A method of recovering from a transmission error in a station having first and second input-output ports which are respectively coupled to two other stations in a communication network includes the steps of: receiving on the first port, messages which are separated by idle characters and regenerating same on the second port; detecting the error during the receiving step; and responding to the detection of the error by (a) transmitting silence on both the first and second ports and (b) waiting for the receipt of silence on the ports, prior to passing any further messages through the station.

Communications circuit connectivity in a bidirectional line-switched ring transmission system is continued in the presence of the failure of a first ring node for communications circuits terminated in the ring node which are redirectable to an alternate (dual hubbing) ring node. The communications circuit are redirected by establishing a bidirectional communications circuit to the alternate ring node. In one example, redirection of the communications circuits is further realized by not squelching communications circuits terminated in the failed ring node in a ring node adjacent the failed ring node on one prescribed side which normally would have been squelched, while squelching communications circuits terminated in the failed ring node in a ring node adjacent to the other side of the failed ring node. This allows the redirectable communications circuits to be loop back switched so that they may be redirected to the alternate ring node. Then, the alternate ring node directly intercepts the redirected communications circuits. This is realized by providing provisioning information to the ring nodes which includes the identity of all communications circuits active in the ring and whether there is an alternate ring node to which any of the communications circuits may be redirected.

An in-line coupling circuit for a POS terminal, includes a coupling section connected in a communication line and electrically connecting the POS terminal to the communication line. The in-line coupling circuit further includes a regeneration error check circuit for monitoring signals transmitted from and received into the POS terminal and generating an abnormal detection signal when a specified character data included in the received signal and indicating the end of a data frame is not generated from the POS terminal and a reporting circuit for generating a defective code inherent to the POS terminal in response to the abnormal detection signal and transmitting the defective code through the communication line.

A Time Divison Multiplex Ring (TDM Ring) comprising a plurality of nodes (central offices) connected together by interchange trunks (main and standby paths) in a ring type configuration. Each node contains a multiplexer, a demultiplexer, data, alarm, bridging, switching circuits, transmitters and receivers on the main and standby paths, all arranged so that (a) data and alarm signals are transmitted in a first direction on the main path and in an opposite direction on the standby path, (b) the bridging circuit forms a transmission path between the transmitter and receiver on the standby path of each node only in response to a predetermined alarm signal originating from an alarm circuit in another node received at a given node on the main transmission path and (c) the switching circuit is responsive to the presence of a predetermined alarm status to switch the data and alarm circuits at each node from a connection where all transmission is on the main path to a connnection whereby such signals are transmitted at least in part over the standby path.

Communications circuit connectivity between a bidirectional line-switched ring transmission system and another ring transmission system is continued in the presence of the failure of a first shared node for communications circuits between the ring transmission systems by employing at least one additional shared node for the communications circuits; provisioning one or more duplex communications circuits between the first shared node and the additional shared node; and selectively allowing the one or more duplex communications circuits between the shared nodes to be established in the bidirectional line-switched ring when a ring node in the bidirectional line-switched ring in the first shared node has failed.