"sh cable-diagnostics tdr interface" shows pair A and B length 0 ????

[leafar1988]

We are troubleshooting an intercom device where audio works but video no longer does. Devices uses POE and is on  a 3650

We've done a ton of troubleshooting and even rebooted the switch. The intercom works fine when plugged into a different switch. Can someone tell me what it means when the pair length shows "zero" for pair A and pair B is that normal?

#show cable-diagnostics tdr interface gigabitEthernet 1/0/23

Interface Speed Local pair Pair length Remote pair Pair status
--------- ----- ---------- ------------------ ----------- --------------------
Gi1/0/23 100M Pair A        0   +/- 1 meters Pair B Normal
                         Pair B        0   +/- 1 meters Pair A Normal
                         Pair C        68 +/- 1 meters N/A Short
                         Pair D        68 +/- 1 meters N/A Short

Switchport is a regular access port. 

[haselldavid]

A normal reading should be more like:

SPS75H#show cable tdr interf gi0/12
TDR test last run on: March 26 21:20:04

Interface Speed Local pair Pair length Remote pair Pair status
--------- ----- ---------- ------------------ ----------- --------------------
Gi0/12 auto Pair A 17 +/- 10 meters N/A Open
Pair B 17 +/- 10 meters N/A Open
Pair C 17 +/- 10 meters N/A Open
Pair D 17 +/- 10 meters N/A Open

I would say that there is a problem with the cable connected to your port and if possible replace it or check the pins inside the port to see if they are bent.  You may want to be more concerned with the "Short" as this indicates a short between the wires.

[Deepak Kumar]

Hi,

ZERO means: it showing pair length. Pair a and Pair B is terminated within 1 meter from the switch. A short question: are you using Cross Cable?

--------- ----- ---------- ------------------ ----------- --------------------
Gi1/0/23 100M Pair A        0   +/- 1 meters Pair B Normal
                         Pair B        0   +/- 1 meters Pair A Normal
                         Pair C        68 +/- 1 meters N/A Short
                         Pair D        68 +/- 1 meters N/A Short

This result is showing that you are using a cross cable. Pair-C and Pair-D are showing some Short circuit. 

intercom device where audio works but video no longer does. Devices uses POE and is on  a 3650

What is POE requirement for the Video intercom? Any other POE device is connected on this switch? What is the current power uses?

Regards,

Deepak Kumar

[Leo Laohoo]

The switch is most likely running a very, very old IOS-XE version.
When they released the 2960X and 3650/3850 with TDR functionality, the developers made a decision that if the pair was GOOD, then they don't want to present the length, which was really a bad idea.
Looking at the TDR result, I can say that the length of the cable run is (around) 68 metres. Pair A & B are good but Pair C & D are not.
This means that the end device will only support 100 Mbps and no PoE.

[Deepak Kumar]

Hi @Leo Laohoo 

sorry I was not aware of these new changes:

Spoiler

When they released the 2960X and 3650/3850 with TDR functionality, the developers made a decision that if the pair was GOOD, then they don't want to present the length

Regards,

Deepak Kumar

[Leo Laohoo]

---

@Deepak Kumar wrote:

sorry I was not aware of these new changes

---

All good.  Apologies not required.