Is it possible to use Skype as a modem?

December 7, 2006 10:08 AM

Finding out for my boss: Can Skype be used as a modem?

No, you didn't mis-read that. He'd like to know if it is feasable to use Skype software as a modem (or component of a modem, with help from other software) to dial into modem-connected (POTS line) facilities that we have, and upload, view or download data from PCs or laptops using broadband or cellular/wireless.

My gut instinct tells me that no, it's not possible (how would the data stream be modulated/demodulated? Plus, skype is encrypted -- doesn't that mess things up?).

I've been searching Google now for 3 days, but putting the words "skype" and "modem" together get me 6 thousand hits about how it's possible to use Skype on 56k dialup. I've varied my search terms to exclude those kinds of results but I can't find anything that fits the bill.

So -- is it possible? Even theoretically? What is available, software-wise, that would make this work? Is there something obvious out there that I'm not even thinking of?

posted by contessa to computers & internet (20 comments total)

Some more info -- the system we need to dial into is on a DEC/Alpha server so the usual Windows sharing solutions (i.e. PC anywhere) might not apply.
posted by contessa at 10:17 AM on December 7, 2006

No it is not possible.
posted by crhanson at 10:17 AM on December 7, 2006

I don't know about in software, but hooking up a real modem to Skype hardware (like this) would work. Skype then essentially acts as a low-quality phone line, so you're baud rates won't be good, but it'll work.

Also, with GSM phones at least you can use them as a real modem without involving Skype. Dial using USB or Bluetooth, the data is sent over the cell network, and the cell provider seamlessly uses a real modem to communicate the last mile to the facility.
posted by cillit bang at 10:19 AM on December 7, 2006

Not with Skype, no. However, the most popular VPN protocol, PPTP, essentially pretends that a connection over the internet is a modem. In fact, the linux PPTP implementations use the same PPP software as you would over a phone line. It would probably be possible to make some sort of connection to your DEC/Alpha server work.
posted by rbs at 10:20 AM on December 7, 2006

cillit bang: i'm skeptical. i suspect the compression they do on voice would totally fuck it up.
posted by rbs at 10:21 AM on December 7, 2006

I don't think you'll get that to work reliably, if it all. Skype specifically mentions that faxing doesn't work over their virtual phone connections and since fax communications are basically just TIFF data sent via a modem, I can't imagine that trying to establish a modem connection over Skype is going to work any better.

As an alternative to Skype, install a serial port to TCP/IP redirector on your PCs or laptops. Then on your corporate network setup a TCP/IP to modem server. Using this setup your laptops and PCs will be able to dial-up to your DEC/Alpha server using a shared modem in your central facility. As an example vendor, take a look at Tactical Software.
posted by RichardP at 10:38 AM on December 7, 2006

i'm skeptical. i suspect the compression they do on voice would totally fuck it up.

Modems produce sounds in the audible range. Skype transmits sounds in the audible range. Why shouldn't it work? They were, after all, created as a hack to get data to travel over a network designed for speech. Yes, compression adds a layer of distortion, but so do phonelines, and modems can cope.

Wack "modem over voip" or "modem over vonage" into Google and there are plenty of success stories. Strangely "modem over skype" returns almost no hits one way or the other.
posted by cillit bang at 10:40 AM on December 7, 2006

Think of it this way - a modem is sending individual bits. Audio compression garbles those individual bits but when they are reproduced on the output end, they kind of sound to the human ear like the bits that were shoved in the other end. Now think of those bits as individual pixels in a 1280x960 desktop image, black and white, on or off. Now save it as a 10kb jpeg file. Will it sort of look the same, to the human eye? Probably, but it won't be anywhere near perfect. Will it look anything like the original on a pixel by pixle basis? Not even close. Next to none of the individual pixels will retain their original color.

[my vote is for not possible without a method for sending bits so slowly that the compression can't muck them up, and that's beyond the scope of your experiment methinks =)]
posted by kaytwo at 10:50 AM on December 7, 2006

Remember that part of any modem handshake is negotiating a mutually supportable speed. This is necessary to deal with line noise, etc. My mother used some kind of primitive phone over powerline adapter in her house, and connected her modem to that (not the same, I know, but humor me). Her throughput was about 1/2 what it was when she plugged directly into a phone jack.

I don't know, but my guess is that if you can make the hardware connection, this would work, but at pretty low bps. At very low bps, modems are only using a few distinct tones, and my guess is that these would survive Skypification well enough to be distinguishable at the far end. So, hey, it might only be 2400 bps, but what's your hurry?
posted by adamrice at 11:28 AM on December 7, 2006

Modems are designed to cope with the sort of distortion added by phone lines (and analog cell phones). They aren't designed to copy with the sort of distortion inflicted by voice compression. You'd probably be lucky to get 9600bps out of it, which might be better than nothing, but it would be miserable for anything interactive.

If you can connect to skype, the right thing to do is probably set up a VPN connection, or some sort of application specific SSL or SSH tunnel if you are likely to be using a connection where some ports are blocked.
posted by Good Brain at 11:34 AM on December 7, 2006

Actually, I think this is possible.
Back when Tivo first came out, you had to pull channel information via a modem. Some of the people back then were already using Vonage for phone service, and found that the Tivo modem would run over Vonage.

