The 3Com Switch S7900E Fabric Module is the engine of the Switch S7900E, performing the route calculations and maintaining the Layer 2 and Layer 3 forwarding tables. The switch fabric also contains a high-speed crossbar connecting all the modules attached to the backplane. Extended forwarding tables provide advanced capabilities. In the 3Com Switch S7900E, all the Layer 2 and Layer 3 switching and routing is fully distributed between the I/O modules. For I/O modules with limited memory, such as the Switch S7900E 48-Port 10/100/1000BASE-T Access Module, the switch fabric can use its own forwarding tables to provide additional performance.