11-2
Cisco ONS 15454 SDH Reference Manual, R5.0
April 2008
Chapter11 SDH Topologies and Upgrades
11.2 Multiplex Section-Shared Protect ion Rings
11.2 Multiplex Section-Shared Protection Rings
There are two types of MS-SPRings: two-fiber and four-fiber. Two-fiber MS-SPRings share service and
protection equally, but only two physical fibers are required. For more information, see the
“11.2.1 Two-Fiber MS-SPRings” section on page 11-2. With four-fiber MS-SPRings, the nodes on both
sides of the failed span perform a span switch and use the second pair of fibers as the new working route.
For more information, see the “11.2.2 Four-Fiber MS-SPRings” section on pa ge 11-6.
The ONS 15454 SDH can support five concurrent MS-SPRings in one of the following configurations:
•Five two-fiber MS-SPRings
•Four two-fiber and one four-fiber MS-SPRings
Each MS-SPRing can have up to 32 ONS 15454 SDH nodes. 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. For information about MS-SPRing protection channels, see the “10.8 MS-SPRing
Protection Channel Access Circuits” section on page 10-14.
Note MS-SPRings with 16 or fewer nodes have a switch time of 50ms. MS-SPRings with 16 or more
nodes have a switch time of 100 ms.
Note For best performance, MS-SPRings should have one LAN connection for every ten nodes in the
MS-SPRing.

11.2.1 Two-Fiber MS-SPRings

In two-fiber MS-SPRings, each fiber is divided into working and protect bandwidths. For example, in an
STM-16 MS-SPRing (Figure 11-1), VC4s 1 to 8 carry the working traffic, and VC4s 9 to 16 are reserved
for protection. Working traffic (VC4s 1 to 8) travels in one direction on one fiber and in the o pposite
direction on the second fiber. The Cisco Transport Controller (CTC) circuit routing routines calculate
the “shortest path” for circuits based on many factors, including user requirements, traffic patterns, a nd
distance. For example, in Figure 11-1, 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 rou ted on either fiber, depending on circuit
provisioning requirements and traffic loads.
5. See the “11.3 Subnetwork Connection Protection” section on page11-13.
6. Total LDCC and SDCC usage must be equal to or less than 84. When LDCC is
provisioned, an SDCC termination is allowed on the same port, but is not
recommended. Using SDCC and LDCC on the same port is only needed during a
software upgrade if the other end of the link does not support LDCC. You can
provision SDCCs and LDCCs on different ports in the same node.