Ethernet protection

Linear MSP

Linear MSP applies to point-to-point networks. MSP provides protection for the services between two multiplex section termination (MST) modules. That is, when an MSP switching occurs, the services are switched from the working section to the protection section. For OptiX RTN 900, linear MSP provides protection for TDM services that are transmitted over SDH fibers.

Linear MSP includes 1+1 linear MSP and 1:N linear MSP.

• 1+1 linear MSP

  In the case of 1+1 linear MSP, one protection channel protects one working channel, and the protection channel does not transmit extra services. When the working channel becomes unavailable, services are switched to the protection channel for transmission, as shown in Figure 1. 1+1 linear MSP is classified into dual-ended revertive, dual-ended non-revertive, single-ended revertive, and single-ended non-revertive modes. The single-ended non-revertive mode is the most common linear MSP mode.

  Figure 1 1+1 linear MSP
  
  

• 1:N linear MSP

  1:N linear MSP requires N working channels and one protection channel. The protection channel may transmit extra services. When a working channel becomes unavailable, the services on this channel are switched to the protection channel for transmission. As a result, extra services are interrupted, as shown in Figure 2. 1:N linear MSP is available only in dual-ended revertive mode.

  Figure 2 1:N linear MSP
  
  

OptiX RTN 910A supports only 1:1 protection for channelized STM-1 services. In 1:1 protection mode, one working channel exclusively uses one protection channel, and the protection channel cannot carry extra services. 1:1 protection for channelized STM-1 services is available only in dual-ended revertive mode.

SNCP

In the case of SNCP, the protection subnet connection takes over when the working subnet connection fails or deteriorates. For OptiX RTN 900, SNCP provides protection for TDM services on STM-1 fiber ring networks, TDM microwave ring networks, Hybrid microwave ring networks, STM-1 fiber ring networks, or Hybrid ring networks.

SNCP is based on dual feed and selective receiving and requires a working subnet and a protection subnet. When the working subnet fails or deteriorates, services are transmitted over the protection subnet, as shown in Figure 3.

Figure 3 SNCP

OptiX RTN 900 supports the coexistence of 1+1 protection, N+1 protection, and SNCP. In this case, you can set the hold-off time for SNCP so that the microwave link protection switching is performed preferentially, therefore preventing circular switchovers.

OptiX RTN 905 does not support N+1 protection.

Two-fiber Bidirectional MSP Ring

OptiX RTN 980 supports two-fiber bidirectional ring MSP, to protect two-fiber bidirectional rings. Two-fiber bidirectional ring MSP provides protection for the services between two MST modules. That is, when a two-fiber bidirectional ring MSP switching occurs, the services are switched from the working section to the protection section.

On a two-fiber bidirectional MSP ring, the first half of VC-4s on each STM-N line are working channels, and the other half of VC-4s are protection channels. Normally, services are transmitted on the working channels. The services transmitted on the two fibers flow in inverse directions. When a fiber cut occurs and the working channel becomes unavailable, the services on both ends of the faulty point are switched from the working channel of the faulty fiber to the protection channel of the reverse directional fiber for transmission. Figure 4 shows application of a two-fiber bidirectional MSP ring.

Figure 4 Two-fiber bidirectional MSP ring