My Phone Techs

Computers & Internet => Computers, Software & Accessories => Topic started by: EV607797 on June 17, 2020, 10:56:25 PM

Title: Modem command issue
Post by: EV607797 on June 17, 2020, 10:56:25 PM
Since most modems use commands comparable to the Hayes "AT" set, I'm scratching my head on this issue I'm having. I have a USB modem 'dongle' that works on a hit-or-miss basis. It used to work flawlessly. I began noticing that many of the integrated modems in systems that I dial into have stopped connecting. Once I started audible monitoring, In noticed that the modems on the far end have started answering in fax mode (an experienced modem user can tell by the sound). I put two and two together and determined that the ones called by this dongle modem are the ones that mysteriously start answering as a fax. The only solution is to reboot the distant systems, requiring a dreaded site visit; the exact reason why we have these modems in the first place.

Another modem I use in my desktop PC has worked flawlessly for years and years. It rarely lets me down, despite the fact that it's hard to get a real phone line any more. Somehow, some way, it always manages to negotiate a connection.

So here's my question. It is obvious that this dongle modem is sending some kind of reversal command to the distant modems to make them start doing this. Again, through the process of elimination, this ONLY happens when I call an otherwise perfectly-functioning modem from the USB modem. What I need to know is what AT command can I send to this dongle modem to disable its fax capabilities and more importantly, how to stop it from sending commands out to the others. I've scoured the lists of AT commands, but the way those things are written isn't very clear to me as to which one is causing the problem. I'd love to disable the fax functionality on this thing entirely, if that's possible.

The terminal software that I am using doesn't seem to send the desired initialization string of commands that I'd like. That's OK, I don't mind just entering the ones that are important each time I use it. I just need to know which command is the culprit for turning my large systems that are hundreds of miles away into fax machines. AT&F and ATZ aren't helping. Any ideas?
Title: Re: Modem command issue
Post by: MacGyver on June 18, 2020, 09:28:44 AM
Ed, this is going old school, but back in those modem days if you had problems connecting we would drop the baud rate. Back in those days to 300 and then work our way up.  I'm thinking set the baud below what a fax uses.  You're probably sending an itit for 9600 or greater.  Try connecting with a forced rate of 1200 or 2400.  It's just a starting place.  Granted if you were connecting to an old Inter-tel cabinet you would have to go on site first and change the jumper, but it would give you intel.
Title: Re: Modem command issue
Post by: silversam on June 18, 2020, 02:35:00 PM
Dear Lord! Modems!

I'm with Trace. Start low and work your way back up - Though there were (AIR) fax machines (Group 1?) that connected at low speed.

Ed, is it possible that the distant ends have changed their DT from CO to VOIP? Could that be causing the trouble?

Back in the mid-to-late'90s I worked on Microwave Radios. We would run fiber (or some other high Speed connection) to some tall building with good roof access. That wass the "A" site. We would then set up numerous short haul microwave radios (mostly 38 Ghz) that shot to buildings in the neighborhood ("B Sites) and used the high speed connection to feed DT and Internet or both to the B-Sites.

But every radio at the A site needed a modem to report back to the Network Operations Center (NOC) if a problem developed (on either end). So the A sites always had a bunch of CO DT coming in from NY Tel to feed them. It was a bear and then one day the new radios came in and......

They were TCP/IP.

What a difference it made in the maintenance! We started routines pulling out the old units and replacing them. I think the company figured that with the cost of DT, the payback was only going to be a couple of years - if that much (I'm trying to remember if we rotated them into the B Sites, but I can't remember).

Anyway, no one realized what a bear modems were (compared to TCP/IP) until we didn't need them anymore....

I'll look to see if I can find any modem books. I used to have them, but I think they're all gone by now.

Title: Re: Modem command issue
Post by: EV607797 on June 18, 2020, 09:53:58 PM
Most are NOT using VoIP for at least the modem lines.  Actually, the ones using IP are performing better than those that are not.  I've tried adjusting the baud rates all the way up and down, but it had no effect.  Keep in mind that every time that this modem manages to connect, it turns the modem at the far-end into a fax and I'm shot dead for the session.  I don't have the luxury of poking around too much since each time, it results in having to reboot some very large systems.  That's not something we can do on a regular basis.

I'm sure it's a device status setting to disable the fax functionality on my end.  I just need to know which AT command that it is.
Title: Re: Modem command issue
Post by: MacGyver on June 18, 2020, 11:35:40 PM
Do you think your modem is throwing the first fax tone, or could it be that the far end throws out a fax tone to see of that's what's calling, and your modem recognizes it and responds in kind.  Whereas if your desktop modem has no fax capability it's incapable of acknowledging it.  Either way I see what you mean about an AT command, I just don't know if those work on what you have.  Still, if you're truly locked at 2400 baud, no fax in the world is going to accept that.
Title: Re: Modem command issue
Post by: telemarv on June 19, 2020, 07:47:56 AM
Try reinstalling your com software. There might be a button during install to enable/disable fax mode.