New implementation of multi-priority pushout for shared memory ATM switches

• Authors: Abhijit K. Choudhury;Ellen L. Hahne
• Venue: Computer Communications
• Year: 1996

In a shared memory ATM switch with output queueing, the output queues share space flexibly in a common cell buffer. Selective Pushout is a technique for efficiently sharing this cell buffer memory among these multiple queues in an environment where cells also belong to various space priority classes. With Selective Pushout, whenever the buffer is full, arriving cells make space for themselves by pushing out low priority cells from the longest queue. In earlier work, we explored the performance of Selective Pushout. In this paper we consider its implementation. First we describe a queue controller implementation for a system without pushout. Then we outline a straightforward implementation of a queue controller with Selective Pushout. Next we propose a novel implementation that requires less control memory for the queue controller's data structures. Finally, we compare these implementations in terms of control memory requirements, processing speed, and design complexity. The control memory savings of the new implementation are significant for switches with large shared cell buffers. Moreover, for a system with only two space priority classes, the new implementation has a particularly simple design that should run nearly as fast as the straightforward implementation.