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TDR cable test

prince.p
Level 1
Level 1
Hi friend
I want to check my connected Ethernet status and I want to check the cable  length from switch to the device.but I can't find the cable status and the length of the cable.i don't know what is pair ABCD AND the length 48,48,50,47,in the below command.
can anyone please guide me to find 
Tri-Sw1#show cable-diagnostics tdr int gi0/21
TDR test last run on: April 26 21:40:14
Interface Speed Local pair Pair length        Remote pair Pair status
--------- ----- ---------- ------------------ ----------- -----------
Gi0/21    1000M Pair A     48   +/- 0  meters Pair A      Normal
                Pair B     48   +/- 0  meters Pair B      Normal
                Pair C     50   +/- 0  meters Pair C      Normal
                Pair D     47   +/- 0  meters Pair D      Normal
Tri-Sw1#test cable-diagnostics tdr int gi0/21
TDR test started on interface Gi0/21
12 Replies 12

Mark Malone
VIP Alumni
VIP Alumni

There are 4 pairs in a copper wire that's why there is  abcd

this doc explains TDR very well

https://supportforums.cisco.com/document/74231/how-use-time-domain-reflectometer-tdr

Thanks for your post.i want to know how the pair length is vary in mtrs ie 48,48,50,47.how this difference will take place. 

Thanks for your post.i want to know how the pair length is vary in mtrs ie 48,48,50,47.how this difference will take place.

The switch, possibly a 2960G or a 3560G, is equipped with a simple TDR system.  It's not a full-blown variety that Fluke has.  

The result in accuracy, can be different but it's not a show-stopper. 

An accuracy reading like that is as good as it gets.  You run the TDR test remotely vs going to both ends, unpatching and running the test, patch the connection back, etc.  

The difference in lengths is because there are a different amount of twists per inch in the pairs. If you strip a cat5/cat6/cat7 sheath and have a look, the orange pair are tightly wound, the brown pair not so much. The blue pair and green pair are somewhere in between. With short cables the lengths will fall within the margin for error. With long cables the differences will be obvious and will show in the output.

Be careful of running the cable test on the current 2960X's. I have discovered that on some IOS versions it has been badly implemented. I had a 6 foot patch cable read back as 28 feet long with a-b b-a c-d and d-c.
That was not a good day!

Google Propagation Delay and Delay Skew. The variation in twist rate over a long cable, creates a large difference in actual wiring length. This is measured on a good TDR as Propagation Delay, Delay Skew is how late the longer pair of data gets to it's destination, and can be a factor as data volume and speed increase. Think of it as a crazy straw and a straight straw, one takes longer to get through the straw, same as the crow flies distance, but in reality longer.

Hi Experts

 

I have connected IP phones on my Catalyst 2960x switch and I want to run a test to the port, checking documentation I found the following commands,

 

SW_01#test cable-diagnostics tdr interface g1/0/5
Link state may be affected during TDR test
TDR test started on interface Gi1/0/5
A TDR test can take a few seconds to run on an interface
Use 'show cable-diagnostics tdr' to read the TDR results.
SW_Despacho_01#show cable-diagnostics tdr int g1/0/5
TDR test last run on: July 18 16:22:58

Interface Speed Local pair Pair length Remote pair Pair status
--------- ----- ---------- ------------------ ----------- --------------------
Gi1/0/5 auto Pair A N/A N/A N/A
                    Pair B N/A N/A N/A
                    Pair C N/A N/A N/A
                    Pair D N/A N/A N/A
Cable Diag is not available at 100 Mbps and 10 Mbps
SW_01#

 

I have connected IP phones on my Catalyst 2960x switch and I want to run a test to the port, checking documentation I found the following commands,

The phones are Cisco 7811 and I wanted to validate if you have a damaged pair, because the phone at times takes time to dial calls,

I faced a similar problem but with Meraki Switches and I saw that the data pairs were bad, inside the Meraki Dashboard there is a part to do the wiring test and it helped me a lot, but with Catalyst it is not like that. I only found those commands,

Anyone know why that data comes out. N / A when I run the cable test.

 

I look forward to your valuable help

 

Regards,

Carlos P.

Depends on the firmware used on the 2960X. Early firmware did not support TDR and it was only in late/later years when the TDR feature was enabled.
In this particular output, I'd say the switch was running an early version of the code where TDR was enabled.
The only way to "improve" the output is to update the firmware.

Hello

Please see the output below... The pair status is normal but the Pair D length is almost 4 times than others !

Also Remote pair is N/A. 

Is this normal !

 

fruda-largfac-sa-uh-08-01#show cable-diagnostics tdr int GigabitEthernet1/0/3
TDR test last run on: August 07 08:46:49

Interface Speed Local pair Pair length Remote pair Pair status
--------- ----- ---------- ------------------ ----------- --------------------
Gi1/0/3 1000M Pair A 55 +/- 10 meters N/A Normal
                        Pair B 60 +/- 10 meters N/A Normal
                        Pair C 59 +/- 10 meters N/A Normal
                        Pair D 193 +/- 10 meters N/A Normal

The output shows like there could be a slight "fault" with the cabling which can cause a spurious error like that.

Hi Sandys
Can you tell me which firmware version you are running and if it is a Catalyst 2960x switches?

I will appreciate your support.

 

 

Regards.

Carlos P.

Hello

Have a look at this excellent post/document from @Leo Laohoo  - here


Please rate and mark as an accepted solution if you have found any of the information provided useful.
This then could assist others on these forums to find a valuable answer and broadens the community’s global network.

Kind Regards
Paul
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