In addition, NEPTUNE will include a low level or out of band control system. This will provide full control of all router functions through a standard serial interface, and can be used to configure the network and download software to the backbone routers. It also inter- faces to the node power supplies. The low level control system is fully redundant, and operates on a pair of dedicated optical fibers. It consists of two separate half duplex systems operating in a master-slave mode. Each link on a given node will operate in a strict slave mode with communications initiated by a master on shore.
Full duplex communication can be established by the master controller using both low level control systems for special purposes like software upgrades at specific routers.