363-206-305
Technical Specifications
Issue 3 June 2000
10-45
Protection Switching
10
Ring Networks
10
Path protection rings feed a SONET payload (STS or 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 loss of
signal (LOS), path alarm indication signal (AIS), and path bit error rate (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. Similarly, for dropped nonterminated paths, if
both incoming STS-1s have any of the previous failures, VT AIS will be inserted in
the dropped signal.
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. DDM-2000 FiberReach 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, if desired.
To Next Page
Loading...
Need help?
General
