Difference between SNC/N and SNC/S in the case of TCM monitoring

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For TCM monitoring, SNC/N and SNC/S differ in termination and modification of overheads. SNC/N monitors PM and TCM sections, while SNC/S monitors only the TCM section.
Moreover, SNC/S can isolate external faults to avoid protection switching triggered by external faults.

Other related questions:
Differences between SNC/I and SNC/N
SNC/I means inherent monitoring and protects services carried over ODUk links (for example, server-layer trail and server/ODUk adaptation). It does not detect faults at the ODUk layer. Connections are monitored by using the inherent data available from the server layer network. SNC/N means non-intrusive monitoring and protects services at the ODUk path (ODUkP) layer or ODUk TCM (ODUkT) sub-layers. It defects faults at the ODUk layer. Connections are monitored by non-intrusive monitoring of the original characteristic information.

Selection of the SNCP protection type during configuration of the ODUk SNCP protection on TOM boards
1. SNC/I: SNC protection for inherent monitoring (1) Description: This method protects services (for example, server-layer trails and server/ODUk adaptation) against defects detected on the ODUk link. No defect detection is performed at the ODUk layer itself. Connections are indirectly monitored by using the data that is inherently available from the server-layer network. (2) Application scenario: a. The subnet that ODUk signals traverse does not have an electrical regeneration site. b. The tributary boards can receive any client-side services. 2. SNC/N: SNC protection for non-intrusive monitoring (1). Description: This method protects services against defects detected at the E2E ODUk path (ODUkP) layer or ODUk TCM (ODUkT) sub-layers. Defect detection is performed at the ODUk layer itself. The connections are directly monitored by use of listen-only (non-intrusive) monitoring of the original characteristic information. (2) Application scenario: a. No limit is set on the type of sites in the subnet where ODUk signals traverse. b. In case of SNC/N (PM), it is recommended that tributary boards receive non-OTN services. In case of SNC/N (TCM), tributary boards can receive any client-side services. 3. SNC/S: SNC protection for sub-layer monitoring (1) Description: This method protects services against defects detected at the TCM sub-layer (ODUkT) of the ODUk protection. Switching can be triggered only by defects of the protected domain. An ODUk fault cannot trigger protection switching. (2) Application scenario: a. No limit is set on the type of sites in the subnet where ODUk signals traverse. b. Tributary boards can receive any client-side services.

Three types of SNC services and their differences
Tributary SNCP protection is classified into SNC/I, SNC/N, and SNC/S. The difference of the three types of protection lies in the capability of monitoring OTN SM, PM, and TCM overheads and therefore they have different alarm trigger conditions.

Monitoring sections of PM and TCM overheads in OTN overheads
The SM, PM, and TCM overheads are generated at the source node and terminated at the sink node. The corresponding boards at the source and sink nodes monitor the signals and report the performance of the signals. The SM overheads need to be terminated and then regenerated at all the nodes that have the 3R functions. That is, all the boards that support the OTN interface must process the SM overheads. The PM overheads are terminated at the sink node of a channel. The TCM overheads can be terminated at a selective sink node based on the actual situation. The TCM overheads have six levels and three allocation modes (cascaded, nested, or overlapped), which can be determined flexibly as required.

ODUk SNCP protection of the SNC/S type
ODUk SNCP (SNC/S) protects services against defects detected at the ODUkT sub-layer trail (TCM). Switching is triggered only on a defect in the protected domain. That is, a defect at the connected ODUk layer does not trigger switching. Some portion of the original trail's capacity is over-written such that the part of the connection that is of interest can be directly monitored by a trail created at a sublayer.

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