Take the 2-minute tour ×
Server Fault is a question and answer site for professional system and network administrators. It's 100% free, no registration required.

I live and work in a building that is nearly 20 years old. My Internet connection is in the cellar along with my servers and has a nominal rating of 100 MBit. I have a gigabit switch in the cellar connecting everything up.

That gigabit switch has a direct ethernet connection to a second gigabit switch three storeys up in my office.

I have tested the speed of the connection from upstairs to the cellar and am getting about 80 Mbit, somewhat less than the nominal speed of my Internet connection. I could live with that, but it would be nice to have a faster connection to my servers, so I'd like a gigabit connection between the switches.

Inspection of the cable from the office to the cellar revealed that it is an ISO/IEC 11801. There is no room in the cable duct for a thicker cable (e.g. CAT6 etc.) because the duct also carries a TV cable.

It seems to me, therefore, that a good way forward would be to put in a duplex fibre optic cable between the two switches and interface it with a gigabit media converter at each end. Is it really as simple as that?

The thing I know I really don't understand is the cable confection. Can one simply cut fibre optic cable to length, and connect it to wall sockets and SC or LC connectors? I can't use ready-made cables because the connectors won't fit down the duct, I think.

If someone could point me at a "howto" or share their wisdom and experience with me, I'd be very grateful.

Steve

share|improve this question
    
If there's already a Cat5 cable in there, can you just tie Cat6a onto the end and pull it through, removing the old cable in the process? "IEC 11801" is ambiguous as that covers Cat1-6 as mentioned below. IIRC, fibre cable is just as chunky as Cat5/5e/6/6a (connectors excluded) –  Mark Henderson Feb 22 '11 at 3:45
    
If that Cat5 cable just isn't able to handle GigE, you could attach a new strand of Cat5e to the existing Cat5, and pull the new strand through. The last Cat5e I bought was pretty thin, and fairly cheap. –  KJ-SRS Feb 22 '11 at 5:24
    
@Mark Henderson, @KJ-SRS: the existing cable was put in for me by an electrician about 8 years ago. It isn't marked as CAT5, CAT6 or anything that I recognise: just ISO/IEC 11801 and EIA/TIA 568A. It's thinner than those CAT5s that I have and a lot thinner than the CAT6s. I have a wire for threading cables through ducts (I don't know what it's called in English: in German it's a "Durchzugskabel"). My concern was more that there is no room for a thicker cable than the existing one. However, please see below... –  Stephen Winnall Feb 22 '11 at 8:31

3 Answers 3

In theory it is as simple as you describe. The problem you will run into is that you need to join two pieces of fiber. In practice you have two options for this:

  1. Mechanical splicing. You use a special clamp to join the parts togeather. Gives high losses, but considering your short distance it is an alternative.
  2. Fusion splicing. You use a large and expensive machine to melt the fiber and combine it.

Also, getting the fiber in there will probably be a challenge. Fiber might be smaller and easier to bend, but it is also more fragile than cat 6.

My recommendation would be to ask your local fiber company to built it for you. They have specialized equipment to get fiber into complicated ducts, the equipment to splice it properly and will be able to provide you with a measurement protocol at the end that shows that the fiber actually works. Around here I would expect to pay perhaps $1000 for the job of running a fiber through an existing duct between floors, including pigtails at the end that are fixed in existing racks.

share|improve this answer
    
+1 for 'ask your local fiber company': with flimsy cable like fibre, they might need to 'blow' it through. –  DutchUncle Feb 21 '11 at 22:33

What exactly is the problem with your existing cable?

You list a cable standard that covers everything from cat1 to cat6a.

If your cables are true cat5 cables (ie you've got 8 wires and they're twisted together a certain times per foot) and you're less than 300 feet from end to end, you should be able to run gig ethernet over that link.

Let me repeat this. Cat5 support gig ethernet. If it can't support gig ethernet, it isn't cat5.

