in
an agent (note that initially for one of the foundations, i.e., f5, an agent (note that initially for one of the foundations, i.e., f5,
there are no candidate pairs): there are no candidate pairs):
</t> </t>
<t>
<figure title="Example of Check List State" anchor="fig-checklist-0"> <table anchor="checklist_table">
<artwork> <name>Example of Checklist State</name>
<![CDATA[ <thead>
+-----------------+------+------+------+------+------+ <tr>
| | f1 | f2 | f3 | f4 | f5 | <th></th> <th>f1</th> <th>f2</th> <th>f3</th> <th>f4</th> <th>f5<
+-----------------+------+------+------+------+------+ /th>
| s1 (Audio.RTP) | F | F | F | | | </tr>
+-----------------+------+------+------+------+------+ </thead>
| s2 (Audio.RTCP) | F | F | F | F | | <tbody>
+-----------------+------+------+------+------+------+ <tr> <td>s1 (Audio.RTP)</td> <td>F</td> <td>F</td><td>F</td><td></td>
| s3 (Video.RTP) | F | | | | | <td/>
+-----------------+------+------+------+------+------+ </tr>
| s4 (Video.RTCP) | F | | | | | <tr> <td>s2 (Audio.RTCP)</td> <td>F</td> <td>F</td><td>F</td><td>F</td>
+-----------------+------+------+------+------+------+ <td/>
]]> </tr>
</artwork> <tr> <td>s3 (Video.RTP)</td> <td>F</td> <td></td><td> </td><td></td>
</figure> <td/>
</t> </tr>
<tr> <td>s4 (Video.RTCP)</td> <td>F</td> <td></td><td> </td><td>
</td><td/>
</tr>
</tbody>
</table>
<t> <t>
Each row in the table represents a component for a given data Each row in the table represents a component for a given data
stream (e.g., s1 and s2 might be the RTP and RTCP components stream (e.g., s1 and s2 might be the RTP and RTP Control Protocol (RTCP)
for audio) and thus a single check list in the check list set. components
for audio) and thus a single checklist in the checklist set.
Each column represents one foundation. Each cell represents one Each column represents one foundation. Each cell represents one
candidate pair. In the tables shown in this section, "F" stands candidate pair. In the tables shown in this section, "F" stands
for "frozen", "W" stands for "waiting", and "S" stands for for "frozen", "W" stands for "waiting", and "S" stands for
"succeeded"; in addition, "^^" is used to notate newly-added "succeeded"; in addition, "^^" is used to notate newly added
candidate pairs. candidate pairs.
</t> </t>
<t> <t>
When an agent commences ICE processing, in accordance with When an agent commences ICE processing, in accordance with
Section 6.1.2.6 of <xref target="rfc5245bis"/>, for each <xref target="RFC8445" format="default" sectionFormat="of" section="6.1 .2.6"/>, for each
foundation it will unfreeze the pair with the lowest component foundation it will unfreeze the pair with the lowest component
ID and, if the component IDs are equal, with the highest priority ID and, if the component IDs are equal, with the highest priority
(this is the topmost candidate pair in every column). (this is the topmost candidate pair in every column).
This initial state is shown in the following table. This initial state is shown in the following table.
</t> </t>
<table anchor="fig-checklist-initial">
<name>Initial Checklist State</name>
<thead>
<tr>
<th></th> <th>f1</th> <th>f2</th> <th>f3</th> <th>f4</th> <th>f5<
/th>
</tr>
</thead>
<tbody>
<tr> <td>s1 (Audio.RTP)</td> <td>W</td> <td>W</td><td>W</td><td></td>
<td/>
</tr>
<tr> <td>s2 (Audio.RTCP)</td> <td>F</td> <td>F</td><td>F</td><td>W</td>
<td/>
</tr>
<tr> <td>s3 (Video.RTP)</td> <td>F</td> <td></td><td> </td><td></td>
<td/>
</tr>
<tr> <td>s4 (Video.RTCP)</td> <td>F</td> <td></td><td> </td><td>
</td><td/>
</tr>
</tbody>
</table>
<t> <t>
<figure title="Initial Check List State" anchor="fig-checklist-initial"> Then, as the checks proceed (see
<artwork> <xref target="RFC8445" format="default" sectionFormat="of" section="7.2.
<![CDATA[ 5.4"/>), for each pair
+-----------------+------+------+------+------+------+
| | f1 | f2 | f3 | f4 | f5 |
+-----------------+------+------+------+------+------+
| s1 (Audio.RTP) | W | W | W | | |
+-----------------+------+------+------+------+------+
| s2 (Audio.RTCP) | F | F | F | W | |
+-----------------+------+------+------+------+------+
| s3 (Video.RTP) | F | | | | |
+-----------------+------+------+------+------+------+
| s4 (Video.RTCP) | F | | | | |
+-----------------+------+------+------+------+------+
]]>
</artwork>
</figure>
</t>
<t>
Then, as the checks proceed (see Section 7.2.5.4 of
<xref target="rfc5245bis"/>), for each pair
that enters the Succeeded state (denoted here by "S"), that enters the Succeeded state (denoted here by "S"),
the agent will unfreeze all pairs for all data streams with the same the agent will unfreeze all pairs for all data streams with the same
foundation (e.g., if the pair in column 1, row 1 succeeds then foundation (e.g., if the pair in column 1, row 1 succeeds then
the agent will unfreeze the pair in column 1, rows 2, 3, and 4). the agent will unfreeze the pairs in column 1, rows 2, 3, and 4).
</t>
<t>
<figure title="Check List State with Succeeded Candidate Pair" anchor="f
ig-checklist-succeeded">
<artwork>
<![CDATA[
+-----------------+------+------+------+------+------+
| | f1 | f2 | f3 | f4 | f5 |
+-----------------+------+------+------+------+------+
| s1 (Audio.RTP) | S | W | W | | |
+-----------------+------+------+------+------+------+
| s2 (Audio.RTCP) | W | F | F | W | |
+-----------------+------+------+------+------+------+
| s3 (Video.RTP) | W | | | | |
+-----------------+------+------+------+------+------+
| s4 (Video.RTCP) | W | | | | |
+-----------------+------+------+------+------+------+
]]>
</artwork>
</figure>
</t> </t>
<table anchor="fig-checklist-succeeded">
<name>Checklist State with Succeeded Candidate Pair</name>
<thead>
<tr>
<th></th> <th>f1</th> <th>f2</th> <th>f3</th> <th>f4</th> <th>f5<
/th>
</tr>
</thead>
<tbody>
<tr> <td>s1 (Audio.RTP)</td> <td>S</td> <td>W</td><td>W</td><td></td>
<td/>
</tr>
<tr> <td>s2 (Audio.RTCP)</td> <td>W</td> <td>F</td><td>F</td><td>W</td>
<td/>
</tr>
<tr> <td>s3 (Video.RTP)</td> <td>W</td> <td></td><td> </td><td></td>
<td/>
</tr>
<tr> <td>s4 (Video.RTCP)</td> <td>W</td> <td></td><td> </td><td>
</td><td/>
</tr>
</tbody>
</table>
<t> <t>
Trickle ICE preserves all of these rules as they apply to Trickle ICE preserves all of these rules as they apply to
"static" check list sets. This implies that if "static" checklist sets. This implies that if
a Trickle ICE agent were to begin connectivity checks with all a Trickle ICE agent were to begin connectivity checks with all
of its pairs already present, the way that pair states change of its pairs already present, the way that pair states change
is indistinguishable from that of a regular ICE agent. is indistinguishable from that of a regular ICE agent.
</t> </t>
<t> <t>
Of course, the major difference with Trickle ICE is that check list Of course, the major difference with Trickle ICE is that checklist
sets can be dynamically updated because candidates can sets can be dynamically updated because candidates can
arrive after connectivity checks have started. When this happens, an arrive after connectivity checks have started. When this happens, an
agent sets the state of the newly formed pair as described below. agent sets the state of the newly formed pair as described below.
</t> </t>
<t> <t>
Rule 1: If the newly formed pair has the lowest component ID and, Rule 1: If the newly formed pair has the lowest component ID and,
if the component IDs are equal, the highest priority of any candidate if the component IDs are equal, the highest priority of any candidate
pair for this foundation (i.e., if it is the topmost pair in the pair for this foundation (i.e., if it is the topmost pair in the
column), set the state to Waiting. For example, this would be the column), set the state to Waiting. For example, this would be the
case if the newly formed pair were placed in column 5, row 1. This case if the newly formed pair were placed in column 5, row 1. This
rule is consistent with Section 6.1.2.6 of <xref target="rfc5245bis"/>. rule is consistent with <xref target="RFC8445"
</t> format="default" sectionFormat="of" section="6.1.2.6"/>.
