Cisco ONS 15454 SDH Specifications Page 212

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5-22
Cisco ONS 15454 SDH Installation and Operations Guide, R3.3
May 2002
Chapter 5 SDH Topologies
Creating MS-SPRings
5.4.2 Four-Fiber MS-SPRings
The ONS 15454 SDH can support many ring combinations if the total DCC usage is equal to or less than
10 DCCs. Each MS-SPRing can have up to 16 ONS 15454 SDHs. Because the working and protect
bandwidths must be equal, you can create only STM-16 or STM-64 MS-SPRings.
Note MS-SPRings with 16 or fewer nodes will meet the ITU G.841 switch time requirement.
Four-fiber MS-SPRings double the bandwidth of two-fiber MS-SPRings. Four-fiber MS-SPRings
increase the reliability and flexibility of traffic protection because they allow span switching as well as
ring switching. Two fibers are allocated for working traffic and two fibers for protection, as shown in
Figure 5-17. To implement a four-fiber MS-SPRing, you must install four STM-16 cards or four STM-64
cards at each MS-SPRing node.
Figure 5-17 A four-node, four-fiber MS-SPRing
Four-fiber MS-SPRings provide span and ring switching:
Span switching occurs when a working span fails (Figure 5-18). Traffic switches to the protect fibers
between the nodes (Node 0 and Node 1 in the Figure 5-18 example) and then returns to the working
fibers that did not fail. Multiple span switches can occur at the same time.
Ring switching occurs when a span switch cannot recover traffic (Figure 5-19), 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.
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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