Isochronous applications do not require jitter-controlled networks (RFC1257)
Original Publication Date: 1991-Sep-01
Included in the Prior Art Database: 2000-Sep-12
Internet Society Requests For Comment (RFCs)
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.
Network Working Group C. Partridge
Request for Comments: 1257 Swedish Institute of Computer Science
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
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.
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
workstations, then beyond sensitivity to interarrival times, the
users will also be sensitive to end-to-end delay. Consider the
difference between conferencing over a satellite link and a
terrestrial link. Furthermore, for the data to be able to arrive in
time, there must be sufficient bandwidth. Bandwidth requirements are
particularly important for video: HDTV, even after compression,
currently requires bandwidth in excess of 100 Mbits/second.
Because multimedia applications are sensitive to jitter, bandwidth
and delay, it has been suggested that the networks that carry
multimedia traffic must be able to allocate and control jitter,
bandwidth and delay [1,2].
This memo argues that a network which simply controls bandwidth and