Nortel Networks OPTera Metro 3500 - Manual (Page 295)

Hardware feature descriptions 3-67
Planning and Ordering Guide—Part 1 of 2 NTRN10AN Rel 12.1 Standard Iss 1 Apr 2004
OC-48 protection switching
OC-48 traffic can be protected by 1+1 linear, UPSR, or BLSR protection.
1+1 linear protection
OC-48 linear protection switching is 1+1 non-revertive, unidirectional or
bidirectional. If a fiber cut occurs in either the receive or transmit fibers of the
active fiber path, or the transmitter or receiver OC-48 optical interface circuit
pack fails at either end of the active fiber span, traffic is switched from the
active OC-48 transmitter or receiver to the standby OC-48 transmitter or
receiver. Switching can also take place under user control.
In bidirectional protection switching, if traffic in one of the two directions is
interrupted, traffic in both directions is switched to the protection line. In
unidirectional protection switching, if traffic in one of the two directions is
interrupted, only the interrupted traffic switches to the protection line; traffic
in the uninterrupted direction remains on the working fiber. Both OC-48
interface circuit packs are active if unidirectional switching occurs and one
fiber fails.
The signal degrade threshold is user-provisionable for the working OC-48
facility of a 1+1 linear protected OC-48 pair. The default value is 10
-6
. The
threshold is provisionable within the range 10
-5
to 10
-9
. If the bit error rate
(BER) drops below the threshold, an autonomous protection switch occurs.
UPSR path protection
OC-48 path switching uses nonrevertive protection. There are no permanent,
VT1.5/, STS-1, STS-3c, STS-12, or STS-12c protection or working paths. The
network element receives two incoming VT1.5/, STS-1, STS-12, STS-3c, or
STS-12c signals: one from the provisioned working optical interface circuit
pack and one from the switchmate optical interface circuit pack. The network
element selects the better of the two signals.
Note: VT1.5 signal rate is supported on OPTera Metro 3500 shelves
equipped with VTX-series circuit packs.
Protection of path failures on a single OC-48 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-48 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).