WDM / OTN Protection
Optical Transport Network (OTN): Linear Protection
This Recommendation defines the APS protocol and protection switching operation for the linear protection schemes for the Optical Transport Network.
Protection switching will occur based on the detection of certain defects on the transport entities (working and protection) within the protected domain. How these defects are detected is the subject of the equipment Recommendations (e.g., ITU-T Recs G.806 and G.798).
The following architectures are possible:
1+1 – In a 1+1 architecture, a single normal traffic signal is protected by a single protection entity.
The bridge at the head end is permanent. Switching occurs entirely at the tail end.
1:N – In a 1:n architecture, 1 or more normal traffic signal(s) are protected by a single protection entity. The bridge at the head end is not established until a protection switch is required. In the case where n > 1, it cannot be known until a defect is detected on one of the protected signals even which of the normal traffic signals should be bridged onto the protection entity.