Unidirectional service refers to the service that needs to go through different routes when receiving and sending services. If you create a unidirectional service between a network element A and a network element B, the direction of the service can only be from the network element A (the source of the service) to the network element B (the host of the service) or from the network element B (the source of the service) to the network element A (the host of the service).

A bidirectional service is a service that passes through the same route when it receives and sends a service. If a bi-directional service is created between Network Element A and Network Element B, then the service can travel both from Network Element A to Network Element B and from Network Element B to Network Element A.

The Multiplexed Segment Protection feature provides the ability to invert signals between two multiplexed segments from the active segment to the protected segment.

The multiplexed segment shared protection ring is an SDH ring structure that provides working and protection channels for each node on the ring. When the service on the working channel is abnormal or interrupted, the communication service will be automatically switched to the protection channel to continue transmission to prevent service loss.

Two optical fibers are needed between two adjacent network elements on the dual-fiber multiplexed segment shared protection ring to form a ring network. Each fiber has half of the channel as a working time slot and the other half as a protection time slot. For example, in an STM-4 service, its VC-4 No. 1-2 is used as the working time slot and VC-4 No. 3-4 is used as the protection time slot. When the working time slot of No. 1-2 is abnormal or fails, the service will be automatically inverted to the protection time slot of No. 3-4 on the opposite board to continue transmission.

The SNCP (Sub-network Connection Protection) function, a protection function in the ITU-T Recommendation, adopts the protection setting of 1+1 single-ended inversion, which is mainly used for realizing the protection of cross-subnet services, and the SNCP protection has the characteristics of double transmitter-receiver selection.

The protection principle of SNCP is characterized by double-issuance and selective-receipt, and when configuring SNCP services, the double-issuance and selective-receipt services should be configured separately. However, because T2000 provides the function of automatic generation of services, when configured on the T2000, when the network element's selective services, T2000 can automatically generate the dual-issuing services of the network element, so in the actual configuration of the service, you only need to configure the selective services of the network element, that is, the SNCP service pairs of the service, and then complete the configuration of the SNCP service of the network element.