Design of a MAC address lookup unit for the gigabit ethernet switch

Abstract

The Gigabit Ethernet is a new technology to be substituted for the current fast Ethernet used widely in local area network. Since the switch used in the Gigabit Ethernet should deal with frames in giga-bps speed, we have a little time budget(608 nanosec) to forward each ethernet frame. The frame forwarding process has many works to do such as MAC address table lookup to read out the forwarding contexts, forwarding decision, VLAN tagging, untagging, and some jobs for multicasting. As a result, the time budget assigned to one lookup is approximately only 100 nanosec. Because it is difficult to satisfy this tight time budget by conventional methods, I propose a new lookup scheme which is accelerated when used with synchronous DRAM. By using the burst mode of RAM we can achieve the statistically faster lookup time and by using the banked structure of SDRAM, we can succeeded to implement the concurrent lookup of source and destination addresses, which manes the lookup time shorter than conventional SRAM oriented schemes. And I designed the lookup unit in the schematic level. And the lookup engine is also support shared bus scheme for the loose requirement conditions.