ethernet over long distance

Discussion in 'PC Technical Talk' started by Graham, Apr 1, 2006.

  1. Graham

    Graham Guest

    Has anybody any experience with using cat5 cable over distances greater than
    the 100 metres specified for ethernet? For example up to 1 km?

    If each end of the cable connects to a switch, the switches should use full
    duplex, so the transport delay would not be a problem. (Managed switches
    would allow you to fix full duplex and 10Mbits/sec.)

    What about loss and crosstalk?

    This is for a domestic application where fibre or wireless would be too
    expensive - but a km of outdoor grade Cat 5 cable plus some home-made
    waterproof junctions would be under £200.

    --- Graham
     
    Graham, Apr 1, 2006
    #1
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  2. Graham

    pete devlin Guest

    You'll get up to 150m in exceptional circumstances but I wouldn't rely
    on it. 1km is out of the question for cat5 unless you use repeaters.
     
    pete devlin, Apr 1, 2006
    #2
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  3. I used to read a mailing list for the operators of campus networks
    (where they regularly ran cables from building to building...)

    My main memory was that one used fibre for this, not copper ... because
    otherwise electrical storms would take out all of your kit! There were
    a number of war stories to emphasise the point :(
     
    Richard Clayton, Apr 1, 2006
    #3
  4. I'd have thought standard wireless gear but with high gain aerials
    would do it at a price well below that, at least if you have
    line-of-sight. And I have an aerial you might be interested in!
     
    Robin Faichney, Apr 1, 2006
    #4
  5. Graham

    Graham Guest

    My sums suggest:

    Buffalo-WLA2-G54L54 Mbps* Wireless Bridge Access Point £40.00
    Buffalo-WLE-LNC AirStation Pigtail Adapter for Outdoor Antenna £12.00
    Lightning arrestor - price guess £5.00
    6 metre antenna cable £20.41
    Buffalo-WLE-HG-DYG yagi antenna £118.00
    Buffalo-LE-KG-VPA small antenna mount kit £30.00
    Total £225.41
    At each end, so £450.82 in all - then the work of mounting the antennae ...

    I can get similar figures using D-Link - although they have a cheaper
    antenna which comes complete with the lightning arrester.


    -- Graham
     
    Graham, Apr 1, 2006
    #5
  6. Yes, but not to 1km. I've had Ethernet working at 200m with the data
    rate fixed to 10Mbps half duplex and using very good quality cable
    (Belkin Cat6), but for a point to point link only, and have not analysed
    the low-level traffic to see if excessive retransmissions are occurring.
    No chance, I would have said, but others may differ. Cable is cheap
    enough in 300m boxes that you could mock up a test bed and try it.
    Connect up two machines using one box of 300m, see if it works, add
    another box of 300m into the link, see if it works, etc. If you do
    this, please post back with your findings!
    agreed in principle.
    Loss is going to be your main worry. Crosstalk is going to be the least
    of your problems (particularly if you force half duplex.)
    Fibre is nowhere as expensive as it once was.
    Your main concerns should be twofold:

    i) you should not connect buildings together using copper, ever. Even
    though ethernet cards have 2kV isolation built in, this is a Bad Idea,
    because: a) different buildings may be on different phases of the mains
    supply, b) a copper cable will be at serious risk of surges from
    lightning strikes, even those that occur miles away, and c) buildings
    1km apart will have non-trivial differences in their earth potential,
    and some non-trivial currents may flow (this particularly applies if
    you're using STP, but shouldn't be disregarded if using UTP.)

    _If_ your test bed works, and you decide to press ahead with a copper
    connection regardless, I'd strongly recommend you invest in some serious
    surge protection and galvanic isolators. Note though that by the time
    you've done this, you've probably exceeded the cost of having a fibre
    installed and terminated.

    ii) Wireless may be do-able using a couple of high-gain antennas. You
    may even get the Pringles can trick to work if you have line-of-sight
    between the two buildings.

    You should also post to comp.dcom.lans.ethernet for good advice from the
    regulars. I've taken the liberty of crossposting there.
     
    Mike Tomlinson, Apr 1, 2006
    #6
  7. Graham

    Tony Wright Guest

    In message <e0lvm7$fao$1$>, Graham

    [CAT5E to 1Km)
    1. Running CAT5e over that kind of distance is dangerous -- particularly
    if the two ends are on different mains power/different earths.
    2. You won't have a signal without repeaters/signal boosters (which need
    power) and you can usually only daisy-chain a max of five repeaters.
    3. 100BaseFX (fiber) is the way to go unless you've line-of-sight in
    which case you could Wifi via 2 directional antennae.
     
    Tony Wright, Apr 1, 2006
    #7
  8. Graham

    Jim Crowther Guest

    Perhaps if you explained what the domestic application was, there might
    be a completely different answer, that did not involve direct
    connection.
     
