rfc8837xml2.original.xml   rfc8837.xml 
<?xml version="1.0" encoding="US-ASCII"?> <?xml version='1.0' encoding='utf-8'?>
<!DOCTYPE rfc SYSTEM "rfc2629.dtd"> <!DOCTYPE rfc SYSTEM "rfc2629-xhtml.ent">
<?rfc toc="yes"?>
<?rfc tocompact="yes"?>
<?rfc tocdepth="3"?>
<?rfc tocindent="yes"?>
<?rfc symrefs="yes"?>
<?rfc sortrefs="yes"?>
<?rfc comments="yes"?>
<?rfc inline="yes"?>
<?rfc compact="yes"?>
<?rfc subcompact="no"?>
<rfc category="std" docName="draft-ietf-tsvwg-rtcweb-qos-18"
ipr="trust200902">
<rfc xmlns:xi="http://www.w3.org/2001/XInclude" number="8837"
submissionType="IETF" consensus="true" category="std"
docName="draft-ietf-tsvwg-rtcweb-qos-18" ipr="trust200902" obsoletes="" upd
ates="" xml:lang="en" tocInclude="true" symRefs="true" sortRefs="true" version="
3">
<!-- xml2rfc v2v3 conversion 2.45.2 -->
<front> <front>
<title abbrev="WebRTC QoS"> <title abbrev="WebRTC QoS">
DSCP Packet Markings for WebRTC QoS Differentiated Services Code Point (DSCP) Packet Markings for WebRTC QoS
</title> </title>
<seriesInfo name="RFC" value="8837"/>
<author fullname="Paul E. Jones" initials="P." surname="Jones"> <author fullname="Paul E. Jones" initials="P." surname="Jones">
<organization>Cisco Systems</organization> <organization>Cisco Systems</organization>
<address> <address>
<email>paulej@packetizer.com</email> <email>paulej@packetizer.com</email>
</address> </address>
</author> </author>
<author fullname="Subha Dhesikan" initials="S." surname="Dhesikan"> <author fullname="Subha Dhesikan" initials="S." surname="Dhesikan">
<organization>Cisco Systems</organization> <organization>Individual</organization>
<address> <address>
<email>sdhesika@cisco.com</email> <email>sdhesikan@gmail.com</email>
</address> </address>
</author> </author>
<author fullname="Cullen Jennings" initials="C." surname="Jennings">
<author fullname="Cullen Jennings" initials="C."
surname="Jennings">
<organization>Cisco Systems</organization> <organization>Cisco Systems</organization>
<address> <address>
<email>fluffy@cisco.com</email> <email>fluffy@cisco.com</email>
</address> </address>
</author> </author>
<author fullname="Dan Druta" initials="D." surname="Druta"> <author fullname="Dan Druta" initials="D." surname="Druta">
<organization>AT&amp;T</organization> <organization>AT&amp;T</organization>
<address> <address>
<email>dd5826@att.com</email> <email>dd5826@att.com</email>
</address> </address>
</author> </author>
<date month="July" year="2020"/>
<date/> <keyword>Diffserv</keyword>
<keyword>rtcweb</keyword>
<abstract> <abstract>
<t> <t>
Many networks, such as service provider and enterprise networks, Networks can provide different forwarding treatments for individual
can provide different forwarding treatments for individual
packets based on Differentiated Services Code Point (DSCP) packets based on Differentiated Services Code Point (DSCP)
values on a per-hop basis. This document provides the values on a per-hop basis. This document provides the
recommended DSCP values for web browsers to use for various recommended DSCP values for web browsers to use for various
classes of WebRTC traffic. classes of Web Real-Time Communication (WebRTC) traffic.
</t> </t>
</abstract> </abstract>
</front> </front>
<middle> <middle>
<section title="Introduction"> <section numbered="true" toc="default">
<name>Introduction</name>
<t> <t>
Differentiated Services Code Point (DSCP) <xref target="RFC2474"/> Differentiated Services Code Point (DSCP) <xref target="RFC2474" format= "default"/>
packet marking can help provide QoS in some environments. packet marking can help provide QoS in some environments.
This specification provides default packet marking for browsers This specification provides default packet marking for browsers
that support WebRTC applications, but does not change any advice that support WebRTC applications, but does not change any advice
or requirements in other IETF RFCs. The contents of this or requirements in other RFCs. The contents of this
specification are intended to be a simple set of implementation specification are intended to be a simple set of implementation
recommendations based on the previous RFCs. recommendations based on previous RFCs.
</t> </t>
<t> <t>
Networks where these DSCP markings are beneficial (likely to Networks in which these DSCP markings are beneficial (likely to
improve QoS for WebRTC traffic) include: improve QoS for WebRTC traffic) include:
</t> </t>
<ol spacing="normal" type="1">
<t> <li>
<list style="numbers">
<t>
Private, wide-area networks. Network administrators have Private, wide-area networks. Network administrators have
control over remarking packets and treatment of packets. control over remarking packets and treatment of packets.
</t> </li>
<li>
<t>
Residential Networks. If the congested link is the Residential Networks. If the congested link is the
broadband uplink in a cable or DSL scenario, often broadband uplink in a cable or DSL scenario, residential
residential routers/NAT support preferential treatment based routers/NAT often support preferential treatment based
on DSCP. on DSCP.
