user manual

11-8
Cisco ONS 15454 SDH Reference Manual, R5.0
April 2008
Chapter 11 SDH Topologies and Upgrades
11.2.3 MS-SPRing Bandwidth
Ring switching occurs when a span switch cannot recover traffic (Figure 11-6), such as when both the
working and protect fibers fail on the same span. In a ring switch, traffic is routed to the protect fibers
throughout the full ring.
Figure 11-6 Four-Fiber MS-SPRing Switch
11.2.3 MS-SPRing Bandwidth
An MS-SPRing node can terminate traffic it receives from either side of the ring. Therefore,
MS-SPRings are suited for distributed node-to-node traffic applications such as interoffice networks and
access networks.
MS-SPRings share the ring bandwidth equally between working and protection traffic. Half of the
payload bandwidth is reserved for protection in each direction, making the communication pipe half-full
under normal operation.
MS-SPRings allow bandwidth to be reused around the ring and can carry more traffic than a network
with traffic flowing through one central hub. MS-SPRings can also carry more traffic than an SNCP ring
operating at the same STM-N rate. Table 11-2 shows the bidirectional bandwidth capacities of two-fiber
MS-SPRings. The capacity is the STM-N rate divided by two, multiplied by the number of nodes in the
ring and minus the number of pass-through VC4 circuits.
Node 0
Node 1
Node 2
Node 3
Span 1
Span 2Span 3
Span 4
Span 8
Span 7Span 6
Span 5
STM-16 Ring
= Working fibers
= Protect fibers
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Table 11-2 Two-Fiber MS-SPRing Capacity
STM Rate Working Bandwidth Protection Bandwidth Ring Capacity
STM-4 VC4 1-2 VC4 3-4 2 x N
1
– PT
2