Foundry Networks Switch and Router Installation And Configuration Manual page 189

Table 6.4: CLI Display of POS Interface Statistics (Continued)
This Field...
Short
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
December 2000
Displays...
The number of packets that were shorter than the minimum valid
length.
BigIron
Working Interface POS 2/1
BigIronA
BigIron
Protect Interface POS 3/1
BigIronB
Using Packet Over SONET (POS) Modules
SONET ADM
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