Configuring Switching Between the Working and Protect Circuits

When there are multiple reasons to switch between the working and protect circuits, a priority scheme is used to decide which circuit to use. The routing platforms and the ADM might automatically switch traffic between the working and protect circuits because of circuit and routing platform failures. You can also choose to switch traffic manually between the working and protect circuits.

When an ATM2 PIC is configured for APS, and the protect circuit comes online for the first time, there are no open VCs and the PIC discards the input traffic received on the protect circuit. The show interface extensive or show monitor interface traffic commands display the statistics as zero since the PIC drops the packets at the VC.

When the APS switches from the working circuit to the protect circuit, VCs are created on the protect circuit to accept traffic. However, the VCs on the working circuit remain open to support any future APS switches even though the interface is down or disabled. The input traffic received on the working circuit (current backup) is accepted by the PIC but discarded in the PFE. The show interface extensive or show monitor interface traffic commands displays live statistics for the traffic since it is ccepted by the PIC.

When APS switches from the protect circuit to the working circuit again, the VCs on the protect circuit remain open to support a future APS switch even though the interface is down or disabled. The input traffic received on the current backup protect circuit is accepted by the PIC but discarded in the PFE. The show interface extensive or the show monitor interface traffic command displays live statistics for this traffic since it is accepted by the PIC.

There are three priority levels of manual configuration, listed here in order from lowest to highest priority:

• Request (also known as manual switch)—Overridden by signal failures, signal degradations, or any higher-priority reasons.
• Force (also known as forced switch)—Overrides manual switches, signal failures, and signal degradation.
• Lockout (also known as lockout of protection)—Do not switch between the working and protect circuits.

A routing platform failure is considered to be equivalent to a signal failure on a circuit.

To perform a manual switch, include the request statement at the [edit interfaces interface-name sonet-options aps] hierarchy level. This statement is honored only if there are no higher-priority reasons to switch.

When the working circuit is operating in nonrevertive mode, use the request working statement to switch the circuit manually to being the working circuit or to override the revert timer.

To perform a forced switch, include the force statement at the [edit interfaces interface-name sonet-options aps] hierarchy level. This statement is honored only if there are no higher-priority reasons to switch. This configuration can be overridden by a signal failure on the protect circuit, thus causing a switch to the working circuit.

To configure a lockout of protection, forcing the use of the working circuit and locking out the protect circuit regardless of anything else, include the lockout statement at the [edit interfaces interface-name sonet-options aps] hierarchy level:

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