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Thread: Connecting cable modem with long cable

  1. #1

    Connecting cable modem with long cable

    I was at a LAN party a couple of nights ago and we were trying to connect the cable modem to the network so we could have internet access using a cable that was about 75' long. When we connected it to the router, it the green network light on the back of the modem would just blink steadily and the activity light was flashing, but we couldn't use it. We tried connecting the cable directly from the modem to a non-networked computer, and it did the same thing. We were able to use a shorter cable with no problems, but it wasn't long enough. The long cable worked fine for anything but internet, but we couldn't use it to connect to the modem.

    The strange thing was that we put a hub in the same room as the modem and used the long cable to connect the hub to a computer in the other room, connected the modem to the hub, and connected a laptop using a short cable to the same hub. We could access the two computers on the hub, and the laptop could access the modem, but the other computer couldn't access the modem. The computer connected to the hub with the long cable could network with the laptop, but couldn't get internet access.

    Is there a limit to how long of a cable you can use to connect a cable modem to a computer or hub? This is probably a little confusing, but I'm not sure how to clearly explain it. It just doesn't make sense to me why the modem didn't work with a long cable while everything else did.

  2. #2
    Cyber Techie cy's Avatar
    Join Date
    Dec 2000
    Toronto, Canada
    I cannot 100% sure about this, but the cable that connects cable modem to computer is different from the one connect between router and computers.

  3. #3
    Moderator YeOldeStonecat's Avatar
    Join Date
    Jan 2001
    Somewhere along the shoreline in New England
    I don't know of any limit, and I've gone pretty far with some patch panel work. It's just ethernet, running at 10Base half dup usually.

    The broadband modems are really just bridges, converting the cable signal over coax, or DSL over RJ-11, to ethernet.

    I'm guessing your modem just isn't putting out enough signal strength for some reason.
    MORNING WOOD Lumber Company
    Guinness for Strength!!!

  4. #4
    Registered User
    Join Date
    Aug 2000


    For Ethernet your standard Cat 5 UTP cable can be 100 meters between points. This applies to 10, 100, and 1000 Mbps networks.

  5. #5
    Regular Member JeffL's Avatar
    Join Date
    May 2002
    It could be this, and this is just a guess because you didn't say what brand of modem you have, but if your network was running at 100MB Full duplex and the modem only support 10 half duplex that would cause things to not work.

    I know a 10mb half duplex hub will do the exact same thing as you say when plugged into a non negotiating 100MB full duplex NIC.

    There is nothing wrong with the cable because if it were of the wrong pinout you wouldn't get a link at all and no "green" light.
    Earthlink 7000/512

  6. #6
    Regular Member polishmafia4u's Avatar
    Join Date
    Aug 2002
    i dotn know waht the prob is but lenght isnt it cause im testing 2 different cables right now to make sure they work and one is 103 ft and the other is 78 ft. and both are working fine. must be a different problem


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