4 wire (600 ohm) VoIP adapter

[rcourtney]

I am too lazy to build up a 4 wire adapter.  I am sure I had seen something in the past, an audio development board perhaps that was E&M compatible.

Any ideas?

[leejor]

While there very well may be some specialty product out there (I wouldn't hold my breath), every Gateway and/or ATA that I've ever come across is a two wire device. I can't see there being a huge market for something like that.
I've been using VoIP for 20 years now, starting with the Sipura devices.

[dsk]

This is something I never have even heard about, what kind of systems used 4 wires, and why?  All my phones use only 2 wires, from the old magneto phones to those "modern ones" with push buttons.  But I have to admit that this made me curious, and I want to learn more. 

[5415551212]

This is something I never have even heard about, what kind of systems used 4 wires, and why?  All my phones use only 2 wires, from the old magneto phones to those "modern ones" with push buttons.  But I have to admit that this made me curious, and I want to learn more. 

4-wire circuits are two of the pairs like you have 2 pairs off a regular phone handset to a phone; 1-pair from the transmitter (mic) and 1-pair to the receiver (speaker), those two audio paths are arranged so that the respective signals are transmitted in one direction only by one path and in the other direction by the other path (they cross over at the switch).
In the old phone company telephone exchange my understanding is they separated back out the two paths with a audio transformer similar to the ones in a phone network.
The cross bar switching happens in baseband audio (4-wire) then when it leaves the switch the last stage is to combine back into two wires (one pair).
If I am not mistaken this is how the crossbars switched, this is my very limited knowledge, hopefully others will chime in and add or correct me.

E&M or Earth and Magnet is a type of signaling you could have on trunk lines from a PBX to a central office, small independent central office to a competitors central office, inter phone company switching lines, basically trunk lines between telephone switches;
On the physical wiring level the E&M pair is for controlling the calls 'supervision'; Wires E and M.
Imagine it as a precursor to a digital T1 / BRI. But with only two channels, voice and control.
There were types of E&M that could use either audio interface type (two-wire or four-wire).
With the 'two-wire' implementation, full-duplex audio signals are transmitted over a single pair which consists of tip (T) and ring (R) leads (like a normal phone line) and there are E and M control leads (two total pairs)

The 'four-wire' implementation provides separate paths to receive and send audio signals which consists of T, R, T1, R1 audio leads and there are E and M control leads (three total pairs), so to accommodate these 4-wire circuits CO switches would have line cards or ports that bypassed the two wire - four wire conversion.

I don't think normal subscribers ever got 4-wire service. There was the AUTOVON system, that used 4-wires.
Before DSL and ISDN 4-wire circuits were sold to universities and corporations as 'tie line' circuits for early computer modems, this was 'local loop' service or 'dedicated line', I am not a expert on this but I believe the advantage for early computer modems was speed and that they could bypass the distortion caused by audio transformers when the circuit is converted back and forth to two wire.
Also by the 1970's when 'mini' and main frame computers would have been starting to use modems on scale, here in the US the phone company was a highly regulated monopoly so probably less hassle with regulators whom had to review their rates if they offer the same 'tie line' service for modems as they did PBX's.
I am not really an expert on any of this but thats my basic understanding links below:

Paper on EM signaling
https://www.cisco.com/c/en/us/support/docs/voice/h323/14003-e-m-overview.html

[leejor]

I had worked with a lot of 4-wire circuits during my career. Usually it was used when long(er) distances were involved as it was easier to amplify when the audio was going in one direction. But, I've seen it used on trunks from a PBX to a central office, if requested by the customer. It was also easy to interface to channel bank cards designed for this.

 There are (or, at least, used to be) 4-wire to 2-wire converter cards, that are meant to interface to either a phone line, or a telephone set. Something like that could then connect to an ATA, or Gateway device.

I used to have documentation on devices like that , unfortunately, at the moment all that is in storage, for another year or so, so not readily accessible. As technology like 4-wire circuits continue to be phased out in favour of digital (VoIP), there will be less and less of this equipment available without people going out of their way to rescue it from the junk heap.

[5415551212]

I had worked with a lot of 4-wire circuits during my career. Usually it was used when long(er) distances were involved as it was easier to amplify when the audio was going in one direction. But, I've seen it used on trunks from a PBX to a central office, if requested by the customer. It was also easy to interface to channel bank cards designed for this.

