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TCPIP over GPRS question

Discussion in 'Electronic Design' started by David Collier, Feb 2, 2006.

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  1. The real question here is - is there a better newsgroup or yahoo group
    or anything to ask this question on?

    We use a Wavecom modem to transmit a TCPIP link over GPRS.

    We work with Linux, and use the TCPIP stack inside Linux. I know some
    modems have a TCPIP stack of their very own, but we consider it would be
    too difficult to wean Linux off this and get it to use the modem's one.

    While a TCPIP link is open, every byte sent to the modem forms part of
    that stream, and we can't send AT commands to the modem to ( for
    instance ) initiate/receive an SMS message, or ask the cell name, signal
    strength or anything. And since we try to keep the GPRS link open all
    the time, that's a bit of an annoyance.


    Wavecom provide a command AT+WMUX, which changes the modem into a mode
    where all AT commands and data are encapsulated in little packets, and a
    flag is added to each packet saying "command", "data", "reply to
    command", etc. if we used this mode we could, in theory, have the best
    of both worlds.

    Trouble is it looks like it would mean diving deep and dirty into the
    depths of Linux, and intercepting all uses of the modem, both in the
    CHAT session which opens + closes the modem, and the PPP s/w which sends
    TCPIP data. I'm not looking forward to that degree of surgery.

    We don't really want to lock in to a single manufacturer, so if this is
    a feature which only exists on this one modem manufacturer's products,
    I'd be less inclined to do the work to use it.

    I have a few questions then...

    1. Anyone done this?

    2. Anyone know if Linux by any chance already support this?

    3. Anyone know if this WMUX command is available on other modems apart
    from this Wavecom one?

    4. I'm aware that there exist modems with a second serial port which
    could help with this, but that looks to me like yet another avenue to
    locking in to a subset of modems.

    5. Any better suggestions?

    David Collier

    email can be sent to , under name [email protected]
  2. Ian Stirling

    Ian Stirling Guest

    I don't know the answers.
    However, I'd approach this by getting pppd to talk to a pipe, not the
    real device, and run a little filter program that then talks to the real

    comp.os.linux.networking may be a better place to ask.
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