<t>
<figure title="Check List State with Newly Formed Pair, Rule 1" anchor="
fig-checklist-rule1">
<artwork>
<![CDATA[
+-----------------+------+------+------+------+------+
| | f1 | f2 | f3 | f4 | f5 |
+-----------------+------+------+------+------+------+
| s1 (Audio.RTP) | S | W | W | | ^W^ |
+-----------------+------+------+------+------+------+
| s2 (Audio.RTCP) | W | F | F | W | |
+-----------------+------+------+------+------+------+
| s3 (Video.RTP) | W | | | | |
+-----------------+------+------+------+------+------+
| s4 (Video.RTCP) | W | | | | |
+-----------------+------+------+------+------+------+
]]>
</artwork>
</figure>
</t> </t>
<table anchor="fig-checklist-rule1">
<name>Checklist State with Newly Formed Pair, Rule 1</name>
<thead>
<tr>
<th></th> <th>f1</th> <th>f2</th> <th>f3</th> <th>f4</th> <th>f5<
/th>
</tr>
</thead>
<tbody>
<tr> <td>s1 (Audio.RTP)</td> <td>S</td> <td>W</td> <td>W</td> <td></td
> <td>&#94;W&#94;</td>
</tr>
<tr> <td>s2 (Audio.RTCP)</td> <td>W</td> <td>F</td><td>F</td><td>W</td>
<td/>
</tr>
<tr> <td>s3 (Video.RTP)</td> <td>W</td> <td></td><td> </td><td></td>
<td/>
</tr>
<tr> <td>s4 (Video.RTCP)</td> <td>W</td> <td></td><td> </td><td>
</td><td/>
</tr>
</tbody>
</table>
<t> <t>
Rule 2: If there is at least one pair in the Succeeded state for Rule 2: If there is at least one pair in the Succeeded state for
this foundation, set the state to Waiting. For example, this would be this foundation, set the state to Waiting. For example, this would be
the case if the pair in column 5, row 1 succeeded and the newly formed the case if the pair in column 5, row 1 succeeded and the newly formed
pair were placed in column 5, row 2. This rule is consistent with pair were placed in column 5, row 2. This rule is consistent with
Section 7.2.5.3.3 of <xref target="rfc5245bis"/>. <xref target="RFC8445" format="default" sectionFormat="of" section="7.2.
</t> 5.3.3"/>.
<t>
<figure title="Check List State with Newly Formed Pair, Rule 2" anchor="
fig-checklist-rule2">
<artwork>
<![CDATA[
+-----------------+------+------+------+------+------+
| | f1 | f2 | f3 | f4 | f5 |
+-----------------+------+------+------+------+------+
| s1 (Audio.RTP) | S | W | W | | S |
+-----------------+------+------+------+------+------+
| s2 (Audio.RTCP) | W | F | F | W | ^W^ |
+-----------------+------+------+------+------+------+
| s3 (Video.RTP) | W | | | | |
+-----------------+------+------+------+------+------+
| s4 (Video.RTCP) | W | | | | |
+-----------------+------+------+------+------+------+
]]>
</artwork>
</figure>
</t> </t>
<table anchor="fig-checklist-rule2">
<name>Checklist State with Newly Formed Pair, Rule 2</name>
<thead>
<tr>
<th></th> <th>f1</th> <th>f2</th> <th>f3</th> <th>f4</th> <th>f5<
/th>
</tr>
</thead>
<tbody>
<tr> <td>s1 (Audio.RTP)</td> <td>S</td> <td>W</td> <td>W</td> <td></td
> <td>S</td>
</tr>
<tr> <td>s2 (Audio.RTCP)</td> <td>W</td> <td>F</td><td>F</td><td>W</td>
<td>&#94;W&#94;</td>
</tr>
<tr> <td>s3 (Video.RTP)</td> <td>W</td> <td></td><td> </td><td></td>
<td/>
</tr>
<tr> <td>s4 (Video.RTCP)</td> <td>W</td> <td></td><td> </td><td>
</td><td/>
</tr>
</tbody>
</table>
<t> <t>
Rule 3: In all other cases, set the state to Frozen. For example, Rule 3: In all other cases, set the state to Frozen. For example,
this would be the case if the newly formed pair were placed in this would be the case if the newly formed pair were placed in
column 3, row 3. column 3, row 3.
</t> </t>
<t>
<figure title="Check List State with Newly Formed Pair, Rule 3" anchor=" <table anchor="fig-checklist-rule3">
fig-checklist-rule3"> <name>Checklist State with Newly Formed Pair, Rule 3</name>
<artwork> <thead>
<![CDATA[ <tr>
+-----------------+------+------+------+------+------+ <th></th> <th>f1</th> <th>f2</th> <th>f3</th> <th>f4</th> <th>f5<
| | f1 | f2 | f3 | f4 | f5 | /th>
+-----------------+------+------+------+------+------+ </tr>
| s1 (Audio.RTP) | S | W | W | | S | </thead>
+-----------------+------+------+------+------+------+ <tbody>
| s2 (Audio.RTCP) | W | F | F | W | W | <tr> <td>s1 (Audio.RTP)</td> <td>S</td> <td>W</td> <td>W</td> <td></td
+-----------------+------+------+------+------+------+ > <td>S</td>
| s3 (Video.RTP) | W | | ^F^ | | | </tr>
+-----------------+------+------+------+------+------+ <tr> <td>s2 (Audio.RTCP)</td> <td>W</td> <td>F</td><td>F</td><td>W</td>
| s4 (Video.RTCP) | W | | | | | <td>W</td>
+-----------------+------+------+------+------+------+ </tr>
]]> <tr> <td>s3 (Video.RTP)</td> <td>W</td> <td></td><td>&#94;F&#94;</td><
</artwork> td></td> <td/>
</figure> </tr>
</t> <tr> <td>s4 (Video.RTCP)</td> <td>W</td> <td></td><td> </td><td>
</td><td/>
</tr>
</tbody>
</table>
</section> </section>
<section title='Generating an End-of-Candidates Indication' <section anchor="end-of-candidates.send" numbered="true" toc="default">
anchor="end-of-candidates.send"> <name>Generating an End-of-Candidates Indication</name>
<t> <t>
Once all candidate gathering is completed or expires for an Once all candidate gathering is completed or expires for an
ICE session associated with a specific data stream, the agent will gener ate an ICE session associated with a specific data stream, the agent will gener ate an
"end-of-candidates" indication for that session and convey it to "end-of-candidates" indication for that session and convey it to
the remote agent via the signaling channel. Although the exact form of the remote agent via the signaling channel. Although the exact form of
the indication depends on the using protocol, the indication the indication depends on the using protocol, the indication
MUST specify the generation (Username Fragment and Password combination) so that an agent <bcp14>MUST</bcp14> specify the generation (Username Fragment and Passwo rd combination), so that an agent
can correlate the end-of-candidates indication with a particular ICE can correlate the end-of-candidates indication with a particular ICE
session. The indication can be conveyed in the following ways: session. The indication can be conveyed in the following ways:
<list style='symbols'>
<t>As part of an initiation request (which would typically be the case
with
the initial ICE description for half trickle)</t>
<t>Along with the last candidate an agent can send for a stream</t>
<t>As a standalone notification (e.g., after STUN Binding requests
or TURN Allocate requests to a server time out and the agent
is no longer actively gathering candidates)</t>
</list>
</t> </t>
<ul spacing="normal">
<li>As part of an initiation request (which would typically be the case
with
the initial ICE description for half trickle)</li>
<li>Along with the last candidate an agent can send for a stream</li>
<li>As a standalone notification (e.g., after STUN Binding requests
or TURN Allocate requests to a server time out and the agent
is no longer actively gathering candidates)</li>
</ul>
<t> <t>
Conveying an end-of-candidates indication in a timely manner is importan t Conveying an end-of-candidates indication in a timely manner is importan t
in order to avoid ambiguities and speed up the conclusion of ICE process ing. in order to avoid ambiguities and speed up the conclusion of ICE process ing.
In particular: In particular:
<list style='symbols'> </t>
<t> <ul spacing="normal">
A controlled Trickle ICE agent SHOULD convey an end-of-candidates <li>
A controlled Trickle ICE agent <bcp14>SHOULD</bcp14> convey an end-o
f-candidates
indication after it has completed gathering for a data stream, indication after it has completed gathering for a data stream,
unless ICE processing terminates before the agent has had a chance unless ICE processing terminates before the agent has had a chance
to complete gathering. to complete gathering.
</t> </li>
<t> <li>
A controlling agent MAY conclude ICE processing prior to conveying A controlling agent <bcp14>MAY</bcp14> conclude ICE processing prior
to conveying
end-of-candidates indications for all streams. However, it is end-of-candidates indications for all streams. However, it is
RECOMMENDED for a controlling agent to convey end-of-candidates <bcp14>RECOMMENDED</bcp14> for a controlling agent to convey end-of- candidates
indications whenever possible for the sake of consistency and to indications whenever possible for the sake of consistency and to
keep middleboxes and controlled agents up-to-date on the state of keep middleboxes and controlled agents up-to-date on the state of
ICE processing. ICE processing.
