Network Working Group S. Dhesikan
Internet-Draft C. Jennings
Intended status: Standards Track Cisco Systems
Expires: May 16, 2015 D. Druta, Ed.
AT&T
P. Jones
J. Polk
Cisco Systems
November 12, 2014
DSCP and other packet markings for RTCWeb QoS
draft-ietf-tsvwg-rtcweb-qos-03
Abstract
Many networks, such as service provider and enterprise networks, can
provide treatment for individual packets based on Differentiated
Services Code Points (DSCP) on a per-hop basis. This document
provides the recommended DSCP values for browsers to use for various
classes of traffic.
Status of This Memo
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provisions of BCP 78 and BCP 79.
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This Internet-Draft will expire on May 16, 2015.
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carefully, as they describe your rights and restrictions with respect
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Relation to Other Standards . . . . . . . . . . . . . . . . . 3
3. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
4. Inputs . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
5. DSCP Mappings . . . . . . . . . . . . . . . . . . . . . . . . 4
6. Security Considerations . . . . . . . . . . . . . . . . . . . 6
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6
8. Downward References . . . . . . . . . . . . . . . . . . . . . 6
9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 6
10. Document History . . . . . . . . . . . . . . . . . . . . . . 6
11. References . . . . . . . . . . . . . . . . . . . . . . . . . 7
11.1. Normative References . . . . . . . . . . . . . . . . . . 7
11.2. Informative References . . . . . . . . . . . . . . . . . 7
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 7
1. Introduction
Differentiated Services Code Points (DSCP) [RFC2474] style packet
marking can help provide QoS in some environments. There are many
use cases where such marking does not help, but it seldom makes
things worse if packets are marked appropriately. In other words, if
too many packets, say all audio or all audio and video, are marked
for a given network condition then it can prevent desirable results.
Either too much other traffic will be starved, or there is not enough
capacity for the preferentially marked packets (i.e., audio and/or
video).
This specification proposes how WebRTC applications can mark packets.
This specification does not contradict or redefine any advice from
previous IETF RFCs but simply provides a simple set of
recommendations for implementers based on the previous RFCs.
There are some environments where priority markings frequently help.
These include:
1. Private, wide-area networks.
2. Residential Networks. If the congested link is the broadband
uplink in a cable or DSL scenario, often residential routers/NAT
support preferential treatment based on DSCP.
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3. Wireless Networks. If the congested link is a local wireless
network, marking may help.
Traditionally DSCP values have been thought of as being site
specific, with each site selecting its own code points for each QoS
level. However in the RTCWeb use cases, the browsers need to set
them to something when there is no site specific information. In
this document, "browsers" is used synonmously with "interactive User
Agent" as defined in the HTML specification, [W3C.WD-html-20110525].
This document describes a reasonable default set of DSCP code point
values drawn from existing RFCs and common usage. These code points
are solely defaults.
This specification defines some inputs that the browser in an WebRTC
application can look at to determine how to set the various packet
markings and defines the mapping from abstract QoS policies (data
type, priority level) to those packet markings.
2. Relation to Other Standards
This document exists as a complement to [I-D.ietf-dart-dscp-rtp],
which describes the interaction between DSCP and real-time
communications. It covers the implications of using various DSCP
values, particularly focusing on Real-time Transport Protocol (RTP)
[RFC3550] streams that are multiplexed onto a single transport-layer
flow.
This specification does not change or override the advice in any
other standards about setting packet markings. It simply provides a
summary of them and provides the context of how they relate in the
RTCWeb context. In some cases, such as DSCP where the normative RFC
leaves open multiple options from which to choose, this clarifies
which choice should be used in the RTCWeb context. This document
also specifies the inputs that are needed by the browser to provide
to the media engine.
The DSCP value set by the endpoint is not always trusted by the
network. Therefore, the DSCP value may be remarked at any place in
the network for a variety of reasons to any other DSCP value,
including default forwarding (DF) which provides basic best effort
service. The mitigation for such action is through an authorization
mechanism. Such authorization mechanism is outside the scope of this
document.
3. Terminology
The key words "MUST", "MUST NOT", "SHOULD", "SHOULD NOT", and "MAY"
in this document are to be interpreted as described in [RFC2119].
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4. Inputs
The below uses the concept of a media flow, however this is usually
not equivalent to a transport flow, i.e. as defined by a 5-tuple
(source address, destination address, source port, destination port,
and protocol). Instead each media flow contains all the packets
associated with an independent media entity within one 5-tuple.
There may be multiple media flows within the same 5- tuple. These
media flows might consist of different media types and have different
priorities. The following are the inputs that the browser provides
to the media engine:
o Data Type: The browser provides this input as it knows if the flow
is audio, interactive video with or without audio, non-interactive
video with or without audio, or data.
o Priority: Another input is the relative treatment of the flow
within that data type. Many applications have multiple media
flows of the same data type and often some are more important than
others. Likewise, in a video conference where the flows in the
conference is of the same data type but contains different media
types, the flow for audio may be more important than the video
flow. JavaScript applications can tell the browser whether a
particular media flow is high, medium, low or very low importance
to the application.
[I-D.ietf-rtcweb-transports] defines in more detail what an
individual media flow is within the WebRTC context.