</t> </li>
<li>
<t>
Wireless Networks. If the congested link is a local Wireless Networks. If the congested link is a local
wireless network, marking may help. wireless network, marking may help.
</t> </li>
</list> </ol>
</t>
<t> <t>
There are cases where these DSCP markings do not help, but, There are cases where these DSCP markings do not help but,
aside from possible priority inversion for "less than best aside from possible priority inversion for "Less-than-Best-Effort
effort traffic" (see Section 5), they seldom make things worse traffic" (see <xref target="dscp-mappings" format="default"/>), they seld
om make things worse
if packets are marked appropriately. if packets are marked appropriately.
</t> </t>
<t> <t>
DSCP values are in principle site specific, with each site DSCP values are, in principle, site specific with each site
selecting its own code points for controlling per-hop-behavior selecting its own code points for controlling per-hop behavior
to influence the QoS for transport-layer flows. However in the to influence the QoS for transport-layer flows. However, in the
WebRTC use cases, the browsers need to set them to something WebRTC use cases, the browsers need to set them to something
when there is no site specific information. This document when there is no site-specific information. This document
describes a subset of DSCP code point values drawn from existing describes a subset of DSCP code point values drawn from existing
RFCs and common usage for use with WebRTC applications. These RFCs and common usage for use with WebRTC applications. These
code points are intended to be the default values used by a code points are intended to be the default values used by a
WebRTC application. While other values could be used, using a WebRTC application. While other values could be used, using a
non-default value may result in unexpected per-hop behavior. It non-default value may result in unexpected per-hop behavior. It
is RECOMMENDED that WebRTC applications use non-default values is <bcp14>RECOMMENDED</bcp14> that WebRTC applications use non-default v alues
only in private networks that are configured to use different only in private networks that are configured to use different
values. values.
</t> </t>
<t> <t>
This specification defines inputs that are provided by the This specification defines inputs that are provided by the
WebRTC application hosted in the browser that aid the browser in WebRTC application hosted in the browser that aid the browser in
determining how to set the various packet markings. The determining how to set the various packet markings. The
specification also defines the mapping from abstract QoS specification also defines the mapping from abstract QoS
policies (flow type, priority level) to those packet markings. policies (flow type, priority level) to those packet markings.
</t> </t>
</section> </section>
<section numbered="true" toc="default">
<section title="Terminology"> <name>Terminology</name>
<t> <t>
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL The key words "<bcp14>MUST</bcp14>", "<bcp14>MUST NOT</bcp14>",
NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "<bcp14>REQUIRED</bcp14>", "<bcp14>SHALL</bcp14>", "<bcp14>SHALL NOT</bcp14>
"OPTIONAL" in this document are to be interpreted as described ",
in <xref target="RFC2119"/>. "<bcp14>SHOULD</bcp14>", "<bcp14>SHOULD NOT</bcp14>",
</t> "<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>
The terms "browser" and "non-browser" are defined in The terms "browser" and "non-browser" are defined in
<xref target="RFC7742"/> and carry the same meaning in this <xref target="RFC7742" format="default"/> and carry the same meaning in this
document. document.
</t> </t>
</section> </section>
<section numbered="true" toc="default">
<section title="Relation to Other Specifications"> <name>Relation to Other Specifications</name>
<t> <t>
This document is a complement to <xref target="RFC7657"/>, which This document is a complement to <xref target="RFC7657" format="default" />, which
describes the interaction between DSCP and real-time describes the interaction between DSCP and real-time
communications. That RFC covers the implications of using communications. That RFC covers the implications of using
various DSCP values, particularly focusing on Real-time various DSCP values, particularly focusing on the Real-time
Transport Protocol (RTP) <xref target="RFC3550"/> streams that Transport Protocol (RTP) <xref target="RFC3550" format="default"/> strea
ms that
are multiplexed onto a single transport-layer flow. are multiplexed onto a single transport-layer flow.
</t> </t>
<t> <t>
There are a number of guidelines specified in There are a number of guidelines specified in
<xref target="RFC7657"/> that apply to marking traffic sent by <xref target="RFC7657" format="default"/> that apply to marking traffic sent by
WebRTC applications, as it is common for multiple RTP streams to WebRTC applications, as it is common for multiple RTP streams to
be multiplexed on the same transport-layer flow. Generally, the be multiplexed on the same transport-layer flow. Generally, the
RTP streams would be marked with a value as appropriate from RTP streams would be marked with a value as appropriate from
<xref target="table-dscp"/>. A WebRTC application might also <xref target="tab-dscp" format="default"/>. A WebRTC application might also
multiplex data channel multiplex data channel
<xref target="I-D.ietf-rtcweb-data-channel"/> traffic over the <xref target="RFC8831" format="default"/> traffic over the
same 5-tuple as RTP streams, which would also be marked as per same 5-tuple as RTP streams, which would also be marked per
that table. The guidance in <xref target="RFC7657"/> says that that table. The guidance in <xref target="RFC7657" format="default"/> s
ays that
all data channel traffic would be marked with a single value all data channel traffic would be marked with a single value
that is typically different than the value(s) used for RTP that is typically different from the value(s) used for RTP
streams multiplexed with the data channel traffic over the same streams multiplexed with the data channel traffic over the same
5-tuple, assuming RTP streams are marked with a value other than 5-tuple, assuming RTP streams are marked with a value other than
default forwarding (DF). This is expanded upon further in the Default Forwarding (DF). This is expanded upon further in the
next section. next section.
