Nortel Networks 3500, NTRN10AN manual Blsr protection

Hardware feature descriptions 3-63

Protection of path failures on a single OC-192 optical interface completes in 60 ms, but protection of simultaneous path failures on multiple optical interfaces completes in less than 200 ms.

BLSR protection

BLSR protection switching is revertive. If a fiber cut occurs in either the receive or transmit fibers of the active channel, or the transmitter or receiver OC-192 optical interface circuit pack fails at either end of the fiber span of the active channel, traffic is switched from the working channel to the protection channel (usually from the short path to the long path on the other side of the ring).

The Wait-to-Restore (WTR) bridge request is issued on both the long and short paths when working channels meet the restoral threshold after a signal degrade or signal fail condition. This request is used to maintain the current state during the WTR period unless one or a combination of the following conditions occurs:

•a bridge request of higher priority than WTR is received

•another failure is detected

•an externally initiated command becomes active

The WTR time is between 1 to 12 minutes (default is 5 minutes). The WTR period is provisionable for each optical interface pair.

Note: You can provision an infinite WTR period, so that BLSRs autonomously switch non-revertively.

Switching can also take place under user control. In BLSR user-initiated switches, the user may initiate a lockout on either the working or protection channels on a span. Both of these effectively ’lock’ traffic onto the working channel. The lockout of the protection channel of the span also prevents any protection switching from occurring anywhere in the ring.

Forced and manual switches on the working channels switch traffic to the protection channel. A forced switch has a higher priority than a manual switch. For the complete BLSR protection switching hierarchy, see Table 2-27 on page 2-119. Both forced and manual switches can be released.

In ring switches, the protection channels are shared among each span of the ring. If a scenario arises where multiple points in a BLSR fail or nodes become isolated, there is the potential for misconnected traffic. Services originally on separate spans but sharing the same time slot may compete for the same protection time slot. Squelching is a mechanism to prevent this.

For more information about squelching, see BLSR networks (2-fiber) on page 2-10.

Planning and Ordering Guide—Part 1 of 2 NTRN10AN Rel 12.1 Standard Iss 1 Apr 2004