3905 IP Phone and cable test failure

[Vyacheslav_Maliev]

Hello! Today we noticed that if trying to run tdr cable test on catalyst 2960s on port with plugged 3905 IP phone we always getting results like that:

Interface Speed Local pair Pair length        Remote pair Pair status
--------- ----- ---------- ------------------ ----------- --------------------
Gi1/0/19  100M  Pair A     67   +/- 0  meters N/A         Normal              
                Pair B     68   +/- 0  meters N/A         Normal              
                Pair C     69   +/- 1  meters N/A         Short               
                Pair D     68   +/- 1  meters N/A         Short    

Is it ok or not? Another phone models have all normal pair in same port.

[Leo Laohoo]

Interface Speed Local pair Pair length        Remote pair Pair status
--------- ----- ---------- ------------------ ----------- --------------------
Gi1/0/19  100M  Pair A     67   +/- 0  meters N/A         Normal              
                Pair B     68   +/- 0  meters N/A         Normal              
                Pair C     69   +/- 1  meters N/A         Short               
                Pair D     68   +/- 1  meters N/A         Short    

Read this:  How to use Time-Domain Reflectometer (TDR)

Pair C controls PoE.  Because there's a "short" at around 68-69 (cable) metres from the switch, it means your device won't power up. 

Pair D controls GigabitEthernet.  Because there's a "short" at around 68-69 (cable) metres from the switch, it means your device won't be able to operate and/or negotiate at GigabitEthernet. 

This is indicative of a cable problem.  The cable is most likely to be the one that's cabled up to the phone.  

[Vyacheslav_Maliev]

Thanks for your reply! We thought about cable problem and tried to change cable but nothing helps. And moreover - all our 3905 phones on any ports and any cable give this error... 

[Leo Laohoo]

Take the phone and plug directly into the switchport.  If the phone works, then your issue could be the following: 

1.  The remote end patch port; and

2.  The remote end patch cable

[Vyacheslav_Maliev]

> Take the phone and plug directly into the switchport.  If the phone works, then your issue could be the following: 

Did it already, error is the same but phone is working regardless it plugged directly or not. So is it normal beaviour for thie phone model or not?

[Leo Laohoo]

Hmmmm ... What is the IOS version of your switch?

[Vyacheslav_Maliev]

Switch Ports Model              SW Version            SW Image                 
------ ----- -----              ----------            ----------               
*    1 28    WS-C2960S-24PS-L   12.2(55)SE7           C2960S-UNIVERSALK9-M     

[Leo Laohoo]

For 2960S, upgrade your IOS to 12.2(55)SE9 or 15.0(2)SE4.  

I remembered seeing an IOS in the early 15.0(2)SE where the TDR result gets "stuck" and you'll need to reboot the entire chassis just to reset the result.