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Configuring APS and MSP

Automatic Protection Switching (APS) is used by SONET add/drop multiplexers (ADMs) to protect against circuit failures. The JUNOS implementation of APS allows you to protect against circuit failures between an ADM and one or more routing platforms, and between multiple interfaces in the same routing platform. When a circuit or routing platform fails, a backup immediately takes over.

Note: For SDH interfaces, the JUNOS software supports multiplex section protection (MSP). You configure MSP with the same CLI statements you use to configure APS.

The JUNOS software supports APS 1+1 switching, either revertive or nonrevertive mode, and bidirectional mode only (although you can configure interoperation with line-terminating equipment [LTE] provisioned for unidirectional mode). The JUNOS software does not transmit identical data on the working and protect circuits, as the APS specification requires for 1+1 switching, but this causes no operational impact.

For DS3 channels on a channelized OC12 interface, you can configure APS on channel 0 only. If you configure APS on channels 1 through 11, it is ignored.

With APS and MSP, you configure two circuits, a working circuit and a protect circuit. Normally, traffic is carried on the working circuit (that is, the working circuit is the active circuit), and the protect circuit is disabled. If the working circuit fails or degrades, or if the working router fails, the ADM and the protect router switch the traffic to the protect circuit, and the protect circuit becomes the active circuit.

To configure APS or MSP, you configure a working and a protect circuit, as shown in Figure 55. To protect against a routing platform failure, you connect two routing platforms to the ADM, configuring one of them as the working router and the second as the protect router. To protect against a PIC or FPC failure, you connect one routing platform to the ADM through both the working and protect circuits, configuring one of the PICs or FPCs as the working circuit and the second as the protect circuit.

Figure 55: APS/MSP Configuration Topologies

Image g017018.gif

To configure APS or MSP, include the aps statement at the [edit interfaces interface-name sonet-options] hierarchy level:



[edit interfaces interface-name sonet-options]

aps {

advertise-interval milliseconds;

authentication-key key;

force;

hold-time milliseconds;

lockout;

neighbor address;

paired-group group-name;

protect-circuit group-name;

request;

revert-time seconds;

switching-mode (bidirectional | unidirectional);

working-circuit group-name;
}

This section includes the following topics:

Note: This implementation of APS is not supported on Layer 2 circuits. For Layer 2 circuits, configure APS by including the protect-interface statement. You can include this statement at the following hierarchy levels:

[edit logical-systems logical-system-name protocols l2circuit neighbor neighbor-id interface interface-name]
[edit protocols l2circuit neighbor neighbor-id interface interface-name]

For more information and a configuration example, see the JUNOS VPNs Configuration Guide.

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