Alcatel-Lucent 1850 TSS-5 complies with SONET/SDH 1+1 unidirectional non-revertive protection switching requirements as specified in GR-253-CORE and ITU-T G.957. Automatic line switches are initiated by signal fail and signal degrade conditions on the received OC-3STM-1 or OC-12/STM-4 optical signal and are completed within 50 milliseconds of a signal failure. The signal's BER is calculated from violations of the 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 provisioned threshold between 10−3 and 10−5 causes a signal degrade to be declared. The user can control switching through protection switching commands.
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 loss of pointer (LOP), path AIS (AIS-P), unequipped signal (UNEQ), signal fail BER (SF) (STS paths only) and signal degrade BER (SD). Line level faults such as LOS and LOF result in downstream AIS-P faults which in turn may result in path switching. On pass-through paths, all detected hard failures (LOS, LOF, LOP, line AIS, or STS-1 path AIS) result in AIS insertion in the outgoing VT and STS 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 transmission degradation on one of the rings requires that the other ring path be selected. Alcatel-Lucent 1850 TSS-5 provides non-revertive 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.
A Sub-Network Connection Protection (SNCP) ring provides path-level protection for VC-n circuits that are routed along two diverse paths in a network. First, each direction of the circuit is bridged onto two paths at the add-node (head-end), then carried through multiple facilities of any type, and finally selected from the two paths at the drop-node (tail-end). The path selection at the tail-end may be between any two tributaries from any SDH port. (Because of the different switching criteria used in the two standards, the two ports cannot be a mix of SONET and SDH.) Alcatel-Lucent 1850 TSS-5 supports STM-1 and STM-4 SNCP rings.
Alcatel-Lucent 1850 TSS-5 supports SNC/Ne non-revertive 1+1 unidirectional switching. This minimizes 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.
Bi-directional forwarding detection (BFD) is a network protocol that provides a low-overhead method of detecting faults across media that does not support failure detection, like asynchronous messaging across Ethernet. Alcatel-Lucent 1850 TSS-5 uses BFD to monitor the integrity of MPLS tunnels between shelves. Duplicate pairs of unidirectional MPLS tunnels with associated pseudowires can be configured to provide two bi-directional links using different paths between Alcatel-Lucent 1850 TSS-5 shelves. One pair of tunnels can carry the active pseudowire and its traffic, while the other pair of tunnels serve as a backup. BFD is configured on each tunnel. If the BFD detects a failure, the VLNC60/VLNC61/VLNC62/VLNC64 circuit pack directs all pseudowire traffic onto the backup tunnel.
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