The SL supervisory system

Long-haul transmission systems often require a supervisory system to accomplish such repeater control and monitor functions as switching in standby components and measuring performance parameters. In an undersea system, it is impractical to provide a physically separate channel on which the repeater can send and receive supervisory signals. In SL, this problem is solved by embedding supervisory signals within the main data channels in such a way that they can be extracted or added within the repeater. Supervisory commands are sent to the repeaters on a subcarrier derived by periodically switching between odd and even parity computed over blocks of data. Supervisory responses are sent from the repeaters by low-index phase modulation of the data stream. This paper details the implementation of this scheme, as well as its benefits and limitations.