</t> </li>
</list> </ul>
</t>
<t> <t>
When conveying an end-of-candidates indication during trickling When conveying an end-of-candidates indication during trickling
(rather than as a part of the initial ICE description or a response ther eto), (rather than as a part of the initial ICE description or a response ther eto),
it is the responsibility of the it is the responsibility of the
using protocol to define methods for associating the using protocol to define methods for associating the
indication with one or more specific data streams. indication with one or more specific data streams.
</t> </t>
<t> <t>
An agent MAY also choose to generate an end-of-candidates An agent <bcp14>MAY</bcp14> also choose to generate an end-of-candidates
indication before candidate gathering has actually completed, if the indication before candidate gathering has actually completed, if the
agent determines that gathering has continued for more than an agent determines that gathering has continued for more than an
acceptable period of time. However, an agent MUST NOT convey any acceptable period of time. However, an agent <bcp14>MUST NOT</bcp14> con vey any
more candidates after it has conveyed an end-of-candidates more candidates after it has conveyed an end-of-candidates
indication. indication.
</t> </t>
<t> <t>
When performing half trickle, an agent SHOULD convey an When performing half trickle, an agent <bcp14>SHOULD</bcp14> convey an
end-of-candidates indication together with its initial ICE description u nless end-of-candidates indication together with its initial ICE description u nless
it is planning to potentially trickle additional candidates (e.g., in it is planning to potentially trickle additional candidates (e.g., in
case the remote party turns out to support Trickle ICE). case the remote party turns out to support Trickle ICE).
</t> </t>
<t> <t>
After an agent conveys the end-of-candidates indication, it will After an agent conveys the end-of-candidates indication, it will
update the state of the corresponding check list as explained update the state of the corresponding checklist as explained
in <xref target="checks"/>. Past that point, an in <xref target="checks" format="default"/>. Past that point, an
agent MUST NOT trickle any new candidates within this ICE session. agent <bcp14>MUST NOT</bcp14> trickle any new candidates within this ICE
session.
Therefore, adding new candidates to the Therefore, adding new candidates to the
negotiation is possible only through an ICE restart (see negotiation is possible only through an ICE restart (see
<xref target='subsequent'/>). <xref target="subsequent" format="default"/>).
</t> </t>
<t> <t>
This specification does not This specification does not
override regular ICE semantics for concluding ICE processing. override regular ICE semantics for concluding ICE processing.
Therefore, even if end-of-candidates indications are conveyed, Therefore, even if end-of-candidates indications are conveyed,
an agent will still need to go through pair nomination. Also, if an agent will still need to go through pair nomination. Also, if
pairs have been nominated for components and data streams, ICE pairs have been nominated for components and data streams, ICE
processing MAY still conclude even if end-of-candidates processing <bcp14>MAY</bcp14> still conclude even if end-of-candidates
indications have not been received for all streams. In all cases, indications have not been received for all streams. In all cases,
an agent MUST NOT trickle any new candidates within an ICE session an agent <bcp14>MUST NOT</bcp14> trickle any new candidates within an IC
after nomination of a candidate pair as described in Section 8.1.1 E session
of <xref target='rfc5245bis'/>. after nomination of a candidate pair as described in
<xref target="RFC8445" format="default" sectionFormat="of" section="8.1.
1"/>.
</t> </t>
</section> </section>
<section title='Receiving an End-of-Candidates Indication' <section anchor="end-of-candidates.recv" numbered="true" toc="default">
anchor="end-of-candidates.recv"> <name>Receiving an End-of-Candidates Indication</name>
<t> <t>
Receiving an end-of-candidates indication enables an agent to Receiving an end-of-candidates indication enables an agent to
update check list states and, in case valid pairs do not exist update checklist states and, in case valid pairs do not exist
for every component in every data stream, determine that ICE for every component in every data stream, determine that ICE
processing has failed. It also enables an agent to speed up the processing has failed. It also enables an agent to speed up the
conclusion of ICE processing when a candidate pair has been validated conclusion of ICE processing when a candidate pair has been validated
but it involves the use of lower-preference transports such as but uses a lower-preference transport such as
TURN. In such situations, an implementation MAY choose to wait TURN. In such situations, an implementation <bcp14>MAY</bcp14> choose to
and see if higher-priority candidates are received; in this case wait
and see if higher-priority candidates are received; in this case,
the end-of-candidates indication provides a notification that such the end-of-candidates indication provides a notification that such
candidates are not forthcoming. candidates are not forthcoming.
</t> </t>
<t> <t>
When an agent receives an end-of-candidates indication for a When an agent receives an end-of-candidates indication for a
specific data stream, it will update the state of the relevant specific data stream, it will update the state of the relevant
check list as per <xref target="checks"/> (which might lead to checklist as per <xref target="checks" format="default"/> (which might l
some check lists being marked as Failed). If the check list is ead to
still in the Running state after the update, the agent will persist some checklists being marked as Failed).
the fact that an end-of-candidates indication has been If the checklist is
still in the Running state after the update, the agent will note that an
end-of-candidates indication has been
received and take it into account in future updates received and take it into account in future updates
to the check list. to the checklist.
</t> </t>
<t> <t>
After an agent has received an end-of-candidates indication, it After an agent has received an end-of-candidates indication, it
MUST ignore any newly received candidates for that data <bcp14>MUST</bcp14> ignore any newly received candidates for that data
stream or data session. stream or data session.
</t> </t>
</section> </section>
<section title='Subsequent Exchanges and ICE Restarts' <section anchor="subsequent" numbered="true" toc="default">
anchor="subsequent"> <name>Subsequent Exchanges and ICE Restarts</name>
<t> <t>
Before conveying an end-of-candidates indication, Before conveying an end-of-candidates indication,
either agent MAY convey subsequent candidate information at any time all either agent <bcp14>MAY</bcp14> convey subsequent candidate information
owed at any time allowed
by the using protocol. When this happens, agents will use by the using protocol. When this happens, agents will use semantics from
<xref target="rfc5245bis"/> semantics (e.g., checking of the <xref target="RFC8445" format="default"/> (e.g., checking of the
Username Fragment and Password combination) to determine whether or not Username Fragment and Password combination) to determine whether or not
the new candidate information requires an ICE restart. the new candidate information requires an ICE restart.
</t> </t>
<t> <t>
If an ICE restart If an ICE restart
occurs, the agents can assume that Trickle ICE is still supported occurs, the agents can assume that Trickle ICE is still supported
if support was determined previously, and thus can engage in Trickle ICE if support was determined previously; thus, they can engage in Trickle I CE
behavior as they would in an initial exchange of ICE descriptions where behavior as they would in an initial exchange of ICE descriptions where
support was determined through a capabilities discovery method. support was determined through a capabilities discovery method.
</t> </t>
</section> </section>
<section title='Half Trickle' anchor="half-trickle"> <section anchor="half-trickle" numbered="true" toc="default">
<name>Half Trickle</name>
<t> <t>
In half trickle, the initiator conveys the initial ICE description In half trickle, the initiator conveys the initial ICE description
with a usable but not necessarily full generation of candidates. This with a usable but not necessarily full generation of candidates. This
ensures that the ICE description can be processed by a regular ICE ensures that the ICE description can be processed by a regular ICE
responder and is mostly meant for use in cases where support for responder and is mostly meant for use in cases where support for
Trickle ICE cannot be confirmed prior to conveying the initial ICE Trickle ICE cannot be confirmed prior to conveying the initial ICE
description. The initial ICE description indicates support for description. The initial ICE description indicates support for
Trickle ICE, so that the responder can respond with something less Trickle ICE, so that the responder can respond with something less
than a full generation of candidates and then trickle the rest. than a full generation of candidates and then trickle the rest.
The initial ICE description for half trickle can contain The initial ICE description for half trickle can contain
an end-of-candidates indication, although this is not mandatory an end-of-candidates indication, although this is not mandatory
because if trickle support is confirmed then the initiator can because if trickle support is confirmed, then the initiator can
choose to trickle additional candidates before it conveys an choose to trickle additional candidates before it conveys an
end-of-candidates indication. end-of-candidates indication.
</t> </t>
<t> <t>
The half trickle mechanism can be used in cases where there is The half-trickle mechanism can be used in cases where there is
no way for an agent to verify in advance whether a remote no way for an agent to verify in advance whether a remote
party supports Trickle ICE. Because the initial ICE description contain party supports Trickle ICE. Because the initial ICE description contains
a full generation of candidates, it can thus be handled by a regular a full generation of candidates, it can thus be handled by a regular
ICE agent, while still allowing a Trickle ICE agent to use ICE agent, while still allowing a Trickle ICE agent to use
the optimization defined in this specification. This prevents the optimization defined in this specification. This prevents
negotiation from failing in the former case while still giving negotiation from failing in the former case while still giving
roughly half the Trickle ICE benefits in the latter. roughly half the Trickle ICE benefits in the latter.
