In article <9a2c1dd5-79bc-4581-9874-cee7bb2adb65@60g2000hsy.googlegroups.com>,
<tc@stoneblue.me.uk> wrote:
>I'm trying to do something similar and am struggling !
>
>I have a bunch of dataloggers at remote locations with gsm modems. On
>the PC at base I have standard analogue modem on a BT line, which I
>use to download data and manage the loggers. I want to discard the BT
>line and to see if I can do this operation via VOIP or another
>internet based process. Download speed only needs to be 9600 (the max
>speed for the GSM modems).
>
>There are useful articles on the principles at
>http://www.modemsite.com/56k/voip.asp
>& http://www.voip-info.org/wiki/index....%20over%20VOIP but
>I have no found any info on a practical "how to" solution. The
>problems seem to be to do with the compression codecs used in VOIP
>being designed for voice and not data - surely there is a software
>solution somewhere ???
>
>Any ideas/help would be appreciated
If you can use VoIP, them you have broadband... If you have broadband
then you either have cable or ADSL, and if you have ADSL, then you need
a phone line - which you can use for a modem...
I'll assume you have cable and you want to save money by dropping the BT
line...
Modem and FAX data don't work well over VoIP because, while we humans
can ignore then odd click, packet loss, or duplication, a modem can't.
On top of that is the digitization of the signal - and if you compress
it with a lossy compression, then you can not reconstruct enough of the
modem signal at the other end to reconstruct the data stream. (Even if
the modem can actually recognise the resulting compressed noise!)
So far better to keep the PC at base with it's standard BT line and
modem to collect data from the remote sites - put ADSL on the BT line,
and use that to send the decoded data to other sites, as required.
How much data are we talking about here? If it's < 160 bytes at a time,
then why not send it as a TXT message? You could then have a GSM modem
on the PC, and from there send the data out via broadband (Cable,
I assume, since if you wanted ADSL, you'd have the phone line)
You could just try it and you might get away with it... Get an ATA
and a VoIP account with a geographic number - make sure the ATA is fixed
to use G711a and connect a modem to the ATA and see what happens ...
If you want to eliminate cables, get a VoIP provider that can give you
an IAX feed and get IAXMODEM -
http://www.voip-info.org/wiki/index....erisk+IAXmodem
Your PC will need to be running Linux though.
Another way might be to get someone to run the "modem" for you at the
end of their VoIP connect - if they have a better than ADSL/Cable
quality connection... Then get that site to post the data to your
processing PC via the Internet... (Or have it processes at a remote site
doing this for you). However I'm guessing that as you want to dump the
BT line to presumably save £11 a month, you're doing this really on the
cheap, so who knows if you'll get anyone to let you do this who might
charge you less than £11 a month. (But if this is an option, drop me an
email!)
Gordon