Cisco ONS 15454 SDH Specifications download pdf (Page 193)

5-3

Cisco ONS 15454 SDH Installation and Operations Guide, R3.3

May 2002

Chapter 5 SDH Topologies

Creating SNCP Rings

The ONS 15454 SDH is a Class 1 (CDRH) and Class 1M (IEC) laser system. Some procedures require

the installation or removal of optical cards and fibers. Take appropriate safety precautions while

performing these procedures.

Caution Hazardous voltage may be present on the backplane when the system is operating. Use caution when

removing or installing cards.

5.2 Creating SNCP Rings

Subnetwork Connection Protection Rings (SNCP) provide duplicate fiber paths around the ring.

Working traffic flows in one direction and protection traffic flows in the opposite direction. If a problem

occurs in the working traffic path, the receiving node switches to the path coming from the opposite

direction. With SNCP rings, switching occurs at the end of the path and is triggered by defects or alarms

along the path.

The network can be divided into a number of interconnected subnetworks. Within each subnetwork,

protection is provided at the path level and the automatic protection switching between two paths is

provided at the subnetwork boundaries. The node at the end of the path and the intermediate nodes in

the path select the best traffic signal. The virtual container is not terminated at the intermediate node,

instead it compares the quality of the signal on the two incoming ports and selects the better signal.

CTC automates ring configuration. SNCP ring traffic is defined within the ONS 15454 SDH on a

circuit-by-circuit basis. If an extended SNCP 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.

Figure 5-1 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. The same signal is also sent on the protect

traffic path through Node D. If a fiber break occurs (Figure 5-2), Node C switches its active receiver to

the protect signal coming through Node D.

Because each traffic path is transported around the entire ring, SNCPs are best suited for networks where

traffic concentrates at one or two locations and is not widely distributed. SNCP ring capacity is equal to

its bit rate. Services can originate and terminate on the same SNCP ring, or they can be passed to an

adjacent access or interoffice ring for transport to the service-terminating node.

Warning

Invisible laser radiation may be emitted from the end of the unterminated fiber cable or

connector. Do not stare into the beam or view directly with optical instruments. Viewing the

laser output with certain optical instruments (for example, eye loupes, magnifiers, and

microscopes) within a distance of 100 mm may pose an eye hazard. Use of controls or

adjustments or performance of procedures other than those specified may result in hazardous

radiation exposure.

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Cisco ONS 15454 SDH Specifications Page 193