</t> </t>
<t> <t>
Use of half trickle is only necessary during an initial Use of half trickle is only necessary during an initial
exchange of ICE descriptions. After both parties have received exchange of ICE descriptions. After both parties have received
an ICE description from their peer, they can each reliably an ICE description from their peer, they can each reliably
determine Trickle ICE support and use it for all subsequent determine Trickle ICE support and use it for all subsequent
exchanges (see <xref target='subsequent'/>). exchanges (see <xref target="subsequent" format="default"/>).
</t> </t>
<t> <t>
In some instances, using half trickle might bring more than In some instances, using half trickle might bring more than
just half the improvement in terms of user experience. This just half the improvement in terms of user experience.
can happen when an agent starts gathering candidates upon user
interface cues that the user will soon be initiating an interaction, This
can happen when an agent starts gathering candidates upon user-interface
cues that the user will soon be initiating an interaction,
such as activity on a keypad or the phone going off hook. This such as activity on a keypad or the phone going off hook. This
would mean that some or all of the candidate would mean that some or all of the candidate
gathering could be completed before the agent actually gathering could be completed before the agent actually
needs to convey the candidate information. Because the responder will be able needs to convey the candidate information. Because the responder will be able
to trickle candidates, both agents will be able to start to trickle candidates, both agents will be able to start
connectivity checks and complete ICE processing earlier than connectivity checks and complete ICE processing earlier than
with regular ICE and potentially even as early as with full with regular ICE and potentially even as early as with full
trickle. trickle.
</t> </t>
<t> <t>
skipping to change at line 1016 skipping to change at line 1069
example, a multipurpose user agent or a WebRTC web page where example, a multipurpose user agent or a WebRTC web page where
communication is a non-central feature (e.g., calling a support communication is a non-central feature (e.g., calling a support
line in case of a problem with the main features) would not line in case of a problem with the main features) would not
necessarily have a way of distinguishing between call necessarily have a way of distinguishing between call
intentions and other user activity. In such cases, using full intentions and other user activity. In such cases, using full
trickle is most likely to result in an ideal user experience. trickle is most likely to result in an ideal user experience.
Even so, using half trickle would be an improvement over regular Even so, using half trickle would be an improvement over regular
ICE because it would result in a better experience for responders. ICE because it would result in a better experience for responders.
</t> </t>
</section> </section>
<section title='Preserving Candidate Order while Trickling'> <section numbered="true" toc="default">
<name>Preserving Candidate Order While Trickling</name>
<t> <t>
One important aspect of regular ICE is that connectivity checks One important aspect of regular ICE is that connectivity checks
for a specific foundation and component are attempted for a specific foundation and component are attempted
simultaneously by both agents, so that any firewalls or NATs simultaneously by both agents, so that any firewalls or NATs
fronting the agents would whitelist both endpoints and allow fronting the agents would whitelist both endpoints and allow
all except for the first ("suicide") packets to go through. This all except for the first ("suicide") packets to go through. This
is also important to unfreezing candidates at the right time. While is also important to unfreezing candidates at the right time. While
not crucial, preserving this behavior in Trickle ICE is likely to not crucial, preserving this behavior in Trickle ICE is likely to
improve ICE performance. improve ICE performance.
</t> </t>
<t> <t>
To achieve this, when trickling candidates, agents SHOULD respect the To achieve this, when trickling candidates, agents <bcp14>SHOULD</bcp14> respect the
order of components as reflected by their component IDs; that is, order of components as reflected by their component IDs; that is,
candidates for a given component candidates for a given component
SHOULD NOT be conveyed prior to candidates for a component with a <bcp14>SHOULD NOT</bcp14> be conveyed prior to candidates for a componen t with a
lower ID number within the same foundation. In addition, candidates lower ID number within the same foundation. In addition, candidates
SHOULD be paired, following the procedures in <xref target='trickle-inse rt'/>, <bcp14>SHOULD</bcp14> be paired, following the procedures in <xref targe t="trickle-insert" format="default"/>,
in the same order they are conveyed. in the same order they are conveyed.
</t> </t>
<t> <t>
For example, the following SDP description contains two For example, the following SDP description contains two
components (RTP and RTCP) and two foundations (host and components (RTP and RTCP) and two foundations (host and
server reflexive): server reflexive):
<figure> </t>
<artwork> <sourcecode type="sdp"><![CDATA[
<![CDATA[
v=0 v=0
o=jdoe 2890844526 2890842807 IN IP4 10.0.1.1 o=jdoe 2890844526 2890842807 IN IP4 10.0.1.1
s= s=
c=IN IP4 10.0.1.1 c=IN IP4 10.0.1.1
t=0 0 t=0 0
a=ice-pwd:asd88fgpdd777uzjYhagZg a=ice-pwd:asd88fgpdd777uzjYhagZg
a=ice-ufrag:8hhY a=ice-ufrag:8hhY
m=audio 5000 RTP/AVP 0 m=audio 5000 RTP/AVP 0
a=rtpmap:0 PCMU/8000 a=rtpmap:0 PCMU/8000
a=candidate:1 1 UDP 2130706431 10.0.1.1 5000 typ host a=candidate:1 1 UDP 2130706431 10.0.1.1 5000 typ host
a=candidate:1 2 UDP 2130706431 10.0.1.1 5001 typ host a=candidate:1 2 UDP 2130706431 10.0.1.1 5001 typ host
a=candidate:2 1 UDP 1694498815 192.0.2.3 5000 typ srflx a=candidate:2 1 UDP 1694498815 192.0.2.3 5000 typ srflx
raddr 10.0.1.1 rport 8998 raddr 10.0.1.1 rport 8998
a=candidate:2 2 UDP 1694498815 192.0.2.3 5001 typ srflx a=candidate:2 2 UDP 1694498815 192.0.2.3 5001 typ srflx
raddr 10.0.1.1 rport 8998 raddr 10.0.1.1 rport 8998
]]> ]]></sourcecode>
</artwork> <t>
</figure> For this candidate information, the RTCP host candidate would not be con
For this candidate information the RTCP host candidate would not be conv veyed
eyed prior to the RTP host candidate. Similarly, the RTP server-reflexive
prior to the RTP host candidate. Similarly the RTP server candidate would be conveyed together with or prior to the
reflexive candidate would be conveyed together with or prior to the RTCP server-reflexive candidate.
RTCP server reflexive candidate.
</t> </t>
</section> </section>
<section title='Requirements for Using Protocols' anchor="reqs"> <section anchor="reqs" numbered="true" toc="default">
<name>Requirements for Using Protocols</name>
<t> <t>
In order to fully enable the use of Trickle ICE, this specification In order to fully enable the use of Trickle ICE, this specification
defines the following requirements for using protocols. defines the following requirements for using protocols.
<list style='symbols'> </t>
<t> <ul spacing="normal">
A using protocol SHOULD provide a way for parties to advertise <li>
A using protocol <bcp14>SHOULD</bcp14> provide a way for parties to
advertise
and discover support for Trickle ICE before an ICE and discover support for Trickle ICE before an ICE
session begins (see <xref target='support'/>). session begins (see <xref target="support" format="default"/>).
</t> </li>
<t> <li>
A using protocol MUST provide methods for incrementally A using protocol <bcp14>MUST</bcp14> provide methods for incremental
ly
conveying (i.e., "trickling") additional candidates after conveying (i.e., "trickling") additional candidates after
conveying the initial ICE description (see conveying the initial ICE description (see
<xref target='trickle-send'/>). <xref target="trickle-send" format="default"/>).
</t> </li>
<t> <li>
A using protocol MUST deliver each trickled candidate A using protocol <bcp14>MUST</bcp14> deliver each trickled candidate
or end-of-candidates indication exactly once or end-of-candidates indication exactly once
and in the same order it was conveyed (see and in the same order it was conveyed (see
<xref target='trickle-send'/>). <xref target="trickle-send" format="default"/>).
</t> </li>
<t> <li>
A using protocol MUST provide a mechanism for both parties A using protocol <bcp14>MUST</bcp14> provide a mechanism for both pa
rties
to indicate and agree on the ICE session in force to indicate and agree on the ICE session in force
(see <xref target='trickle-send'/>). (see <xref target="trickle-send" format="default"/>).
</t> </li>
<t> <li>
A using protocol MUST provide a way for parties to communicate the A using protocol <bcp14>MUST</bcp14> provide a way for parties to co
end-of-candidates indication, which MUST specify the particular ICE mmunicate the
session to which the indication applies (see <xref target='end-of-ca end-of-candidates indication, which <bcp14>MUST</bcp14> specify the
ndidates.send'/>). particular
</t> ICE session to which the indication applies (see <xref
</list> target="end-of-candidates.send" format="default"/>).
