Check Cable Status Using Time Domain Reflectometer
The Time Domain Reflectometer (TDR) feature allows you to determine if a cable is OPEN or SHORT when it is at fault.
Running the TDR Test
To start the TDR test, perform this task:
Procedure
| Command or Action | Purpose | |
|---|---|---|
|
Step 1 |
test cable-diagnostics tdr {interface { interface-number }} |
Starts the TDR test. |
|
Step 2 |
show cable-diagnostics tdr {interface interface-number} |
Displays the TDR test counter information. |
TDR Guidelines
The following guidelines apply to the use of TDR:
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Do not change the port configuration while the TDR test is running.
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If you connect a port undergoing a TDR test to an Auto-MDIX enabled port, the TDR result might be invalid.
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If you connect a port undergoing a TDR test to a 100BASE-T port such as that on the device, the unused pairs (4-5 and 7-8) are reported as faulty because the remote end does not terminate these pairs.
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To run a TDR test, the cable length should be at least 10 meters. If the cable is shorter than 10 meters, the test is considered as invalid.
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Due to cable characteristics, you should run the TDR test multiple times to get accurate results.
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Do not change port status (for example, remove the cable at the near or far end) because the results might be inaccurate.
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TDR works best if the test cable is disconnected from the remote port. Otherwise, it might be difficult for you to interpret results correctly.
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TDR operates across four wires. Depending on the cable conditions, the status might show that one pair is OPEN or SHORT while all other wire pairs display as faulty. This operation is acceptable because you should declare a cable faulty provided one pair of wires is either OPEN or SHORT.
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TDR intent is to determine how poorly a cable is functioning rather than to locate a faulty cable.
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When TDR locates a faulty cable, you should still use an offline cable diagnosis tool to better diagnose the problem.
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