Isochronous applications do not require jitter-controlled networks (RFC1257)
Original Publication Date: 1991-Sep-01
Included in the Prior Art Database: 2019-Feb-11
Internet Society Requests For Comment (RFCs)
This memo argues that jitter control is not required for networks to support isochronous applications. This memo provides information for the Internet community. It does not specify an Internet standard.
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.
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
Partridge [Page 1]
RFC 1257 Isochronous and Jitter September 1991
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 delay is sufficient to support networked multimedia applications. Jitter control is not required.
Isochrony without Jitter Control