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Cisco ONS 15310-CL and Cisco ONS 15310-MA Ethernet Card Software Feature and Configuration Guide R8.5
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Chapter 14 Configuring Resilient Packet Ring on the ML-Series Card
Understanding RPR
Figure 14-1 RPR Packet Handling Operations
Ring Wrapping
RPR initiates ring wraps in the event of a fiber cut, node failure, node restoration, new node insertion,
or other traffic problem. This protection mechanism redirects traffic to the ori ginal destination by
sending it in the opposite direction around the ring after a link state change or after receiving SONET
path level alarms. Ring wrapping on the ML-Series card allows convergence times of less than 50 ms.
RPR convergence times are comparable to SONE T and much faster than STP or RSTP.
RPR on the ML-Series card survives both unidirectional and bidirectional transmission failures within
the ring. Unlike STP or RSTP, RPR restoration is scalable. Increasing the number of ML-Series cards in
a ring does not increase the convergence time.
Ring wraps occur within 50 msec after the failure condition with the default spr wrap immediate
configured. If spr wrap delay is configured, the wrap is delayed until the POS interface goes link-down.
The link goes down after the time specified with the CLI pos trigger delay <msec>. If the circuits are
VCAT then the Cisco IOS CLI command pos vcat defect delayed also needs to be configured. The delay
helps ensure that when RPR is configured with SONET bandwidth protecti on, this Layer 1 protection
has a chance to take effect before the Layer 2 RPR protection. If the interface goes down without a
SONET error, then the carrier delay also take effect. Figure 14-2 illustrates ring wrapping.
ML-Series RPR
Strip
Bridge
Pass through
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