</t> </t>
<t> <t>
This specification does not change or override the advice in any This specification does not change or override the advice in any
other IETF RFCs about setting packet markings. Rather, it other RFCs about setting packet markings. Rather, it
simply selects a subset of DSCP values that is relevant in the simply selects a subset of DSCP values that is relevant in the
WebRTC context. WebRTC context.
</t> </t>
<t> <t>
The DSCP value set by the endpoint is not trusted by the The DSCP value set by the endpoint is not trusted by the
network. In addition, the DSCP value may be remarked at any network. In addition, the DSCP value may be remarked at any
place in the network for a variety of reasons to any other DSCP place in the network for a variety of reasons to any other DSCP
value, including default forwarding (DF) value to provide basic value, including the DF value to provide basic
best effort service. Even so, there is benefit in marking best-effort service. Even so, there is a benefit to marking
traffic even if it only benefits the first few hops. The traffic even if it only benefits the first few hops. The
implications are discussed in Secton 3.2 of implications are discussed in
<xref target="RFC7657"/>. Further, a mitigation for such action <xref target="RFC7657" sectionFormat="of" section="3.2"/>. Further, a m
itigation for such action
is through an authorization mechanism. Such an authorization is through an authorization mechanism. Such an authorization
mechanism is outside the scope of this document. mechanism is outside the scope of this document.
</t> </t>
</section> </section>
<section numbered="true" toc="default">
<section title="Inputs"> <name>Inputs</name>
<t> <t>
WebRTC applications send and receive two types of flows of This document recommends DSCP values for two classes of WebRTC flows:
significance to this document:
<list style="symbols">
<t>
media flows which are RTP streams
<xref target="I-D.ietf-rtcweb-rtp-usage"/>
</t>
<t>
data flows which are data channels
<xref target="I-D.ietf-rtcweb-data-channel"/>
</t>
</list>
</t> </t>
<ul spacing="normal">
<li>
media flows that are RTP streams
<xref target="RFC8834" format="default"/>
</li>
<li>
data flows that are data channels
<xref target="RFC8831" format="default"/>
</li>
</ul>
<t> <t>
Each of the RTP streams and distinct data channels consists of Each of the RTP streams and distinct data channels consist of
all of the packets associated with an independent media entity, all of the packets associated with an independent media entity,
so an RTP stream or distinct data channel is not always so an RTP stream or distinct data channel is not always
equivalent to a transport-layer flow defined by a 5-tuple equivalent to a transport-layer flow defined by a 5-tuple
(source address, destination address, source port, destination (source address, destination address, source port, destination
port, and protocol). There may be multiple RTP streams and data port, and protocol). There may be multiple RTP streams and data
channels multiplexed over the same 5-tuple, with each having a channels multiplexed over the same 5-tuple, with each having a
different level of importance to the application and, therefore, different level of importance to the application and, therefore,
potentially marked using different DSCP values than another RTP potentially marked using different DSCP values than another RTP
stream or data channel within the same transport-layer flow. stream or data channel within the same transport-layer flow.
(Note that there are restrictions with respect to marking (Note that there are restrictions with respect to marking
different data channels carried within the same SCTP association different data channels carried within the same Stream Control
as outlined in <xref target="dscp-mappings"/>.) Transmission Protocol (SCTP) association
as outlined in <xref target="dscp-mappings" format="default"/>.)
</t> </t>
<t> <t>
The following are the inputs provided by the WebRTC application The following are the inputs provided by the WebRTC application
to the browser: to the browser:
<list style="symbols"> </t>
<t> <ul spacing="normal">
<li>
Flow Type: The application provides this input because it knows Flow Type: The application provides this input because it knows
if the flow is audio, interactive video <xref target="RFC4594"/> if the flow is audio, interactive video (<xref target="RFC4594" form
<xref target="G.1010"/> with or without audio, or data. at="default"/>
</t> <xref target="G.1010" format="default"/>) with or without audio, or da
ta.
<t> </li>
<li>
Application Priority: Another input is the relative Application Priority: Another input is the relative
importance of an RTP stream or data channel. Many importance of an RTP stream or data channel. Many
applications have multiple flows of the same Flow Type and applications have multiple flows of the same flow type and
often some flows are more important than others. For some flows are often more important than others. For
example, in a video conference where there are usually audio example, in a video conference where there are usually audio
and video flows, the audio flow may be more important than and video flows, the audio flow may be more important than
the video flow. JavaScript applications can tell the the video flow. JavaScript applications can tell the
browser whether a particular flow is high, medium, low or browser whether a particular flow is of High, Medium, Low, or
very low importance to the application. Very Low importance to the application.
</t> </li>
</list> </ul>
</t>
<t> <t>
<xref target="I-D.ietf-rtcweb-transports"/> defines in more <xref target="RFC8835" format="default"/> defines in more
detail what an individual flow is within the WebRTC detail what an individual flow is within the WebRTC
context and priorities for media and data flows. context and priorities for media and data flows.
