100m line length

Discussion in 'Home Networking' started by jas0n, Oct 21, 2006.

  1. jas0n

    jas0n Guest

    I need to get a network point to a seperate building, which is approx
    150m from the switch.

    The line length of 100m that's specified, ive never tried running
    anything beyond 100m - is t a fairly fixed limit, unlikely to run to 50%
    beyond ... ?

    I think the only other option is wireless, probably a couple of external
    wifi points in bridge mode, maybe.
     
    jas0n, Oct 21, 2006
    #1
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  2. jas0n

    Dr Zoidberg Guest

    Is there anywhere midpoint that you could stick another small switch?
    --
    Alex

    "I laugh in the face of danger. Then I hide until it goes away"

    www.drzoidberg.co.uk www.ebayfaq.co.uk
     
    Dr Zoidberg, Oct 21, 2006
    #2
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  3. jas0n

    Alex Fraser Guest

    There can be trouble (regardless of the distance) if the buildings have
    different mains supplies. It is not clear to me why this is a problem
    (presumably different phases is part of the reason), but but it has been
    mentioned before so I think it is worth pointing out. Maybe someone else can
    elaborate.

    There is a limit on the maximum propagation time in a collision domain; this
    is a hard limit and breaking it will cause major trouble. If you are
    exclusively using switches (rather than hubs) then everything should be full
    duplex which means no collision domains. I think you will be OK unless you
    have hubs at both ends of the run.

    The only remaining issue is signal degradation. I think it is likely that
    you will find the link only works reliably at 10Mbit/s.
    You could do that. Using Yagi antennas would probably be a good idea.

    If possible, Dr Zoidberg's suggestion of a hub (or switch) somewhere in the
    middle would be preferable.

    Another option is to acquire a pair of 10BASE2/10BASE-T bridges and join
    them using 50ohm co-ax cable (using a couple of T-pieces and 50ohm
    terminators). You may be able to pick up the bridges second-hand quite
    cheaply - devices with a single 10BASE2 port and a few 10BASE-T ports were
    common when 10BASE-T was coming in, to ease transition. This avoids the
    potential security issues of a wireless link and is within the specified
    cable length limit for 10BASE2 (185m according to Wikipedia, which sounds
    familiar).

    Alex
     
    Alex Fraser, Oct 21, 2006
    #3
  4. jas0n

    John Steele Guest

    To be accurate there is another option which completely eliminates the
    problem with earthing differences that can cause problems between two
    buildings. This could cause equipment damage in electrical storms.. It is
    probably more expensive but guaranteed to work - Fibre Optics.

    Fibre converters at either end cost around £50 each for 100 Mbps.
    http://www.netshop.co.uk/productcategorydetail.aspx?categoryid=51930

    I am not sure how much a fibre cable would be but probably about the same.
    You can buy this pre-terminated. Netshop do not have long lengths listed but
    they are helpful and could probably quote you. It should work at any speed
    you are likely to want up to 1 Gbit at 250-500 metres over the cheaper
    multimode fibre (I don't have the actual distance specifications to hand).
     
    John Steele, Oct 21, 2006
    #4
  5. jas0n

    stephen Guest

    260 m for "old good quality" 62.5/125 micron core cable. 550m on 50/125, or
    various more modern 62 types

    limit isnt fibre loss for GigE on m/mode, but smearing of the pulses, so
    lower data rates can go much further.

    100 Mbps is good for 400m in 1/2 duplex (limit of the collision domain
    without a repeater), 2 Km full duplex (AFAIR).

    make sure you get the same connector types on kit and cable - lots of
    different F/O connectors, and if you need patch leads they will up the cost
    significantly.
     
    stephen, Oct 21, 2006
    #5
  6. jas0n

    jas0n Guest

    No, its basically going from a construction site office to the security
    gate office across the yard in a pre laid duct.

    They've run a couple cat5e cables which ive used 1 of for the telephone
    extension which works fine but knowing the 100m limit for networks didnt
    even try the data side ... I might just patch it up and see if it works
    at all just for the sake of trying.

    The mentions in the thread of the fibre converters sound ideal - one of
    those each end of a fibre run would work great. Only problem of pre
    terminated is knowing the length as I wouldnt want too much cable coming
    out either end, trying to keep things tidy as there's 450+ network
    points on this one.

    Is fibre difficult to terminate or just a matter of having the right kit
    and its straight forward?

    Im going to have to provide wireless of some description to this site
    anyway so I might put in a full coverage wds wireless solution which
    would cover this building and a fair bit of the site around the main
    office building.
     
    jas0n, Oct 21, 2006
    #6
  7. jas0n

    linker3000 Guest

    The issue is that if the two endpoints are at a different ground
    potentials, the entire gubbins of two buildings and the ground in
    between looks and behaves like a battery - and you have just strung your
    data wire between the terminals so you get a flow of current through the
    data cable. Best case, this screws data transmission, worse case you
    damage stuff with the voltage difference.

    I once measured the voltage difference between a buidling's earth point
    and some coax that they'd strung to an outbuilding - it came to 70-80v.

    Fibre or wireless would be best
     
    linker3000, Oct 21, 2006
    #7
  8. jas0n

    Dr Zoidberg Guest

    It won't do any harm to try it certainly.
    Pass. We always get people to do it for us at work :0)

    --
    Alex

    "I laugh in the face of danger. Then I hide until it goes away"

    www.drzoidberg.co.uk www.ebayfaq.co.uk
     
    Dr Zoidberg, Oct 22, 2006
    #8
  9. jas0n

    stephen Guest

    Also when you order fibre let them know what you are doing with it as you
    may get different types - e.g in a duct it is likely to be in water for most
    of its life, or if you want to just bury it you probably want an armoured
    type, or yet another flavour if it is going to be on poles with a suspension
    wire.
    you need the right kit - but the kit isnt all that cheap, and some skill is
    required to terminate on conventional connectors.

    tthe connectors also are not cheap. If you end up with a damaged end of the
    connector or grit, then it may damage "stuff" you plug into it, so this is
    one of those areas that can be unforgiving if you go DIY.

    there are a few specialised splicing systems which just need a special tool.

    i suggest you see if you can find a local supplier who can install and hand
    over a working link - at least for your 1st one....
     
    stephen, Oct 22, 2006
    #9
  10. I haven't personally built one but there are a couple of open projects
    with details of how to build optical data links, probably the most
    promising is here: http://ronja.twibright.com/
    You have to make some electronics and hardware construction but it would
    be a very interesting project to try building if you're into electronics.
    Anyway probably not what you're after but might be of interest.

    Tony
     
    tony broughton, Oct 24, 2006
    #10
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