RFC 1257 (rfc1257) - Page 1 of 5

Isochronous applications do not require jitter-controlled networks

Network Working Group                                       C. Partridge
Request for Comments: 1257         Swedish Institute of Computer Science
                                                          September 1991


   Isochronous Applications Do Not Require Jitter-Controlled Networks

Status of this Memo

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

Abstract

   This memo argues that jitter control is not required for networks to
   support isochronous applications.  A network providing bandwidth and
   bounds delay is sufficient.  The implications for gigabit
   internetworking protocols are briefly considered.

Introduction

   An oft-stated goal of many of the ongoing gigabit networking research
   projects is to make it possible to support high bandwidth isochronous
   applications.  An isochronous application is an application which
   must generate or process regular amounts of data at fixed intervals.
   Examples of such applications include telephones, which send and
   receive voice samples at regular intervals, and fixed rate video-
   codecs, which generate data at regular intervals and which must
   receive data at regular intervals.

   One of the properties of isochronous applications like voice and
   video data streams is that their users may be sensitive to the
   variation in interarrival times between data delivered to the final
   output device.  This interarrival time is called "jitter" for very
   small variances (less than 10 Hz) and "wander" if it is somewhat
   larger (less than one day).  For convenience, this memo will use the
   term jitter for both jitter and wander.

   A couple of examples help illustrate the sensitivity of applications
   to jitter.  Consider a user watching a video at her workstation.  If
   the screen is not updated regularly every 30th of a second or faster,
   the user will notice a flickering in the image.  Similarly, if voice
   samples are not delivered at regular intervals, voice output may
   sound distorted.  Thus the user is sensitive to the interarrival time
   of data at the output device.

   Observe that if two users are conferring with each other from their



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