</t> </li>
</ul>
</section> </section>
<section title='IANA Considerations'> <section numbered="true" toc="default">
<name>IANA Considerations</name>
<t> <t>
IANA is requested to register the following ICE option in the "ICE IANA has registered the following ICE option in the "ICE
Options" sub-registry of the "Interactive Connectivity Establishment Options" subregistry of the "Interactive Connectivity Establishment
(ICE) registry", following the procedures defined in (ICE) registry", following the procedures defined in
<xref target='RFC6336'/>. <xref target="RFC6336" format="default"/>.
</t> </t>
<t> <dl newline="false" spacing="normal">
<list style='hanging'> <dt>ICE Option:</dt>
<t hangText="ICE Option:">trickle</t> <dd>trickle</dd>
<t hangText="Contact:">IESG, iesg@ietf.org</t> <dt>Contact:</dt>
<t hangText="Change control:">IESG</t> <dd>IESG &lt;iesg@ietf.org&gt;</dd>
<t hangText="Description:"> <dt>Change controller:</dt>
An ICE option of "trickle" indicates support for incremental <dd>IESG</dd>
<dt>Description:</dt>
<dd>
An ICE option of 'trickle' indicates support for incremental
communication of ICE candidates. communication of ICE candidates.
</t> </dd>
<t hangText="Reference:">RFC XXXX</t> <dt>Reference:</dt>
</list> <dd>RFC 8838</dd>
</t> </dl>
</section> </section>
<section title='Security Considerations'> <section numbered="true" toc="default">
<name>Security Considerations</name>
<t> <t>
This specification inherits most of its semantics from This specification inherits most of its semantics from
<xref target="rfc5245bis"/> and as a result all security <xref target="RFC8445" format="default"/>, and as a result, all security
considerations described there apply to Trickle ICE. considerations described there apply to Trickle ICE.
</t> </t>
<t> <t>
If the privacy implications of revealing host addresses on an If the privacy implications of revealing host addresses on an
endpoint device are a concern (see for example the discussion endpoint device are a concern (see, for example, the discussion
in <xref target='I-D.ietf-rtcweb-ip-handling'/> and in Section 19 in <xref target="RFC8828" format="default"/> and in
of <xref target="rfc5245bis"/>), agents can generate ICE descriptions th <xref target="RFC8445" section="19" sectionFormat="of"/>), agents can ge
at contain no nerate ICE descriptions that contain no
candidates and then only trickle candidates that do not reveal candidates and then only trickle candidates that do not reveal
host addresses (e.g., relayed candidates). host addresses (e.g., relayed candidates).
</t> </t>
</section> </section>
<section title='Acknowledgements'>
<t>
The authors would like to thank Bernard Aboba, Flemming Andreasen,
Rajmohan Banavi, Taylor Brandstetter, Philipp Hancke, Christer Holmberg,
Ari Keranen, Paul Kyzivat, Jonathan Lennox, Enrico Marocco, Pal Martinse
n,
Nils Ohlmeier, Thomas Stach, Peter Thatcher, Martin Thomson, Brandon Wil
liams,
and Dale Worley for their reviews and suggestions on improving this docu
ment.
Sarah Banks, Roni Even, and David Mandelberg completed opsdir, genart, a
nd
security reviews, respectively. Thanks also to Ari Keranen and Peter Tha
tcher
in their role as chairs, and Ben Campbell in his role as responsible Are
a
Director.
</t>
</section>
</middle> </middle>
<back> <back>
<references title='Normative References'> <references>
<?rfc include="reference.RFC.2119"?> <name>References</name>
<references>
<name>Normative References</name>
<xi:include href="https://xml2rfc.tools.ietf.org/public/rfc/bibxml/refer
ence.RFC.2119.xml"/>
<xi:include href="https://xml2rfc.tools.ietf.org/public/rfc/bibxml/refer
ence.RFC.8174.xml"/>
<!--note: rfc5245bis is now RFC 8445-->
<xi:include href="https://xml2rfc.tools.ietf.org/public/rfc/bibxml/referen
ce.RFC.8445.xml"/>
</references>
<references>
<name>Informative References</name>
<xi:include href="https://xml2rfc.tools.ietf.org/public/rfc/bibxml/refer
ence.RFC.1918.xml"/>
<xi:include href="https://xml2rfc.tools.ietf.org/public/rfc/bibxml/refer
ence.RFC.3261.xml"/>
<xi:include href="https://xml2rfc.tools.ietf.org/public/rfc/bibxml/refer
ence.RFC.3264.xml"/>
<xi:include href="https://xml2rfc.tools.ietf.org/public/rfc/bibxml/refer
ence.RFC.4566.xml"/>
<xi:include href="https://xml2rfc.tools.ietf.org/public/rfc/bibxml/refer
ence.RFC.4787.xml"/>
<xi:include href="https://xml2rfc.tools.ietf.org/public/rfc/bibxml/refer
ence.RFC.5389.xml"/>
<xi:include href="https://xml2rfc.tools.ietf.org/public/rfc/bibxml/refer
ence.RFC.6120.xml"/>
<xi:include href="https://xml2rfc.tools.ietf.org/public/rfc/bibxml/refer
ence.RFC.6336.xml"/>
<xi:include href="https://xml2rfc.tools.ietf.org/public/rfc/bibxml/refer
ence.RFC.8656.xml"/>
<reference anchor='rfc5245bis'> <!--draft-ietf-mmusic-trickle-ice-sip-18 in C238 -->
<front> <reference anchor="RFC8840" target="https://www.rfc-editor.org/info/rfc88
<title>Interactive Connectivity Establishment (ICE): A Protocol for Network Addr 40">
ess Translator (NAT) Traversal</title> <front>
<author initials='A' surname='Keranen' fullname='Ari Keranen'> <title>A Session Initiation Protocol (SIP) Usage for Incremental Pro
<organization /> visioning of Candidates for the Interactive Connectivity Establishment (Trickle
</author> ICE)</title>
<author initials='C' surname='Holmberg' fullname='Christer Holmberg'>
<organization />
</author>
<author initials='J' surname='Rosenberg' fullname='Jonathan Rosenberg'>
<organization />
</author>
<date month='March' day='8' year='2018' />
<abstract><t>This document describes a protocol for Network Address Translator (
NAT) traversal for UDP-based multimedia. This protocol is called Interactive Co
nnectivity Establishment (ICE). ICE makes use of the Session Traversal Utilitie
s for NAT (STUN) protocol and its extension, Traversal Using Relay NAT (TURN).
