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Cisco ONS 15454 SDH Installation and Operations Guide, R3.3
May 2002
Chapter 5 SDH Topologies
Creating MS-SPRings
If a break occurs on one fiber, working traffic targeted for a node beyond the break switches to the protect
bandwidth on the second fiber. The traffic travels in the reverse direction on the protect bandwidth until
it reaches its destination node. At that point, traffic is switched back to the working bandwidth.
Figure 5-12 shows a sample traffic pattern on a four-node, two-fiber MS-SPRing.
Figure 5-12 Four-node, two-fiber MS-SPRing sample traffic pattern
Figure 5-13 shows how traffic is rerouted after a line break between Node 0 and Node 3.
• All circuits originating on Node 0 and carried to Node 2 on Fiber 2 are switched to the protect
bandwidth of Fiber 1. For example, a circuit carried on VC4-1 on Fiber 2 is switched to VC4-9 on
Fiber 1. A circuit carried on VC4-2 on Fiber 2 is switched to VC4-10 on Fiber 1. Fiber 1 carries the
circuit to Node 3 (the original routing destination). Node 3 switches the circuit back to VC4-1 on
Fiber 2 where it is routed to Node 2 on VC4-1.
• Circuits originating on Node 2 that were normally carried to Node 0 on Fiber 1 are switched to the
protect bandwidth of Fiber 2 at Node 3. For example, a circuit carried on VC4-2 on Fiber 1 is
switched to VC4-10 on Fiber 2. Fiber 2 carries the circuit to Node 0 where the circuit is switched
back to VC4-2 on Fiber 1 and then dropped to its destination.
Node 0
Node 1
Traffic flow
Node 2
Node 3 STM-16 Ring
Fiber 1
Fiber 2
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