Network Working Group S. Dhesikan
Internet-Draft C. Jennings
Intended status: Standards Track Cisco Systems
Expires: January 07, 2016 D. Druta, Ed.
AT&T
P. Jones
J. Polk
Cisco Systems
July 06, 2015
DSCP and other packet markings for RTCWeb QoS
draft-ietf-tsvwg-rtcweb-qos-04
Abstract
Many networks, such as service provider and enterprise networks, can
provide treatment for individual packets based on Differentiated
Services Code Point (DSCP) values 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
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on January 07, 2016.
Copyright Notice
Copyright (c) 2015 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
Dhesikan, et al. Expires January 07, 2016 [Page 1]
Internet-Draft RTCWeb QoS July 2015
carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Relation to Other Standards . . . . . . . . . . . . . . . . . 3
3. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4
4. Inputs . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
5. DSCP Mappings . . . . . . . . . . . . . . . . . . . . . . . . 5
6. Security Considerations . . . . . . . . . . . . . . . . . . . 6
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 7
8. Downward References . . . . . . . . . . . . . . . . . . . . . 7
9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 7
10. Document History . . . . . . . . . . . . . . . . . . . . . . 7
11. References . . . . . . . . . . . . . . . . . . . . . . . . . 7
11.1. Normative References . . . . . . . . . . . . . . . . . . 7
11.2. Informative References . . . . . . . . . . . . . . . . . 8
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 8
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 merely provides a simple set of
recommendations for implementers based on the previous RFCs
There are some environments where DSCP 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.
Dhesikan, et al. Expires January 07, 2016 [Page 2]
Internet-Draft RTCWeb QoS July 2015
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
controlling per-hop-behavior to influence the QoS for transport
flows. 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 synonymously with "Interactive User
Agent" as defined in the HTML specification,
[W3C.REC-html5-20141028]. This document describes a subset of DSCP
code point values drawn from existing RFCs and common usage for use
with WebRTC applications. These code points are solely defaults.
This specification defines some inputs that the browser in a WebRTC
application can consider to aid in determining 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.
There are a number of guidelines specified in
[I-D.ietf-dart-dscp-rtp] that should be followed when marking traffic
sent by WebRTC applications, as it is common for multiple RTP streams
to be multiplexed on the same transport flow. Generally, the RTP
streams would be marked with a value as appropriate from Table 1. A
WebRTC application might multiplex data channel traffic over the same
5-tuple as RTP streams, which would also be marked as per that table.
The guidance in [I-D.ietf-dart-dscp-rtp] indicates that all data
channel traffic would be marked with a single value that is different
than the value(s) used for RTP streams multiplexed with the data
channel traffic over the same 5-tuple, assuming RTP streams are
marked with a value other than default forwarding (DF).
In the event that RTP streams are carried over a reliable transport
(e.g., TCP), all such packets, even there are multiple RTP streams
that would be marked differently if sent via an unreliable transport,
must be marked with a single DSCP value.
This specification does not change or override the advice in any
other standards about setting packet markings. It simply selects a
Dhesikan, et al. Expires January 07, 2016 [Page 3]
Internet-Draft RTCWeb QoS July 2015
subset of DSCP values that is relevant 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 values 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) value to provide basic best effort
service. The mitigation for such action is through an authorization
mechanism. Such authorization mechanism is outside the scope of this
document. There is benefit in marking traffic even if it only
benefits the first few hops.
3. Terminology
The key words "MUST", "MUST NOT", "SHOULD", "SHOULD NOT", and "MAY"
in this document are to be interpreted as described in [RFC2119].
4. Inputs
The below uses the concept of a media flow, however this is usually
not equivalent to a transport flow 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
levels of importance to the application and, therefore, each
potentially marked using different DSCP values than for another media
flow multiplexed over the same transport flow. 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 Application Priority: Another input is the relative importance of
the flow within that data type. Many applications have multiple
media flows of the same data type and often some flows are more
important than others. For example, in a video conference where
there are usually audio and video flows, the audio flow 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.
Dhesikan, et al. Expires January 07, 2016 [Page 4]
Internet-Draft RTCWeb QoS July 2015
As an example of different media flows that might be multiplexed over
the same transport flow, packets related to one RTP stream (e.g., an
audio flow) carried over UDP might be one media flow, packets related
to a second RTP stream (e.g., presentation video) carried over UDP
might be a second media flow, and finally data channel packets
carried via SCTP over DTLS might be third media flow.
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
subset 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.
+---------------------------+-------+------+------------+-----------+
| 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, |
| 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" signify the
relative importance of the media flow within the application and is
an input that the browser receives to assist it in selecting the DSCP
value. These are referred to as application priority in this
document. Application priority does not refer to priority in the
network transport.
The browser SHOULD first select the data type of the media flow.
Within the data type, the relative importance of the media flow
SHOULD be used to select the appropriate DSCP value. All packets
Dhesikan, et al. Expires January 07, 2016 [Page 5]
Internet-Draft RTCWeb QoS July 2015
within a media flow SHOULD have the same application 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
same media flow. Therefore, all packets in the media flow SHOULD be
marked with the same application priority, but can have difference
drop precedences.
The combination of data type and application 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 have
medium application 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.
If a packet enters a QoS domain that has no support for the above
defined data types/application priority (service class), then the
network node at the edge will remark the DSCP value based on
policies. This could result in the media flow not getting the
network treatment it expects based on the original DSCP value in the
packet. Subsequently, if the packet enters a QoS domain that
supports a larger number of 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.
The above table assumes that packets marked with CS1 are 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 actual priority (or, more
precisely, the per-hop-behavior) of the packets may be changed from
what is intended. Implementers should also note that the excess EF
traffic is dropped. This could mean that a packet marked as EF may
not get through as opposed to a packet marked with a different DSCP
value.
In summary, there are no guarantees or promised level of service with
the use of DSCP. The service provided to a packet is dependent upon
the network design along the path, as well as the congestion levels
at every hop.
6. Security Considerations
This specification does not add any additional security implication
other than the normal application use of DSCP. For security
Dhesikan, et al. Expires January 07, 2016 [Page 6]
Internet-Draft RTCWeb QoS July 2015
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.
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.
[I-D.ietf-rtcweb-transports]
Alvestrand, H., "Transports for WebRTC", draft-ietf-
rtcweb-transports-08 (work in progress), February 2015.
Dhesikan, et al. Expires January 07, 2016 [Page 7]
Internet-Draft RTCWeb QoS July 2015
[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.
[W3C.REC-html5-20141028]
Hickson, I., Berjon, R., Faulkner, S., Leithead, T.,
Navara, E., O'Connor, E., and S. Pfeiffer, "HTML5",
World Wide Web Consortium Recommendation REC-
html5-20141028, October 2014,
<http://www.w3.org/TR/2014/REC-html5-20141028>.
Authors' Addresses
Subha Dhesikan
Cisco Systems
Email: sdhesika@cisco.com
Cullen Jennings
Cisco Systems
Email: fluffy@cisco.com
Dhesikan, et al. Expires January 07, 2016 [Page 8]
Internet-Draft RTCWeb QoS July 2015
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
Dhesikan, et al. Expires January 07, 2016 [Page 9]
