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Strange cable problem, network connects and disconnects constantly

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mikeloaf

mikeloaf

Technical User
Dec 20, 2002
32
GB
I installed some Cat 5 sockets as a favour for a friends company. Wish I had never bother now!

I tested them with a cable tester (cheap and nasty - just checks each wire in turn for breaks) and then I patched a phone through to every socket.

The phones worked and still work perfectly. The problem is that when thay patch data through to the sockets, the network connection was very erratic. The icon on the tool bar said "network cable now connected" and kept switching to "cable unplugged".

Anyone seen this before, have I just cabled it up wrong?

Thanks,

Mike

 
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Well, why dont you explain how you cabled it, how many cables, how many jacks? Which wiring scheme?
How long are the cables? What speed are you trying to run?
Need more information to give you an eduacted answer.

Richard S. Anderson, RCDD
 
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When ethernet tries to auto negotiate, only the electronics are allowed a vote. So two cards may decide 'hey we can both go 100/F, lets choose that' if the cable can't do 100/F, they will fail and shift down to 10/H. This will work and the first thing the cards will do once it works is auto negotiate 100/F.

That fails, and the cycle continues. On the PC end, you can force the card to 10/H, and break the cycle.

I tried to remain child-like, all I acheived was childish.
 
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You will have to forgive my ignorance on this. As you can guess, this is not my usual chosen type of work.

The cables are all less than about 50m long and run from patch panel to socket. The patch leads are ready made ones that have been in use with the existing sockets without a problem. The cable is cat5e.

There were two wiring diagrams for the sockets, one labeled A, the other labeled B. I didnt actually terminate the sockets myself, another friend was doing that as I ran cables. I beieve he followed the "A" standard. Would this explain it?

Thanks all,

Mike
 
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1) Did you use Cat. 5 or Cat. 5e cable from a reputable manufacturer?

2) Does this happen on all or just some jacks?

3) Did you (your friend) keep the pair twisted up to within 3/4" of the connectors?

4)Sure he followed the A or B standard correctly? You must not split pairs

5)Did you use solid cable for the main runs and reserve the stranded for patch cable only? Stranded is not for use as the main backbone, only patch cables.

6) Are you mixing multiple uses within the same 4 pair jackets? Even though most data applications use only 2 of the 4 pairs you should not use anything else on those spare pairs (just connect them on ewither end and be prepared for the future).

7) If you crimped any RJ plugs did you use the appropriate plug for the cable used (e.g. stranded vs solid)

Good luck
 
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what do you mean by "readymade?" If you mean you made them onsite, I would start by replacing those with store-bought. It's much easier to get a fault (2-3 months later) on a hand terminated patch cable than on jacks and patch panels. I have seen your described problem many times on "self installs". All of the above questions could be the problem, but hand made patch cables is where I would start. If you had mixed the A-B code, the problem would not be intermittent-- you would have no connection at all.

If the cabling is good, the problem may be solved by having a pro come in and re-terminate everything. Worst case scenario- they replace it all, and finally learn that you do get what you pay for.
 
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The "on-again-off-again" problem is typical of a split-pair. Usually the W/OR & W/GR have their whites swapped. Another possiblity is that one end of the pairs is rolled.

Justin T. Clausen
Physical Layer Implementation
California State University, Monterey Bay
 
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What brand of jacks (sockets) are you using? Another possible cause could be that the pins in the jack are bent.

When you plugged in the phones, did you plug them into the data jacks? If so, the RJ-11 could have bent some adjacent pins, most notably the green and brown pairs on an A (T-568A) installation.
 
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Your wiring could be fine. The hub/switch could have problems.

Check your hub/switch using store bought patch cables and several machines. You will need three or four 50m (lenght depending on how much you want to move equipment around) patch cables.

Once you get a couple of computers working start patching in the building wiring to see what the problem is.

Good luck.
 
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I solved the problem. As stated there were two standards A and B in the socekts. We used a in all of them. When I was told that the problem was only on some sockets I was thinking faulty cables, interference from mains etc etc.

Upon further exazmination I found that the sockets that did work were patched into a newer switch than the ones that didnt work. They all worked fine with the new switch. The old switch worked fine with the existing sockets.

I changed all sockets to B and it worked perfectly with both switches.

Can anyone shed any more light on this. The difference between A and B was just the swaping of two pairs. Similar to the advice given by Jtodd. What are these two standards A and B? What should I have used in the first place and what spec does the switch need to be to work with A?





 
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Did you switch to B on all sockets, field and patchpanel? If so, that seems odd that it would suddenly work.

If you only switched one side to B, then it's possible that the new switch was auto-sensing as crossover or straight.
 
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When you mix A and B you create a x-over cable. dRost is probably correct in stating that one of your swtiches was autosensing, and one was not. Swithces will work with either standard...you just have to make sure you use the same standard on both ends of the cable.

To get more info on the differnces of A-B, just do a search here or google.
 
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A switch could care less whether you use A or B.
They don't "Autosense" cross-overs they look for a connection on Tx and Rx pairs, using a crossover cable simply swaps the Transmit and Recieve at one end so a second device that is designed for Tx and Rx to be on certain pairs can connect.

If you swapped one end to B and it now works, that means the other ends was already B, I assume the other end is terminated on a patch panel that is a B panel. That is the only way swapping from A to B would matter.

Had you given that information in the first place, this would have been a much shorter thread.


Richard S. Anderson, RCDD
 
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Richard, you can plug either another switch or a PC with a NIC card into some of our switches and it will work without any other intervention.
 
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