Abstract: A telecommunications system (18) is provided that includes a first controller (20) and a second controller (22) coupled using a packet-switched network (32). The controllers provide a low cost means of coupling isochronous telecommunication devices. The first controller (20) receives one or more isochronous input channels from a common control shelf (24), such as a private branch exchange (PBX), over a circuit-switched network (27). The first controller (20) encapsulates an isochronous frames from the common control shelf (27) into a data frame that is transferrable over the packet-switched network (32). The second controller (22) is configured to receive the data frame and extract the isochronous frame, which is then transmitted to a peripheral shelf (26), such as a line trunk unit (LTU), using an isochronous circuit-switched network (38). The controllers contain identical functionality, permitting bi-directional transmission of data between the common control and peripheral shelves.

Abstract: A telecommunications system (20) includes a fail-safe subsystem (22) capable of maintaining call services to remote users in the event of a communication failure. The fail-safe subsystem (22) is coupled to a communication link (16) between a main switch (12) and a remote shelf (14). The subsystem (22) passively monitors the status of the communication link (16). Upon detecting a failure, the subsystem (22) provides a limited set of call services to remote users by providing local switching services. Upon re-establishing communications with the main switch (12), the fail-safe subsystem (22) re-synchronizes the main switch (12) and remote shelf (14) by emulating a conventional call setup procedure for each call placed through the remote shelf (14) during the failure.