Huawei OptiX RTN 600 Product Description page 29

signal from the ODU , it selects the better-quality signal transmitted from the other unit.
The cross-connect unit always selects the service signal from the active IF unit.
Note:
1+1 SD is compatible with HSB. If the active IF unit or the active ODU becomes
faulty, the cross-connect unit selects the service signal from the standby IF unit.
The HSB switching can interrupt services.
1+1 SD also supports reverse switching. The HSB can be triggered when the local
NE receives the RDI signal coming from the remote NE.
Commercial in Confidence
Product Description
OptiX RTN 600
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