SNC-P / I (Sub-network Connection Protection with Inherent monitoring)

This protection mechanism uses 1+1 architecture, which means it needs a spare sub-network connection to protect a working sub-network protection. It is single ended that is both directions of traffic are protected independently. The faults under which SNC-P / I is able to react and protect are those due to hard failures, occurring as equipment failure, optical interface failures and link failures. Radio link short period interruptions initiating Tributary Unit – Alarm Indication Signal (TU AIS) or Tributary Unit – Loss of Power (TU LOP) will also cause SNCP-I to protect. SNC-P / I may be implemented on a VC per VC basis allowing a given transmission facility to transport unprotected traffic and protected traffic.

SNC-P / N (Sub-network Connection Protection with Non intrusive Monitoring)

This protection mechanism differs from the previous one, only in the fault conditions under which it is able to protect. SNC-P / N protects against the usual hard failures as described for SNC-P / I but it also protects against failures such as human related activities, operating system mismanagement or mis-provisioning. These types of failures could be originated by a wrong matrix connection or opening of connections. Further, SNC-P / N also protects against soft failures due to degradation of optical interfaces or to errors occurring in a radio link exceeding the predetermined threshold value for maximum acceptable BER.