PPP and AT Command Set - PPP

This is a discussion on PPP and AT Command Set - PPP ; Hi All, If IP passes a datagram of data to PPP containing a series of bytes with value 43 decimal (the AT command escape sequence), PPP does not do anything to escape these values does it? I've got an application ...

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Thread: PPP and AT Command Set

  1. PPP and AT Command Set

    Hi All,
    If IP passes a datagram of data to PPP containing a series of bytes
    with value 43 decimal (the AT command escape sequence), PPP does not
    do anything to escape these values does it?

    I've got an application sending streams of data across a PPP link and
    every so often I find the modem is no longer communicating with the
    application. Upon investigation the modem is in command mode and its
    settings have been screwed up. The data stream are series of voltage
    measurements with considerable precision so there can be just about
    any value in the data and I just want to know if its possible to foul
    up the modem with random data inside of a PPP frame.

    Thanks,

    Ben

  2. Re: PPP and AT Command Set

    stocksb@ieee.org (Benjamin M. Stocks) writes:
    > If IP passes a datagram of data to PPP containing a series of bytes
    > with value 43 decimal (the AT command escape sequence), PPP does not
    > do anything to escape these values does it?


    Technically, it cannot. It's not legal to escape anything in the
    range (hex) 20 through 3F -- and that's 2B.

    The right thing to do is use an AT command to disable the escape
    character.

    > I've got an application sending streams of data across a PPP link and
    > every so often I find the modem is no longer communicating with the
    > application. Upon investigation the modem is in command mode and its
    > settings have been screwed up. The data stream are series of voltage
    > measurements with considerable precision so there can be just about
    > any value in the data and I just want to know if its possible to foul
    > up the modem with random data inside of a PPP frame.


    ATS2=255 should turn off that nonsense. It might not fix the problem
    you're seeing, though.

    --
    James Carlson, IP Systems Group
    Sun Microsystems / 1 Network Drive 71.234W Vox +1 781 442 2084
    MS UBUR02-212 / Burlington MA 01803-2757 42.497N Fax +1 781 442 1677

  3. Re: PPP and AT Command Set

    stocksb@ieee.org (Benjamin M. Stocks) writes:

    ]Hi All,
    ]If IP passes a datagram of data to PPP containing a series of bytes
    ]with value 43 decimal (the AT command escape sequence), PPP does not
    ]do anything to escape these values does it?

    ]I've got an application sending streams of data across a PPP link and
    ]every so often I find the modem is no longer communicating with the
    ]application. Upon investigation the modem is in command mode and its
    ]settings have been screwed up. The data stream are series of voltage
    ]measurements with considerable precision so there can be just about
    ]any value in the data and I just want to know if its possible to foul
    ]up the modem with random data inside of a PPP frame.

    Highly unlikely unless you have been playing with the setup of the
    modem. Most modems are set up to require at least 1 second of no data,
    then three +++ within a second and then one second of no data.

    This is unlikely to occur at random.


  4. Re: PPP and AT Command Set

    unruh@string.physics.ubc.ca (Bill Unruh) writes:
    > Highly unlikely unless you have been playing with the setup of the
    > modem. Most modems are set up to require at least 1 second of no data,
    > then three +++ within a second and then one second of no data.


    That particular mechanism (the guard time; sometimes known as the
    "TIES" [Time-Invariant Escape Sequence]) is patented by Hayes
    (US Patent Number 4,549,302), and some manufacturers avoided it.

    http://www.faqs.org/faqs/modems/ZyXE...ection-12.html
    http://patft.uspto.gov/netacgi/nph-P...S=PN/4,549,302

    Assuming I read that correctly (patents from 1985 had a 20-year
    lifespan, right?) this should run out next year, and we'll then
    finally be able to have reliable modems. Just in time for analog
    modems to be entirely and utterly obsolete. ;-}

    --
    James Carlson, IP Systems Group
    Sun Microsystems / 1 Network Drive 71.234W Vox +1 781 442 2084
    MS UBUR02-212 / Burlington MA 01803-2757 42.497N Fax +1 781 442 1677

  5. Re: PPP and AT Command Set

    James Carlson writes:

    ]unruh@string.physics.ubc.ca (Bill Unruh) writes:
    ]> Highly unlikely unless you have been playing with the setup of the
    ]> modem. Most modems are set up to require at least 1 second of no data,
    ]> then three +++ within a second and then one second of no data.

