Cisco ONS 15454 SDH Specifications Page 207

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5-17
Cisco ONS 15454 SDH Installation and Operations Guide, R3.3
May 2002
Chapter 5 SDH Topologies
Creating MS-SPRings
5.4.1 Two-Fiber Multiplex Section Shared Protection Ring
The ONS 15454 SDH can support a number of 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-4 (two-fiber 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.
In two-fiber MS-SPRings, each fiber is divided into working and protect bandwidths. For example, in an
STM-16 MS-SPRing (Figure 5-11), VC4s 1 8 carry the working traffic, and VC4s 9 16 are reserved
for protection. Working traffic (VC4s 1 8) travels in one direction on one fiber and in the opposite
direction on the second fiber. The Cisco Transport Controller (CTC) circuit routing routines calculate
the shortest path for circuits based on requirements set by the circuit provisioner, traffic patterns, and
distance. For example, in Figure 5-11, circuits going from Node 0 to Node 1 typically travel on Fiber 1,
unless that fiber is full, in which case circuits are routed on Fiber 2 through Node 3 and Node 2. Traffic
from Node 0 to Node 2 (or Node 1 to Node 3), can be routed on either fiber, depending on circuit
provisioning requirements and traffic loads.
Figure 5-11 A four-node, two-fiber MS-SPRing
The SDH K1 and K2 bytes carry the information that governs MS-SPRing protection switches. Each
MS-SPRing node monitors the K bytes to determine when to switch the SDH signal to an alternate
physical path. The K bytes communicate failure conditions and actions taken between nodes in the ring.
Node 0
Node 1
Node 2
Node 3 STM-16 Ring
= Fiber 1
= Fiber 2
71491
VC4s 1-8 (working)
VC4s 9-16 (protect)
VC4s 1-8 (working)
VC4s 9-16 (protect)
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