Browse Prior Art Database

Flow Control of Prioritized Data in a Multimedia Communications System

IP.com Disclosure Number: IPCOM000110946D
Original Publication Date: 1994-Jan-01
Included in the Prior Art Database: 2005-Mar-26
Document File: 2 page(s) / 119K

Publishing Venue

IBM

Related People

Evans, LS: AUTHOR [+2]

Abstract

Described is a dataflow control technique for use in multimedia networks to cope with the different priorities of signals encountered. The solution addresses the specific need of high priority data to get quickly to its destination rather than waiting around in queues for a long time before transmission. It also permits the regulation of low priority data to prevent it clogging-up a queue and preventing the transmission of more urgent data. Provided are varying sized FIFO queues, one for each priority, and apportioning data throughput according to priority.

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Flow Control of Prioritized Data in a Multimedia Communications System

      Described is a dataflow control technique for use in multimedia
networks to cope with the different priorities of signals
encountered.  The solution addresses the specific need of high
priority data to get quickly to its destination rather than waiting
around in queues for a long time before transmission.  It also
permits the regulation of low priority data to prevent it clogging-up
a queue and preventing the transmission of more urgent data.
Provided are varying sized FIFO queues, one for each priority, and
apportioning data throughput according to priority.

      In a computer-based multimedia system supporting co-operative
working between users of physically separate machines linked by some
communication medium such as a Local Area Network, it is usual to
find data packets of various sizes with various transmission
priorities queued for transmission in a queue which has limited
resources for packet storage.  A problem arises if a multimedia
application is producing data for transmission faster than it can be
physically transmitted over the communications network.  The number
of packets in the queues builds up, and the "transit delay" may
become very long, with most of the time spent waiting in a queue.  In
a typical multimedia system, there will be a mixture of data with
different priorities.  At one end of the scale, the transmission of
data such as full-motion video and the movement of on-screen pointers
requires near-instantaneous distribution, ideally.  At the other end
of the priority scale will be the much slower transfer of data such
as large bitmap images and file data involved in File Transfer
operations, which may be transmitted over a period of minutes.

      It follows that the communications queueing mechanism should
not allow a large volume of high-priority data to build up in the
queues, as this will lead to an unacceptable transit delay.
Similarly, the queue should not become filled to its physical
capacity with low-priority packets, leaving no room for the queueing
of high priority data.  The technique that follows solves this
problem of the build-up of varying priority data packets in a
queueing system.

      The flow control regime imposed by the proposed queueing
mechanism is a straightforward go/no-go indication to the sending
application, indicating either that outgoing data packets may be
given to the queue, or that no data of any priority may be enqueued.
To avoid the build-up of large amounts of high priority data, the
queue should assert flow control to stop the application when there
are a relatively small number of high priority packets in the queue.
However, if there are a moderately large number of low priority
packets in the queue, then it is unnecessary and undesirable to
assert flow control, as this would prevent the application
transmitting any data, in particular, high-priority, which would
bypass the...