The data bus, or D bus, is used by the EARL chipset to transfer data between modules. The speed of the D bus is 32 Gbps. The D bus is shared much like a traditional Ethernet network in that all modules receive all frames that are placed on the bus. When frames need to be forwarded from a port on one module to a port on another module, assuming the crossbar fabric bus is not in use or available to the modules, they will traverse this bus. R bus The results bus, or R bus, handles communication between the modules and the switching logic on the supervisors. 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. Line-control code downloads to the line cards 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. 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. Chapter 17: Cisco 6500 Multilayer Switches The crossbar fabric shown in Figure 17-2 shows one black intersection. This is an active connection, whereas the other connections are inactive. The active connec- tion shown here indicates that port 2 is communicating with port 3. The crossbar fabric bus, combined with a Supervisor-2 and an SFM is capable of 256 Gbps and 30 million packets per second (Mpps). With the addition of a dis- tributed forwarding card, this combination is capable of 210 Mpps. With a Super- visor-720 module, the crossbar fabric supports up to 720 Gbps. When distributed Cisco Express Forwarding (dCEF) int