Maintenance4-153170-A2-GB20-20 December 1996Local Loopback TestsThe Local Loopback tests enable you to conduct circuittesting and fault isolation for the digital line. Thesupported local loopback tests are:• Line Loopback (LLB)• Payload Loopback (PLB)• DTE Loopback (DLB)• Repeater Loopback (RLB)• Data Channel Loopback (DCLB)• Data Terminal Loopback (DTLB)NOTEDLB does not appear when theDTE Drop/Insert interface isdisabled.The Line Loopback command can be activated anddeactivated in response to commands received over thenetwork interface. The Network Interface configurationoption NET LLB controls whether the E1 DSU/CSUresponds to the commands transmitted on the networkinterface to initiate LLBs (see Appendix C, ConfigurationOptions).The data port configuration option NET DCLBcontrols whether the E1 DSU/CSU responds to inbandV.54 commands to initiate DCLB for that port (seeAppendix C, Configuration Options).Local loopback tests can be aborted (Abort Command)at any time.No more than two local loopbacks can be active at anyone time. An additional restriction prohibits certainloopbacks from running at the same time. Valid loopbackcombinations listed in Table 4-8 are identified by YES.Table 4-8Valid Loopback CombinationsLLB PLB DLB RLB DCLB DTLBLLB N/A NO YES YES NO YESPLB NO N/A YES NO NO YESDLB YES YES N/A NO YES YESRLB YES NO NO N/A NO YESDCLB NO NO YES NO YES(on separateports)YES(on separateports)DTLB YES YES YES YES YES(on separateports)YES(on separateports)
