Note: Refer to the Local Loop to Router in the diagram above.Īlthough you can do both software and hardware loopback tests on a CSU/DSU, a loopback plug is more effective to isolate problems. Note: All loopback testing is done with High-Level Data Link Control (HDLC) encapsulation. Therefore, while you troubleshoot your circuit, you will be unable to pass traffic across that link. Warning: All loopback testing is intrusive to the circuit.
#RJ45 56K LOOPBACK PLUG SERIAL#
This diagram describes the various loopback tests you can do to isolate your serial line issue accurately. If CSU/DSU loopback tests prove that the router equipment, CSU/DSU, and connecting cables are not faulty, conduct further tests with the telco or provider of the circuit. Software local loopbacks are usually implemented with a Cisco IOS configuration command, or with a loopback button for some CSU/DSUs.Ī loopback plug or cable inserted into the CSU/DSU can be used for hardware loopbacks. Whether it is an internal or external CSU/DSU, you can do both software and hardware loopbacks back towards the router. Two kinds of loopback tests can be used to isolate problems on the serial link: software loopbacks and hardware plug loopbacks. Refer to Cisco Technical Tips Conventions for more information on document conventions. The information in this document is based on Cisco IOS® Software Release 12.0. There are no specific requirements for this document. Then proceed on to loopback tests that involve the telco or provider. Begin loopback tests on the customer premises with channel service unit/data service unit (CSU/DSU) loopback tests. Loopback tests allow you to isolate pieces of the circuit, and test them separately. When a serial line does not come up as it must, the best way to troubleshoot the circuit is to perform loopback tests.
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