# Cable Diagnostics Function

### 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 test cable-diagnostics tdr interface command.

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. 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.
Estimated cable length | If the cable status is OK for all pairs, the estimated cable length is displayed. Measurement is possible only when the link is up.

Results from executing cable diagnostics the previous time can be checked using the show test 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 test 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 | test cable-diagnostics tdr interface
Display cable diagnostics | show test cable-diagnostics tdr
Clear cable diagnostic results | clear test cable-diagnostics tdr

### 5. Setting Examples

#### 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 ↓
    Cable-diagnostic is running...

    Port     Pair  Status  Fault distance  Length
    --------------------------------------------------
    port1.1  1     OK      -               50 +/- 15 m
             2     OK      -
             3     OK      -
             4     OK      -

#### 5.2. Checking previous diagnostic results

Display the previous diagnostic results as follows.

    Yamaha# show test cable-diagnostics tdr
    Last run on Fri Feb 26 10:30:00 2021

    Port     Pair  Status  Fault distance  Length
    -------------------------------------------------
    port1.3  1     OK      -               -
             2     OK      -
             3     Open    5 +/- 3 m
             4     Open    5 +/- 3 m

### 6. Points of Caution

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

- When the shutdown command is set for the port to be diagnosed, cable diagnosis cannot be performed.

- Be aware that communication is temporarily stopped during cable diagnostics.

- The estimated cable length cannot be measured when the opposing port is linked up with a link speed of less than 1 Gbps or is shut down.

### 7. Related Documentation

- None

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