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

With an enhanced UBR service, applications like le transfer and WWW browsing
and downloading become viable over this service.
The service categories of ATM can also be compared to those o ered by air-
lines [51]. CBR is con rmed reservations with no recourse if you do not show up.
VBR is like con rmed reservation but you do not pay ifyou do not show up.ABR is
standby. You get to go if seats are available. Having standby service is good for the
airline. They can ll their seats that would otherwise would have gone empty. The
service is also good for passengers. They can travel cheaply particularly if they don't
have to be at their destinations at a certain time. UBR service is not currently o ered
by the airlines. Passengers travelling on UBR class may beallowed to board a plane
but may be strangled at the subsequent airports forever if seats are not available.
ABR users would generally be asked to stay home as much as possible if their routes
are congested.
10.2 Issues in ABR Implementation Complexity
From an architecture viewpoint, currently, ABR is a complex service to implement.
The importantarchitectural tradeo s we will encounter involve requirements in terms
of processing speed, latency, memory, and compactness. We will encounter processing
speed mismatches for RM cells versus data cells. Further, the RM cell might need to
be processed in both the forward and reverse directions. The latency issue arises when
RM cells are processed separately, and/or in software, and/or block on a slow shared
DRAM for information access. Memory requirements and access speed requirements
vary depending upon the RM cell processing strategy. Compactness and overall cost
depends upon the particular implementation (for example: ASIC or FPGA). In this
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