Self-Contained POTS System?

[dcr]

Has anyone ever tried, or is it even possible, to build an analog telephone system?  Not one that would connect to the outside world, but one that would be limited to your house or building.

I've tried to research this before, but so much information on phone systems these days leads to VoIP systems that I've found it difficult to find info on what it would take to create something like this.

The purpose would be to demonstrate (or just play around with) modems.  You'd need to be able to manage telephone numbers (both for the software to understand and also to demonstrate tone dialing) and you'd have to have a dial tone and busy signals.  And of course you'd get all the old modem noises.  As a bonus, maybe you could make actual phone calls from one room to another.  (If you've got the system, you might as well make additional use out of it.)

You could have one computer running a BBS and another connecting to it as a client.  You wouldn't have outside connections but this would be for demonstration and historical replication of how computers used to get online.

You might also set a computer up as a server and allow older Macs (those that could use modems but didn't have networking options) to dial in and connect to the Internet via Lynx or whatever software you might have set up on the server.

I would think it must be possible to build such a system.  Whether it could be done economically is another matter.  But it would be neat to be able to replicate the experience of the modem era.

 

[joethezombie]

I came across this a little while ago, and wanted to experiment with an Asterisk PBX, but never got around to it.

http://www.insentricity.com/a.cl/230/using-modems-without-phone-lines

Maybe something like that?

 

[nickpunt]

 

[dcr]

Close but it looks like both of those examples rely on a connection to the outside world whereas way I'm hoping for would be fully set-contained.

I have looked at Asterisk before but it just seemed that most of the documentation and tutorials focus on VoIP services and not really on how to create an internal analog phone system.  I also looked at Asterisk for building an info-on-demand type system whereby you could call into the system (this time from the outside world) and, once connected, you'd enter a numerical code on the touch tone phone and a specific audio file would play.  I didn't get anywhere with that idea either.

 

[Dog Cow]

Has anyone ever tried, or is it even possible, to build an analog telephone system?  Not one that would connect to the outside world, but one that would be limited to your house or building.

It's possible up to varying levels of sophistication. The absolute simplest system is you can rig two phones with a 9-volt battery to make 2-way "field phone" setup. You'll have to cut a RJ-11 modular cord to do it. There's no dial tone or dialing or ringing. This is as far as I've gone.

You can extend this concept and create a home intercom system with a switch board. Getting the phones to ring can be done the old fashioned way with a hand crank. Ring voltage is a high(er) voltage at an unusual frequency (selected I believe because it directly powers the ringer solenoids in phones with real bells).

This is still within reach for most people at home. But still there's no dial tone, and no dialing.

I would imagine by now there are "switchboards on a chip," some kind of small, integrated Touch-Tone system that could be installed to run a private telephone network. I've never looked into it, but I have no doubt that such a system is available today.

 

[joethezombie]

Close but it looks like both of those examples rely on a connection to the outside world [...]

I don’t see where either of those projects rely on a connection to the outside world.

 

[Trash80toHP_Mini]

Probably any multi-line POTS phone system for a small office would work. Pretty sure my old Merlin system would operate off grid. When it died I had another brand in stock that a friend gave me when his company upgraded. Almost certain you could use the "office to office" extension dialing and paging features within a home orbuilding.

Wouldn't be surprised if you could hook it up to a cell phone for grid connectivity.

 

[NJRoadfan]

They made dummy adapters that allow two modems to communicate with each other. Basically it generates the correct line voltage and dummy ringback tones to fool a modem into thinking its a real line. What you really want is an old PBX system that supports direct connection of analog phones. Something like the AT&T (later Avaya) PARTNER system works for this and generates dial tones and supports direct dialing between extensions.

 

[TechEdison]

If one of your goals is to just connect to the internet (which it may not be), you can do it much easier using serial. I created an updated guide on doing that. I'm sure it could be somewhat useful at least:

 

[PowerPup]

If you want to go hardcore and build some circuits, you can totally make a self-contained PBX system:
http://wandel.ca/homepage/pbx.html

http://www.instructables.com/id/Homemade-Intercom-PBX-With-GPIO/

 

[Trash80toHP_Mini]

What I think of as the most cool application would be to tie together a collection of vintage single line phones.

Recreating a PhoneNet type setup over a single POTS line in a home that mimics Ma Bell. Using something on the order of a Pi Zero Plus or a miniaturized PLDthingie tucked away inside each phone ought to work. You'd need to provide tip/ring power somewhere along the line.

I imagine doing it as Ethernet ought to work over 2 pair copper, no?

 

[dcr]

What you really want is an old PBX system that supports direct connection of analog phones. Something like the AT&T (later Avaya) PARTNER system works for this and generates dial tones and supports direct dialing between extensions.

That sounds like that would be what I am looking for.