This document obsoletes RFC 5245.</t></abstract>
</front>
<seriesInfo name='Internet-Draft' value='draft-ietf-ice-rfc5245bis-20' />
<format type='TXT'
target='http://www.ietf.org/internet-drafts/draft-ietf-ice-rfc5245bis-20
.txt' />
</reference>
</references> <author initials="E" surname="Ivov" fullname="Emil Ivov">
<references title='Informative References'> <organization/>
<?rfc include="reference.RFC.1918"?> </author>
<?rfc include="reference.RFC.3261"?> <author initials="T" surname="Stach" fullname="Thomas Stach">
<?rfc include="reference.RFC.3264"?> <organization/>
<?rfc include="reference.RFC.4566"?> </author>
<?rfc include="reference.RFC.4787"?> <author initials="E" surname="Marocco" fullname="Enrico Marocco">
<?rfc include="reference.RFC.5389"?> <organization/>
<?rfc include="reference.RFC.5766"?> </author>
<?rfc include="reference.RFC.6120"?> <author initials="C" surname="Holmberg" fullname="Christer Holmberg"
<?rfc include="reference.RFC.6336"?> >
<reference anchor='I-D.ietf-mmusic-trickle-ice-sip'> <organization/>
<front> </author>
<title>A Session Initiation Protocol (SIP) usage for Trickle ICE</title> <date month="June" year="2018"/>
<author initials='E' surname='Ivov' fullname='Emil Ivov'> </front>
<organization /> <seriesInfo name="DOI" value="10.17487/RFC8840"/>
</author> <seriesInfo name="RFC" value="8840"/>
<author initials='T' surname='Stach' fullname='Thomas Stach'> </reference>
<organization />
</author> <!--draft-ietf-rtcweb-ip-handling-09 in C238 -->
<author initials='E' surname='Marocco' fullname='Enrico Marocco'> <reference anchor="RFC8828" target="https://www.rfc-editor.org/info/rfc88
<organization /> 28">
</author> <front>
<author initials='C' surname='Holmberg' fullname='Christer Holmberg'> <title>WebRTC IP Address Handling Requirements</title>
<organization /> <author initials="J" surname="Uberti" fullname="Justin Uberti">
</author> <organization/>
<date month='February' day='24' year='2018' /> </author>
<abstract><t>The Interactive Connectivity Establishment (ICE) protocol describes <author initials="G" surname="Shieh" fullname="Guo-wei Shieh">
a Network Address Translator (NAT) traversal mechanism for UDP-based multimedia <organization/>
sessions established with the Offer/Answer model. The ICE extension for Increm </author>
ental Provisioning of Candidates (Trickle ICE) defines a mechanism that allows I <date month="May" year="2020"/>
CE agents to shorten session establishment delays by making the candidate gather </front>
ing and connectivity checking phases of ICE non-blocking and by executing them i <seriesInfo name="DOI" value="10.17487/RFC8828"/>
n parallel. This document defines usage semantics for Trickle ICE with the Sess <seriesInfo name="RFC" value="8828"/>
ion Initiation Protocol (SIP).</t></abstract> </reference>
</front>
<seriesInfo name='Internet-Draft' value='draft-ietf-mmusic-trickle-ice-sip-14' / <reference anchor="XEP-0176">
> <front>
<format type='TXT' <title>XEP-0176: Jingle ICE-UDP Transport Method</title>
target='http://www.ietf.org/internet-drafts/draft-ietf-mmusic-trickle-ic <seriesInfo name="XMPP Standards Foundation," value="XEP-0176"/>
e-sip-14.txt' /> <author initials="J." surname="Beda" fullname="Joe Beda">
</reference> <organization abbrev="Google">Google</organization>
<reference anchor='I-D.ietf-rtcweb-ip-handling'> </author>
<front> <author initials="S." surname="Ludwig" fullname="Scott Ludwig">
<title>WebRTC IP Address Handling Requirements</title> <organization abbrev="Google">Google</organization>
<author initials='J' surname='Uberti' fullname='Justin Uberti'> </author>
<organization /> <author initials="P." surname="Saint-Andre" fullname="Peter Saint-An
</author> dre">
<author initials='G' surname='Shieh' fullname='Guo-wei Shieh'>
<organization />
</author>
<date month='March' day='1' year='2018' />
<abstract><t>This document provides information and requirements for how IP addr
esses should be handled by WebRTC implementations.</t></abstract>
</front>
<seriesInfo name='Internet-Draft' value='draft-ietf-rtcweb-ip-handling-06' />
<format type='TXT'
target='http://www.ietf.org/internet-drafts/draft-ietf-rtcweb-ip-handlin
g-06.txt' />
</reference>
<reference anchor="XEP-0176">
<front>
<title>XEP-0176: Jingle ICE-UDP Transport Method</title>
<author initials='J.' surname='Beda' fullname='Joe Beda'>
<organization abbrev='Google'>Google</organization>
</author>
<author initials='S.' surname='Ludwig'
fullname='Scott Ludwig'>
<organization abbrev='Google'>Google</organization>
</author>
<author initials='P.' surname='Saint-Andre'
fullname='Peter Saint-Andre'>
</author>
<author initials='J.' surname='Hildebrand'
fullname='Joe Hildebrand'>
<organization abbrev='Cisco'>Cisco</organization>
</author>
<author initials='S.' surname='Egan' fullname='Sean Egan'>
<organization abbrev='Google'>Google </organization>
</author>
<author initials='R.' surname='McQueen'
fullname='Robert McQueen'>
<organization abbrev='Collabora'>Collabora</organization>
</author>
<date month="June" year="2009" />
</front>
<seriesInfo name="XEP" value="XEP-0176" />
</reference>
<reference anchor="XEP-0030">
<front>
<title>XEP-0030: Service Discovery</title>
<author initials='J.' surname='Hildebrand'
fullname='Joe Hildebrand'>
<organization abbrev='Cisco'>Cisco</organization>
</author> </author>
<author initials='P.' surname='Millard' <author initials="J." surname="Hildebrand" fullname="Joe Hildebrand"
fullname='Peter Millard'> >
<organization abbrev="Cisco">Cisco</organization>
</author>
<author initials="S." surname="Egan" fullname="Sean Egan">
<organization abbrev="Google">Google </organization>
</author>
<author initials="R." surname="McQueen" fullname="Robert McQueen">
<organization abbrev="Collabora">Collabora</organization>
</author>
<date month="June" year="2009"/>
</front>
</reference>
<reference anchor="XEP-0030">
<front>
<title>XEP-0030: Service Discovery</title>
<seriesInfo name="XMPP Standards Foundation," value="XEP-0030"/>
<author initials="J." surname="Hildebrand" fullname="Joe Hildebrand"
>
<organization abbrev="Cisco">Cisco</organization>
</author>
<author initials="P." surname="Millard" fullname="Peter Millard">
</author> </author>
<author initials='R.' surname='Eatmon' <author initials="R." surname="Eatmon" fullname="Ryan Eatmon">
fullname='Ryan Eatmon'>
</author> </author>
<author initials='P.' surname='Saint-Andre' <author initials="P." surname="Saint-Andre" fullname="Peter Saint-An
fullname='Peter Saint-Andre'> dre">
</author> </author>
<date month="June" year="2008" /> <date month="June" year="2008"/>
</front> </front>
<seriesInfo name="XEP" value="XEP-0030" /> </reference>
</reference> </references>
</references> </references>
<section title='Interaction with Regular ICE' <section anchor="interaction" numbered="true" toc="default">
anchor='interaction'> <name>Interaction with Regular ICE</name>
<t> <t>
The ICE protocol was designed to be flexible enough to The ICE protocol was designed to be flexible enough to
work in and adapt to as many network environments as work in and adapt to as many network environments as
possible. Despite that flexibility, ICE as specified in possible. Despite that flexibility, ICE as specified in
<xref target="rfc5245bis"/> does not by itself support trickle <xref target="RFC8445" format="default"/> does not by itself support Tri ckle
ICE. This section describes how trickling of candidates ICE. This section describes how trickling of candidates
interacts with ICE. interacts with ICE.
</t> </t>
<t> <t>
<xref target="rfc5245bis"/> describes the conditions required to <xref target="RFC8445" format="default"/> describes the conditions requi
update check lists and timer states while an ICE agent is in the red to
update checklists and timer states while an ICE agent is in the
Running state. These conditions are verified upon transaction Running state. These conditions are verified upon transaction
completion and one of them stipulates that: completion, and one of them stipulates that:
</t> </t>
<t> <ul empty="true" spacing="normal">
<list style='empty'> <li>
<t>
If there is not a pair in the valid list for each component If there is not a pair in the valid list for each component
of the data stream, the state of the check list is set to of the data stream, the state of the checklist is set to
Failed. Failed.
</t> </li>
</list> </ul>
</t>
<t> <t>
This could be a problem and cause ICE processing to fail This could be a problem and cause ICE processing to fail
prematurely in a number of scenarios. Consider the following prematurely in a number of scenarios. Consider the following
case: case:
</t> </t>
<t> <ol spacing="normal" type="1">
<list style='numbers'> <li>
<t>
Alice and Bob are both located in different networks with Alice and Bob are both located in different networks with
Network Address Translation (NAT). Alice and Bob themselves Network Address Translation (NAT). Alice and Bob themselves
have different address but both networks use the same have different addresses, but both networks use the same
private internet block (e.g., the "20-bit block" private internet block (e.g., the "20-bit block"
172.16/12 specified in <xref target="RFC1918"/>). 172.16/12 specified in <xref target="RFC1918" format="default"/>).
</t> </li>
<t> <li>
Alice conveys to Bob the candidate 172.16.0.1 which also happens Alice conveys to Bob the candidate 172.16.0.1, which also happens
to correspond to an existing host on Bob's network. to correspond to an existing host on Bob's network.
</t> </li>
<t> <li>
Bob creates a check list consisting solely of 172.16.0.1 and Bob creates a candidate pair from his host candidate and
starts checks. 172.16.0.1, puts this one pair into a checklist, and starts
</t> checks.
<t> </li>
<li>
These checks reach the host at 172.16.0.1 in Bob's network, These checks reach the host at 172.16.0.1 in Bob's network,
which responds with an ICMP "port unreachable" error; per which responds with an ICMP "port unreachable" error; per
<xref target="rfc5245bis"/> Bob marks the transaction as <xref target="RFC8445" format="default"/>, Bob marks the transaction as
Failed. Failed.
</t> </li>
</list> </ol>
At this point the check list only contains Failed candidates and <t>
the valid list is empty. This causes the data stream and At this point, the checklist only contains a Failed pair, and
potentially all ICE processing to fail, even though if Trickle ICE agent the valid list is empty.
s This causes the data stream and
could subsequently convey candidates that potentially all ICE processing to fail, even though Trickle ICE agents
would cause previously empty check lists to become non-empty. can subsequently convey candidates that could succeed.
</t> </t>
<t> <t>
A similar race condition would occur if the initial ICE description from A similar race condition would occur if the initial ICE description from
Alice contain only candidates that can be determined as Alice contains only candidates that can be determined as
unreachable from unreachable from
any of the candidates that Bob has gathered (e.g., this would be the any of the candidates that Bob has gathered (e.g., this would be the
case if Bob's candidates only contain IPv4 addresses and the case if Bob's candidates only contain IPv4 addresses and the
first candidate that he receives from Alice is an IPv6 one). first candidate that he receives from Alice is an IPv6 one).
