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Cisco ONS 15600 Reference Manual, R7.2
Chapter 7 Circuits and Tunnels
7.7 Protection Channel Access Circuits
Figure 7-5 Viewing Path Protection Switch Counts
If ONS 15600s are connected to a third-party network, you can create an open-ended path protection
circuit to route a circuit through it. To do this, you create three circuits. One circuit is created on the
source ONS 15600 network. This circuit has one source and two destinations, one at each ONS 15600
that is connected to the third-party network. The second circuit is created on the third-party network so
that the circuit travels across the network on two paths to the ONS 15600s. That circuit routes the two
circuit signals across the network to ONS 15600s that are connected to the network on other side. At the
destination node network, the third circuit is created with two sources, one at each node connected to the
third-party network. A selector at the destination node chooses between the two signals that arrive at the
node, similar to a regular path protection circuit.
7.7 Protection Channel Access Circuits
You can provision circuits to carry traffic on BLSR protection channels when conditions are fault-free
and set up BLSR diagnostic test circuits. Traffic routed on BLSR PCA circuits, called extra traffic, has
lower priority than the traffic on the working channels and has no means for protection. During ring or
span switches, PCA circuits are preempted and squelched. For example, in a two-fiber OC-48 BLSR,
STSs 25 to 48 can carry extra traffic when no ring switches are active, but PCA circuits on these STSs
are preempted when a ring switch occurs. When the conditions that caused the ring switch are resolved
and the ring switch is removed, PCA circuits are restored. If the BLSR is provisioned as revertive, this
occurs automatically after the fault conditions are cleared and the reversion timer has expired.
Traffic provisioning on BLSR protection channels is performed during circuit provisioning. The
Protection Channel Access check box appears whenever Fully Protected Path is unchecked on the circuit
creation wizard. Refer to the Cisco ONS 15600 Procedure Guide for more information. When
provisioning PCA circuits, two considerations are important to keep in mind:
•
If BLSRs are provisioned as nonrevertive, PCA circuits are not restored automatically after a ring
or span switch. You must switch the BLSR manually.