 There are (or, at least, used to be) 4-wire to 2-wire converter cards, that are meant to interface to either a phone line, or a telephone set. Something like that could then connect to an ATA, or Gateway device.

I used to have documentation on devices like that , unfortunately, at the moment all that is in storage, for another year or so, so not readily accessible. As technology like 4-wire circuits continue to be phased out in favour of digital (VoIP), there will be less and less of this equipment available without people going out of their way to rescue it from the junk heap.

Interesting, thanks for sharing,
I imagine up in Canada you'd need to cover some distances.
I am pretty sure 4-wire E&M analog circuits (3-pair) were replaced here (by the 1990's) with digital 4-wire T1/PRI T1/BRI (2-pair)   
but now I am curious about the distance thing.
What would be a cutoff distance from the CO where you say lets go to a 4-wire?
Cheers
--Stephen

[5415551212]

Well I did some checking and it looks like you could order a 4-wire unbundeled loop from our ILEC US-West / Quest aka CenturyLink aka Lumen up until last year
more info if any of you are interested;
https://www.centurylink.com/wholesale/pcat/unloop24wireanalogvoice.html
https://www.centurylink.com/techpub/77310/77310.pdf

[rcourtney]

When using leased line modems or PBX trunks
https://xds.amtelco.com/boards/em-voip-gateway-appliance

This 4 wire EM appliance would do the trick if I had lots of cash sitting around.

[leejor]

After some digging in my old archives I came across some PDFs on the Telabs 6131 and 6132 2 wire to 4 wire interface cards, but I can't figure out how to attach them to the post.

[HarrySmith]

Everything you need to know, and a lot you dont, about attachments in the forum is here:

https://www.classicrotaryphones.com/forum/index.php?board=84.0

[5415551212]

This 4 wire EM appliance would do the trick if I had lots of cash sitting around.

rcourtney thats a interesting device a custom asterisk box that does E&M, how much does it cost?
If its more than ~$200 I would consider this route;
Grab a Cisco VG310 or VG320.
A VG310 can be had for ~$100 or less and is basically a 24 line PBX / ATA.
Granted you'd need to roll up the sleeves and do a little install work, you'd need a 66 block some 25 pair with a female RJ21 to mount in your home phone closet.
Here is one on ebay:
https://www.ebay.com/itm/306332344561

Then grab a E&M, a Cisco VIC3-2EM 2-Port VIC card will set you back another ~75-$100
Here is one on ebay;
https://www.ebay.com/itm/266521442130
I am not a Cisco expert nor affiliated with them, nor the ebay seller, and you'd need to verify that card works in a VG310, but Cisco stuff is carrier grade, supports pulse dial, REN is 3-5 on each port and just works reliably with old phones and you cant beat the price.
You'd have 24 POTS lines and two E&M lines for $200. You can have it route calls like a PBX and or connect your VIOP provider even possibly c*net.
There are also even less costly older 2800 series Cisco gear that people practically give away. 
Cheers
--Stephen

[leejor]

Can't see anything about posting a file, or a PDF, only JPGs. Tried an on-line converter but it didn't work properly, besides each document it about 12 pages long. If you do want to pursue it, do a search for the Telabs 6131 and 6132. I'm sure someone has the PDFs on-line, which is probably where I got the files to begin with. The cards may be available on Ebay if they look like they'd work for you. I'm sure telephone companies are junking them left and right.

[TelePlay]

Can't see anything about posting a file, or a PDF, only JPGs.

When starting to attach a file, the file types allowed would show below the text box (red box). SMF is upgrading their software this weekend so the elimination of this information may be temporary.

Within the red box are the file types allowed. Keep in mind that the forum, due to its free server space, has set a minimum of 3 MBytes per file. If the file, no matter which type, is larger than 3Mbytes, it will not upload.

[5415551212]

Telabs 6131 and 6132

I think this is it:
https://www.telephonecollectors.info/index.php/browse/bc-switching-library/tellabs/11072-tellabs-6132/file

[leejor]

I was always doing the "Quick Reply" , so didn't see the option to attach a file, sorry. I'll attach the 6131 PDF as you've already seem to have found a link to the 6132.