Host-To-Host Data Sharing via Modem

Discussion in 'Linux Networking' started by Josh Converse, Feb 14, 2007.

  1. Here's my conundrum - I have a remote base node (Slackware 11) of a
    sensor network which aggregates data collected from the various
    sampling nodes in the radio network. This data is stored temporarily
    in a relational database, to be offloaded to a server later. I'm
    trying to transfer that data to a server located at a university
    campus over a 56k Modem. The problem lies in the fact that there is no
    internet access available at this location (i.e. the ISP fees are not
    available in the budget of this project), and the phone call to the
    university is long-distance. This means that the connection will have
    to be (automatically) initiated from the server on campus (Also
    Slackware 11) to the remote site. The point of this question is this:
    What would be an appropriate protocol/application/etc for
    accomplishing this? In my searches, I've come across a few different

    * Initiating the connection and using ppp (I assume from there things
    behave more like a tcp/ip connection)
    * Snagging a terminal using something like mgetty
    * UUCP

    Ultimately speed isn't a serious issue, since the amount of data will
    be small, but reliability is of the utmost importance. I would greatly
    appreciate any input on any of these protocols or others that weren't
    listed. I'm fine with writing scripts to take care of the automation
    portion of things - it's just the communications aspect is a hurdle.
    I've spent a lot of time googling the web and the newsgroups, but I
    feel like my search queries aren't as effective as they could be
    because of my lack of knowledge/intuition on the matter. I have no
    problems with doing lots of research on the topic, so even if anyone
    has some starting points, it would be greatly appreciated.

    Thank you for your time and energy!!
    Josh Converse
    Josh Converse, Feb 14, 2007
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  2. Josh Converse

    David M Guest
    David M, Feb 14, 2007
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  3. Josh Converse

    Moe Trin Guest

    On 13 Feb 2007, in the Usenet newsgroup comp.os.linux.networking, in article
    OK. Key point is that there is a modem that can "answer the phone"
    at this remote site. That's all that is needed.
    ppp connection - the remote becomes a mini ISP, and you dialin from
    the university. The university end is merely a cron-job to initiate a
    connection, download a file when connected, and hang up. See the
    PPP-HOWTO and Bill Unruh's web page at or I'd set a cron entry
    like "03 05 * * * /usr/local/bin/" (assumes Dillon
    cron normally found in Slackware), where '' is a dumb
    script something like

    exec /usr/sbin/pppd connect "/usr/sbin/chat -f /etc/ppp/dialscript" lock \
    defaultroute noipdefault nodetach /dev/modem 115200 crtscts idle 20 \
    user datagrabber

    and /etc/ppp/dialscript contains a simple string to make the connection,
    such as


    The file /etc/ppp/pap-secrets would contain "datagrabber * p42Sw0rD"
    as appropriate. /see the ppp and chat man pages for the meaning of the
    various options. The file '/etc/ppp/ip-up' can be used to kick off
    an FTP data retrieval. The 'idle 20' in the script causes pppd to
    disconnect after 20 seconds of inactivity on the link. The 'AT&F0'
    is suitable for nearly all modems - US Robotics want 'AT&F1'. See the
    manual for your modem.

    On the remote system, you run a "ppp server" as detailed in the web
    page and HOWTO. I'd recommend using PAP (or CHAP) authentication rather
    than an old fashioned UNIX style "Login:" prompt. If you use CHAP, the
    file on the box dialing in changes from 'pap-secrets' to 'chap-secrets'
    and no other change is needed.

    As far as using UUCP - that's also a possibility, though it's rarely
    used any more. There is a UUCP-HOWTO, and an entire chapter in the
    Linux Network Administrator's guide available at any LDP mirror if it's
    not on your system as well. Try
    I'd suggest the pppd solution, as it's a pretty solid protocol that's
    been around for years (as has UUCP - but pppd is in wide use current;y).
    You grabbing data, and doing any housekeeping then becomes a simple
    networking task. Using a non-obvious username (and good password) will
    protect you against any phone phreaks that may still exist and happen
    upon the telephone number.

    Old guy
    Moe Trin, Feb 14, 2007
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