Long round-trip time support with shared-memory crosspoint buffered packet switch

The amount of memory in buffered crossbars in combined input-crosspoint buffered switches is proportional to the number of crosspoints, or O(N/sup 2/), where N is the number of ports, and to the crosspoint buffer size, which is defined by the distance between the line cards and the buffered crossbar, to achieve 100% throughput under port-rate data flows. A long distance between these two components can make a buffered crossbar costly to implement. In this paper, we propose and examine two shared-memory crosspoint buffered packet switches that use small crosspoint buffers to support a long round-trip time, which is mainly affected by the transmission delay caused by the distance between line cards and the buffered crossbar. The proposed switch reduces the required buffer memory of the buffered crossbar by 50% or more. We show that a shared-memory crosspoint buffer switch can provide high this improvement without speedup.