ATM Traffic Control Based on Cell Loss Priority and Performance Analysis

Shim, Heung-Sub
shim_hs@hanmail.net

Abstract
ATM, a ultimate solution of B-ISDN to provide integrated multimedia services including voice, video and data, has entered into the limelight with increased demand for such services. Hence, ATM is to be capable of supporting a variety of service classes and providing appropriate QoS according to classes. This may force us to sacrifice low priority traffic classes for high priority traffic classes to satisfy the QoS requirements for the high priority traffic classes in case of congestion.

There have been many possibilities suggested for traffic control in terms of QoS and 'cell loss priority control', which was originally introduced in ATM networks for the purpose of congestion control, must be one of them. An application can offer two types of traffic streams to the ATM network. The cell loss priority (CLP) bit in the header of the ATM cell may be used to declare two levels of QoS. This CLP based cell loss priority control can be implemented by a variety of schemes. However, I will focus on three major methods; push-out, partial buffer sharing and separate buffer. In the push-out mechanism, the buffer accepts incoming cells until it becomes full and then rearranges them giving priority to high priority cells over low priority cells when new cells arrive. This is of high efficiency but has a disadvantage of complicated buffer management logic. In the partial buffer sharing, the buffer accepts high priority cells only once a reference queue size (threshold) is met. This mechanism has an advantage of simple implementation. Lastly, we may want have two separate buffers, one of which is for high priority cells and the other is for low priority cells, so as to make the cell loss ratio (CLR) of high priority cells as low as possible.

I will use Opnet to implement and simulate the above three methods and compare their performances in terms of critical parameters such as CLR and delay.

References
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