Cable Problem

[witch]

I have an ethernet port in a classroom which stopped working - no computer could connect to the network or the internet or anything. My cable tester showed no issues though.

As the faceplate had been pushed in and the catches broken, I have had it replaced and the wiring checked. It is one long cable that goes across the room, outside for a couple of metres and then across the IT suite directly into the switch (no patch panel connection). I have changed the port on the switch as well, just in case. (it is a new Procurve).

The cable tester reports no issues but it still doesnt work.

The cable has been in place for a couple of years and has been fine up until now, so it isnt a distance issue.

 

My question is this - if the cable buzzes out as OK, what other issue could be doing this? Could moisture or something be a problem?

I don't want to go to the expense of replacing the whole thing only to find that the issue persists!

Sometimes it sucks to be a lone tech. No-one to discuss things with, and no-one else to share the blame!!

[webman]

Try another computer on that port, or that computer on another port.

[AceDaz]

Do you get a connection light on the switch?

 

What tester did you use? Did all 8 lights come on?

 

I know what you mean, I have Manager jobs to do and Techy jobs!!!

[witch]

Sorry, didnt explain very well. Have tried the teacher's computer elsewhere around the school and it works fine. Have tried other computers which work elsewhere around the school on that port - no go. No connection light on the switch that I can see. I also used a brand new cable between the port and the tester - in fact I tried several cables.

I used my trusty cable tester and it hasnt failed me yet - all lights came on in the correct order.

[AceDaz]

Well it sounds more like your switch. Have you tried plugging the socket that is not working into a different port?

 

Also one thing to try, is when you are testing the plug that goes into the switch to the socket is to wriggle the wire on the plug end at the switch. I had that where it worked when I had it out but failed when I put it back in because of the angle the cable was at.

[plexer]

Your basic tester only checks that there in connectivity from one end of the cable to the other so even though it shows as ok there could still be issues with the cable.

 

Ben

[witch]

Have changed switch port

 

Just worried about the cost and upheaval to change the cable if it isnt the problem

 

* Have now stood and wiggled the cable at the switch end whilst someone else checks on the connection to the machine - no sign of a flicker

Edited September 16, 2010 by witch

[SYNACK]

Your basic tester only checks that there in connectivity from one end of the cable to the other so even though it shows as ok there could still be issues with the cable.

 

Ben

 

+1

 

The basic cable testers only test conductivity not for things like sque and jitter, I suggest asking around the local area to se if anyone has a good quality Fluke cable tester that you can try on it which can test for stuff like this. One of the High Schools or the LA network team may have one that you could borrow. I used to borrow them from my old University for a while. I have also heard that some places do offer them for hire, none here but the UK is much more tech friendly.

 

Running a good quality tester over it should give you a solid answer so that you can do whatever is required with realitive confidence.

 

It does concern me to hear that it goes outside for a couple of meters as I'd gamble that it is not outdoor cable and had probably become a bit corroded leading to higher resistance or signal jitter.

[plexer]

Equipment Specifications - Testerhire.co.uk - providing hire of the Fluke DTX1800 cable analyzer hire fluke testing equipment but otherwise may be able to get a company to come in and test it if they will get the job of replacing it should it turn out to be faulty.

 

Ben

[witch]

Equipment Specifications - Testerhire.co.uk - providing hire of the Fluke DTX1800 cable analyzer hire fluke testing equipment but otherwise may be able to get a company to come in and test it if they will get the job of replacing it should it turn out to be faulty.

 

Ben

 

lovely idea but no one is going to spring that sort of money to test one cable. I will ask the high school if they have a better one than I have got to see if I can find a problem.

If not I will contact a local company

[earlyriser]

outside for a couple of metres

 

If it isn't outdoor rated cable, it is likely to be moisture ingress through the jacket or general degradation of the copper. Any cabling that goes outside either needs to be outdoor rated, or encased in something. I have had exactly the same experience at a rural school here in NZ, continuity tested OK with the cable tester, but no go for connectivity. Unfortunately, the only fix was to replace the cable......

[FN-GM]

lovely idea but no one is going to spring that sort of money to test one cable. I will ask the high school if they have a better one than I have got to see if I can find a problem.

If not I will contact a local company

 

I agree seems allot for one cable. You can get a brand new one fitted cheaper.

[SYNACK]

I agree seems allot for one cable. You can get a brand new one fitted cheaper.

 

Thats why you turn it into a survey project when you get a hold of one or at least thats what I did. The enhanced testers will give you the length etc and the high end ones even store the tests in a downloadable format. I did a full survey of all the ports in the school and found/pre-emptivly fixed some that were likely to fail. It also means that I have a table of the run lengths and cable types of each cable run in the school which can be really useful if you need a quick answer about how capible a certain part of the network is.

 

I would try to go for the borrowing route as that does look rather expencive an if you do end up replacing the cable then make certain it is done wih outdoor grade cable (about double the cost but it will keep working).

[witch]

Have contacted a couple of local NMs and no one has a tester that is any better than mine. I have eyeballed the wire and it is encased in a black plastic sleeve. It was only put in a couple of years ago and we have others that have been there for many more years and not caused any trouble

I'm going to have to have to bite the bullet, I think , and go for a replacement.

May the GeekDeity help me

[Brpilot99]

Have contacted a couple of local NMs and no one has a tester that is any better than mine. I have eyeballed the wire and it is encased in a black plastic sleeve. It was only put in a couple of years ago and we have others that have been there for many more years and not caused any trouble

I'm going to have to have to bite the bullet, I think , and go for a replacement.

May the GeekDeity help me

 

Silly thought ... is it worth disconecting the cable from the classroom socket and putting a standard rj45 plug on it to see if that makes a difference ?? That would eliminate the socket having some kind of silly problem ..

