Cisco ASR 900 Series Configuration Guide

Scenario for Bidirectional APS 1+1
Figure 4: Bidirectional APS 1+1
In the above figure, two devices are connected to provide APS 1+1 bi-directional protection. The highlighted
one is the working line and the other is the protection line. The traffic is transmitted on both working and
protection lines and received only on one line.
In a scenario where you encounter a fiber cut,
1
There is a cable cut in the working line. So, the device 2 receives a Loss of Signal (LOS) on working line.
2
Device 2 starts generating K2 byte and sends it to the Device 1 over the protection line.
3
Device 1 receives the K2 byte and reacts on the receiving K2 byte.
4
Device 1 starts sending K1 byte to the Device 2 on the protection line.
5
Device 1 starts sending K2 byte to Device 2 on the protection line.
6
Device 2 receives the K1/K2 byte and starts receiving the data from protection line. The protection line
now acts as the active line.
7
Device 2 sends K2 byte over the new active line to Device 1 . Device 1 receives this signal and starts
accepting the data from this new active line.
1-Port OC-192 or 8-Port Low Rate CEM Interface Module Configuration Guide, Cisco IOS XE Everest 16.7.x
(Cisco ASR 900 Series)
30
Configuring SONET
1+1 APS

Cisco ASR 900 Series Specifications

General

Brand	Cisco
Model	ASR 900 Series
Category	Network Router
Language	English