Aps 1+1; Automatic Protection Switching (Aps) - Alcatel-Lucent 7750 SR OS Interface Configuration Manual

Automatic Protection Switching (APS)

APS is designed to protect SONET/SDH equipment from linear uni or bi-directional 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.
This section discusses the different APS architectures and their implementations.
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APS 1+1

The 7750 SR supports the 1+1 architecture. When the 1+1 architecture is implemented, the active
OC-N signal is permanently transmitted to both the working and protection ports so, in the egress
direction, the same payloads are transmitted identically to the working and protection ports.
However, in the ingress direction, the working and protection signals are selected independently.
The 7750 SR only transmits data on the active circuit. For a single failure, this may cause a data
hit up to 100 milliseconds. When APS protects IMA groups, IMA cells, but not user traffic, are
sent on the inactive circuit to keep IMA protocol up on an APS switch.
The APS channel (bytes K1 and K2 in the SONET header) is used to exchange requests and
acknowledgments for protection switch actions. The bit assignment for the K1 and K2 bytes is
defined in the following sections:
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7750 SR OS Interface Configuration Guide
APS 1+1 on page 47
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K1 byte on page 48
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K2 Byte on page 49
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APS Protection Switching Byte Failure on page 50
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APS Channel Mismatch Failure on page 50
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APS Mode Mismatch Failure on page 50
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APS Far-End Protection Line Failure on page 51
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1+1 Switch Operation Example on page 51
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APS 1+1 Protection and Working Port Management Operations on page 53
K1 byte on page 48
K2 Byte on page 49
Interface Configuration
Page 47