Cisco Systems IC-23 manual Using Connection Management Information, IC-38

Configuring LAN Interfaces

Configuring a Fiber Distributed Data Interface

The scatter-gather architecture used by particle-based switching provides the following advantages:

•Allows drivers to use memory more efficiently (especially when using media that has a large maximum transmission unit [MTU]). For example, Token Ring buffers could be 512 bytes rather than 16 KB.

•Allows concurrent use of the same region of memory. For example, on IP multicast a single packet is received and sent out on multiple interfaces simultaneously.

•Allows insertion or deletion of memory at any location in a packet (not just at the beginning or end).

For information about configuring SRB over FDDI, refer to the “Configuring Source-Route Bridging” chapter of the Cisco IOS Bridging and IBM Networking Configuration Guide.

Using Connection Management Information

Connection management (CMT) is an 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 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 ALS

Phy-B state is active, neighbor is A, cmt signal bits 20C/08, status ILS

CFM is thru A, token rotation 5000 usec, ring operational 0:01:42

Upstream 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 PCM state machine, 08 indicates that the port type is A, the port compatibility is set, and the LCT duration requested is short. The receive signal bits are 20C, which indicate the neighbor type is B, port compatibility is set, there is a MAC on the port output, and so on.

The neighbor is determined from the received signal bits, as follows:

Bit Positions	9	8	7	6	5	4	3	2	1	0
Value Received	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 ten 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.

Note 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-cmtcommand has been issued. (The fddi if-cmtcommand applies to the Cisco 7500 series routers only.)

Cisco IOS Interface Configuration Guide

IC-38