RFC 2963 (rfc2963) - Page 2 of 19


A Rate Adaptive Shaper for Differentiated Services



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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
   [RFC 2697] and [RFC 2698].









Bonaventure & De Cnodder     Informational