Outside connectivity would be a bonus but the main system needs to be self-contained.  If I have, say, three computers with modems, I don't want to have to have three phone lines (i.e. $$$).  And not being connected to the outside world would allow you to do stuff like dialing 555-2368 which would connect to a device that would play the Ghostbusters theme song or whatever you wanted to do.

Once I had such a system, getting those computers on the Internet wouldn't be difficult.  I used to offer dial-up Internet services and have the equipment for that end of things, although I would probably need to make use of the proxy setup described in the post TechEdison linked to.

 

[MacintoshMan1999]

Would this work?

https://www.amazon.com/KOOKYE-F208-Exchange-Telephone-Extensions/dp/B01HCUNDWC/ref=sr_1_3?ie=UTF8&qid=1524709887&sr=8-3&keywords=PBX&dpID=41pbjhLZkaL&preST=_SY300_QL70_&dpSrc=srch

 

[Cory5412]

A PBX would do this. JT mentioned the AT&T Merlin which is itself collectible, so unless you're also specifically an AT&T nerd, you might avoid that one, but newer AT&T and then Avaya/Lucent systems like Legend should also work.

I have a bit of a newer system, which also supports VoIP, although I don't have it on my POTS line or on my network, an IP Office Small Office Edition. These were available in a few configs. Mine has room for 4 analog extensions and 8 digital ones, although there was a version for 8 analog devices. They can dial out to the CO lines or in to other analog extensions.

I don't know what kinds of speeds you can expect out of such a device. My guess is it'll be limited, especially if you're thinking about like newer modems - those might be best if you coupled them directly, since most of these PBXes are likely to suffer the same problems your Internet did if it went through an SLC96 back in the '90s: the overall bit rate would be limited severely by compression used to squeeze a bunch of lines into a certain capacity. (There were work-arounds later on, but you had to complain to your RBOC to fix it, but at least in Bell areas Qwest bought, RTs later became areas where remote DSLAMs were installed, which today means your best bet at fast Internet in those areas, but that's a different thing.)

Anyway, the KOOKYE device linked will probably also work, there's a few other modern mini-PBXes that allow a few internal analog lines, but i don't know how well they work outside of voice and fax specifically. (Notably, I actually haven't tested my IPOSOE in this config, so I know it'll "work" but i don't know for sure that it'll work, it's on my long list of things to eventually work up energy and do.)

 

[TrueNorthStrong]

Just chiming in because I have this setup at home. Mind you I got quite lucky with the finds needed to get it running. 

I use my Cisco 2821 router with a WIC-2AM installed for the ISP end of the connection. Those are both cheap and plentiful, and configuration is easy (if you've worked with Cisco gear before). 

At for the POTS network- I managed to find a MicroSeven LS-200 phone line simulator for a heck of a lot less than they are sold for online. Supports just about everything you could possibly want it to, but I don't have the DTMF option board. Oh well, I'm only doing one call at a time. 

Aside from that, it's just plug the phone lines in, dial "041" (the first line is hooked to the Cisco router), and the modems do the rest of the work. 

For network connectivity- I have the Cisco hooked up to my LAN, and because I'm too lazy to add a new route into the house router, I use NAT (PAT) to translate the dial-up network address to a LAN address.

I've also hooked up an RPi running LegacyProxy to translate HTTP 1.1 requests to modern requests, and to strip newer content that can't be read by older browsers. 

I've also picked up a Panasonic D816 PBX system, which I'm going to look into mirroring this solution to see how it compares. Theoretically it should be the same, aside from what number to dial. If you'd like me to test it with the PBX system, let me know. D816s are common enough to find (as are regular PBX systems), and so may be the least expensive option to get it up and running. 

 

[Cory5412]

Idly: using one of the more sophisticated PBXes, it would be neat to see if you could create a ring group with one number for that wic-2am card, or larger such installations. Potentially useful if you have a bunch of different systems and you don't necessarily want to have to keep track of which lines you're using.

I've heard of some bigger Cisco gear that dealt mostly in like either ISDN or T1 connectins you might be able to break out, but I don't know at what scale that becomes worth doing vs. having one (or maybe two?) of those wic-2am cards. There appears to be some (possibly less common? I don't know what Cisco gear is like) 8 and 16 line cards, potentially neat if you were setting something up for a bunch of people or you had a bigger PBX. The NM-8AM seems slightly older, but good if you aren't relying on getting like 56k out of this kind of setup. (LBR: almsot nobody connected to dial-up at 50k or more anyway )

Though, I have never tested the IPOSOE like this and couldn't vouch for whether or not you'd even be able to get 33.6 through that kind of system, so something simpler that just creates the direct electrical connection may end up being better.

 

[TrueNorthStrong]

Cisco does have ISDN and T1 interfaces, but keep in mind that when you start getting to digital connections, you start having problems in that the underlying infrastructure is a lot more complex than POTS. Those are both based on DS0 bundles, so while they're voice channels, I wouldn't know enough about actually breaking them out to single phone connections. 

