RFC 2681 (rfc2681) - Page 2 of 20

A Round-trip Delay Metric for IPPM

RFC 2681          Round-trip for Delay Metric for IPPM    September 1999


   The structure of the memo is as follows:

   +  A 'singleton' analytic metric, called Type-P-Round-trip-Delay,
      will be introduced to measure a single observation of round-trip
      delay.

   +  Using this singleton metric, a 'sample', called Type-P-Round-trip-
      Delay-Poisson-Stream, will be introduced to measure a sequence of
      singleton delays measured at times taken from a Poisson process.

   +  Using this sample, several 'statistics' of the sample will be
      defined and discussed.

   This progression from singleton to sample to statistics, with clear
   separation among them, is important.

   Whenever a technical term from the IPPM Framework document is first
   used in this memo, it will be tagged with a trailing asterisk.  For
   example, "term*" indicates that "term" is defined in the Framework.

1.1. Motivation

   Round-trip delay of a Type-P* packet from a source host* to a
   destination host is useful for several reasons:

   +  Some applications do not perform well (or at all) if end-to-end
      delay between hosts is large relative to some threshold value.

   +  Erratic variation in delay makes it difficult (or impossible) to
      support many interactive real-time applications.

   +  The larger the value of delay, the more difficult it is for
      transport-layer protocols to sustain high bandwidths.

   +  The minimum value of this metric provides an indication of the
      delay due only to propagation and transmission delay.

   +  The minimum value of this metric provides an indication of the
      delay that will likely be experienced when the path* traversed is
      lightly loaded.

   +  Values of this metric above the minimum provide an indication of
      the congestion present in the path.








Almes, et al.               Standards Track