Alcatel-Lucent 7750 Configuration Manual page 85

Annex B (1+1 Optimized) Operation
Operation and behavior conferment with Annex B of ITU.T G.841 can be configured for an APS
group.
Characteristics of this mode include are the following:
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•
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Due to the request/reverse-request nature of an Annex B switchover, the data outage is longer than
a typical (non Annex B single chassis) APS switchover. IMA bundles that are protected with
Annex B APS have to resynchronize after a switchover. It is recommended to use maintenance
commands (tools>perform>aps...) for planned switchovers (not MDA or IOM shutdown) to
minimize the outage.
Annex B APS Outage Reduction Optimization
Typical standard Annex B behavior when a local SF is detected on the primary section (circuit),
and this SF is the highest priority request on both the local side and from the remote side as per the
APS specifications, is to send a request to the remote end and then wait until a reverse request is
received before switching over to the secondary section. To reduce the recovery time for traffic,
SR-OS will switch over to the secondary section immediately upon detecting the local SF on the
primary section instead of waiting for the reverse request from the remote side. If the remote
request is not received after a period of time then an "PSB Failure is declared" event is raised
(Protection Switching Byte Failure – indicates an inconsistent or invalid Rx K1 Bytes), and the
APS group on the local side switches back to the primary section.
When the remote side is in Lockout, and a local SF is detected then a reverse request will not be
received by the local side. In this case, the traffic will no longer flow on the APS group since
neither the primary nor secondary sections can carry traffic, and the outage reduction optimization
will cause a temporary switchover from the primary to the secondary and then back again (which
causes no additional outage or traffic issue since neither section is usable). If this temporary
switchover is not desired then it is recommended to either perform Lockout from the 7x50 side, or
to Lockout both sides, which will avoid the possibility of the temporary switchover.
Failures detected on the secondary section cause immediate switch over as per the Annex B
specification. There is no outage reduction optimization in SR-OS for this case as it is not needed.
Some examples of events that can cause a local SF to be detected include: a cable being cut, laser
transmitter or receiver failure, a port administratively "shutdown", MDA failure or shutdown,
IOM failure or shutdown.
7750 SR Interface Configuration Guide
Annex B operates in non-revertive bi-directional switching mode only as defined in
G.841.
Annex B in SR-OS operates with 1+1 signaling, but 1:1 data path where by data is
transmitted on the active link only.
K bytes are transmitted on both circuits.
Interface Configuration
Page 85