1. A variable bandwidth private branch exchange system for interfacing a network ring and a plurality of local stations, said system comprising: means for communicating a network ring signal stream to an input port of a node connected to the network ring; means for determining that a local station connected to the node is being addressed by a remote station not connected to the node; means for assigning a discrete segment of the network ring signal stream for communication between the local station and the remote station such that at least one bit of the assigned segment of the network ring signal stream is used both to transmit data going from the remote station to the local station and from the local station to the remote station; means for disabling the normal network ring signal stream path through the node and enabling a network ring communication path to a local station when the assigned segment is accessible at the node, thereby disposing the local station in series electrical connection with the network ring signal stream; means for disabling the communication path to the local station and enabling the normal network ring signal stream path through the node after passing the assigned segment to the local station; and means for extracting the network ring signal stream from the output port of the node.