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Versions: (draft-dhesikan-tsvwg-rtcweb-qos) 00 01 02 03 04 05 06 07 08 09 10 11 12 13 14 15 16 17 18 Draft is active
In: MissingRef
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

   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 May 16, 2015.

Copyright Notice

   Copyright (c) 2014 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



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   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 . . . . . . . . . . . . . . . . . . . . . . . . .   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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