IBM 8260 manual Static Switch on the Per-Port Switching Modules

Note

With the 18-port active per-port switching module the lobe ports can be distributed concurrently across a total of 11 segments which can be a mixture of backplane token-ring segments and isolated segments on the module. However, on the same per-port switching module you cannot allocate an isolated segment number which matches the number of a backplane segment to which other ports on the module are attached. For example, you cannot assign any ports to isolated_1 if you already have ports assigned to

token-ring_1. The consequence of this limitation is that, the total number of segments to which the ports on the active modules can be attached to is 11 segments.

Also, since by default the module ships with ports switched to backplane token-ring_1, you cannot have an isolated_1 allocated on the module unless you detach the ports from token-ring_1.

One general tip which you might follow is that when assigning ports to backplane and isolated segments you start numbering the backplane segments from 1 upwards and the isolated segments from 11 downwards.

8.6.2 Static Switch on the Per-Port Switching Modules

Each 8260 active per-port switching module implements a static switch for each of its port. The static switch may be used as a safeguard against switching an open adapter from one ring to another.

To understand the reasons for the static switch, let′s review the functions which are performed by each station when it first attaches to a token-ring. The following is a summary of these functions:

1. Lobe test

The station sends a series of Lobe Test MAC frames on the lobe to make sure that the lobe is not faulty.

2. Insert into the ring

The station applies the phantom signal and enters the ring.

3. Check for active monitor

After entering the ring, the station checks to see if an active monitor station is present on the ring by listening for Active Monitor Present, Standby Monitor Present or Ring Purge MAC frames. If any of these types of frame are seen within a time frame called ″T(attach)″ timer, it is assumed that there is an active monitor present on the ring and the station will assume the role of a standby monitor. However, if the ″T(attach)″ timer expires and none of the above frame types are seen, the station assumes that either it is the first station on the ring or there is no active monitor; it will then initiate the

″token-claiming″process.

Note: Token-claiming process is used to elect an active monitor on the ring.

4. Duplicate address test

The station checks for the presence of another station with the same address on the ring using the Duplicate Address Test MAC frame. If a duplicate address is found, the station removes itself from the ring.

Chapter 8. 8260 Token-Ring Support 145