Time Domain Reflectometry (TDR) technology is used to detect faults in metallic cables that are connected to the Ethernet electrical interface of a switch. When a pulse signal is transmitted through a cable, part of the energy is reflected back if it encounters a cable end or a fault point. The TDR algorithm measures the time that a pulse travelling through the cable, reaching the fault point, and returning, and then converts the measured time into a distance.
Assume the distance between the interface and the fault point is Distance, the time interval from the pulse signal being sent to when it is received is T, and the transmission rate of the pulse signal in the cable is V. Then the formula for calculating the distance from the fault point to the switch interface is as follows:
Distance = (V x T) / 2
The TDR test command detects the cable connected to the Ethernet electrical interface and display the detection result:
When employing TDR test on a switch interface, pay attention to the following points:
run show interface diagnostics tdr <interface-name>
After the command is issued, the test result will be displayed. The time consumed for TDR test is different on different platforms, from 2 to 8 seconds.
admin@Xorplus# run show interface diagnostics tdr ge-1/1/1 Interface Local pair Pair length(meter) Remote pair Pair status ---------- ---------- ------------------ ----------- ----------- ge-1/1/1 Pair A 31 +/- 10 Pair A OK Pair B 31 +/- 10 Pair B OK Pair C 31 +/- 10 Pair C OK Pair D 30 +/- 10 Pair D OK
Table 1. Description of the run show interface diagnostics tdr output
Indicates the interface name of the switch.
Local four pairs.
Displays the length and error of the cable pair in meters.
Remote four pairs.
The pair status could be "OK", "OPEN", "SHORT", "OPENSHORT", "CROSSTALK" or "N/A".