A Rate Adaptive Shaper for Differentiated Services
RFC 2963

Document Type RFC - Informational (October 2000; No errata)
Last updated 2013-03-02
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Network Working Group                                      O. Bonaventure
Request for Comments: 2963                                          FUNDP
Category: Informational                                     S. De Cnodder
                                                             October 2000

           A Rate Adaptive Shaper for Differentiated Services

Status of this Memo

   This memo provides information for the Internet community.  It does
   not specify an Internet standard of any kind.  Distribution of this
   memo is unlimited.

Copyright Notice

   Copyright (C) The Internet Society (2000).  All Rights Reserved.


   This memo describes several Rate Adaptive Shapers (RAS) that can be
   used in combination with the single rate Three Color Markers (srTCM)
   and the two rate Three Color Marker (trTCM) described in RFC2697 and
   RFC2698, respectively.  These RAS improve the performance of TCP when
   a TCM is used at the ingress of a diffserv network by reducing the
   burstiness of the traffic.  With TCP traffic, this reduction of the
   burstiness is accompanied by a reduction of the number of marked
   packets and by an improved TCP goodput.  The proposed RAS can be used
   at the ingress of Diffserv networks providing the Assured Forwarding
   Per Hop Behavior (AF PHB).  They are especially useful when a TCM is
   used to mark traffic composed of a small number of TCP connections.

1. Introduction

   In DiffServ networks [RFC2475], the incoming data traffic, with the
   AF PHB in particular, could be subject to marking where the purpose
   of this marking is to provide a low drop probability to a minimum
   part of the traffic whereas the excess will have a larger drop
   probability.  Such markers are mainly token bucket based such as the
   single rate Three Color Marker (srTCM) and two rate Three Color
   Marker (trTCM) described in [RFC2697] and [RFC2698], respectively.

   Similar markers were proposed for ATM networks and simulations have
   shown that their performance with TCP traffic was not always
   satisfactory and several researchers have shown that these
   performance problems could be solved in two ways:

Bonaventure & De Cnodder     Informational                      [Page 1]
RFC 2963                 A Rate Adaptive Shaper             October 2000

   1. increasing the burst size, i.e. increasing the Committed Burst
      Size (CBS) and the Peak Burst Size (PBS) in case of the trTCM, or

   2. shaping the traffic such that a part of the burstiness is removed.

   The first solution has as major disadvantage that the traffic sent to
   the network can be very bursty and thus engineering the network to
   provide a low packet loss ratio can become difficult.  To efficiently
   support bursty traffic, additional resources such as buffer space are
   needed.  Conversely, the major disadvantage of shaping is that the
   traffic encounters additional delay in the shaper's buffer.

   In this document, we propose two shapers that can reduce the
   burstiness of the traffic upstream of a TCM.  By reducing the
   burstiness of the traffic, the adaptive shapers increase the
   percentage of packets marked as green by the TCM and thus the overall
   goodput of the users attached to such a shaper.

   Such rate adaptive shapers will probably be useful at the edge of the
   network (i.e. inside access routers or even network adapters).  The
   simulation results in [Cnodder] show that these shapers are
   particularly useful when a small number of TCP connections are
   processed by a TCM.

   The structure of this document follows the structure proposed in
   [Nichols].  We first describe two types of rate adaptive shapers in
   section two.  These shapers correspond to respectively the srTCM and
   the trTCM.  In section 3, we describe an extension to the simple
   shapers that can provide a better performance. We briefly discuss
   simulation results in the appendix.

2. Description of the rate adaptive shapers

2.1. Rate adaptive shaper

   The rate adaptive shaper is based on a similar shaper proposed in
   [Bonaventure] to improve the performance of TCP with the Guaranteed
   Frame Rate [TM41] service category in ATM networks.  Another type of
   rate adaptive shaper suitable for differentiated services was briefly
   discussed in [Azeem].  A RAS will typically be used as shown in
   figure 1 where the meter and the marker are the TCMs proposed in
   [RFC2697] and [RFC2698].

Bonaventure & De Cnodder     Informational                      [Page 2]
RFC 2963                 A Rate Adaptive Shaper             October 2000

                                  |          |
                                  |          V
                 +--------+   +-------+   +--------+
      Incoming   |        |   |       |   |        |   Outgoing
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