Contents. Network Topology. Common Network Topology. Chain Network. Protection Mode. Ring with Chain Network, страница 4

2.3.2  Protection Mode

The ring network composed of the OptiX OSN 3500 has the following protection modes:

n  Two-Fiber bidirectional multiplex section protection ring

n  Four-Fiber bidirectional multiplex section protection ring

n  Sub-Network connection protection (SNCP)

Table 2-4 shows the features and applications of these protection modes.

Table 2-4 Comparison of the two protection modes

1.  Two-Fiber Bidirectional MSP Ring

This protection mode is applicable when the service is distributed. If the service is only transmitted between adjacent nodes, the service capacity can reach STM-N x K/2 (K is the number of nodes) at most in the ring. However, it is a complicated protection mechanism, requiring the support of automatic protection switching (APS) protocol and high-level network maintenance.

n  Configuration plan

As shown in Figure 2-8, a ring network is composed of four NEs: A, B, C, and D, with the line rate of STM-16.

Figure 2-8 Typical ring network

Table 2-5 shows the service allocation between adjacent NEs.

Table 2-5 Service allocation of NEs

The service in a ring network is distributed and there are services to be added/dropped between adjacent nodes. Moreover, if we take the service capacity and source utilization into consideration, the two-fiber bidirectional MSP is preferable.

n  Configuration description

The service on the two-fiber bidirectional MSP ring tends to be transmitted over the “uniform route”, so the bidirectional service should be configured for each direction. For services that are not added/dropped at this station, configure them as bidirectional pass-through services.

Take the service between NE A and NE C as an example, the 63 x E1 service occupies #1 VC-4 in the line, and the normal service flow is: NE A tributary unit®NE A east line unit®fiber line®NE B west line unit®NE B east line unit®NE C west line unit®NE C tributary unit, as shown in Figure 2-9.

Figure 2-9 Service flow between NE A and NE C (normal)

If the fiber between A and B breaks, the 63 x E1 services between A and C will be switched to #9 VC-4. The service flow from A to C is: NE A tributary unit®NE A west line unit (#9 VC-4)®NE D east line unit (#9 VC-4)®NE D west line unit (#9 VC-4)®NE C east line unit (#9 VC-4) ®NE C west line unit (#9 VC-4) ®NE B east line unit (#9 VC-4) ®NE B east line unit (#1 VC-4) ®NE C west line unit (#1 VC-4)®NE C tributary unit, as shown in Figure 2-10. The service from C to A is the same over the other fiber.