Moto Surfboard 5100 Modem Problem

Discussion in 'Mac OS X Server, Xserve, and Networking' started by Tonewheel, Jan 12, 2010.

  1. Tonewheel macrumors 6502a

    Sep 28, 2007
    I have the subject cable modem in my setup here at home. Also 2 Airport Extremes, one of which is set up as a WDS remote. System has been in place for almost 18 months with no issues.

    Last week, the modem started kicking out, at least that's what the front lights were indicating. But the strange thing is that when this happens, connectivity is just fine, no problem whatsoever. A simple reset of the modem and all is well again, until it kicks out again. This usually happens every day or two.

    You can see the modem here, after this happens:

    I called the cable company, and they say the signal is clear and strong. They also said this can happen if a wireless router is used. Perhaps, but it has been trouble-free for 18 months.

    Thoughts? Thanks!
  2. Tonewheel thread starter macrumors 6502a

    Sep 28, 2007
  3. huntercr macrumors 65816

    Jun 6, 2006
    In my experience, when I used to have the cbale co as my internet provider, this sort of thing would happen at least ever 2-3 months.
    ( except that my internet was disrupted ) . A reset always fixed it. They said the same thing to be, about the signal being fine blah blah. I think in reality, there was a grounding issue somewhere, or something.

    But in your case...if it doesn't disrupt your internet, why does it bother you?
  4. CarlJ macrumors 68020


    Feb 23, 2004
    San Diego, CA, USA
    I have an Airport Extreme hooked up to an SB5100 (on Cox Cable in San Diego), in a WDS network with an Airport Express. Works fabulously. Except every once in a while, the cablemodem locks up similar to yours.

    I suspect the excuse about the wireless router is just that, an excuse. They are quick (even trained?) to blame your troubles first on your internal network (how convenient). Remember, you're on the same cable as people in a possibly-several-block area. Someone a couple blocks over gets a new hookup, and maybe the new connections aren't put together as cleanly as they should be. Or maybe the new connections are within spec, but degrade the overall signal a little, and now it's out of spec (or nearly so) over by your house.

    When your modem boots up, it first works out the signal levels needed for receiving data from the head-end (the receive light blinking), then works out the signal levels needed for sending data to the head-end (while the send light is blinking). The thing to keep in mind is that it's sort of a negotiation process, based on the current condition of the local cable loop (and the signal levels being used by all the other cablemodems on the loop). And there are lower and upper limits on both the send and receive signal levels.

    What I've experienced occasionally, is the signal level necessary for sending to the head-end exceeds the level the modem is allowed to send/capable of sending, and the modem essentially gets stuck trying to establish a workable power level for sending. I suspect that this means the local cable network has degraded a bit (oxidation of connectors from weather, or something chewing on cables, or simple overloading, or the problems mentioned above about new installations, or some such). In all cases, pulling out the power and replugging it to restart the modem, gets it to run through the signal level negotiation process again, and this time it works. Until it gets stuck again a few days or weeks later (and I reboot it yet again). Yeah, I ought to report this to the cable company, but haven't gotten around to it yet. Up to you whether you complain or not; you'll probably have to work around the front line tech support who will want a great deal of unecessary plugging and unplugging of equipment, and rebooting of your "PC", before getting to the higher-ups who grok signal levels and such.

    On a SB5100 you can access an internal webserver with some useful diagnostic info by connecting to (since the cablemodem is likely configured to be your gateway for any/all non-local addresses, that url ought to work from any machine on the local network, with no special configuration).

    The page at on my modem usually shows an upstream power level of 55 dBmV, which I believe is that upper limit, the most the modem is allowed to transmit (on this network).

    Lots more interesting information to be found here:

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