A study and analysis of a transmission scheduling and discard algorithm for ATM networks

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Virginia Tech


This research intends to propose and analyze an integrated algorithm for ATM networks. The integrated algorithm can be divided into three separate policies: buffer management policy, transmission po1icy, and discard policy. The buffer management policy is presented by previous publications, thus not analyzed in this research. The objective of the transmission policy is to minimize the conflicting goals of minimizing delay and 1-point cdv at an ATM node, while the objective of the discard policy is to distribute loss fairly among connections.

The transmission policy utilizes the time-varying priority concept to assign a priority index to each connection in an ATM node. A priority index of a connection is the weighted sum of the scaled time-varying priorities associated with delay and 1-point cdv for the cell waiting at the head of the connection's queue. The set of priority indices from all connections gives an indication of relative urgency for connections to transmit cells. Thus, the selection of a connection to transmit a cell is simply to choose the connection with the highest urgency as indicated by its priority index.

The discard policy tries to allocate loss of cells fairly among connections. A two-stage approach is proposed. Stage one involves the use of a modified version of generic cell rate algorithm (MGCRA) to enforce incoming cell rates compliance from all connections. Stage two implements a rotation index scheme such that the long term pair-wise cell loss ratios among connections approach the pair-wise ratios of the aliocated-CLR's (ACLR).

The behavior of these two policies under Bernoulli distribution arc studied and analyzed. A theoretical approximation approach is developed to find the wait time and the cdv-count distributions for a two-connection system example. Simulation is used to studied these two policies under various conditions.



transmission police, buffer management policy, discard policy