Dial-up Emulation?

[Raven]

Yeah NICs are way better - I just assumed he wanted to do something modem-based for some reason.

 

[wmmullaney]

Yeah NICs are way better - I just assumed he wanted to do something modem-based for some reason.

Because he doesn't have rj45 access in that room.

 

[Ole Juul]

Because he doesn't have rj45 access in that room.

Can you explain what that means? As I see it, it's the computers that have the connectors and not the room. That is, he wants to connect one computer to the other. Perhaps I misunderstood. (again)

 

[jthiemann]

From my quick reading of this thread, it seems to me the OP wants to connect two MODEMS, in a "simulated telco" way. Maybe due to his modern computer not having a serial port (common nowadays) while still having a built-in modem (perhaps it's a laptop).

This is possible, to various degrees, but not necessarily easy. You can connect two modems using phone cable if you add a few resistors, a battery (~ 12V works) and a capacitor (or 2), BUT this will neither provide a dial tone, a ringing signal, etc: you need to make sure both modems can be manually forced into the connected state, and this is hard - for many modern modems impossible. You will not be able to get high speed (>4800 baud IIRC) since the modems would need to negotiate to determine line conditions.

Still, with sufficiently old controllable modems it can be done.

 

[Ole Juul]

From my quick reading of this thread, it seems to me the OP wants to connect two MODEMS, in a "simulated telco" way. Maybe due to his modern computer not having a serial port (common nowadays) while still having a built-in modem (perhaps it's a laptop)..

Exactly.

Still, with sufficiently old controllable modems it can be done.

LOL, this is not a matter of age. Modems connect to modems - that's their job.

 

[tingo]

Exactly.


LOL, this is not a matter of age. Modems connect to modems - that's their job.

Yes, and most modems I used back in the days could be configured to do blind dialing, in other words dial without waiting for a dial tone. In this case, the OP needs to make two modems do a direct connect, without the dialing step.

 

[Maniak]

If your after the real deal, as in you want to hear the modem dial, the other to pickup listen to the screeches you can get a line simulator. Here is a cheap line simulator I found on ebay. http://cgi.ebay.com/Skutch-AS-26-Te...ltDomain_0&hash=item483b16c04c#ht_1666wt_1137

Edit: I've personally used the Viking DLE-200B and the Teltone TLS-3 ones and they worked great. Apparently I sold them way too cheap compared to what they are going for on ebay now.


~Mark

 

[jthiemann]

LOL, this is not a matter of age. Modems connect to modems - that's their job.

True, but modern modems are dumbed down to a degree where they will ONLY go into originate mode if a dial tone is present; send one or more DTMF digits; then a ringing tone.
They will ONLY go into answer mode if the +/- 40 V (min) ringing signal is detected.

The two modems will then perform the V.24bis (or whatever standard) negotiation sequence. This involves sending several test tones and known coded sequences; they will deduce channel conditions (noise profile, near- and far echo, and delay) and adjust the filters and coding schemes accordingly.

Modern hard- and softmodems tend to not let you do this by hand. Noone implements the AT codes that you could force them to do it, or if someone did, good luck finding documentation. I may be wrong, but I have never seen a newish modem tell you how to do this. Things may be different for "professional" (non-consumer) modems. Certainly ones that are in PBX's.

A "telephone line simulator" would certainly do the trick. In fact, I remember seeing DIY instructions for building a "home PBX" in some issue of Elektor in the 90's. That would solve the problem, since it presents the modem with exactly the environment they are expecting to see.

I have a "dumb" line simulator, battery + a few passive components. I wonder if I could make it into a proper "manual" PBX simulator by adding a relay and a ac ringing injector...

 

[Ole Juul]

True, but modern modems are dumbed down to a degree where they will ONLY go into originate mode if a dial tone is present; send one or more DTMF digits; then a ringing tone.
They will ONLY go into answer mode if the +/- 40 V (min) ringing signal is detected.

Thanks for the education. I didn't realize things had gotten that bad. I've never used a softmodem but just assumed they "did their job". In fact I usually just throw out those "winmodem" thingies when I come across them, so that would contribute to my ignorance.

Cheers,
Ole