sors. The speed of the R bus is 4 Gbps. C bus The control bus, or C bus, is also sometimes referred to as the Ethernet Out-of- Band Channel (EOBC). The C bus is used for communication between the line cards and the network management processors on the supervisors. The C bus is actually a 100 Mbps half-duplex network. When line-control code is downloaded to the line cards, it is done on this bus. Crossbar fabric bus Crossbar is a type of switching technology where each node is connected to every other node by means of intersecting paths. An alternative switching fabric is the fully interconnected model, where each port is directly connected to every other port. Architecture Figure 17-2 shows visual representations of such switching fabrics. The term fab- ric is used to describe the mesh of connections in such designs, as logically, the connections resemble interwoven strands of fabric. Fully interconnected Crossbar fabric fabric Input Output Input ports ports ports Output ports Figure 17-2. Switch fabric examples The crossbar fabric shown in Figure 17-2 shows one black intersection. This is an active connection, whereas the others are inactive connections. The active connection shown here indicates that port 2 is in communication with port 3. The crossbar fabric bus, in combination with a Supervisor-2 and a Switch Fabric Module, is capable of 256 Gbps and 30 million packets per second (Mpps). With the addition of a distributed forwarding card, this combination is capable of 210 Mpps. With a Supervisor-720 module, the crossbar fabric supports up to 720 Gbps. When using distributed Cisco Express Forwarding (dCEF) interface mod- ules, a Sup-720-equipped 6500 is capable of 400 Mpps. The SFM is what provides the actual switch fabric between all the fabric-enabled modules (recall that the SFM's functionality is included in the Supervisor-720, SO in this case, a separate module is not required). The module is actually a switch in and of itself that uses the backplane fabric bus as a communication channel between the modu