The first step in troubleshooting a T1 is to determine where the problem lies. Usually, itâs cabling-, hardware-, or telco-related. Running some simple tests can help you determine what steps to take. All of these tests are invasive, which means you must take the T1 out of service to perform them.
Loopback tests involve setting one piece of equipment to a loopback state and sending data over the link. The data should return to you exactly as you sent it. When the data does not come back as expected, something has happened to alter it. FigureÂ 21-9 shows how a loopback test might fail.
FigureÂ 21-9.Â Conceptual loopback test failure
When you perform a loopback test, failed results wonât typically be as clean as ones being changed into zeros. Usually, the problem is more electrical in nature, like the scenario shown in FigureÂ 21-10, or framing errors cause the data to become entirely unreadable.
FigureÂ 21-10.Â BPVs seen during loopback test
When youâre performing loopback tests, the logical way to proceed is to start at one end of the link and move across it until the symptom appears.
CSU/DSUs generally offer the option of setting multiple types of loopback, which greatly assists in this process: you can usually set a loopback at the interface connecting ...