</t> </t>
<t> <t>
Currently in WebRTC, media sent over RTP is assumed to be Currently in WebRTC, media sent over RTP is assumed to be
interactive <xref target="I-D.ietf-rtcweb-transports"/> and interactive <xref target="RFC8835" format="default"/> and
browser APIs do not exist to allow an application to to browser APIs do not exist to allow an application to
differentiate between interactive and non-interactive video. differentiate between interactive and non-interactive video.
</t> </t>
</section> </section>
<section anchor="dscp-mappings" title="DSCP Mappings"> <section anchor="dscp-mappings" numbered="true" toc="default">
<name>DSCP Mappings</name>
<t> <t>
The DSCP values for each flow type of interest to WebRTC based The DSCP values for each flow type of interest to WebRTC based
on application priority are shown in <xref target="table-dscp"/>. on application priority are shown in <xref target="tab-dscp" format="def ault"/>.
These values are based on the framework and recommended values in These values are based on the framework and recommended values in
<xref target="RFC4594"/>. A web browser SHOULD use these values <xref target="RFC4594" format="default"/>. A web browser <bcp14>SHOULD<
to mark the appropriate media packets. More information on EF /bcp14> use these values
can be found in <xref target="RFC3246"/>. More information on to mark the appropriate media packets. More information on Expedited
AF can be found in <xref target="RFC2597"/>. DF is default Forwarding (EF) and Assured Forwarding (AF) can be found in <xref
forwarding which provides the basic best effort service target="RFC3246" format="default"/> and <xref target="RFC2597"
<xref target="RFC2474"/>. format="default"/>, respectively. DF is Default Forwarding, which provid
es the basic best-effort service
<xref target="RFC2474" format="default"/>.
</t> </t>
<t> <t>
WebRTC use of multiple DSCP values may encounter network blocking WebRTC's use of multiple DSCP values may result in packets with
of packets with certain DSCP values. See section 4.2 of certain DSCP values being blocked by a network. See
<xref target="I-D.ietf-rtcweb-transports"/> for further <xref target="RFC8835" sectionFormat="of" section="4.2"/> for further
discussion, including how WebRTC implementations establish and discussion, including how WebRTC implementations establish and
maintain connectivity when such blocking is encountered. maintain connectivity when such blocking is encountered.
</t> </t>
<table anchor="tab-dscp" align="center">
<texttable anchor="table-dscp" <name>Recommended DSCP Values for WebRTC Applications</name>
title="Recommended DSCP Values for WebRTC Applications"> <thead>
<ttcol align="center">Flow Type</ttcol> <tr>
<ttcol align="center">Very Low</ttcol> <th align="center">Flow Type</th>
<ttcol align="center">Low</ttcol> <th align="center">Very Low</th>
<ttcol align="center">Medium</ttcol> <th align="center">Low</th>
<ttcol align="center">High</ttcol> <th align="center">Medium</th>
<c>Audio</c> <th align="center">High</th>
<c>CS1 (8)</c> </tr>
<c>DF (0)</c> </thead>
<c>EF (46)</c> <tbody>
<c>EF (46)</c> <tr>
<c> </c> <td align="center">Audio</td>
<c> </c> <td align="center">LE (1)</td>
<c> </c> <td align="center">DF (0)</td>
<c> </c> <td align="center">EF (46)</td>
<c> </c> <td align="center">EF (46)</td>
<c>Interactive Video with or without Audio</c> </tr>
<c>CS1 (8)</c> <tr>
<c>DF (0)</c> <td align="center"> </td>
<c>AF42, AF43 (36, 38)</c> <td align="center"> </td>
<c>AF41, AF42 (34, 36)</c> <td align="center"> </td>
<c> </c> <td align="center"> </td>
<c> </c> <td align="center"> </td>
<c> </c> </tr>
<c> </c> <tr>
<c> </c> <td align="center">Interactive Video with or without Audio</td>
<c>Non-Interactive Video with or without Audio</c> <td align="center">LE (1)</td>
<c>CS1 (8)</c> <td align="center">DF (0)</td>
<c>DF (0)</c> <td align="center">AF42, AF43 (36, 38)</td>
<c>AF32, AF33 (28, 30)</c> <td align="center">AF41, AF42 (34, 36)</td>
<c>AF31, AF32 (26, 28)</c> </tr>
<c> </c> <tr>
<c> </c> <td align="center"> </td>
<c> </c> <td align="center"> </td>
<c> </c> <td align="center"> </td>
<c> </c> <td align="center"> </td>
<c>Data</c> <td align="center"> </td>
<c>CS1 (8)</c> </tr>
<c>DF (0)</c> <tr>
<c>AF11</c> <td align="center">Non-Interactive Video with or without Audio</td>
<c>AF21</c> <td align="center">LE (1)</td>
</texttable> <td align="center">DF (0)</td>
<td align="center">AF32, AF33 (28, 30)</td>
<td align="center">AF31, AF32 (26, 28)</td>
</tr>
<tr>
<td align="center"> </td>
<td align="center"> </td>
<td align="center"> </td>
<td align="center"> </td>
<td align="center"> </td>
</tr>
<tr>
<td align="center">Data</td>
<td align="center">LE (1)</td>
<td align="center">DF (0)</td>
<td align="center">AF11</td>
<td align="center">AF21</td>
</tr>
</tbody>
</table>
<t> <t>
The application priority, indicated by the columns "very low", The application priority, indicated by the columns "Very Low",
"low", "Medium", and "high", signifies the relative importance "Low", "Medium", and "High", signifies the relative importance
of the flow within the application. It is an input that the of the flow within the application. It is an input that the
browser receives to assist in selecting the DSCP value and browser receives to assist in selecting the DSCP value and
adjusting the network transport behavior. adjusting the network transport behavior.
