Input Buffering Output Buffering

Figure 7-7 Three-stage MIN configuration for a 16×16 nonblocking switch with four concurrent internal paths for each inputoutput pair.

IV. Buffer Management

Kamoun and Kleinrock [Kamoun 1980] studied the performance of five limited buffer management schemes under general traffic conditions. These five buffer management schemes can actually be reduced to three main categories: Complete Sharing CS, Complete Partitioning CP, and Partial Sharing PS. The three schemes are mentioned in [Kamoun 1980]. Sharing with Maximum Queue Lengths SMXQ, Sharing with a Minimum Allocation SMA, and Sharing with a Maximum Queue and Minimum Allocation SMQMA, are actually variations of the PS scheme with a varying degree of upper and lower bounds on sharing. As indicated in [Kamoun 1980], CS scheme provides a better performance under low to medium input traffic loads and for fairly balanced traffic distribution across all input ports over CP. However, for highly unbalanced traffic patterns and for high input traffic load even with fairly balanced distribution CP and PS perform better than CS. With respect to buffer utilization, the CS allows full utilization whereas CP and PS do not allow full utilization due to pre-allocation of buffers to certain input ports full utilization may be possible for these schemes only in very extreme overload conditions. The buffer utilization is a significant factor in determining the required buffer size for a system under consideration. The CS scheme requires smaller buffer size than the other two schemes.

V. Broadcast and Multicast Requirements for ATM Switching Networks

Broadcast and multicast capabilities are two essential requirements for ATM switching networks due to the nature of traffic carried by these networks. The difference between the broadcast and multicast is that broadcast multiplies an ATM cell to all destinations whereas multicast multiplies an ATM cell to only a specified number of destinations. Two specific applications, which require broadcastmulticast capabilities, are VideoAudio broadcast and conferencing, and LAN emulation. Although broadcastmulticast of ATM cells can be achieved by the source by generating the necessary number of copies of ATM cells to be broadcasted or multicasted at the source node, this is not a very efficient approach.