Abstract: A communication system extending Ethernet Operation and Management (OAM) Loopback Message (LBM) and Loopback Replay (LBR) functionality into a time division multiplexing (TDM) domain has a first interworking function (IWF) of an Ethernet network that transmits an Ethernet Operation and Management (OAM) Loopback Message (LBM) having a first type length value (TLV) field. The first IWF controls the first TLV field to indicate that a connectivity test is to extend beyond the Ethernet network. The communication system further has a second IWF of the Ethernet network that receives the Ethernet OAM LBM and interprets the first TLV field. In addition, the second IWF performs a TDM connectivity test across a TDM connection in response to the Ethernet OAM LBM and based on the first TLV field and transmits a reply for the Ethernet OAM LBM to the first IWF, the reply prompted by the LBM and comprising data based on the TDM connectivity test.

Abstract: A communication system for propagating time division multiplexing (TDM) fault notifications has a first interworking function (IWF) of a packet network and a second IWF of the packet network. The second IWF detects a TDM fault of a TDM network and transmits continuity check messages (CCMs) to the first IWF. Further, the second IWF controls the CCMs in response to a detection of the TDM fault such that a TDM fault notification is propagated from the second IWF to the first IWF based on the CCMs, and the first IWF propagates the TDM fault notification to a second TDM node via a TDM signal.

Abstract: A (DS3) network interface unit (NIU) by-pass architecture places the NIU on its own circuit card and exclusive of by-pass switching (and relay) components, which are installed in the equipment shelf, proper, so that physical removal of the NIU card will leave the by-pass circuitry intact. The by-pass circuit responds to an abnormality of the NIU card, such as malfunction or physical removal of the NIU from its card slot, and also to a power supply failure. It also contains an indicator to draw attention to a failed NIU, increasing the likelihood that someone will notice a damaged card.

Abstract: A (DS3) network interface unit (NIU) by-pass architecture places the NIU on its own circuit card and exclusive of by-pass switching (and relay) components, which are installed in the equipment shelf, proper, so that physical removal of the NIU card will leave the by-pass circuitry intact. The by-pass circuit responds to an abnormality of the NIU card, such as malfunction or physical removal of the NIU from its card slot, and also to a power supply failure. It also contains an indicator to draw attention to a failed NIU, increasing the likelihood that someone will notice a damaged card.