1+1 automatic protection switching (APS) is a line protection scheme used in SONET/SDH. In this protection scheme, the optical signal is bridged at the source termination point and traverses two optical lines (working and protection). The destination termination point selects one of the lines based on standard switching criteria. Thus, if a signal on a working path is lost or significantly degraded, the destination switch automatically selects the signal on the protection path. The 1 + 1 APS protection protocol allows both unidirectional and bidirectional protection switching modes.
Physical configuration in a protection group shows the physical configuration of the 1+1 Protection Group, in which traffic is bridged at the source node and selected at the destination node.
Classes and relationships used in 1+1 protection shows the classes and relationships used to model 1 + 1 protection. The connection running over the protection group is represented by a TopologicalLinkGroup, which is ComposedOf the two topological link objects that represent the two fiber pairs that make up the protection group.
For 1 + 1 protection TopologicalLinkGroup ComposedOf two object instances, one for Route, one for AlternateRoute.
The Route may be a DropSideTopologicalLink or BBDropSideTopologicalLink with an AlternateRoute of DropSideTopologicalLink or BBDropSideTopologicalLink. Or the Route may be a TopologicalLink or BBTopologicalLink with an AlternateRoute of TopologicalLink or BBTopologicalLink.
The Route and/or AlternateRoute can be black boxes in this protection scheme. For example, a BBTopologicalLink can be an alternate route for a TopologicalLink, or vice versa. And a BBDropSideTopologicalLink can be an alternate route for a DropSideTopologicalLink, or vice versa.
For root-cause analysis, the TopologicalLinkGroup object creates a Route relationship with the working fiber connection, and an AlternateRoute relationship with the protected fiber connection.
For impact analysis, the HighOrder_Circuit or LowOrder_Circuit object creates a LayeredOver/Underlaying relationship with the HighOrder_Trail object. The HighOrder_Trial object creates a LayeredOver/Underlaying relationship with the TopologicalLinkGroup object.