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Cisco ONS 15454 SDH Reference Manual, R5.0
April 2008
Chapter 10 Circuits and Tunnels
10.8 MS-SPRing Protection Channel Access Circuits
Figure 10-5 SNCP Go-and-Return Routing
10.8 MS-SPRing Protection Channel Access Circuits
You can provision circuits to carry traffic on MS-SPRing protection channels when conditions are fault
free. Traffic routed on MS-SPRing 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 STM-16 MS-SPRing, STMs 9 to 16 can carry
extra traffic when no ring switches are active, but PCA circuits on these STMs are preempted when a
ring switch occurs. When the conditions that caused the ring switch are remedied and the ring switch is
removed, PCA circuits are restored if the MS-SPRing is provisioned as revertive.
Provisioning traffic on MS-SPRing 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 15454 SDH Procedure Guide for more information. When
provisioning PCA circuits, two considerations are important:
• If MS-SPRings are provisioned as nonrevertive, PCA circuits are not restored automatically after a
ring or span switch. You must switch the MS-SPRing manually.
• PCA circuits are routed on working channels when you upgrade a MS-SPRing from a two-fiber to
a four-fiber or from one STM-N speed to a higher STM-N speed. For example, if you upgrade a
two-fiber STM-16 MS-SPRing to an STM-64, STMs 9 to 16 on the STM-16 MS-SPRing become
working channels on the STM-64 MS-SPRing.
Node B
Go and Return working connection
Go and Return protecting connection
Node A
96953
Any network Any network