One route I didn't end up taking (because I bought the LS-200) is that Cisco does make FXS modules. These provide phone line simulation, at least to the basic capacity of dial tone and dialing capabilities. Plus, they'll work with 28XX series routers, so it does streamline the setup and remove the need for a separate box to simulate the line. Single console for management, too. 

You can probably find it for a much better price than a dedicated simulator (Like this one for $44), but it might not provide the flexibility you want. I've also never worked with one of those cards, so I can't guarantee it'll work (although I highly doubt it won't).

I'll look into more complex, enterprise-level configurations of this sort of thing, but to be frank it doesn't really interest me. Having the Cisco router act as my dial-up ISP for modem connections is about as far as I'll go with dial-up itself. Beyond that, I'm just going to hunt around for an inexpensive 1U DSLAM to I can start simulating DSL connections to modems. With the way things are headed, that'll soon be a legacy technology.

As for having more ports- why? Unless you're simultaneously dialing several computers at the same time, I see no need. You've also got to worry as to whether the POTS simulator supports multiple calls- mine does not, and it isn't a common requirement. 

I really ought to test out the connection speed I'm able to pull with this setup, but I'd imagine it's quite high. The "local loop" in this case is extraordinarily short, so there's virtually no insertion losses or environmental conditions that would normally degrade the signal. My box provides the ability to simulate various lengths and noise conditions, too, so I've got a lot of fiddling and testing to do in my spare time. 

 

[Cory5412]

The multiple calls thing would depend on what systems you have with modems and whether it might be relevant to use more than one of them. If, for example, you've got a couple of old Macs with modems, you might dial them both into your LAN and use that to negotiate a file transfer, or connect them both to a server, or transfer files from one to a server while you hop on the other machine do connect to the IRC network, or whatever strikes your fancy.

Ultimately, doing that would rely on having a real PBX, and not just a line simulator.

And, yes, I have no trouble believing that in a home environment using reasonable wiring and good moddems, you'd have no trouble reaching the maximum sync speed for the modems involved, at least with a plain line simulator. My concern with PBXes is that internally they tend to be a little more like telco remote terminals in that they use digital compression to move voice data around.

ISDN or T1 out of a Cisco product would actually be extremely interesting, just idly. I'm not familiar there, but I know some of the higher end small PBXes had ISDN and T1 options available, so it's not strictly out of the question that you could get a Legend or IPOSOE or the contemporary Nortel (BCM50) with ISDN connectivity and connect it to something upstream for however many active calls. Most PBX systems support several when using digital uplinks. Others are specified in terms of how many trunk/CO lines they have and how many internal extensions they have, and the extensions can either call each other or they can call out via the trunks. (8+ or 9+ dialing, basically.) How that's handled would be worked out with the phone company and whether they just send you four POTS lines that are all trunked to one number or one ISDN or a fraction of a T1 that can handle, say, 4 calls, really depends on where you are and what kind of money you have.

Anyway, not out of the question and it could be fun to try.

Speaking briefly to the DSL stuff, I'd be interested in hearing why you aren't interested in moving up on the phone system thing, but you would build a mini DSL network.

Industrial Point-to-point VDSL/VDSL2 links would be interesting from a practical perspective, say to link an out-building if you had a larger piece of land, but doing that with a DSLAM wouldn't make sense unless you had a couple such out-buildings, and even then, you'd need to reach a certain point before it would make sense to buy, say, an 8-port desktop DSLAM (something last i checked XyCEL makes or made) rather than just putting in a few of the host modems in one spot.

To me, there's a little less interest in doing that unless I were to suddenly come into possession of a town and its associated local phone infrastructure, or something smaller but similar like a campus environment.

 

[TrueNorthStrong]

I see what you're saying. The PBX that I've got can handle an ISDN expansion, so I'll keep my eyes open for one and also look into snagging an ISDN interface for my Cisco. It'll take some time for my budget, but if that ends up going well I'll post on the forums about it. 

Quite frankly I'm really only interested in "home" technologies. ISDN and T1 lines aren't what you'd have at home, and so I don't have the memories of those like I do with dial-up. 

It's also a limitation if my knowledge regarding the technologies involved. I know enough about standard POTS, but it's relatively simple. I've got a lot to learn about ISDN and the such, which is becoming harder as it is phased out from most courses.

As it stands for me, given the space I have, and the number of systems, having multiple calls simultaneously isn't anything I will need. 

As for DSL- again, it's more of a home technology. It's a little more graspable for me at the moment. 

Isn't a DSLAM necessary for a DSL connection? I'll preface this by saying this is the limit of my knowledge, but isn't the DSLAM the piece that injects the digital signal into the telephone line on the local loop? I can't imagine how I'd set it up without one, unless you're more knowledgeable in the matter.