Sub-Network Connection Protection
Subnetwork connection protection ( SNCP , German subnetwork connection protection ) is a protective mechanism for connections in telecommunications .
This protective mechanism is used in the synchronous digital hierarchy to switch VC paths (for example VC-12) to a previously defined substitute path in the event of failure of the active work path. If a route fails (for example due to a cable defect), the system automatically switches to another route within the subnet. This replacement route connects the same endpoints with each other as the failed route before.
A distinction is made between SNCP-I ( inherent ) and SNCP-N ( nonintrusive ). The difference between the two lies in the type of error that can trigger a switchover of the connection to the alternative route. The SNCP-I trigger the Loss of Pointer (LOP) and Alarm Indication Signal (AIS) errors . SNCP-N can also be triggered by the Signal Degraded (SD) , Trace Identifier Mismatch (TIM) and excessive Error Bitrate (exBER) errors . To do this, it is necessary to monitor the path overhead of the VC, since the information contained in this overhead enables monitoring for these errors.
Older network elements that do not have path monitoring also have no SNCP-N functionality, so that only SNCP-I can then be used.
The next higher protection level to the SNCP is the Multiplex Section Protection (MSP), in which not individual VCs are protected, but an entire section with many VCs.