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Technical Specifications
10-54 Issue 3 June 2001
Protection Switching 10
Linear Networks 10
Automatic line switches are initiated by signal fail and signal degrade conditions
on the received OC-3 signal and are completed within 50 milliseconds of a signal
failure. This signal's BER is calculated from violations of the SONET line
overhead B2 parity bytes. Signal fail is declared for incoming LOS, LOF, line AIS,
or a BER exceeding 10
-3
, while a BER exceeding a provisionable threshold
between 10
-5
and 10
-9
causes a signal degrade to be declared.
Ring Networks 10
Path protection rings feed a SONET payload (STS or virtual tributary [VT]) from
the ring entry point, simultaneously in both rotations of the ring, to the signal's ring
exit point. The node that terminates the signal from the ring monitors both ring
rotations and is responsible for selecting the signal that has the highest quality
based on LOS, path AIS, and path BER performance. On pass-through paths, all
detected hard failures (LOS, LOF, LOP, line AIS, STS-1 path AIS, or STS-1 path
signal failure based on BER) result in VT AIS insertion in the outgoing signals.
This allows the terminating node to be aware of the failure and to switch to
protection. Protection switching is completed within 50 milliseconds of failure
detection.
Under normal conditions, both incoming SONET path signals to the switch
selection point are of high quality, and the signal can be selected from either ring.
A failure or a transmission degradation on one of the rings requires that the other
ring path be selected. Release 5.1 provides nonrevertive switching to minimize
the impact on critical customer services by giving the service provider control,
when and if, the critical service should revert to a particular ring. A manual path
protection switching command allows switching back to the original path for ease
of ring maintenance.
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