</t> </t>
<t> <t>
The above table assumes that packets marked with CS1 are treated The above table assumes that packets marked with LE are treated as
as "less than best effort", such as the LE behavior described in lower effort (i.e., "less than best effort"), such as the LE behavior
<xref target="RFC3662"/>. However, the treatment of CS1 is described in <xref target="RFC8622" format="default"/>. However, the treatme
implementation dependent. If an implementation treats CS1 as nt of LE is
other than "less than best effort", then the actual priority implementation dependent. If an implementation treats LE as other
(or, more precisely, the per-hop-behavior) of the packets may be than "less than best effort", then the actual priority (or, more
changed from what is intended. It is common for CS1 to be precisely, the per-hop behavior) of the packets may be changed from
treated the same as DF, so applications and browsers using CS1 what is intended. It is common for LE to be treated the same as DF,
cannot assume that CS1 will be treated differently than DF so applications and browsers using LE cannot assume that LE will be
<xref target="RFC7657"/>. However, it is also possible per treated differently than DF <xref target="RFC7657" format="default"/>. Durin
<xref target="RFC2474"/> for CS1 traffic to be given better g development of this
treatment than DF, thus caution should be exercised when document, the CS1 DSCP was recommended for "very low" application
electing to use CS1. This is one of the cases where marking priority traffic; implementations that followed that recommendation
packets using these recommendations can make things worse. <bcp14>SHOULD</bcp14> be updated to use the LE DSCP instead of the CS1 DSCP.
</t> </t>
<t> <t>
Implementers should also note that excess EF traffic is dropped. Implementers should also note that excess EF traffic is dropped.
This could mean that a packet marked as EF may not get through, This could mean that a packet marked as EF may not get through,
although the same packet marked with a different DSCP value would although the same packet marked with a different DSCP value would
have gotten through. This is not a flaw, but how excess EF have gotten through. This is not a flaw, but how excess EF
traffic is intended to be treated. traffic is intended to be treated.
</t> </t>
<t> <t>
The browser SHOULD first select the flow type of the flow. The browser <bcp14>SHOULD</bcp14> first select the flow type of the flow .
Within the flow type, the relative importance of the flow Within the flow type, the relative importance of the flow
SHOULD be used to select the appropriate DSCP value. <bcp14>SHOULD</bcp14> be used to select the appropriate DSCP value.
</t> </t>
<t> <t>
Currently, all WebRTC video is assumed to be interactive Currently, all WebRTC video is assumed to be interactive
<xref target="I-D.ietf-rtcweb-transports"/>, for which the <xref target="RFC8835" format="default"/>, for which the
Interactive Video DSCP values in Table 1 SHOULD be used. interactive video DSCP values in Table 1 <bcp14>SHOULD</bcp14> be used.
Browsers MUST NOT use the AF3x DSCP values (for Non-Interactive Browsers <bcp14>MUST NOT</bcp14> use the AF3x DSCP values (for non-inter
Video in Table 1) for WebRTC applications. Non-browser active
implementations of WebRTC MAY use the AF3x DSCP values for video video in Table 1) for WebRTC applications. Non-browser
implementations of WebRTC <bcp14>MAY</bcp14> use the AF3x DSCP values fo
r video
that is known not to be interactive, e.g., all video in a WebRTC that is known not to be interactive, e.g., all video in a WebRTC
video playback application that is not implemented in a video playback application that is not implemented in a
browser. browser.
</t> </t>
<t> <t>
The combination of flow type and application priority provides The combination of flow type and application priority provides
specificity and helps in selecting the right DSCP value for the specificity and helps in selecting the right DSCP value for the
flow. All packets within a flow SHOULD have the same application flow. All packets within a flow <bcp14>SHOULD</bcp14> have the same app lication
priority. In some cases, the selected application priority cell priority. In some cases, the selected application priority cell
may have multiple DSCP values, such as AF41 and AF42. These offer may have multiple DSCP values, such as AF41 and AF42. These offer
different drop precedences. The different drop precedence different drop precedences. The different drop precedence
values provides additional granularity in classifying packets values provide additional granularity in classifying packets
within a flow. For example, in a video conference the video within a flow. For example, in a video conference, the video
flow may have medium application priority, thus either AF42 or flow may have medium application priority, thus either AF42 or
AF43 may be selected. More important video packets (e.g., a AF43 may be selected. More important video packets (e.g., a
video picture or frame encoded without any dependency on any video picture or frame encoded without any dependency on any
prior pictures or frames) might be marked with AF42 and less prior pictures or frames) might be marked with AF42 and less
important packets (e.g., a video picture or frame encoded based important packets (e.g., a video picture or frame encoded based
on the content of one or more prior pictures or frames) might be on the content of one or more prior pictures or frames) might be
marked with AF43 (e.g., receipt of the more important packets marked with AF43 (e.g., receipt of the more important packets
enables a video renderer to continue after one or more packets enables a video renderer to continue after one or more packets
are lost). are lost).