Here are some sites with tips:
Site 1

Site 2

Skype is different, obviously, but I don't see why it wouldn't work.
posted by Eddie Mars at 12:09 PM on December 7, 2006

It's been a few years since I've dealt with this, but isn't pretty much everything over 2400bps "clever" in one way or another? Multiple tones sent simultaneously, that kind of thing. Layering "clever" codecs on top of each other doesn't sound reliable to me. Also, what's the maximum window before one end or the other assumes that the data was lost? Latency is going to be higher on a packet-switched connection.

Won't cost much to try it though, I think you should go for it just to find out what happens. My vote is for 300/300, personally.

cillit bang: audio compression algorithms that are optimised for voice do all kinds of clever, lossy things, to squeeze the signal through a narrow channel (MP3 on steroids).

The human voice can't flip from a high pitch to a low pitch several hundred times a second, so the codecs that are used in cell phones, Skype, VoIP, etc., can't handle a signal that does that. If you try it, you tend to get audio salad out the other end.
posted by Leon at 12:20 PM on December 7, 2006

This is pretty much guaranteed to failure, at least with Skype specifically. I have to dial into a conference call and input a PIN with skype and it usually takes me a dozen tries to get simple DTMF tones through.

Now, you can either investigate another VOIP solution, there are plenty out there and some may have more suitable settings for modem/fax use. This is guaranteed to be massively slow though.

Without further details about your specific setup I can't be very useful, but I can think of a few ways of (maybe) getting the end result done.

1) PC Anywhere, but not the way you're thinking. Get a cheap PC, set it up to dial the modem and connect to it via Remote Desktop. You're down to one session at a time, but anything can use rdesktop.

2) If your app is standard TCP/IP, a Linux box with a null modem cable and pppd could probably be made into a gateway.

3) If your app is standard TCP/IP AND it's usually accessible without dialing in, you need a VPN which will solve this nicely.
posted by Skorgu at 1:23 PM on December 7, 2006

Correct me if I'm wrong, but ISTM that a better question is: How can I establish a data connection between my roaming device and a server with a dedicated dial-in modem, without incurring long-distance phone charges?

I would be incredibly surprised to find that a DEC/Alpha server is incapable of running TCP/IP and associated protocols over a modem connection. Even if they're not (because they're running some kind of legacy embedded app instead of a standard OS), a super-cheap Linux gateway box sitting between the server and the modem certainly could (the low performance level required would make such a box cost less than a dialup modem). Which means that the problem can be broken into several sub-problems:

1. How can a roaming device initiate a connection to the server it wants to connect to, without letting the whole world do the same thing?

2. How can digital traffic make its way between the roaming device and the server, without being intercepted or modified by third parties?

The second problem has a standard solution: ssh tunnel. You can run anything through a ssh tunnel that you can run through a modem connection. VPN's are essentially TCP/IP networks built on top of ppp running through ssh tunnels. So the only tricky bit is the first problem.

It ought to be possible to make the following work:

1. Remote station dials the existing modem's phone number, lets it ring a few times, and hangs up.

2. Server (or gateway box) reacts to incoming Ring Indicator signal by waiting until it goes away, then places a local phone call to an ISP, updates a dynamic DNS service to associate its IP with a known DNS name, and starts a ssh server listening for incoming connections on a known port.

3. Remote station dials (or connects by whatever other means) to its own ISP, and initiates a ssh session to the appropriate server on the appropriate port.

Dialup Internet access costs next to nothing these days, and this scheme will certainly perform better than any kind of hack involving Skype or VoIP generally.
posted by flabdablet at 5:44 PM on December 7, 2006

Wow -- thanks everybody for the great answers. Honestly, I don't know what I'll do now but everybody has given me some things to chew on for a while. I think my boss' impression was that this was some easy peasy thing that I could just whip together in half an afternoon, because skype=phone!! and how come it isn't working yet?

With all the ideas here, I can give him a rundown of the alternatives. If I somehow manage to get something working in the next 30 days, I'll update and let everybody know how it went.

Thanks again mefi!!
posted by contessa at 6:07 PM on December 7, 2006

With a low enough baudrate and plenty of error correction, sure. I mean, at worst, you can call and hang up as a way of transmitting information, all without creating a single sound.

The "link layer" is lossy and laggy, and that will cause big problems.

In practice, no, you can't get anything useful out of it.
posted by cmiller at 7:11 PM on December 7, 2006

A note about digital voice compression and data transmission. I have, in situations where Wi-Fi was not available, used my Bluetooth-enabled phone to establish a dial-up connection on a laptop. The phone does have EGPRS, but as far as I can tell the Bluetooth DUN profile is dialing it as a standard voice call over a GSM network (the EGPRS icon never shows). I get the equivalent of between a 16.6k and a 28.8k modem, depending on conditions.

For what it's worth.
posted by Spike at 9:43 PM on December 7, 2006

Spike: That's HSCSD (or possibly ordanry CSD), which I described in my first post on this thread. It's not a voice call until it leaves the cell network.
posted by cillit bang at 10:32 PM on December 7, 2006

Err... yeah. That'll teach me to skim. Thanks for the clarification, though.
posted by Spike at 10:56 PM on December 7, 2006

Tried this when Skype first came out - the best I did was 75 baud, and I was getting a *lot* of Kermit retries.
posted by dmd at 6:13 AM on December 8, 2006