</t> </t>
<t> <t>
Another potential problem could arise when a non-trickle Another potential problem could arise when a non-Trickle
ICE implementation initiates an interaction with a Trickle ICE ICE implementation initiates an interaction with a Trickle ICE
implementation. Consider the following case: implementation. Consider the following case:
<list style='numbers'> </t>
<t> <ol spacing="normal" type="1">
<li>
Alice's client has a non-Trickle ICE implementation. Alice's client has a non-Trickle ICE implementation.
</t> </li>
<t> <li>
Bob's client has support for Trickle ICE. Bob's client has support for Trickle ICE.
</t> </li>
<t> <li>
Alice and Bob are behind NATs with address-dependent Alice and Bob are behind NATs with address-dependent
filtering <xref target="RFC4787"/>. filtering <xref target="RFC4787" format="default"/>.
</t> </li>
<t> <li>
Bob has two STUN servers but one of them is currently Bob has two STUN servers, but one of them is currently
unreachable. unreachable.
</t> </li>
</list> </ol>
</t>
<t> <t>
After Bob's agent receives Alice's initial ICE description it would After Bob's agent receives Alice's initial ICE description, it would
immediately start connectivity checks. It would also start gathering immediately start connectivity checks. It would also start gathering
candidates, which would take a long time because of the unreachable candidates, which would take a long time because of the unreachable
STUN server. By the time Bob's answer is ready and conveyed to STUN server. By the time Bob's answer is ready and conveyed to
Alice, Bob's connectivity checks might have failed: until Alice, Bob's connectivity checks might have failed: until
Alice gets Bob's answer, she won't be able to start connectivity Alice gets Bob's answer, she won't be able to start connectivity
checks and punch holes in her NAT. The NAT would hence be checks and punch holes in her NAT. The NAT would hence be
filtering Bob's checks as originating from an unknown endpoint. filtering Bob's checks as originating from an unknown endpoint.
</t> </t>
</section> </section>
<section title='Interaction with ICE Lite'> <section numbered="true" toc="default">
<name>Interaction with ICE-Lite</name>
<t> <t>
The behavior of ICE lite agents that are capable of Trickle ICE does not The behavior of ICE-lite agents that are capable of Trickle ICE does not
require any particular rules other than those already defined require any particular rules other than those already defined
in this specification and <xref target="rfc5245bis"/>. This section in this specification and <xref target="RFC8445" format="default"/>. Thi s section
is hence provided only for informational purposes. is hence provided only for informational purposes.
</t> </t>
<t> <t>
An ICE lite agent would generate candidate information An ICE-lite agent would generate candidate information
as per <xref target="rfc5245bis"/> and as per <xref target="RFC8445" format="default"/> and
would indicate support for Trickle ICE. Given would indicate support for Trickle ICE. Given
that the candidate information will contain a full generation of candida tes, that the candidate information will contain a full generation of candida tes,
it would also be accompanied by an end-of-candidates indication. it would also be accompanied by an end-of-candidates indication.
</t> </t>
<t> <t>
When performing full trickle, a full ICE implementation could When performing full trickle, a full ICE implementation could
convey the initial ICE description or response thereto with no candidate s. After receiving convey the initial ICE description or response thereto with no candidate s. After receiving
a response that a response that
identifies the remote agent as an ICE lite implementation, the identifies the remote agent as an ICE-lite implementation, the
initiator can choose to not trickle any additional initiator can choose to not trickle any additional
candidates. The same is also true in the case when the ICE lite candidates. The same is also true in the case when the ICE-lite
agent initiates the interaction and the full ICE agent is the responder. In agent initiates the interaction and the full ICE agent is the responder. In
these cases the connectivity checks would be enough for the ICE these cases, the connectivity checks would be enough for the ICE-lite
lite implementation to discover all potentially useful implementation to discover all potentially useful
candidates as peer reflexive. The following example illustrates candidates as peer reflexive. The following example illustrates
one such ICE session using SDP syntax: one such ICE session using SDP syntax:
</t> </t>
<figure title="Example " anchor="fig-ice-lite"> <figure anchor="fig-ice-lite">
<artwork> <name>Example</name>
<![CDATA[ <artwork name="" type="" align="left" alt=""><![CDATA[
ICE Lite Bob ICE-Lite Bob
Agent Agent
| Offer (a=ice-lite a=ice-options:trickle) | | Offer (a=ice-lite a=ice-options:trickle) |
|---------------------------------------------->| |---------------------------------------------->|
| |no cand | |no cand
| Answer (a=ice-options:trickle) |trickling | Answer (a=ice-options:trickle) |trickling
|<----------------------------------------------| |<----------------------------------------------|
| Connectivity Checks | | Connectivity Checks |
|<--------------------------------------------->| |<--------------------------------------------->|
peer rflx| | peer rflx| |
cand disco| | cand disco| |
|<========== CONNECTION ESTABLISHED ===========>| |<========== CONNECTION ESTABLISHED ===========>|
]]></artwork>
]]>
</artwork>
</figure> </figure>
<t> <t>
In addition to reducing signaling traffic this approach also In addition to reducing signaling traffic, this approach also
removes the need to discover STUN bindings or make TURN removes the need to discover STUN Bindings or make TURN
allocations, which can considerably lighten ICE processing. allocations, which can considerably lighten ICE processing.
</t> </t>
</section> </section>
<section title='Changes from Earlier Versions'> <section numbered="false" toc="default">
<name>Acknowledgements</name>
<t> <t>
Note to the RFC Editor: please remove this section prior to The authors would like to thank
publication as an RFC. <contact fullname="Bernard Aboba"/>,
<contact fullname="Flemming Andreasen"/>,
<contact fullname="Rajmohan Banavi"/>,
<contact fullname="Taylor Brandstetter"/>,
<contact fullname="Philipp Hancke"/>,
<contact fullname="Christer Holmberg"/>,
<contact fullname="Ari Keränen"/>,
<contact fullname="Paul Kyzivat"/>,
<contact fullname="Jonathan Lennox"/>,
<contact fullname="Enrico Marocco"/>,
<contact fullname="Pal Martinsen"/>,
<contact fullname="Nils Ohlmeier"/>,
<contact fullname="Thomas Stach"/>,
<contact fullname="Peter Thatcher"/>,
<contact fullname="Martin Thomson"/>,
<contact fullname="Brandon Williams"/>, and
<contact fullname="Dale Worley"/> for their reviews and
suggestions on improving this document. <contact fullname="Sarah
Banks"/>, <contact fullname="Roni Even"/>, and <contact
fullname="David Mandelberg"/> completed OPSDIR, GenART, and security
reviews, respectively. Thanks also to Ari Keranen and Peter Thatcher
in their role as chairs and Ben Campbell in his role as responsible
Area Director.
</t> </t>
<section title='Changes from draft-ietf-ice-trickle-20'>
<t>
<list style='symbols'>
<t>
Slight corrections to hanlding of peer reflexive candidates.
</t>
<t>
Wordsmithing in a few sections.
</t>
</list>
</t>
</section>
<section title='Changes from draft-ietf-ice-trickle-19'>
<t>
<list style='symbols'>
<t>
Further clarified handling of remote peer reflexive
candidates.
</t>
<t>
To improve readibility, renamed and restructured some
sections and subsections, and modified some wording.
</t>
</list>
</t>
</section>
<section title='Changes from draft-ietf-ice-trickle-18'>
<t>
<list style='symbols'>
<t>
Cleaned up pairing and redundancy checking rules for
newly discovered candidates per IESG feedback and WG
discussion.
</t>
<t>
Improved wording in half trickle section.
</t>
<t>
Changed "not more than once" to "exactly once".
</t>
<t>
Changed NAT examples back to IPv4.
</t>
</list>
</t>
</section>
<section title='Changes from draft-ietf-ice-trickle-17'>
<t>
<list style='symbols'>
<t>
Simplified the rules for inserting a new pair in a check list.
</t>
<t>
Clarified it is not allowed to nominate a candidate
pair after a pair has already been nominated (a.k.a.
renomination or continuous nomination).
</t>
<t>
Removed some text that referenced older versions of
rfc5245bis.
</t>
<t>
Removed some text that duplicated concepts and procedures
specified in rfc5245bis.
</t>
<t>
Removed the ill-defined concept of stream order.
</t>
<t>
Shortened the introduction.
</t>
</list>
</t>
</section>
<section title='Changes from draft-ietf-ice-trickle-16'>
<t>
<list style='symbols'>
<t>
Made "ufrag" terminology consistent with 5245bis.
</t>
<t>
Applied in-order delivery rule to end-of-candidates indication.
</t>
</list>
</t>
</section>
<section title='Changes from draft-ietf-ice-trickle-15'>
<t>
<list style='symbols'>
<t>
Adjustments to address AD review feedback.
</t>
</list>
</t>
</section>
<section title='Changes from draft-ietf-ice-trickle-14'>
<t>
<list style='symbols'>
<t>
Minor modifications to track changes to ICE core.