</t> </t>
skipping to change at line 407 skipping to change at line 391
flow may have medium application priority, thus either AF42 or flow may have medium application priority, thus either AF42 or
AF43 may be selected. More important video packets (e.g., a AF43 may be selected. More important video packets (e.g., a
video picture or frame encoded without any dependency on any video picture or frame encoded without any dependency on any
prior pictures or frames) might be marked with AF42 and less prior pictures or frames) might be marked with AF42 and less
important packets (e.g., a video picture or frame encoded based important packets (e.g., a video picture or frame encoded based
on the content of one or more prior pictures or frames) might be on the content of one or more prior pictures or frames) might be
marked with AF43 (e.g., receipt of the more important packets marked with AF43 (e.g., receipt of the more important packets
enables a video renderer to continue after one or more packets enables a video renderer to continue after one or more packets
are lost). are lost).
</t> </t>
<t> <t>
It is worth noting that the application priority is utilized by It is worth noting that the application priority is utilized by
the coupled congestion control mechanism for media flows per the coupled congestion control mechanism for media flows per
<xref target="I-D.ietf-rmcat-coupled-cc"/> and the SCTP <xref target="RFC8699" format="default"/> and the SCTP
scheduler for data channel traffic per scheduler for data channel traffic per
<xref target="I-D.ietf-rtcweb-data-channel"/>. <xref target="RFC8831" format="default"/>.
</t> </t>
<t> <t>
For reasons discussed in Section 6 of For reasons discussed in
<xref target="RFC7657"/>, if multiple flows are multiplexed <xref target="RFC7657" sectionFormat="of" section="6"/>, if multiple flo
using a reliable transport (e.g., TCP) then all of the packets ws are multiplexed
for all flows multiplexed over that transport-layer flow MUST be using a reliable transport (e.g., TCP), then all of the packets
for all flows multiplexed over that transport-layer flow <bcp14>MUST</bc
p14> be
marked using the same DSCP value. Likewise, all WebRTC data marked using the same DSCP value. Likewise, all WebRTC data
channel packets transmitted over an SCTP association MUST be channel packets transmitted over an SCTP association <bcp14>MUST</bcp14> be
marked using the same DSCP value, regardless of how many data marked using the same DSCP value, regardless of how many data
channels (streams) exist or what kind of traffic is carried over channels (streams) exist or what kind of traffic is carried over
the various SCTP streams. In the event that the browser wishes the various SCTP streams. In the event that the browser wishes
to change the DSCP value in use for an SCTP association, it MUST to change the DSCP value in use for an SCTP association, it <bcp14>MUST< /bcp14>
reset the SCTP congestion controller after changing values. reset the SCTP congestion controller after changing values.
Frequent changes in the DSCP value used for an SCTP association However, frequent changes in the DSCP value used for an SCTP association
are discouraged, though, as this would defeat any attempts at are discouraged, as this would defeat any attempts at
effectively managing congestion. It should also be noted that effectively managing congestion. It should also be noted that
any change in DSCP value that results in a reset of the any change in DSCP value that results in a reset of the
congestion controller puts the SCTP association back into slow congestion controller puts the SCTP association back into slow
start, which may have undesirable effects on application start, which may have undesirable effects on application
performance. performance.
</t> </t>
<t> <t>
For the data channel traffic multiplexed over an SCTP For the data channel traffic multiplexed over an SCTP
association, it is RECOMMENDED that the DSCP value selected be association, it is <bcp14>RECOMMENDED</bcp14> that the DSCP value select ed be
the one associated with the highest priority requested for all the one associated with the highest priority requested for all
data channels multiplexed over the SCTP association. Likewise, data channels multiplexed over the SCTP association. Likewise,
when multiplexing multiple flows over a TCP connection, when multiplexing multiple flows over a TCP connection,
the DCSP value selected should be the one associated with the the DCSP value selected <bcp14>SHOULD</bcp14> be the one associated with the
highest priority requested for all multiplexed flows. highest priority requested for all multiplexed flows.
</t> </t>
<t> <t>
If a packet enters a network that has no support for a flow If a packet enters a network that has no support for a flow-type-applica
type-application priority combination specified in tion priority combination specified in
<xref target="table-dscp"/>, then the network node at the edge <xref target="tab-dscp" format="default"/>, then the network node at the
edge
will remark the DSCP value based on policies. This could result will remark the DSCP value based on policies. This could result
in the flow not getting the network treatment it expects based in the flow not getting the network treatment it expects based
on the original DSCP value in the packet. Subsequently, if the on the original DSCP value in the packet. Subsequently, if the
packet enters a network that supports a larger number of these packet enters a network that supports a larger number of these
combinations, there may not be sufficient information in the combinations, there may not be sufficient information in the
packet to restore the original markings. Mechanisms for packet to restore the original markings. Mechanisms for
restoring such original DSCP is outside the scope of this restoring such original DSCP is outside the scope of this
document. document.
