# Cable Diagnostics

## 1. Function Overview

The cable diagnostic function can be used to easily check whether or not the LAN cable connected to the LAN port has a faulty connection/circuit.
It can be used to troubleshoot network problems or as an easy way to check cables when setting up networks.

## 2. Definition of Terms Used

TDR (Time Domain Reflector)

The TDR is used to measure the length of LAN cables or the location of damage based on the reflected signals from a pulse signal sent through the LAN cables.

## 3. Function Details

### 3.1. How to diagnose cables

The cable diagnostic function can easily diagnose LAN cables using the time domain reflection (TDR) method.
Cable diagnostics is started by executing the cable-diagnostics tdr execute interface command.
If the show cable-diagnostics tdr command is executed after the diagnostics process is finished, the following diagnostic results are displayed.

Item | Description
--- | ---
Cable status | The following cable states can be detected. * OK: The cable is electrically connected. * Open: Either no device is connected on the opposite end or the cable is faulty. * Short: A short circuit occurred. * Busy: Diagnostics cannot be performed due to the port status or device limitations. Results are displayed for each pair.
Distance to the cable failure point | If the cable status is “Open” or “Short”, then the distance to the fault is displayed. Results are displayed for each pair.

Results from executing cable diagnostics the previous time can be checked using the show cable-diagnostics tdr command.
Only the immediately previous diagnostic results are retained and then overwritten the next time the cable diagnostics command is executed again.
The immediately previous results can be deleted using the clear cable-diagnostics tdr command.

## 4. Related Commands

Related commands are indicated below.
For command details, refer to the command reference.

Operations | Operating commands
--- | ---
Perform the cable diagnostics | cable-diagnostics tdr execute interface
Display cable diagnostics | show cable-diagnostics tdr
Clear cable diagnostic results | clear cable-diagnostics tdr

The following commands included in smart switches can be used in the same way as the commands above.

- test cable-diagnostics tdr interface

- show test cable-diagnostics tdr

- clear test cable-diagnostics tdr

## 5. Examples of Command Execution

### 5.1. Perform the cable diagnostics

Diagnose of the LAN cable connected to port 1.1 as follows.

    Yamaha# test cable-diagnostics tdr interface port1.1
    The port will be temporarily down during test. Continue? (y/n): y
    % To check result, enter "show cable-diagnostics tdr"

### 5.2. Checking previous diagnostic results

Display the previous diagnostic results as follows.

    Yamaha# show test cable-diagnostics tdr
    Last run on Tue May 31 18:12:13 2022
    Port      Pair  Status  Fault distance
    -------------------------------------------
    port1.1   1     OK      -
              2     OK      -
              3     Open    15  m
              4     Open    15  m

## 6. Points of Caution

- This function performs simplified diagnostics. Note that it cannot be used for precision diagnosis of more specialized equipment.

- Cables 10 m or longer can be diagnosed. Cables shorter than 10 m cannot be diagnosed in some cases.

- Communication is temporarily stopped during cable diagnostics.

- Diagnostics cannot be performed if a shutdown command is specified for a corresponding port or the port is shut down either because a loop was detected or for any other reason.

- Diagnostics cannot be performed properly in some cases if the port on the opposite end is linked at a speed less than 1 Gbps.

- Diagnostics cannot be performed properly if PoE power is supplied at a corresponding port.

- If a stack is configured, commands cannot be executed from member switches in the stack.

## 7. Related Documentation

- None

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