Aps 1+1 For Sonet Layer 1 Traffic; Scenario For Bidirectional Aps 1+1 - Cisco ASR 900 Series Configuration Manual

Configuring SONET

APS 1+1 for SONET Layer 1 traffic

SONET linear APS 1+1 provides protection against both fiber cuts and front card or back card failures. APS
1+1 requires a redundant protection line for every working line. The traffic is simultaneously carried by the
working and the protection lines. Hence, the receiver that terminates the APS 1+1 should select the traffic
from one of the lines and continue to forward the traffic. APS 1+1 provides protection in unidirectional and
bi-directional modes:
• Uni-directional Protection: The receiving end can switch from working to protection line without any
coordination at the transmit end since both lines transmit the same information.
• Bi-directional Protection: The receiving end switches from working to protection line by coordinating
at the transmit end.

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 OC48/ 4 port OC12/OC3 + 12 port T1/E1 + 4 port T3/E3 CEM Interface Module Configuration Guide, Cisco IOS
XE Fuji 16.7.x (Cisco ASR 900 Series)
1+1 APS
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