The AtRisk notification identifies when a HighOrder_Circuit or LowOrder_Circuit has lost its redundancy and therefore its failure protection. The HighOrder_Circuit or LowOrder_Circuit goes into an AtRisk condition when a member of a redundancy group that underlays the HighOrder_Circuit or LowOrder_Circuit has failed.

The redundancy or protection group contains two or more of the same type of network objects, for example TopologicalLinks, that also share the same A-end and Z-end points. The following table shows the various redundancy groups, the type of object each contains, and the protection scheme it implements.

Table 1. Protection objects, elements contained, and protection schemes

Protection group object

Network element contained

Protection scheme



1+1 APS









1:N Card/Equipment protection 1+1 Card/Equipment protection


OchLink (WDM)OcnLink (WDM)

1+1 ClientCircuit protection (WDM)1+1 TopologicalLink protection (SONET/SDH)

The way protection is modeled for the WDM-NG domain differs from other domains. WDM-NG protection is described in“SNC (Subnetwork connection) protection:” on page 110 and “Y-Cable protection” on page 110.

When one of the network elements contained in the protection group fails, the protection group object goes into an AtRisk condition. The AtRisk condition propagates up to the object layered over the protection group, such as:

  • HighOrder_Trail

  • ClientTrail

  • TopologicalLink

  • OcnLink

    One of these object going into an AtRisk condition propagates up to the object it is layered over, such as:

  • HighOrder_Circuit

  • LowOrder_Circuit

  • ClientCircuit

    Details of each protection scheme and the classes and relationships used to model each protection scheme are described in the sections following in this chapter.