I'm over your way next week if you want a hand or 2nd opinion

Cheers

Brian

Courthill School

[witch]

Silly thought ... is it worth disconecting the cable from the classroom socket and putting a standard rj45 plug on it to see if that makes a difference ?? That would eliminate the socket having some kind of silly problem ..

I'm over your way next week if you want a hand or 2nd opinion

Cheers

Brian

Courthill School

 

Thanks

[sted]

do you have an asus pcs/laptops as some of them have some network cable testing software in their bios not sure how good it is but may be betetr than the std cable tester

[witch]

No Asus' here - just Dells and the odd Tosh

[SYNACK]

Silly thought ... is it worth disconecting the cable from the classroom socket and putting a standard rj45 plug on it to see if that makes a difference ?? That would eliminate the socket having some kind of silly problem ..

I'm over your way next week if you want a hand or 2nd opinion

Cheers

Brian

Courthill School

 

Another good idea, if you are able to reterminate each end it may also fix it in the case of one of the terminations causing issues. This is probably way cheaper to do, the fact that it is in a black sheith indicates that it probably is outdoor cable but this 'building grade' solid core wire should always be terminated to a socket connector on each end as the way that RJ45 plugs terminate into it create horribly unreliable links. RJ45 plug conectors should only ever be used with multicore cat5/6 cable as this is what the connective wedges are designed to work with.

[teejay]

There are a lot of cabling companies who are very helpful to schools and would do a cable test for you free of charge, if you were up t'North I'd put you in touch with the company we use. Contact your local schools and see if there are any companies they recommend, wouldn't bother with asking the LEA as if anything like ours they'll use a company that charges a fortune:rolleyes:

[mac_shinobi]

Try a known working laptop and if the laptop works and the desktop does not then is it the onboard NIC or is it a dedicated one ?

 

If onboard then you need to obviously ensure its enabled in the bios, if its dedicated then I would take the NIC out and reseat it and ensure latest NIC drivers are installed for it and test again.

 

If the laptop does not work and the desktop does not then if you try the laptop on the same port with a shorter cable, if it works with the shorter cable on the same port then the port is fine and I would then look at the longer network cable

 

Are you able to re terminate the longer network cable ( both ends - not sure if its a pre purchased network cable or not ) - if its a custom made one then I would re terminate the network cable , if its a purchased one I would try and get the said company to replace the network cable and send you a new one.

 

If it does not work with the shorter network cable you could try on other port(s) on the same switch or try it with another switch, if it works on the other switch then may be switch configuration - reminds me there was one switch at one place that I had to power cycle occasionally to rebuild the routing table so may be worth doing that ( long shot though )

[witch]

mac_shinobi:

There isnt a desktop around, only laptops, of which I have now tried 3 - all of which work fine on the network elsewhere in the school.

The cable from the port to the laptop has been a)remade and b)replaced (twice) and is pretty short now.

The port has had a new faceplate including the wiring.

The cable runs, through trunking across the room, across the gap outside, across my IT suite and straight into my main switch (NO patch panel involved) - which is my new procurve off which runs the whole IT suite - all ports are fine AFAIK. I did change the port just in case but no go.

Looking at the cable, I think it is standard indoor cable that has been put in some sort of sheathing for the bit outside. (or does outside cable look the same?) I can reterminate the end that goes into my switch although, due to its location, I will have to do it standing on a chair!

Brpilot99:

I'm not sure about disconnecting the port and terminating the cable with an rj45 - well, I can do that, but reattaching it to the port is a different thing again and not something I have ever done - when are you over my way? (CM, not U)

[sted]

mac_shinobi:

There isnt a desktop around, only laptops, of which I have now tried 3 - all of which work fine on the network elsewhere in the school.

The cable from the port to the laptop has been a)remade and b)replaced (twice) and is pretty short now.

The port has had a new faceplate including the wiring.

The cable runs, through trunking across the room, across the gap outside, across my IT suite and straight into my main switch (NO patch panel involved) - which is my new procurve off which runs the whole IT suite - all ports are fine AFAIK. I did change the port just in case but no go.

Looking at the cable, I think it is standard indoor cable that has been put in some sort of sheathing for the bit outside. (or does outside cable look the same?) I can reterminate the end that goes into my switch although, due to its location, I will have to do it standing on a chair!

Brpilot99:

I'm not sure about disconnecting the port and terminating the cable with an rj45 - well, I can do that, but reattaching it to the port is a different thing again and not something I have ever done - when are you over my way? (CM, not U)

 

patching a cable into a patch panel is easy if you have the right tool line wire up push down job done

[SYNACK]

across the gap outside, across my IT suite and straight into my main switch (NO patch panel involved)

 

Looking at the cable, I think it is standard indoor cable that has been put in some sort of sheathing for the bit outside. (or does outside cable look the same?) I can reterminate the end that goes into my switch although, due to its location, I will have to do it standing on a chair!

 

This wireing right into the switch is one of the bits that concerns me and where I would start. It is horribly bad practice from a wireing point of view to do it this way and is much more reliable if it is terminated to a patch pannel then patched in to the switch with a small patch lead. I suggest reterminating at the switch end even if it is with a RJ45 plug just to check.

 

Outdoor cable does look different and is generally thicker and black, it usually has writing on it to indicate that it is exterior grade as well. If it is off the ground and fully sheltered from rain it may be alright via internal cable but if you can see it directly when outside it is still a concern.

[witch]

Not talking about wiring a patch panel, but I mean the termination at the port end. I havent got a tool for that anyway, only the one for putting ends on cables.

Will re-terminate the cable (already an RJ45) on Monday (standing on a chair, as I said) and then we will see....

 

Looks like internal cable covered in that black corrugated flexible stuff but TBH it is difficult to see

Edited September 18, 2010 by witch