Testing7-77612-A2-GB20-00 June 1997LoopbacksLoopbacks can be started from a variety of points in the network. Refer toTable 7-1 for further information.Table 7-1. LoopbacksLoopback Type Initiated By NotesBilateral Loopback ATI NMS Remote unit sendingV.54 sequenceWhen enabled, running a DSUloopback also automaticallystarts a local loopback. Refer toData Port Options, Table A-3, toenable.56 kbps CSU Loopback(Non-latching loopback)64 kbps CC CSU Loopback(Latching loopback) ATI (Network tests) NMS DDS Network, byloop current reversalWhen initiated by the network,CSU Loopback cannot bedisabled by the user. When IMCis enabled, the aggregate datais looped back to the network.DSU Loopback (Digital) ATI NMSWhen IMC is enabled, only userdata is looped back to thenetwork. Refer to Data PortOptions, Table A-3.Local Loopback ATI DTE via CT141 NMSControl via CT141 can bedisabled.Refer to Data Port Options,Table A-3.Network-initiated56 kbps DSU Loopback(Non-latching loopback) DDS Network When IMC is enabled, theaggregate data stream is loopedback to the network. Cannot bedisabled by user.Network-initiated64 kbps CC DSU Loopback(Latching loopback) DDS Network Includes optional datascrambling and uses 25-secondtimer to detect the networksequence. When IMC isenabled, the aggregate datastream is looped back to thenetwork. Can be disabled byuser.Remote Digital Loopback Remote unit sendingV.54 sequenceSame as a DSU Loopback butinitiated by a remote unit viaV.54 sequence. When IMC isenabled, only user data islooped back to the network. Canbe disabled locally. Refer toNetwork Interface Options,Table A-2.V.54 Sequences to remoteunit ATI NMS DTE via CT140Control via CT140 can bedisabled. Refer to Data PortOptions, Table A-3.