</t>
</list>
</t>
</section>
<section title='Changes from draft-ietf-ice-trickle-13'>
<t>
<list style='symbols'>
<t>
Removed independent monitoring of check list "states" of
frozen or active, since this is handled by placing a check
list in the Running state defined in ICE core.
</t>
</list>
</t>
</section>
<section title='Changes from draft-ietf-ice-trickle-12'>
<t>
<list style='symbols'>
<t>
Specified that the end-of-candidates indication must
include the generation (ufrag/pwd) to enable association
with a particular ICE session.
</t>
<t>
Further editorial fixes to address WGLC feedback.
</t>
</list>
</t>
</section>
<section title='Changes from draft-ietf-ice-trickle-11'>
<t>
<list style='symbols'>
<t>
Editorial and terminological fixes to address WGLC feedback.
</t>
</list>
</t>
</section>
<section title='Changes from draft-ietf-ice-trickle-10'>
<t>
<list style='symbols'>
<t>
Minor editorial fixes.
</t>
</list>
</t>
</section>
<section title='Changes from draft-ietf-ice-trickle-09'>
<t>
<list style='symbols'>
<t>
Removed immediate unfreeze upon Fail.
</t>
<t>
Specified MUST NOT regarding ice-options.
</t>
<t>
Changed terminology regarding initial ICE parameters
to avoid implementer confusion.
</t>
</list>
</t>
</section>
<section title='Changes from draft-ietf-ice-trickle-08'>
<t>
<list style='symbols'>
<t>
Reinstated text about in-order processing of messages
as a requirement for signaling protocols.
</t>
<t>
Added IANA registration template for ICE option.
</t>
<t>
Corrected Case 3 rule in Section 8.1.1 to ensure
consistency with regular ICE rules.
</t>
<t>
Added tabular representations to Section 8.1.1 in order
to illustrate the new pair rules.
</t>
</list>
</t>
</section>
<section title='Changes from draft-ietf-ice-trickle-07'>
<t>
<list style='symbols'>
<t>
Changed "ICE description" to "candidate information" for
consistency with 5245bis.
</t>
</list>
</t>
</section>
<section title='Changes from draft-ietf-ice-trickle-06'>
<t>
<list style='symbols'>
<t>
Addressed editorial feedback from chairs' review.
</t>
<t>
Clarified terminology regarding generations.
</t>
</list>
</t>
</section>
<section title='Changes from draft-ietf-ice-trickle-05'>
<t>
<list style='symbols'>
<t>
Rewrote the text on inserting a new pair into a
check list.
</t>
</list>
</t>
</section>
<section title='Changes from draft-ietf-ice-trickle-04'>
<t>
<list style='symbols'>
<t>
Removed dependency on SDP and offer/answer model.
</t>
<t>
Removed mentions of aggressive nomination, since it is
deprecated in 5245bis.
</t>
<t>
Added section on requirements for signaling protocols.
</t>
<t>
Clarified terminology.
</t>
<t>
Addressed various WG feedback.
</t>
</list>
</t>
</section>
<section title='Changes from draft-ietf-ice-trickle-03'>
<t>
<list style='symbols'>
<t>
Provided more detailed description of unfreezing behavior, specifi
cally
how to replace pre-existing peer-reflexive candidates with higher-
priority
ones received via trickling.
</t>
</list>
</t>
</section>
<section title='Changes from draft-ietf-ice-trickle-02'>
<t>
<list style='symbols'>
<t>
Adjusted unfreezing behavior when there are disparate foundations.
</t>
</list>
</t>
</section>
<section title='Changes from draft-ietf-ice-trickle-01'>
<t>
<list style='symbols'>
<t>
Changed examples to use IPv6.
</t>
</list>
</t>
</section>
<section title='Changes from draft-ietf-ice-trickle-00'>
<t>
<list style='symbols'>
<t>
Removed dependency on SDP (which is to be provided
in a separate specification).
</t>
<t>
Clarified text about the fact that a check list
can be empty if no candidates have been sent or
received yet.
</t>
<t>
Clarified wording about check list states so as not
to define new states for "Active" and "Frozen" because
those states are not defined for check lists (only for
candidate pairs) in ICE core.
</t>
<t>
Removed open issues list because it was out of date.
</t>
<t>
Completed a thorough copy edit.
</t>
</list>
</t>
</section>
<section title='Changes from draft-mmusic-trickle-ice-02'>
<t>
<list style='symbols'>
<t>
Addressed feedback from Rajmohan Banavi and Brandon Williams.
</t>
<t>
Clarified text about determining support and about how to
proceed if it can be determined that the answering agent
does not support Trickle ICE.
</t>
<t>
Clarified text about check list and timer updates.
</t>
<t>
Clarified when it is appropriate to use half trickle or
to send no candidates in an offer or answer.
</t>
<t>
Updated the list of open issues.
</t>
</list>
</t>
</section>
<section title='Changes from draft-ivov-01 and draft-mmusic-00'>
<t>
<list style='symbols'>
<t>
Added a requirement to trickle candidates by order of
components to avoid deadlocks in the unfreezing algorithm.
</t>
<t>
Added an informative note on peer-reflexive candidates
explaining that nothing changes for them semantically but
they do become a more likely occurrence for Trickle ICE.
</t>
<t>
Limit the number of pairs to 100 to comply with 5245.
</t>
<t>
Added clarifications on the non-importance of how newly
discovered candidates are trickled/sent to the remote
party or if this is done at all.
</t>
<t>
Added transport expectations for trickled candidates
as per Dale Worley's recommendation.
</t>
</list>
</t>
</section>
<section title='Changes from draft-ivov-00'>
<t>
<list style='symbols'>
<t>
Specified that end-of-candidates is a media level
attribute which can of course appear as session level,
which is equivalent to having it appear in all m-lines.
Also made end-of-candidates optional for cases such as
aggressive nomination for controlled agents.
</t>
<t>
Added an example for ICE lite and Trickle ICE to
illustrate how, when talking to an ICE lite agent doesn't
need to send or even discover any candidates.
</t>
<t>
Added an example for ICE lite and Trickle ICE to
illustrate how, when talking to an ICE lite agent doesn't
need to send or even discover any candidates.
</t>
<t>
Added wording that explicitly states ICE lite agents
have to be prepared to receive no candidates over
signaling and that they should not freak out if this
happens. (Closed the corresponding open issue).
</t>
<t>
It is now mandatory to use MID when trickling candidates
and using m-line indexes is no longer allowed.
</t>
<t>
Replaced use of 0.0.0.0 to IP6 :: in order to avoid
potential issues with RFC2543 SDP libraries that interpret
0.0.0.0 as an on-hold operation. Also changed the port
number here from 1 to 9 since it already has a more
appropriate meaning. (Port change suggested by Jonathan
Lennox).
</t>
<t>
Closed the Open Issue about use about what to do with
cands received after end-of-cands. Solution: ignore, do
an ICE restart if you want to add something.
</t>
<t>
Added more terminology, including trickling, trickled
candidates, half trickle, full trickle,
</t>
<t>
Added a reference to the SIP usage for Trickle ICE as
requested at the Boston interim.
</t>
</list>
</t>
</section>
<section title='Changes from draft-rescorla-01'>
<t>
<list style='symbols'>
<t>
Brought back explicit use of Offer/Answer. There are no
more attempts to try to do this in an O/A independent way.
Also removed the use of ICE Descriptions.
</t>
<t>
Added SDP specification for trickled candidates, the
trickle option and 0.0.0.0 addresses in m-lines, and
end-of-candidates.
</t>
<t>
Support and Discovery. Changed that section to be less
abstract. As discussed in IETF85, the draft now says
implementations and usages need to either determine
support in advance and directly use trickle, or do
half trickle. Removed suggestion about use of discovery in
SIP or about letting implementing protocols do what they
want.
</t>
<t>
Defined Half Trickle. Added a section that says how it
works. Mentioned that it only needs to happen in the first
o/a (not necessary in updates), and added Jonathan's
comment about how it could, in some cases, offer more than
half the improvement if you can pre-gather part or all of
your candidates before the user actually presses the call
button.
</t>
<t>
Added a short section about subsequent offer/answer
exchanges.
</t>
<t>
Added a short section about interactions with ICE Lite
implementations.
</t>
<t>
Added two new entries to the open issues section.
</t>
</list>
</t>
</section>
<section title='Changes from draft-rescorla-00'>
<t>
<list style='symbols'>
<t>
Relaxed requirements about verifying support following
a discussion on MMUSIC.
</t>
<t>
Introduced ICE descriptions in order to remove ambiguous
use of 3264 language and inappropriate references to
offers and answers.
</t>
<t>
Removed inappropriate assumption of adoption by RTCWEB
pointed out by Martin Thomson.
</t>
</list>
</t>
</section>
</section> </section>
</back> </back>
</rfc> </rfc>
 End of changes. 234 change blocks. 
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