Automatic Protection Switching (APS) allows users to protect a SONET/SDH port or link with a backup (protection) facility of the same speed but from a different adapter card. APS provides protection against a port, signal, or adapter card failure. The 7705 SAR supports 1+1 APS protection in compliance with GR-253-CORE and ITU-T Recommendation G.841 to provide SONET/SDH carrier-grade reliability. All SONET/SDH paths and channels within a SONET/SDH port are protected.
When APS is enabled, the 7705 SAR constantly monitors the health of the APS links, APS ports, and APS-equipped adapter cards. If the signal on the active (working) port degrades or fails, the network proceeds through a predefined sequence of steps to transfer (or switch over) traffic processing to the protection port. This switchover is done very quickly to minimize traffic loss. Traffic is streamed from the protection port until the fault on the working port is cleared, at which time the traffic may optionally revert to the working port.
The 7705 SAR supports 1+1 single-chassis APS (SC-APS) and 1+1 multi-chassis APS (MC-APS). In an SC-APS group, both the working and protection circuit must be configured on the same node. In an MC-APS group, the working and protection circuits are configured on two separate nodes, providing protection from node failure in addition to protection from link and hardware failure.
Unidirectional and bidirectional modes are supported:
unidirectional APS (Uni-1Plus1) — in unidirectional mode, only the port in the failed direction switches to the protection port. Unidirectional mode is supported only on SC-APS.
bidirectional APS — in bidirectional mode, a failure in either direction causes both the near-end and far-end equipment to switch to the protection port in each direction. Bidirectional mode is the default mode and is supported on both SC-APS and MC-APS.
For SC-APS and MC-APS with MEF 8 services where the remote device performs source MAC validation, the MAC address of the channel group in each of the redundant interfaces may be configured to the same MAC address using the mac CLI command.