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Using Packet Over SONET (POS) Modules
December 2000
6 - 27
Configuring Automatic Protection Switching (APS)
The Automatic Protection Switching (APS) feature provides redundancy for a POS link. Foundry’s implementation
of POS APS supports 1 + 1 protection architecture, where a
working
interface is paired with a
protect
or backup
interface.
When the signal on the working interface degrades below a user-configurable threshold, or the working interface
is manually taken down, the protect interface automatically takes over, becoming the working interface, while the
previously working interface becomes the protect interface. When the previously working interface is available
again, it can be switched back to working status manually or configured to automatically revert to working status
after becoming available.
Typically the working and protect interfaces are on separate routers. Both interfaces are connected to a SONET
add/drop multiplexer (ADM), which sends identical traffic through them. Switching is controlled by the K1 and K2
bytes of the line overhead (LOH) in a SONET frame.
Information on signal quality is exchanged between the working and protect interface using the APS Protect
Group Protocol, running on top of UDP. This communication takes place on a channel independent of the working
and protect interfaces themselves.
Configuring POS APS consists of the following steps:
1.
Configuring the working interface
2.
Configuring the protect interface
3.
Setting optional parameters
You can also display information about an APS configuration.
Basic POS APS Configuration
Figure 6.7 shows a basic POS APS configuration, where a POS interface on one router serves as a protect
interface for a working interface on another router.
Figure 6.7
Basic POS APS configuration
Short
The number of packets that were shorter than the minimum valid
length.
Table 6.4: CLI Display of POS Interface Statistics (Continued)
This Field...
Displays...
BigIron
BigIron
SONET ADM
Working Interface POS 2/1
Protect Interface POS 3/1
BigIronA
BigIronB
Summary of Contents for Switch and Router
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