System Functions. Structure of Functional Units. Functional Units. Synchronous Timing Unit and Clock Interface Unit, страница 5

Protection of the ring network is based on MS, that is, whether to perform protection switching depends on the quality of MS signals.

The services between two stations are transmitted bidirectionally. In normal conditions, services are carried on the working ring, but they will be switched over to the protection ring at fault occurrence for protection.

Advantage of the two-fiber MSP ring lies in that the standby optical fiber can be used to transmit extra service, thus enlarging transmission capacity of the ring network to up to 2 x STM-N. It is because the standby fiber (P) is in an absolutely idle status since no service signals are sent to it. The extra service transmitted on this protection ring actually expands the transmission capacity of the ring.

n  Two-fiber bidirectional MS shared protection rings

They are also called MSP shared protection rings, composed of two pieces of optical fibers. However, each optical fiber can only use half of its capacity for service, with another half for protection of the working path of another optical fiber in opposite direction.

The services between two stations are transmitted bidirectionally. The MS is taken as the basis for the ring network protection.

In normal conditions, the rings formed by the working paths of the two optical fibers are used to transmit service signals. Once fault occurs, the service in the working paths will be switched over to the protection paths on the other optical fiber for protection. The switching time for a MSP ring composed of the OptiX OSN 9500 is less than 50ms, prior to that specified in ITU-T Recommendation.

The most outstanding advantage of the two-fiber bidirectional MS shared protection rings is that the timeslots can be re-used, which increases the transmission capacity of the ring up to k/2 x STM-N (k is the total node number in the ring network). Moreover, their protection paths can be used to transmit extra services, because these two protection paths (P1 and P2) are idle in normal conditions.

The two-fiber bidirectional MS protection rings are especially suitable for the network configuration with decentralized traffic flows. That is to say, in the ring network the traffic flows between the nodes, especially between adjacent nodes, are dense and evenly distributed.

n  Four-fiber bidirectional MS shared protection rings

They consist of four optical fibers: S1, S2, P1 and P2, with the former two being the working rings and the latter two being protection rings (in the same or opposite direction).

The services between two stations are transmitted bidirectionally. The MS is taken as the basis for the ring network protection.

In normal conditions, services are carried on the working rings, but they will be switched over to the protection rings at fault occurrence for protection.

The four-fiber bidirectional MS shared protection rings have three advantages as below:

n  The timeslots can be re-used to increase the transmission capacity up to k x STM-N (k is the total node number in the ring network).

n  Extra traffics can be transmitted over the protection fibers P1 and P2.

n  Span protection scheme is supported by the ring network.

3.  Inter-Ring Interconnection Service Protection

The inter-ring interconnection service can be classified into single node interconnection (SNI) mode and dual node interconnection (DNI) mode.

In DNI mode, the OptiX OSN 9500 provides a fully G.842-compliant protection for the inter-ring interconnection service.

The DNI has an advantage that it can provide protection not only for the traffic crossing from one ring to another, but also for either of the interconnected nodes.

4.  SNCP

The OptiX OSN 9500 features powerful higher order cross-connect and overhead processing capability. This helps to realize higher order SNCP. The OptiX OSN 9500 allows multiple SNCPs, and at the same time ensures the switching time being less than 50ms, fully satisfying the requirement in ITU-T Recommendation G.841 and G.842.

5.  Fiber-Shared Virtual Path Protection