Automatic Protection Switching (Aps); Figure 11: Aps Protection (Single Chassis Aps) And Switchover - Alcatel-Lucent 7750 Configuration Manual

Automatic Protection Switching (APS)

APS is designed to protect SONET/SDH equipment from linear unidirectional or bidirectional
failures. The Network Elements (NEs) in a SONET/SDH network constantly monitor the health of
the network. When a failure is detected, the network proceeds through a coordinated predefined
sequence of steps to transfer (or switchover) live traffic to the backup facility (protection facility).
This happens very quickly to minimize lost traffic. Traffic remains on the protection facility until
the primary facility (working facility) fault is cleared, at which time the traffic may optionally be
reverted to the working facility.

Figure 11: APS Protection (Single Chassis APS) and Switchover

Note that "facility" in the SR-OS context refers to the physical line (including intermediate
transport/switching equipment) and directly attached line terminating hardware (SFP module,
MDA and IOM). "Circuit" is also a term used for a link/facility (working-circuit).
A 1+1 APS group contains two circuits.
APS is configured on a port by port basis. If all ports on an MDA or IOM need to be protected
then each port on the MDA or IOM must be individually added into an APS group.
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