direction, the circuit pack bridges the same path-level signal to the
working and protection paths.
Path protection rings feed a SONET payload (STS-N or VT) from the
ring entry point, simultaneously in both rotations of the ring, to the
signal’s ring drop or exit point as shown by traffic AC and CA. This
duplication of the signal that enters the ring is called a head-end
bridge. The node that drops the signal from the ring monitors both
ring rotations and is responsible for selecting the signal that has the
highest quality based on LOS, LOF, path AIS, LOP, STS-N/VT
unequipped, and STS-N/VT path BER performance. This function at
the ring exit point is called a tail-end switch.
Figure 4-1 UPSR switching example
Node D
Node D
Node B
Node B
Node A
Node C
AC
CA
AC
CA
AIS inserted on Path
as a result of LOS on Line
Node A
Node C
AC
CA
AC
CA
Fiber
Cut
MA-Xpress-110
Pre-Failure Configuration
Path Failure Response
Unidirectional path-switched ring switching
Maintenance overview
....................................................................................................................................................................................................................................
365-372-333 R2.1
Issue 4, June 2005
Lucent Technologies
4 - 1 5