</t> </t>
<t> <t>
In summary, DSCP marking provides neither guarantees nor In summary, DSCP marking provides neither guarantees nor
promised levels of service. However, DSCP marking is expected promised levels of service. However, DSCP marking is expected
to provide a statistical improvement in real-time service as a to provide a statistical improvement in real-time service as a
whole. The service provided to a packet is dependent upon the whole. The service provided to a packet is dependent upon the
network design along the path, as well as the network conditions network design along the path, as well as the network conditions
at every hop. at every hop.
</t> </t>
</section> </section>
<section numbered="true" toc="default">
<section title="Security Considerations"> <name>Security Considerations</name>
<t> <t>
Since the JavaScript application specifies the flow type and Since the JavaScript application specifies the flow type and
application priority that determine the media flow DSCP values application priority that determine the media flow DSCP values
used by the browser, the browser could consider application use used by the browser, the browser could consider application use
of a large number of higher priority flows to be suspicious. of a large number of higher priority flows to be suspicious.
If the server hosting the JavaScript application is compromised, If the server hosting the JavaScript application is compromised,
many browsers within the network might simultaneously transmit many browsers within the network might simultaneously transmit
flows with the same DSCP marking. The DiffServ architecture flows with the same DSCP marking. The Diffserv architecture
requires ingress traffic conditioning for reasons that include requires ingress traffic conditioning for reasons that include
protecting the network from this sort of attack. protecting the network from this sort of attack.
</t> </t>
<t> <t>
Otherwise, this specification does not add any additional Otherwise, this specification does not add any additional
security implications beyond those addressed in the following security implications beyond those addressed in the following
DSCP-related specifications. For security implications on use DSCP-related specifications. For security implications on use
of DSCP, please refer to Section 7 of <xref target="RFC7657"/> of DSCP, please refer to <xref target="RFC7657"
and Section 6 of <xref target="RFC4594"/>. Please also see sectionFormat="of" section="7"/>
<xref target="I-D.ietf-rtcweb-security"/> as an additional and <xref target="RFC4594" sectionFormat="of" section="6"/>. Please als
o see
<xref target="RFC8826" format="default"/> as an additional
reference. reference.
</t> </t>
</section> </section>
<section title="IANA Considerations"> <section numbered="true" toc="default">
<t> <name>IANA Considerations</name>
This specification does not require any actions from IANA. <t>This document has no IANA actions.</t>
</t>
</section> </section>
<section title="Downward References"> <section numbered="true" toc="default">
<name>Downward References</name>
<t> <t>
This specification contains a downwards reference to This specification contains downwards references to
<xref target="RFC4594"/> and <xref target="RFC7657"/>. However, <xref target="RFC4594" format="default"/> and <xref target="RFC7657" for
the parts of the former RFC used by this specification are mat="default"/>. However,
sufficiently stable for this downward reference. The guidance the parts of the former RFCs used by this specification are
sufficiently stable for these downward references. The guidance
in the latter RFC is necessary to understand the Diffserv in the latter RFC is necessary to understand the Diffserv
technology used in this document and the motivation technology used in this document and the motivation
for the recommended DSCP values and procedures. for the recommended DSCP values and procedures.
</t> </t>
</section> </section>
</middle>
<back>
<references>
<name>References</name>
<references>
<name>Normative References</name>
<xi:include href="https://xml2rfc.tools.ietf.org/public/rfc/bibxml/refer
ence.RFC.4594.xml"/>
<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.7657.xml"/>
<xi:include href="https://xml2rfc.tools.ietf.org/public/rfc/bibxml/refer
ence.RFC.7742.xml"/>
<xi:include href="https://xml2rfc.tools.ietf.org/public/rfc/bibxml/refer
ence.RFC.8174.xml"/>
<section title="Acknowledgements"> <!-- draft-ietf-rtcweb-data-channel: 8831 -->
<reference anchor="RFC8831" target="https://www.rfc-editor.org/info/rfc8831">
<front>
<title>WebRTC Data Channels</title>
<author initials="R" surname="Jesup" fullname="Randell Jesup">
<organization/>
</author>
<author initials="S" surname="Loreto" fullname="Salvatore Loreto">
<organization/>
</author>
<author initials="M" surname="Tüxen" fullname="Michael Tüxen">
<organization/>
</author>
<date month='July' year='2020'/>
</front>
<seriesInfo name="RFC" value="8831"/>
<seriesInfo name="DOI" value="10.17487/RFC8831"/>
</reference>
<!--draft-ietf-rtcweb-security: RFC 8826 -->
<reference anchor="RFC8826" target="https://www.rfc-editor.org/info/rfc8826">
