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Configuring Automatic Protection Switching
Automatic protection switching (APS) is a protection mechanism for SONET networks that enables
SONET connections to switch to another SONET circuit when a circuit failure occurs. A protect
interface serves as the backup interface for the working interface. When the working interface fails, the
protect interface quickly assumes its traffic load. This chapter describes the following APS features:
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Multirouter Automatic Protection Switching
The Multirouter Automatic Protection Switching (MR-APS) feature enables interface connections to
switch from one circuit to another circuit if a circuit failure occurs. Interfaces can be switched in
response to a router failure, degradation or loss of channel signal, or manual intervention. In a
multirouter environment, the Multirouter APS (MR-APS) feature allows the protect SONET interface to
reside in a different router from the working SONET interface.
The protection mechanism used for this feature has a linear 1+1 architecture as described in the Bellcore
publication TR-TSY-000253, SONET Transport Systems; Common Generic Criteria, Section 5.3. The
connection may be bidirectional, and revertive or nonrevertive. Unidirectional MR-APS is not supported.
The default is bidirectional. The switching mode must be the same on the far end of the connection.
In the 1+1 architecture, a protect interface (circuit) is paired with each working interface. Normally, the
protect and working interfaces are connected to an ADM (add/drop multiplexer), which sends the same
signal payload to the working and protect interfaces.
Figure 1 shows a multirouter APS configuration. In the figure, the working and protect circuits terminate
on different line cards that are installed in two different routers. Interfaces in a multirouter APS
configuration can be configured with either SONET or SDH framing.
OL-2226-23
Multirouter Automatic Protection Switching, page 14-19
Single-router Automatic Protection Switching, page 14-27
C H A P T E R
Cisco 10000 Series Router Software Configuration Guide
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14-19
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