Network Working Group                                        S. Dhesikan
Internet-Draft                                               C. Jennings
Intended status: Standards Track                           Cisco Systems
Expires: July 26, 2016                                     D. Druta, Ed.
                                                                P. Jones
                                                           Cisco Systems
                                                        January 23, 2016

             DSCP and other packet markings for WebRTC QoS


   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 web browsers to use for
   various classes of WebRTC 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
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   Internet-Drafts are draft documents valid for a maximum of six months
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   This Internet-Draft will expire on July 26, 2016.

Copyright Notice

   Copyright (c) 2016 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
   ( in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect

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   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 . . . . . . . . . . . . . . . . . . .   7
   7.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   7
   8.  Downward References . . . . . . . . . . . . . . . . . . . . .   7
   9.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .   7
   10. Dedication  . . . . . . . . . . . . . . . . . . . . . . . . .   7
   11. Document History  . . . . . . . . . . . . . . . . . . . . . .   8
   12. References  . . . . . . . . . . . . . . . . . . . . . . . . .   8
     12.1.  Normative References . . . . . . . . . . . . . . . . . .   8
     12.2.  Informative References . . . . . . . . . . . . . . . . .   9
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   9

1.  Introduction

   Differentiated Services Code Points (DSCP) [RFC2474] packet marking
   can help provide QoS in some environments.  This specification
   proposes how WebRTC applications can mark packets, but does not
   contradict or redefine any advice from previous IETF RFCs.  Rather,
   it merely provides a simple set of recommendations for implementers
   based on the previous RFCs.

   There are many use cases where such marking does not help, but it
   seldom makes things worse if packets are marked appropriately.  As
   one example of where it does not help, 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).

   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.

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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
   controlling per-hop-behavior to influence the QoS for transport-layer
   flows.  However in the WebRTC 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
   (flow type, priority level) to those packet markings.

2.  Relation to Other Standards

   This document exists as a complement to [RFC7657], 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 [RFC7657] 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-layer flow.  Generally, the RTP streams would be marked
   with a value as appropriate from Table 1.  A WebRTC application might
   also multiplex data channel [I-D.ietf-rtcweb-data-channel] traffic
   over the same 5-tuple as RTP streams, which would also be marked as
   per that table.  The guidance in [RFC7657] says that all data channel
   traffic would be marked with a single value that is typically
   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).  This is
   expanded upon further in the next section.

   This specification does not change or override the advice in any
   other standards about setting packet markings.  It simply selects a
   subset of DSCP values that is relevant in the WebRTC context.  This
   document also specifies the inputs that are needed by the browser to
   provide to the media engine.

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   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", "REQUIRED", "SHALL", "SHALL NOT",
   document are to be interpreted as described in [RFC2119].

4.  Inputs

   WebRTC entities transmit and receive two types of media of
   significance to this document:

   o  media flows which are RTP streams [I-D.ietf-rtcweb-rtp-usage]
   o  data flows which are data channels [I-D.ietf-rtcweb-data-channel]

   Each of the RTP streams and distinct data channels consists of all of
   the packets associated with an independent media entity and are not
   always equivalent to a transport-layer flow defined by a 5-tuple
   (source address, destination address, source port, destination port,
   and protocol).  There may be multiple RTP streams and data channels
   multiplexed over the same 5-tuple, with each having a different level
   of importance to the application and, therefore, potentially marked
   using different DSCP values than another RTP stream or data channel
   within the same transport-layer flow.  (Note that there are
   restrictions with respect to marking different data channels carried
   within the same SCTP association as outlined in Section 5.)

   The following are the inputs that the browser provides to the media

   o  Flow 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
      an RTP stream or data channel.  Many applications have multiple
      flows of the same Flow 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

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      tell the browser whether a particular flow is high, medium, low or
      very low importance to the application.

   [I-D.ietf-rtcweb-transports] defines in more detail what an
   individual flow is within the WebRTC context.

5.  DSCP Mappings

   The DSCP markings for each flow type of interest to WebRTC given the
   application priority is shown in the following table.  The DSCP
   values for each flow 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.

   |       Flow Type        |  Very | Low  |    Medium   |     High    |
   |                        |  Low  |      |             |             |
   |         Audio          |  CS1  |  DF  |   EF (46)   |   EF (46)   |
   |                        |  (8)  | (0)  |             |             |
   |                        |       |      |             |             |
   | Interactive Video with |  CS1  |  DF  |  AF42, AF43 |  AF41, AF42 |
   |    or without audio    |  (8)  | (0)  |   (36, 38)  |   (34, 36)  |
   |                        |       |      |             |             |
   | Non-Interactive Video  |  CS1  |  DF  |  AF32, AF33 |  AF31, AF32 |
   | with or without audio  |  (8)  | (0)  |   (28, 30)  |   (26, 28)  |
   |                        |       |      |             |             |
   |          Data          |  CS1  |  DF  |     AF11    |     AF21    |
   |                        |  (8)  | (0)  |             |             |

         Table 1: Recommended DSCP Values for WebRTC Applications

   The application priority, indicated by the columns "very low", "low",
   "Medium", and "high", signifies the relative importance of the flow
   within the application.  It is an input that the browser receives to
   assist it in selecting the DSCP value.  Application priority does not
   refer to priority in the network transport.