5. DSCP Mappings
Below is a table of DSCP markings for each data type of interest to
RTCWeb. These DSCP values for each data type listed are a reasonable
default set of code point values taken from [RFC4594]. A web browser
SHOULD use these values to mark the appropriate media packets. More
information on EF can be found in [RFC3246]. More information on AF
can be found in [RFC2597]. DF is default forwarding which provides
the basic best effort service. The mitigation for such action is
through an authorization mechanism. Such authorization mechanism is
outside the scope of this document.
+---------------------------+-------+------+------------+-----------+
| Data Type | Very | Low | Medium | High |
| | Low | | | |
+---------------------------+-------+------+------------+-----------+
| Audio | CS1 | DF | EF (46) | EF (46) |
| | (8) | (0) | | |
| | | | | |
| Interactive Video with or | CS1 | DF | AF42, AF43 | AF41, |
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| without audio | (8) | (0) | (36, 38) | AF42 (34, |
| | | | | 36) |
| | | | | |
| Non-Interactive Video | CS1 | DF | AF32, AF33 | AF31, |
| with or without audio | (8) | (0) | (28, 30) | AF32 (26, |
| | | | | 28) |
| | | | | |
| Data | CS1 | DF | AF1x (10, | AF2x (18, |
| | (8) | (0) | 12, 14) | 20, 22) |
+---------------------------+-------+------+------------+-----------+
Table 1
The columns "very low", "low", "Medium" and "high" are the priority
levels. This priority value signifies the relative priority of the
media flow within the application and is provided to the browser to
assist it in selecting the DSCP value. The browser SHOULD first
select the data type of the media flow. Within the data type, the
priority of the media flow SHOULD be selected. All packets within a
media flow SHOULD have the same priority. In some cases, the
selected cell may have multiple DSCP values, such as AF41 and AF42.
These offer different drop precedences. One may select difference
drop precedences for the different packets in the media flow.
Therefore, all packets in the stream SHOULD be marked with the same
priority but can have difference drop precedences.
The combination of data type and priority provides specificity and
helps in selecting the right DSCP value for the media flow. In some
cases, the different drop precedence values provides additional
granularity in classifying packets within a media flow. For example,
in a video conference, the video media flow may be medium priority.
If so, either AF42 or AF43 may be selected. If the I frames in the
stream are more important than the P frames then the I frames can be
marked with AF42 and the P frames marked with AF43.
The above table assumes that packets marked with CS1 is treated as
"less than best effort". However, the treatment of CS1 is
implementation dependent. If an implementation treats CS1 as other
than "less than best effort", then the priority of the packets may be
changed from what is intended.
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If a packet enters a QoS domain that has no support for the above
defined Data Types/Application (service) classes, then the network
node at the edge will remark the DSCP value based on policies.
Subsequently, if the packet enters a QoS domain that supports a
larger number of Data types/Application (service) classes, there may
not be sufficient information in the packet to restore the original
markings. Mechanisms for restoring such original DSCP is outside the
scope of this document.
6. Security Considerations
This specification does not add any additional security implication
other than the normal application use of DSCP. For security
implications on use of DSCP, please refer to Section 6 of RFC 4594.
Please also see [I-D.ietf-rtcweb-security] as an additional
reference.
7. IANA Considerations
This specification does not require any actions from IANA.
8. Downward References
This specification contains a downwards reference to [RFC4594].
However, the parts of that RFC used by this specification are
sufficiently stable for this downward reference.
9. Acknowledgements
Thanks To David Black, Magnus Westerland, Paolo Severini, Jim
Hasselbrook, Joe Marcus, and Erik Nordmark for their help.
10. Document History
Note to RFC Editor: Please remove this section.
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. This document is now being
submitted as individual submission to the TSVWG with the hope that WG
will select it as a WG draft and move it forward to an RFC.
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11. References
11.1. Normative References
[I-D.ietf-dart-dscp-rtp]
Black, D. and P. Jones, "Differentiated Services
(DiffServ) and Real-time Communication", draft-ietf-dart-
dscp-rtp-10 (work in progress), November 2014.
[I-D.ietf-rtcweb-security]
Rescorla, E., "Security Considerations for WebRTC", draft-
ietf-rtcweb-security-07 (work in progress), July 2014.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC4594] Babiarz, J., Chan, K., and F. Baker, "Configuration
Guidelines for DiffServ Service Classes", RFC 4594, August
2006.
11.2. Informative References
[RFC2474] Nichols, K., Blake, S., Baker, F., and D. Black,
"Definition of the Differentiated Services Field (DS
Field) in the IPv4 and IPv6 Headers", RFC 2474, December
1998.
[RFC2597] Heinanen, J., Baker, F., Weiss, W., and J. Wroclawski,
"Assured Forwarding PHB Group", RFC 2597, June 1999.
[RFC3246] Davie, B., Charny, A., Bennet, J., Benson, K., Le Boudec,
J., Courtney, W., Davari, S., Firoiu, V., and D.
Stiliadis, "An Expedited Forwarding PHB (Per-Hop
Behavior)", RFC 3246, March 2002.
[RFC3550] Schulzrinne, H., Casner, S., Frederick, R., and V.
Jacobson, "RTP: A Transport Protocol for Real-Time
Applications", STD 64, RFC 3550, July 2003.
Authors' Addresses
Subha Dhesikan
Cisco Systems
Email: sdhesika@cisco.com
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Cullen Jennings
Cisco Systems
Email: fluffy@cisco.com
Dan Druta (editor)
AT&T
Email: dd5826@att.com
Paul E. Jones
Cisco Systems
Email: paulej@packetizer.com
James Polk
Cisco Systems
Email: jmpolk@cisco.com
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