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

variant background tra c conditions, and for LAN, WAN and satellite con gura-
tions. To introduce highly variant conditions, we use conventional ON-OFF models
and also propose new models of MPEG-2 transport streams (resulting in long-range
dependent tra c) multiplexed over VBR. We observe that the ABR control system
only pushes the queues to the edge of the network - where an edge router has to again
handle the issue of large TCP queues.
We note that the system can theoritically be loaded with unbounded queues when
bursty tra c like WWW is used. However, under practical conditions, the average
load when a large number of WWW exist increases more smoothly than expected.
Since the ABR switch scheme reacts to load and can tolerate variation in load and
capacity, we see that queues are controlled and high throughput is attained even
under such conditions.
In Chapter 9 we look at the switch design issues for a speci c ABR framework
option called the \Virtual Source/Virtual Destination" option. In this option, the
switch splits the network into two segments and shortens the feedback loop for both
segments. We show that this option has the potential to increase the performance of
the network, but the implementation can be complex and has to be carefully done. In
our study of multiple implementation options of this feature, we found that only a very
few performed well, and we identify the properties of the best option. This chapter is
followed up by Chapter 10 where we brie y address certain implementation issues.
11.2 Future Work
At the time of this writing, the ABR service is being actively implemented and
is currently facing interesting cost-performance tradeo questions. Field trials and
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