   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.  It is common for CS1 to be treated the same as DF,

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   so anyone using CS1 cannot assume that CS1 will be treated
   differently than DF.  Implementers should also note that 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

   The browser SHOULD first select the flow type of the flow.  Within
   the flow type, the relative importance of the flow SHOULD be used to
   select the appropriate DSCP value.

   The combination of flow type and application priority provides
   specificity and helps in selecting the right DSCP value for the flow.
   All packets within a flow SHOULD have the same application priority.
   In some cases, the selected application priority cell may have
   multiple DSCP values, such as AF41 and AF42.  These offer different
   drop precedences.  The different drop precedence values provides
   additional granularity in classifying packets within a flow.  For
   example, in a video conference, the video 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.

   For reasons discussed in Section 6 of [RFC7657], if multiple flows
   are multiplexed using a reliable transport (e.g., TCP) then all of
   the packets for all flows multiplexed over that transport-layer flow
   MUST be marked using the same DSCP value.  Likewise, all WebRTC data
   channel packets transmitted over an SCTP association MUST be marked
   using the same DSCP value, regardless of how many data channels
   (streams) exist or what kind of traffic is carried over the various
   SCTP streams.  In the event that the browser wishes to change the
   DSCP value in use for an SCTP association, it MUST reset the SCTP
   congestion controller after changing values.  Frequent changes in the
   DSCP value used for an SCTP association are discouraged, though, as
   this would defeat any attempts at effectively managing congestion.
   It should also be noted that any change in DSCP value that results in
   a reset of the congestion controller puts the SCTP association back
   into slow start, which may have undesirable effects on application

   For the data channel traffic multiplexed over an SCTP association, it
   is RECOMMENDED that the DSCP value selected be the one associated
   with the highest priority requested for all data channels multiplexed
   over the SCTP association.  Likewise, when multiplexing multiple
   flows over a TCP connection, the DCSP value selected should be the
   one associated with the highest priority requested for all
   multiplexed flows.

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   If a packet enters a QoS domain that has no support for the above
   defined flow 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 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.

   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
   implications on use of DSCP, please refer to Section 6 of [RFC4594].
   Please also see [I-D.ietf-rtcweb-security] as an additional

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, Erik Nordmark, and Michael Tuexen for their
   invaluable input.

10.  Dedication

   This document is dedicated to the memory of James Polk, a long-time
   friend and colleague.  James made important contributions to this
   specification, including being one of its primary authors.  The IETF
   global community mourns his loss and he will be missed dearly.

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11.  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.

12.  References

12.1.  Normative References

              Jesup, R., Loreto, S., and M. Tuexen, "WebRTC Data
              Channels", draft-ietf-rtcweb-data-channel-13 (work in
              progress), January 2015.

              Perkins, C., Westerlund, M., and J. Ott, "Web Real-Time
              Communication (WebRTC): Media Transport and Use of RTP",
              draft-ietf-rtcweb-rtp-usage-25 (work in progress), June

              Rescorla, E., "Security Considerations for WebRTC", draft-
              ietf-rtcweb-security-08 (work in progress), February 2015.

              Alvestrand, H., "Transports for WebRTC", draft-ietf-
              rtcweb-transports-10 (work in progress), October 2015.

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/
              RFC2119, March 1997,

   [RFC4594]  Babiarz, J., Chan, K., and F. Baker, "Configuration
              Guidelines for DiffServ Service Classes", RFC 4594, DOI
              10.17487/RFC4594, August 2006,

   [RFC7657]  Black, D., Ed. and P. Jones, "Differentiated Services
              (Diffserv) and Real-Time Communication", RFC 7657, DOI
              10.17487/RFC7657, November 2015,

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12.2.  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, DOI
              10.17487/RFC2474, December 1998,

   [RFC2597]  Heinanen, J., Baker, F., Weiss, W., and J. Wroclawski,
              "Assured Forwarding PHB Group", RFC 2597, DOI 10.17487/
              RFC2597, 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, DOI 10.17487/RFC3246, March 2002,

   [RFC3550]  Schulzrinne, H., Casner, S., Frederick, R., and V.
              Jacobson, "RTP: A Transport Protocol for Real-Time
              Applications", STD 64, RFC 3550, DOI 10.17487/RFC3550,
              July 2003, <>.

              Hickson, I., Berjon, R., Faulkner, S., Leithead, T.,
              Navara, E., O&#039;Connor, E., and S. Pfeiffer, "HTML5",
              World Wide Web Consortium Recommendation REC-
              html5-20141028, October 2014,

Authors' Addresses

   Subha Dhesikan
   Cisco Systems


   Cullen Jennings
   Cisco Systems


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   Dan Druta (editor)


   Paul E. Jones
   Cisco Systems


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