Data Communications Networking Devices - 4th Ed.pdf

5.4 LAN SWITCHES _______________________________________________________________ 609Figure 5.47 Port-based switching. A port-based switch associates one address with eachport, minimizing the time required to match the destination address of a frame against atable of destination addresses and associated port numberssupport a maximum throughput of …N=2†10 Mbps; since up to N=2 simultaneousclient±server frame ¯ows can occur through the switch.It is important to compare the maximum potential throughput through a switchto its rated backplane speed. If the maximum potential throughput is less than therated backplane speed, the switch will not cause delays based upon the traf®c beingrouted through the device. For example, consider a 64-port switch that has abackplane speed of 400 Mbps. If the maximum port rate is 10 Mbps, then themaximum throughput assuming 32 active cross-connections were simultaneouslyestablished) becomes 320 Mbps. In this example the switch has a backplanetransfer capability suf®cient to handle the worst-case data transfer scenario. Nowlet's assume that the maximum backplane data transfer capability was 200 Mbps.This would reduce the maximum number of simultaneous cross-connectionscapable of being serviced to 20 instead of 32 and adversely affect switch performanceunder certain operational conditions.Since a port-based switch has to store only one address per port, search times areminimized. When combined with a pass-through or cut-through switchingtechnique, this type of switch results in a minimal latency to include the overheadof the switch in determining the destination port of a frame.Segment-based switchingAsegment-based switching technique requires a LAN switch to support multipleaddresses per port. Through the use of this type of switch, you achieve additional