can you do this with cat5 cable

[stirling]

Hi all - This is my first post - pleased to meet you all.
In the context of a 100Base-TX LAN, I'd be grateful for any comments about using the normally redundant 4 wires of cat5 to provide a second link. As far as I'm aware, this is 'non-standard' use, but is it likely to cause bandwidth (or any other) problems?

[johnwill]

Well, I'd have to say yes.

I have a CAT5e cable running to my basement for distribution of network to my TiVo and MediaGate MG-35, as well as a downstairs computer. When I got Verizon FiOS, I needed another link, and I didn't want to string cable through the attic and fish it down to the basement again. I split my line and put two jacks at each end, using just the two pairs for each.

This arrangement runs fine, and I've experienced no issues. Many businesses used to run phone lines on the unused pairs, as long as you never connect them to your Ethernet connections, it works fine.

[stirling]

Thanks johnwill for your reply.

I'll move on a bit if I may (if this should be a new thread pls advise). My reason for asking is that a friend of mine has a small business LAN suffering appalling performance issues and I'm trying to pick off obvious things before he calls in a network engineer.

his LAN is as the pic attached

c's are XP clients
s is a Win2003 SBS server

The server's main purpose is to share a couple of file systems to all clients.
Generally, clients don't have a need to 'talk' to each other.
All cabling is cat5

The single cat5 cable (~80 metres long) connecting the switch to the hub and the switch to c6 is the one I referred to in my original post. I can't understand why this would have been done by his network installer. I'd have thought given the above general (file sharing) use, c6 might as well connect into the hub.

The point is that his network installer is suggesting doing away with the hub and running (more) cables such that c4..c6 each have their own cable to the switch.

Can anyone see any advantage to the way it's done at the moment and then can anyone see any logic in the extra (expensive I'd have thought) cable idea?

I should add that ALL clients access the shares equally slowly - i.e. it's not that c4..c6 in particular, have the problem.

P.S. I suspect that the slowness is actually more to do with share problems but that's probably another thread in another forum.

[ebackhus]

The topology sounds very similar to what I have in my apartment. What may be the problem is that the hardware is not capable of full-duplex operation, effectively cutting the potential speeds in half.

[Cellus]

Keep in mind that hubs are just dumb multi-port repeaters - they regenerate an incoming signal and squawk it out every port. They're Layer 1 devices, which means they do not look at frames or packets - no matter where the frame or packet is destined, they'll go out all ports, taking up more throughput on the cable and forcing interfaces to discard frames/packets not destined for them, not to mention collisions. However with that being said, if you only have two or three workstations on a hub, it shouldn't affect things too much. It is possible, depending on the cable run lengths and the location of the workstations, that it was logical to have C6 connected to the switch and not the hub, however I can not definitively answer that without knowing what the lengths were as well as any extenuating circumstances.

Logically you can use the 4 unused wires for a second signal, however there may be issues with signal quality. There will be an increase in crosstalk, and electro-magnetic interference will affect the line more at both ends as you monster up two homemade RJ45 jacks on the one cable. Also the physical line coding used on the cable (MLT-3) only took into consideration using the four wires, not all eight, so you may have more signal issues.

Like John said, there is no real problem using those spare wires for phone connections. This is because voice only uses 64kbps (as in kilo, not mega), so attenuation and what-not doesn't affect it too much because it isn't using a lot. However if you want to get 100mbps for data on those four wires, you're definitely going to run into problems.

[stirling]

Many thanks to all for your input - much appreciated.

Latest update is that my friend is under pressure for more speed like now... So he's going for the extra cables from his network guy. Obviously I need to back away for now.

I've got a small wager that nothing changes :-) watch this space...

[crazijoe]

Using the spare wires wouldn't work in my network since I use PoE.

[johnwill]

You need to get rid of any the hubs and use switches, that will help with internal network speed. However, from your drawing, I don't see how it will help. I'd be seriously considering a gigabit connection from the server to the switch, then home runs to each of the computers, there aren't that many systems.

[Cellus]

Is there any plans for expansion? Since you're getting this structured cabling done now, if the company intends to grow you should take the added hosts (and therefore load) into account.

[stirling]

Thanks to all for your input. Much appreciated.

As I said above, it's now out of my hands as it's not my network - it's my friends. It's a bit 'political' but basically he was happy for me to investigate all possibilities (network, OS, databases, apps etc) as to why the whole nine yards was so slow, but his partners want this other guy to come in and just run the cables. So it's a 2:1 vote for the network guy against me.

To be honest I wouldn't be surprised if the issue didn't turn out to be something like out-of-date indexes on the db tables or maybe it's (not uncommon) issues with shares between W2003 & XP. Who knows until someone's actually taken time to properly investigate?

For now I'll have to wait to see what effect the cables have and take it from there (if I'm asked back in).

Rest assured if he asks me back on the case I'll be back to you guys.

[Cellus]

I see. Well we can only hope, yes?

Cheers to you.