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Controlling the Trade-Off between Reserved Bandwidth and Delay for Variable Bit Rate Multimedia Streams

IP.com Disclosure Number: IPCOM000114076D
Original Publication Date: 1994-Nov-01
Included in the Prior Art Database: 2005-Mar-27
Document File: 4 page(s) / 112K

Publishing Venue

IBM

Related People

Vogt, C: AUTHOR

Abstract

Disclosed is a mechanism by which the trade-off between the bandwidth reserved for a multimedia stream and the observed delays can be controlled. A parameter is introduced which allows to restrict the bandwidth reserved for a multimedia stream in a distributed environment and at the same time to guarantee a maximum delay for the processing or the transmission of the stream's packets. Mechanisms formerly only applicable to streams with a distinct periodic behavior are extended to the realm of variable bit rate streams. Prominents application examples are compressed video streams in the DVI (1) or MPEG (2) environments.

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Controlling the Trade-Off between Reserved Bandwidth and Delay for
Variable Bit Rate Multimedia Streams

      Disclosed is a mechanism by which the trade-off between the
bandwidth reserved for a multimedia stream and the observed delays
can be controlled.  A parameter is introduced which allows to
restrict the bandwidth reserved for a multimedia stream in a
distributed environment and at the same time to guarantee a maximum
delay for the processing or the transmission of the stream's packets.
Mechanisms formerly only applicable to streams with a distinct
periodic behavior are extended to the realm of variable bit rate
streams.  Prominents application examples are compressed video
streams in the DVI (1) or MPEG (2) environments.

      The mechanism is based on the following scenario: A source
generates at periodic instants (i.e., equidistant points in time)
single frames.  Let R[F]  be the corresponding frame rate of the
source traffic.  Depending on the underlying transmission network a
frame has to be segmented into a number of packets which are
individually transferred across the network (Fig. 1).  Each of the
packets requires a certain amount of processing and/or transmission
time.  It is assumed that these amounts are all equal and that the
number of packets per frame does not exceed some bound p(max).Let
p(ave) be the average number of packets per frame.

      For processing or transmitting this packet stream and giving
"Quality-of-Service" (QoS) guarantees, resource capacities are
reserved.  For this, time slots are reserved for a (fictitious)
source generating a purely periodic packet traffic, but then used for
the real bursty process (i.e.  the real transmission process which
generates bursts of packets at the frame rate).  For the reservation
and corresponding calculation of QoS guarantees, methods from
real-time scheduling theory are used.  One of these methods is based
on the fact that under certain conditions the delay observed by a
packet does not exceed the streams period, i.e., the reciprocal
value of the packet rate (3).

      The rate of the underlying (fictitious) periodic process is
chosen between R(F).p(ave) and R(F).p(max), thus avoiding both
overload situations and execessive reservations.  If it equals
R(F).p(ave,) almost all reserved processing slots are utilized but
delays can be very long.  If it equals R(F).p(max), delays are short,
as all packets of a frame can be processed before the next frame
arrives, but many reserved processing slots remain unused (Fig. 2).
Hence, selecting the rate of th...