Datasheet

12-14
Cisco ONS 15454 SDH Reference Manual, R7.0
October 2008
Chapter 12 SDH Topologies and Upgrades
12.3 Subnetwork Connection Protection
CTC automates ring configuration. SNCP ring network traffic is defined within the ONS 15454 SDH on
a circuit-by-circuit basis. If an extended SNCP ring mesh network circuit is not defined within a 1+1 or
MS-SPRing line protection scheme and path protection is available and specified, CTC uses an SNCP
ring as the default protection mechanism.
An SNCP ring circuit requires two DCC-provisioned optical spans per node. SNCP ring circuits can be
created across these spans until their bandwidth is consumed.
The span bandwidth consumed by an SNCP ring circuit is two times the circuit bandwidth because the
circuit is duplicated. The cross-connection bandwidth consumed by an SNCP ring circuit is three times
the circuit bandwidth at the source and destination nodes only. The cross-connection bandwidth
consumed by an intermediate node has a factor of one.
The SNCP ring circuit limit is the sum of the optical bandwidth containing 84 regenerator-section data
communication channels (RS-DCCs) or 28 multiplex-section data communication channels
(MS-DCCs), divided by two. The spans can be of any bandwidth from STM-1 to STM-64.
Figure 12-13 shows a basic SNCP ring configuration. If Node A sends a signal to Node C, the working
signal travels on the working traffic path through Node B.
Figure 12-13 Basic Four-Node SNCP Ring
The same signal is also sent on the protect traffic path through Node D. If a fiber break occurs
(Figure 12-14), Node C switches its active receiver to the protect signal coming through Node D.
ONS 15454 SDH
Node A
ONS 15454 SDH
Node B
ONS 15454 SDH
Node C
ONS 15454 SDH
Node D
= Fiber 1
= Fiber 2
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