Encapsulating packets for multiplexed modem? - PPP

This is a discussion on Encapsulating packets for multiplexed modem? - PPP ; I'm trying to use an external USB wireless modem in a "multiplexed mode". This means that the modem will respond to PPP commands and AT commands at the same time, provided that they are couched in simple packets that disambiguate ...

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  1. Encapsulating packets for multiplexed modem?

    I'm trying to use an external USB wireless modem in a "multiplexed
    mode". This means that the modem will respond to PPP commands and AT
    commands at the same time, provided that they are couched in simple
    packets that disambiguate them to the modem.

    One packet header tells the modem that the packet is meant to be
    processed as data (PPP). Another packet header informs the modem that
    the packet is meant to be processed as an AT command.

    This is useful because the modem is aware of certain things that it
    would be useful for the Linux box to know and keep track of -- signal
    strength, location, and a number of other pieces of information. That
    information can be retrieved with AT commands; I'd like to get it
    without having to tear down and re-establish PPP.

    I'm trying to figure out which functions in Linux (kernel 2.4.32) I
    will need to modify in order to do this. I'm looking at
    ppp_async_push() and ppp_async_input() in ppp_async.c. Can anyone
    with insight into the kind of thing I'm trying to do let me know if
    I'm headed in the right direction, or let me know if there's some
    other direction I should be going in, or just be willing to lend me
    some friendly advice? Kernel hacking has got me a little nervous.


  2. Re: Encapsulating packets for multiplexed modem?

    "addams013" writes:

    >I'm trying to use an external USB wireless modem in a "multiplexed
    >mode". This means that the modem will respond to PPP commands and AT
    >commands at the same time, provided that they are couched in simple
    >packets that disambiguate them to the modem.


    >One packet header tells the modem that the packet is meant to be
    >processed as data (PPP). Another packet header informs the modem that
    >the packet is meant to be processed as an AT command.


    >This is useful because the modem is aware of certain things that it
    >would be useful for the Linux box to know and keep track of -- signal
    >strength, location, and a number of other pieces of information. That
    >information can be retrieved with AT commands; I'd like to get it
    >without having to tear down and re-establish PPP.


    >I'm trying to figure out which functions in Linux (kernel 2.4.32) I
    >will need to modify in order to do this. I'm looking at
    >ppp_async_push() and ppp_async_input() in ppp_async.c. Can anyone
    >with insight into the kind of thing I'm trying to do let me know if
    >I'm headed in the right direction, or let me know if there's some
    >other direction I should be going in, or just be willing to lend me
    >some friendly advice? Kernel hacking has got me a little nervous.



    It should. And playing with a carefully crafted piece of code should get
    you far more nervous.
    Anyway, the modem already has such. One second of abxolute silence, +++ and
    another second of absolute silence tells teh modem to go into command mode.
    And then there is an AT commend (ATO0 on the modem I have immediate access
    to) to tell the modem to go back into
    communication mode. Of course, the far modem may well hang up the line when
    your modem behaves in this way, but you cannot make an ommelete without
    breaking eggs.

    Alternatively buy a modem with separate command and data links. I believe
    they exist-- and cost a lot. But then if you value your time at more than
    10 cents an hour, you would probably be able to buy the modem manufacturing
    company with the time you spend on your project.

    I do not know if this is friendly advice.


  3. Re: Encapsulating packets for multiplexed modem?

    "addams013" writes:
    > I'm trying to figure out which functions in Linux (kernel 2.4.32) I
    > will need to modify in order to do this. I'm looking at
    > ppp_async_push() and ppp_async_input() in ppp_async.c. Can anyone


    Yep, this is the right place to be looking.

    > with insight into the kind of thing I'm trying to do let me know if
    > I'm headed in the right direction, or let me know if there's some
    > other direction I should be going in, or just be willing to lend me
    > some friendly advice? Kernel hacking has got me a little nervous.


    There's nothing quite like working without a net.

    --
    James Carlson, Solaris Networking
    Sun Microsystems / 1 Network Drive 71.232W Vox +1 781 442 2084
    MS UBUR02-212 / Burlington MA 01803-2757 42.496N Fax +1 781 442 1677

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