You should look into your existing wires are not performing up to spec. It may be as simple as re-terminating both ends carefully.

Borrow a decent cable tester and find out what's going on. Only then should you look into dumping lots of money into the project.

You may also consider yanking all the cables out of the conduit and running new cables. Buy a pre-terminated fiber and buy a new bit of TV cable and re-terminate that in the field. Use the old cable as a pull for the new cable. Just don't make a mistake...

share|improve this answer
    
Cat5e supports gig ethernet. I'm guessing in an early 90's building it will be good old regular Cat5, which means it's only rated to 100Mb. –  Mark Henderson Feb 22 '11 at 3:41
    
@Mark: gig ethernet works just fine on cat5. Read the spec. en.wikipedia.org/wiki/Gigabit_Ethernet#1000BASE-T –  chris Feb 22 '11 at 3:48
1  
Please see my comment above. It transpires that the existing cable is OK. In my initial tests, I was getting bad results on an internal iperf test, and I suspected the cable, the more so because it had no obvious markings (CAT5, CAT6 etc) on it. However, the machine I ran the iperf server on has more than one ethernet port, and I ran the server on a slow one. Rerunning the tests with the server on a gigabit port gave me over 600 MBit throughput. So, to answer @chris's question: there is no problem with the existing cable, which dates from 2003. My problem is solved. Thanks for your help. –  Stephen Winnall Feb 22 '11 at 8:57

I think you're going down the wrong track in your diagnostic.

But, no I'm not going to discourage you from putting in fibre yet. First, you need to clearly identify where the problem is.

First off, check the internet speed from your downstairs server with speedtest.net or similar.

If it's a windows server perhaps you can RDP to it and then do the speedtest. Make sure you do this when no one else is using the internet... like at night or early morning before all the workers come in.

Do you get 80Mbit/s average? If you do, then congratulations, that's the bottleneck for your so called 100Mbit/s internet connection (i.e. not the upstairs/downstairs link). By the way, if you're paying for 100Mbit, don't expect to get that. 100Mbit/s is theoretical maximum throughput. However, it doesn't take into account the protocol overheads and such like. In actual fact, within 80% of maximum is quite acceptable.

Secondly, have you tried some speed testing between your server in the basement and your PC upstairs? You should get around 600+Mbit/s... You are unlikely to get more than 750Mbit/s throughput. There are good reasons for that. Part of it is again, protocol overhead. Also PCI bus speed and so on. If on the other hand, you're getting much less than this, then I'd consider either putting in fibre, or a higher grade cable like CAT6 just because it's less prone to error at high speed and a little more shielded. If you know you've got power and other things running down this same duct then this could be a source of error. I believe there are testing tools for checking error rates.. maybe you can hire something?

But, if you want fibre, as others have mentioned I'd get a company that specializes in this to do it for you. You can terminate them yourself, but you need the right gear to do it, and probably a couple of attempts to get it right. It's not hard, although more work than copper and requires a lot more patience. As with all things we do ourselves, if we're not familiar it can take us 10 times longer than someone qualified.

share|improve this answer
    
Thanks for this. You made me think, which often helps :-) –  Stephen Winnall Feb 22 '11 at 8:38
1  
The speed tests I performed were within my own network from a desktop upstairs to a server in the cellar. I used iperf and was only getting 80 MBit. If I got 80 MBit out of my 100 MBit Internet connection, I'd be quite pleased, as you say. I couldn't understand why I was getting so little internally when the switch showed the backbone as being gigabit. I had assumed the cable was at fault. But it was I: I had run the iperf server on a slow port. If I run it on a gigabit port, I get 600+ MBit. So, problem solved. Thanks. –  Stephen Winnall Feb 22 '11 at 8:49

Your Answer

 
discard

By posting your answer, you agree to the privacy policy and terms of service.

Not the answer you're looking for? Browse other questions tagged or ask your own question.