Traffic Management for the Available Bit Rate (ABR) Service in ...

controlled ABR queues and high utilization. The maximum ABR queue length is
a function of the feedback delay and round trip time. This implies that switches
terminating satellite links should provide bu ers proportional to the length of the
satellite link in order to deliver high performance. Further, if they implement the
VSVD option, they can isolate downstream workgroup switches from the e ects of
the long delay satellite path. We also brie y survey VBR video modeling techniques,
the MPEG-2 over ATM approach, and propose a model for MPEG-2 video over VBR
which incorporates the long-range dependence property in compressed video.
8.19 E ect of bursty TCP applications
In a related work [79], we have studied the e ect of bursty applications running on
top of TCP. An example of such an application is the World Wide Web application.
The WWW application sets up TCP connections for its data transfers [30]. The
WWW application di ers from a large le transfer application in that while the
latter looks like an \in nite or persistant" application to TCP, the former looks like
a \bursty" application (with active andidle transmission periods). The e ect of this
on tra c management isdescribed below.
TCP increases its \congestion window" as it receives acknowledgements for seg-
ments correctly received by the destination. If the application (eg. le transfer or
WWW server/client) has data to send, it transmits the data. Otherwise, the window
remains open until either the application has data to send or TCP times out (using
a timer set by its RTT estimation algorithm). If the timer goes o , TCP reduces the
congestion window to one segment (the minimum possible), and rises exponentially
(\slow start") once the source becomes active again.
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