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Asterisk and dialup modems


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#1 darkslider

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Posted 14 November 2005 - 10:24 PM

I'm looking for a solution using Asterisk as a means of getting an inbound dialup connection to my box, where the dialup user will connect to a shell. Since it's a remote server, modem hardware is not an option. I'm fully aware that even the ULAW codec causes data attenuation, but tat's not an issue since the modem connection will be used at a fairly low bit rate. If you know how to do this, please let me know. :borg:

#2 BlackRatchet

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Posted 15 November 2005 - 12:15 AM

I'm looking for a solution using Asterisk as a means of getting an inbound dialup connection to my box, where the dialup user will connect to a shell. Since it's a remote server, modem hardware is not an option. I'm fully aware that even the ULAW codec causes data attenuation, but tat's not an issue since the modem connection will be used at a fairly low bit rate. If you know how to do this, please let me know. :borg:

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A lot of the concepts are explained in Vox's how to wardial with VoIP. The issue isn't the attentuation, but mostly the lag. Modems don't like asynchronus data.

EDIT: 1337th post!

#3 darkslider

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Posted 15 November 2005 - 12:58 AM

A lot of the concepts are explained in Vox's how to wardial with VoIP. The issue isn't the attentuation, but mostly the lag. Modems don't like asynchronus data.

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You completely missed the point. I want to receive inbound modem calls, to access a shell via modem, not dial out with a modem.

#4 Strom Carlson

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Posted 15 November 2005 - 02:39 AM

A lot of the concepts are explained in Vox's how to wardial with VoIP. The issue isn't the attentuation, but mostly the lag. Modems don't like asynchronus data.

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You completely missed the point. I want to receive inbound modem calls, to access a shell via modem, not dial out with a modem.

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Ratchet suggested the read because although the article deals with outbound rather than inbound calls, a lot of the issues you'll run into (latency, packet loss, and so on) are the same.

As far as actually getting asterisk itself to answer a modem call goes, though, I don't know if it's possible without extra hardware. Theoretically, if there were some kind of soft modem for linux that you could pipe audio to and from, that might work. The capability to do the audio piping with asterisk is definitely there, since that's what I use to stream binary revolution radio when we do the live show, but I don't know of any sort of modem emulator that would work entirely in the realm of audio piping. Perhaps there's someone on these forums that knows more about that than I do.

If you do have two PCI slots in the remote server and have the option of populating them, you could stick in a Zaptel card and a modem, then run a very short modular mounting cord from one to the other. Calls come in via voip, the zaptel card rings the modem, modem answers, and all is well within your rackspace.

#5 Dr^ZigMan

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Posted 15 November 2005 - 11:04 AM

Please forgive me for saying so, but I don't understand the purpose of what your trying to do...

You want people to be able to call in and have a shell right? Why use asterisk? Have one modem that people can call, and then jsut set up SSH access for the internet (realm of VoIP). Is there something else you wanted to do that makes you want to use asterisk?
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#6 BlackRatchet

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Posted 15 November 2005 - 11:10 AM

You completely missed the point. I want to receive inbound modem calls, to access a shell via modem, not dial out with a modem.

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It was meant as "look at all the crazy crap you have to do for outbound, you're going to have to tweak the hell out of your setup the same way for incoming"

To put it simply: Don't do this. It will be absolutely horrid, very unreliable, and probably dependent on the phase of the moon. VoIP can do lots of things right now. Sadly, this is not one of them.

#7 unity

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Posted 15 November 2005 - 01:15 PM

I'm able to get acceptable quality on 2400 baud with u-law.

#8 darkslider

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Posted 15 November 2005 - 01:27 PM

Please forgive me for saying so, but I don't understand the purpose of what your trying to do...

You want people to be able to call in and have a shell right?  Why use asterisk?  Have one modem that people can call, and then jsut set up SSH access for the internet (realm of VoIP).  Is there something else you wanted to do that makes you want to use asterisk?
-Dr^ZigMan

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Because as stated I can't attach hardware to the server. I have SSH access but the problem is that I want to give my friend, who has a DOS palmtop, dialup access to the shell so that he can use Lynx and such.

#9 darkslider

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Posted 15 November 2005 - 01:40 PM

You completely missed the point. I want to receive inbound modem calls, to access a shell via modem, not dial out with a modem.

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It was meant as "look at all the crazy crap you have to do for outbound, you're going to have to tweak the hell out of your setup the same way for incoming"

To put it simply: Don't do this. It will be absolutely horrid, very unreliable, and probably dependent on the phase of the moon. VoIP can do lots of things right now. Sadly, this is not one of them.

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Well, you won't acheive decent dialup speeds, but it's good enough for shell access.
The problem is handing the connection off to a soft modem and finding a software modem to begin with. It's hard to find an open source software modem.
/me downloads and plays with IAXModem

#10 Beave

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Posted 15 November 2005 - 03:03 PM

Well, you won't acheive decent dialup speeds, but it's good enough for shell access.
The problem is handing the connection off to a soft modem and finding a software modem to begin with. It's hard to find an open source software modem.
/me downloads and plays with IAXModem

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I've actually been looking for a "soft modem" (modem based in software) for my project IWar. I looked into IAXModem and it's a pretty nifty little thing. Its built off libiax2 (Mark Spencer) and uses spandsp
for signal processing. I could be wrong about this, and I'm still researching it, but it appears
the spandsp won't do standard modem support. Right now, and I could be wrong about this,
it's primarly for class 1 faxes - and some other little signal processing do-da's.

The "idea" would be to add iax2 and spandsp into IWar so you could scan without the need of any hardware. At this point, i'm not sure that's possible with spandsp. I hope I'm wrong.

#11 ro0t2

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Posted 16 November 2005 - 08:59 AM

I too looked at that, looks promising as far as data only the V.22bis was only supported data mode (don't quote me here) others where all fax protocols but if anything looks like a good starting point.

I've only been able to get 1200baud working with modem, ATA etc. but providers I am using are shit so even that is sketchy at best :P there seems to be alot of chatter about building an asterisk modem channel (analog modem) but in my travels have not seen anybody attempting this yet. I was planning on having a crack at it some time in the near future but doubt I would get very far.....possible group project ?? :D

Edited by ro0t2, 16 November 2005 - 09:00 AM.


#12 Beave

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Posted 16 November 2005 - 02:11 PM

I too looked at that, looks promising as far as data only the V.22bis was only supported data mode (don't quote me here) others where all fax protocols but if anything looks like a good starting point.

I've only been able to get 1200baud working with modem, ATA etc. but providers I am using are shit so even that is sketchy at best :P there seems to be alot of chatter about building an asterisk modem channel (analog modem) but in my travels have not seen anybody attempting this yet. I was planning on having a crack at it some time in the near future but doubt I would get very far.....possible group project ?? :D

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My record is 4800 baud that was still usable. For how long? thats another matter.. hehe.

A bundy of mine, JFalcon, who's also doing lot's of weird serial/DATAPAC/network projects pointed me to this.

http://fabrice.bella...r/linmodem.html

Hasn't been updated since 2000.. However, it's a step in the right direction.




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