Sample Line-Switching Scenario - Extreme Networks PoS Installation And User Manual

Configuring and Monitoring APS Functions
Virtual APS router Neighbor PPP router
PoS 192.168.10.1 SONET 192.168.10.2 PoS
PoS_014
Figure 3-14: Logical PPP connectivity to virtual APS router
Another important characteristic of the virtual APS router configuration shown in
Figure 3-13 is the Ethernet link between BlackDiamond #1 and BlackDiamond #2. This
Ethernet link provides an out-of-band communications channel that provides a way for
the two switches to synchronize their use of the SONET interfaces. For example, if
BlackDiamond #1 detects poor signal quality on the working line, it sends a message
over the Ethernet link to BlackDiamond #2, which initiates a switch to the protection
line. The Ethernet link is also used to carry heartbeat messages that enable the
protection switch to take over if the working switch fails.
The two-module and single-module configurations are similar to the two-switch
configuration, except that there is no out-of-band Ethernet communications link. These
configurations are simpler, because a single switch manages both the working line and
the protection line. One advantage of the simpler single-switch configurations is faster
network-recovery times following a line or module failure. The single-module
configuration protects against line failures, while the two-module configuration protects
against both line and module failures. The two-switch configuration further expands the
protection scope to include line, module, and switch failures.

Sample Line-Switching Scenario

In the following sample line-switching scenario, the working router initiates the APS
switch to the protection line. In this sample scenario, assume that the working line is
active, and that the working router initiates a switch to the protection line upon
detecting a signal fail or signal degrade condition on the working line. The working
router initiates the line switch by sending a message to the protection router over the
Packet Over SONET Module Installation and User Guide 3-79