<front>
<title>Security Considerations for WebRTC</title>
<author initials='E.' surname='Rescorla' fullname='Eric Rescorla'>
<organization/>
</author>
<date month='July' year='2020'/>
</front>
<seriesInfo name="RFC" value="8826"/>
<seriesInfo name="DOI" value="10.17487/RFC8826"/>
</reference>
<!-- draft-ietf-rtcweb-rtp-usage; RFC 8834 -->
<reference anchor="RFC8834" target="https://www.rfc-editor.org/info/rfc8834">
<front>
<title>Media Transport and Use of RTP in WebRTC</title>
<author initials="C." surname="Perkins" fullname="Colin Perkins">
<organization />
</author>
<author initials="M." surname="Westerlund" fullname="Magnus Westerlund">
<organization />
</author>
<author initials="J." surname="Ott" fullname="Jörg Ott">
<organization />
</author>
<date month="July" year="2020" />
</front>
<seriesInfo name="RFC" value="8834" />
<seriesInfo name="DOI" value="10.17487/RFC8834"/>
</reference>
<!-- draft-ietf-rtcweb-transports-17: 8835 -->
<reference anchor="RFC8835" target="https://www.rfc-editor.org/info/rfc8835">
<front>
<title>Transports for WebRTC</title>
<author initials="H." surname="Alvestrand" fullname="Harald Alvestrand">
<organization />
</author>
<date month="July" year="2020" />
</front>
<seriesInfo name="RFC" value="8835" />
<seriesInfo name="DOI" value="10.17487/RFC8835"/>
</reference>
<xi:include href="https://xml2rfc.tools.ietf.org/public/rfc/bibxml/reference.RFC
.8622.xml"/>
</references>
<references>
<name>Informative References</name>
<xi:include href="https://xml2rfc.tools.ietf.org/public/rfc/bibxml/refer
ence.RFC.2474.xml"/>
<xi:include href="https://xml2rfc.tools.ietf.org/public/rfc/bibxml/refer
ence.RFC.2597.xml"/>
<xi:include href="https://xml2rfc.tools.ietf.org/public/rfc/bibxml/refer
ence.RFC.3246.xml"/>
<xi:include href="https://xml2rfc.tools.ietf.org/public/rfc/bibxml/refer
ence.RFC.3550.xml"/>
<!-- draft-ietf-rmcat-coupled-cc (RFC 8699) (Published) -->
<xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.8699.
xml"/>
<reference anchor="G.1010">
<front>
<title>End-user multimedia QoS categories</title>
<author>
<organization>ITU-T</organization>
</author>
<date month="November" year="2001"/>
</front>
<seriesInfo name="ITU-T Recommendation" value="G.1010"/>
</reference>
</references>
</references>
<section numbered="false" toc="default">
<name>Acknowledgements</name>
<t> <t>
Thanks to David Black, Magnus Westerlund, Paolo Severini, Jim Thanks to <contact fullname="David Black"/>, <contact fullname="Magnus
Hasselbrook, Joe Marcus, Erik Nordmark, Michael Tuexen, and Westerlund"/>, <contact fullname="Paolo Severini"/>, <contact fullname="J
Brian Carpenter for their invaluable input. im
Hasselbrook"/>, <contact fullname="Joe Marcus"/>, <contact fullname="Eri
k
Nordmark"/>, <contact fullname="Michael Tüxen"/>, and
<contact fullname="Brian Carpenter"/> for their invaluable input.
</t> </t>
</section> </section>
<section numbered="false" toc="default">
<section title="Dedication"> <name>Dedication</name>
<t> <t>
This document is dedicated to the memory of James Polk, a This document is dedicated to the memory of <contact fullname="James Pol k"/>, a
long-time friend and colleague. James made important long-time friend and colleague. James made important
contributions to this specification, including serving initially contributions to this specification, including serving initially
as one of the primary authors. The IETF global community mourns as one of the primary authors. The IETF global community mourns
his loss and he will be missed dearly. his loss and he will be missed dearly.
</t> </t>
</section> </section>
<section title="Document History">
<t>
Note to RFC Editor: Please remove this section.
</t>
<t>
This document was originally an individual submission in RTCWeb WG.
The RTCWeb working group selected it to be become a WG document.
Later the transport ADs requested that this be moved to the TSVWG WG
as that seemed to be a better match.
</t>
</section>
</middle>
<back>
<references title="Normative References">
<?rfc include='reference.RFC.4594'?>
<?rfc include='reference.RFC.2119'?>
<?rfc include='reference.RFC.7657'?>
<?rfc include='reference.RFC.7742'?>
<?rfc include='reference.I-D.ietf-rtcweb-security'?>
<?rfc include='reference.I-D.ietf-rtcweb-transports'?>
<?rfc include='reference.I-D.ietf-rtcweb-rtp-usage'?>
<?rfc include='reference.I-D.ietf-rtcweb-data-channel'?>
</references>
<references title="Informative References">
<?rfc include='reference.RFC.2474'?>
<?rfc include='reference.RFC.2597'?>
<?rfc include='reference.RFC.3246'?>
<?rfc include='reference.RFC.3550'?>
<?rfc include='reference.RFC.3662'?>
<?rfc include='reference.I-D.ietf-rmcat-coupled-cc'?>
<reference anchor="G.1010">
<front>
<title>End-user multimedia QoS categories</title>
<author>
<organization>International Telecommunications Union</organization>
</author>
<date month="November" year="2001"/>
</front>
<seriesInfo name="Recommendation" value="ITU-T G.1010"/>
</reference>
</references>
</back> </back>
</rfc> </rfc>
 End of changes. 106 change blocks. 
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