Host-To-Host Data Sharing via Modem

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
options:

* 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

On 13 Feb 2007, in the Usenet newsgroup comp.os.linux.networking, in article
<1171416740.898158.137950@s48g2000cws.googlegroups .com>, Josh Converse wrote:

>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.

OK. Key point is that there is a modem that can "answer the phone"
at this remote site. That's all that is needed.

>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
>options:
>
>* 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

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
http://www.theory.physics.ubc.ca/ppp-linux.html or
http://axion.physics.ubc.ca/ppp-linux.html I'd set a cron entry
like "03 05 * * * /usr/local/bin/call.remote.site" (assumes Dillon
cron normally found in Slackware), where 'call.remote.site' is a dumb
script something like

#!/bin/bash
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

ABORT BUSY ABORT 'NO CARRIER' "" AT&F0 OK ATDT2662902 CONNECT \d\c

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 http://tldp.org/guides.html

>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'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