    Jim Crowther, Apr 1, 2006
    #8
  9. Graham

    Graham Guest

    All your points well taken, but...
    I think Half Duplex uses the traditional 10Base-2 collision detection
    mechanism to manage the traffic on just one pair, and so is sensitive to the
    length of the cable, whereas full duplex does not need to worry about
    collisions because it uses two separate pairs for send and receive.

    As you say, a good reason for half duplex.

    -- Graham
     
    Graham, Apr 1, 2006
    #9
  10. Graham

    Graham Guest

    Perhaps if you explained what the domestic application was, there might
    Good idea!

    This is for a friend who lives in a *****very****** rural location. His
    phone line measures 8km to the local exchange, and Zen and BT between them
    were unable to get ADSL to work even at a specially slow 256 kbits/sec rate.

    However there is a farm about 1km away and he is on very good terms with
    the owner. They are getting ADSL - I think their phone line goes to a
    different exchange which is only about 5km distant, so 512Mbit/sec ADSL
    should be possible.

    So could friend share their ADSL service by extending their network?

    I have posted my costings for wireless (at about £450) since he will need
    external antennae and some clever mounting to get the signal past the
    trees - even though the land is basically flat.

    I haven't yet done costings for fibre but two AT-MC101XL copper to fibre
    convertors were about £150 the pair last time I bought any. I expect
    ready-terminated fibre with proper termination boxes will be few hundred
    quid. We then only have to dig a couple of trenches across some farm
    tracks - the fibre can then be hidden in the bottom of a hedge.

    Alternatively, can BT be persuaded to re-route his phone line to the nearer
    exchange? Do you think we should contact the local MP and make a political
    issue out of it?

    -- Graham
     
    Graham, Apr 1, 2006
    #10
  11. OK, I was thinking of bog-standard wireless router and adaptor with a
    couple of, say, 17dB directional aerials off eBay.

    Have you considered one-way satellite internet? I have it here and
    it's not great but much better for surfing and downloads than dialup
    (no good for gaming). I think inclusive DIY setup was around £160 a
    couple of years ago.
     
    Robin Faichney, Apr 2, 2006
    #11
  12. Graham

    Graham Guest

    Yes, that is an option we're looking at. But am I right that you still need
    the dial-up for the control channel (to tell it what web page to look at,
    etc.) so you still tie up the phone line?

    -- Graham
     
    Graham, Apr 2, 2006
    #12
  13. Graham

    J C Guest

    Yes, but we used to put up with that when we mostly all used conventional
    modems. Phone lines are cheap anyway.
     
    J C, Apr 2, 2006
    #13
  14. I looked into this a while back. Don't remember the details but there
    did seem to be an obligation to provide a line capable of 28kbps. My
    line is 8.1km and of very variable quality. My impression is that WHEN
    it's capable of 28k dialup, it also manages 512k ADSL. But your
    mileage may vary.
     
    Robin Faichney, Apr 2, 2006
    #14
  15. I've used the AT-MC103XL copper to fibre converters for a fibre link of
    about 4km. They work fine.
    You could try, but BT's service obligation to provide a line at a
    universal fixed price was lifted when they were privatised, IIRC.
     
    Mike Tomlinson, Apr 2, 2006
    #15
  16. That's _Belden_ Cat6, not Belkin. Apologies.
     
    Mike Tomlinson, Apr 2, 2006
    #16
  17. Graham

    Graham Guest

    Exactly. The dial-up achieves about 40kbits/sec. But the cable is buried
    underground for at least 3km and was installed over 20 years ago (not by BT,
    a local farmer volunteered to do it because after many months delay BT still
    had not done it - they simply left the cable on its reel at the side of the
    road.)

    -- Graham
     
    Graham, Apr 2, 2006
    #17
  18. Graham

    Graham Guest

    Cheap they may be, but at this location BT won't install another cable, they
    will fit a DACS. I've suggested asking for ISDN - does that work at
    distances over 8km ? The raw data rate is only 192 kbits/sec with error
    correction to give two by 64k B-channels plus one 16k D-channel. ISDN or
    DACS would allow internet connection and phone calls simultaneously.

    At this location mobile phones work but only with an external antenna - and
    my friend is using a £1 per day Orange data service - he has to apply every
    day to get the day's service - and I think the connection speed is only
    about 10kbits/sec.

    -- Graham
     
    Graham, Apr 2, 2006
    #18
  19. Graham

    J C Guest

    Depends on the cable if it's overhead single line then it should be just a
    single pair, if it's more modern it should be two pair, if its proper
    underground cable then it could be any pair. DACS will work but will give
    low speed probably less than 28.8K

    I've suggested asking for ISDN - does
    Not sure. The voltage is higher, so it may be better, but I think I saw that
    they weren't doing any new ISDN lines? from April 2006 maybe that was
    business?

    The raw data rate is only 192
    Of the two ISDN would be better, of course. Much better
     
    J C, Apr 2, 2006
    #19
  20. Can't get it here (8.1km).
     
    Robin Faichney, Apr 2, 2006
    #20
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