    I think I still stand by the "most" but I certainly was not aware that
    this was patented. (sheesh).


    ]That particular mechanism (the guard time; sometimes known as the
    ]"TIES" [Time-Invariant Escape Sequence]) is patented by Hayes
    ](US Patent Number 4,549,302), and some manufacturers avoided it.

    ]http://www.faqs.org/faqs/modems/ZyXEL/FAQ/part3/section-12.html
    ]http://patft.uspto.gov/netacgi/nph-Parser?Sect1=PTO1&Sect2=HITOFF&d=PALL&p=1&u=/netahtml/srchnum.htm&r=1&f=G&l=50&s1=4,549,302.WKU.&OS=PN/4,549,302&RS=PN/4,549,302

    ]Assuming I read that correctly (patents from 1985 had a 20-year
    ]lifespan, right?) this should run out next year, and we'll then
    ]finally be able to have reliable modems. Just in time for analog
    ]modems to be entirely and utterly obsolete. ;-}


  6. Re: PPP and AT Command Set

    James Carlson writes:
    >unruh@string.physics.ubc.ca (Bill Unruh) writes:
    >> Highly unlikely unless you have been playing with the setup of the
    >> modem. Most modems are set up to require at least 1 second of no data,
    >> then three +++ within a second and then one second of no data.

    >
    >That particular mechanism (the guard time; sometimes known as the
    >"TIES" [Time-Invariant Escape Sequence]) is patented by Hayes
    >(US Patent Number 4,549,302), and some manufacturers avoided it.
    >


    No, TIES is the mechanism that is *different* from the Hayes
    Heatherington patent.

    The solution is still to configure the modems at each end of
    the link to not switch to command mode as a result of data patterns
    in the transmitted/received data.

    -Greg
    --
    Do NOT reply via e-mail.
    Reply in the newsgroup.

  7. Re: PPP and AT Command Set

    gerg@panix.com (Greg Andrews) writes:
    > James Carlson writes:
    > >That particular mechanism (the guard time; sometimes known as the
    > >"TIES" [Time-Invariant Escape Sequence]) is patented by Hayes
    > >(US Patent Number 4,549,302), and some manufacturers avoided it.
    > >

    >
    > No, TIES is the mechanism that is *different* from the Hayes
    > Heatherington patent.


    Ah, shoot, you're right. I misremembered that part.

    In any event, the mechanism with the guard times that Bill Unruh
    referred to is the Hayes mechanism, and is (still) patented. There
    are modems that do _not_ implement this mechanism and even a few that
    are susceptible to upset by data patterns. The right answer (as we're
    all agreeing ;-}) is to disable the escape character.

    --
    James Carlson, IP Systems Group
    Sun Microsystems / 1 Network Drive 71.234W Vox +1 781 442 2084
    MS UBUR02-212 / Burlington MA 01803-2757 42.497N Fax +1 781 442 1677

  8. Re: PPP and AT Command Set

    James Carlson writes:

    ]gerg@panix.com (Greg Andrews) writes:
    ]> James Carlson writes:
    ]> >That particular mechanism (the guard time; sometimes known as the
    ]> >"TIES" [Time-Invariant Escape Sequence]) is patented by Hayes
    ]> >(US Patent Number 4,549,302), and some manufacturers avoided it.
    ]> >
    ]>
    ]> No, TIES is the mechanism that is *different* from the Hayes
    ]> Heatherington patent.

    ]Ah, shoot, you're right. I misremembered that part.

    ]In any event, the mechanism with the guard times that Bill Unruh
    ]referred to is the Hayes mechanism, and is (still) patented. There
    ]are modems that do _not_ implement this mechanism and even a few that
    ]are susceptible to upset by data patterns. The right answer (as we're
    ]all agreeing ;-}) is to disable the escape character.

    Unless you expect to be needing it. Then you had better make sure that your particular modem
    actually does impliment some sort of protection for the escape characters (like the Hayes
    protection) or you will find yourself with your modem going offline at random times.

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