Abstract: A terminal multiplexer is constructed in such a manner that it can be upgraded for adapting to a change in a transmission system. Line terminating equipment (LTE) having working high speed transmission lines and protection high speed transmission lines in 1:1, is constructed from such units as two sets of 10G interfaces responsible for interface with the high speed transmission lines, and SELH which selects a high speed transmission line for which multiplex conversion is performed in relation to low speed transmission lines When this LTE is to be upgraded to ADM adapted for 2-Fiber BLSR, the unit SELH is replaced with SWH which performs switching of signals in each time slot between a high speed transmission line and the low speed transmission lines. Upgrading during the system operation is possible by making signal interfaces with the outside common for SELH and SWH, and by making delay times between signal input and output coincide for various signals.

Abstract: A uni-direction protection switched ring node which switches from a working path to a protection path or vice versa includes a failure-information detect circuit which detects a failure occurring on the working path and a failure occurring on the protection path independently of each other as failure information. A failure-information-path identifying circuit determines whether a working path with a failure occurring thereon is an active or standby path or determines whether a protection path with a failure occurring thereon is an active or standby path. A select circuit selects either the working or protection path as an active path in accordance with results of detection and determination by the failure-information detect circuit and the failure-information-path identifying circuit respectively.

Abstract: A terminal multiplexer is constructed in such a manner that it can be upgraded for adapting to a change in a transmission system. Line terminating equipment (LTE) having working high speed transmission lines and protection high speed transmission lines in 1:1, is constructed from such units as two sets of 10 G interfaces responsible for interface with the high speed transmission lines, and SELH which selects a high speed transmission line for which multiplex conversion is performed in relation to low speed transmission lines. When this LTE is to be upgraded to ADM adapted for 2-Fiber BLSR, the unit SELH is replaced with SWH which performs switching of signals in each time slot between a high speed transmission line and the low speed transmission lines. Upgrading during the system operation is possible by making signal interfaces with the outside common for SELH and SWH, and by making delay times between signal input and output coincide for various signals.

Abstract: An alarm detect unit (a path switching apparatus) for selecting an active path comprises a path-alarm detect circuit and a guard timer for a working path as well as a path-alarm detect circuit and a guard timer for a protection path. When an alarm is detected on the active path, alarm information, that is, information on the generation of the alarm, is delayed by a predetermined time by the guard timer of the working or protection path that serves as the active path.By the same token, when an alarm is detected on a standby path, alarm information, that is, information on the recovery of the alarm, is delayed by a predetermined time by the guard timer of the working or protection path that serves as the standby path. Either the working or protection path is then selected as the active path in accordance with pieces of alarm information output by the two guard timers which indicate the line-failure-occurrence states of the active and standby paths.