Cisco 15327 - Manual (Page 255)

17-3
Ethernet Card Software Feature and Configuration Guide, R7.2
Chapter 17 Configuring Cisco Proprietary Resilient Packet Ring
Ring Wrapping
Figure 17-1 Cisco Proprietary RPR Packet Handling Operations
Ring Wrapping
Cisco proprietary RPR initiates ring wraps in the event of a fiber cut, node failure, node restoration, new
node insertion, deletion of the circuit on POS port of SPR, SPR keepalive failure or other traffic problem.
This protection mechanism redirects traffic to the original destination by sending it in the opposite
direction around the ring after a link state change or after receiving SONET/SDH path level alarms. Ring
wrapping on the ML-Series card allows convergence times of less than 50 ms for unicast and
pass-through traffic. Cisco proprietary RPR convergence times are comparable to SONET/SDH and
much faster than STP or RSTP.
Cisco proprietary RPR on the ML-Series card survives both unidirectional and bidirectional
transmission failures within the ring. Unlike STP or RSTP, Cisco proprietary 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 Cisco proprietary RPR is configured with SONET/SDH bandwidth protection,
this Layer 1 protection has a chance to take effect before the Layer 2 Cisco proprietary RPR protection.
If the interface goes down without a SONET error, then the carrier delay also take effect.
Figure 17-2
illustrates ring wrapping.
ML-Series RPR
Strip
Bridge
Pass through
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