Connection management (CMT) is a FDDI process that handles the transition of the ring through its various states (off, on, active, connect, and so on) as defined by the X3T9.5 specification. The FIP (FDDI Interface Processor) provides CMT functions in microcode.
A partial sample output of the show interfaces fddi command follows, along with an explanation of how to interpret the CMT information in the output.
Phy-A state is active, neighbor is B, cmt signal bits 08/20C, status ALSPhy-B state is active, neighbor is A, cmt signal bits 20C/08, status ILSCFM is thru A, token rotation 5000 usec, ring operational 0:01:42Upstream neighbor 0800.2008.C52E, downstream neighbor 0800.2008.C52E
The show interfaces fddi example shows that Physical A (Phy-A) completed CMT with its neighbor. The state is active, and the display indicates a Physical B-type neighbor.
The sample output indicates CMT signal bits 08/20C for Phy-A. The transmit signal bits are 08. Looking at the pulse code modulation (PCM) state machine, 08 indicates that the port type is A, that the port compatibility is set, and that the LCT duration requested is short. The receive signal bits are 20C, that indicate that the neighbor type is B, that port compatibility is set, that there is a MAC on the port output, and so on.
The neighbor is determined from the received signal bits, as follows:
9 8 7 6 5 4 3 2 1 0
1 0 0 0 0 0 1 1 0 0
Interpreting the bits in the diagram above, the received value equals 0x20C. Bit positions 1 and 2 (0 1) indicate a Physical B-type connection.
The transition states displayed indicate that the CMT process is running and actively trying to establish a connection to the remote physical connection. The CMT process requires state transition with different signals being transmitted and received before moving on to the state ahead as indicated in the PCM state machine. The 10 bits of CMT information are transmitted and received in the Signal State. The NEXT state is used to separate the signaling performed in the Signal State. Therefore, in the preceding sample output, the NEXT state was entered 11 times.
The display line showing transition states is not generated if the FDDI interface has been shut down, or if the cmt disconnect command has been issued, or if the fddi if-cmt command has been issued. (The fddi if-cmt command applies to the Cisco 7500 series routers only.)
The CFM state is through A in the sample output, which means the Phy-A of this interface has successfully completed CMT with the Phy-B of the neighbor and Phy-B of this interface has successfully completed CMT with the Phy-A of the neighbor.
The display (or nondisplay) of the upstream and downstream neighbor does not affect the ability to route data. Because the upstream neighbor is also its downstream neighbor in the sample, there are only two stations in the ring: the network server and the router at address 0800.2008.C52E.