Off Premises Extension 2

[bradcarter]

Hi guys, we have an off premises extension hooked up to our Definity PBX. The original purpose for this extension was voice but now we are using it for a modem-to-modem connection. I bought a couple 2-wire leased line modems hoping to bypass the PBX and use the line provided by the telco. The modems will establish a connection when using a standard phone cord between the modems but when we try to use the modems with this 'off premises extension' they don’t' work.

How does an off premises extension work? I figured we could make this work assuming that the line from the telco would simply pass what we're feeding it but it doesn't seem to work that way. Any of you guys know how these work?

Thanks,

Brad

 

[cms18]

Hi Brad,

I had the same situation with off premises extensions. I had a group of four lines in the main building and wanted to pass service to the other building. It of course didn't work. OPX lines aren't cheap either. They ran about $25/month for each line.

From my understanding, the OPX are treated as circuit lines and they feed separately from the central office (or remote terminal) to each location (the primary location and circuit location). You most likely will need a direct line connecting your two buildings, which we ended up doing. Hope this helps.

Chris

 

[techninut]

You could always use an MCK unit as a cheaper alternative. You can find them used for around $100 each.

 

[phonman123]

A leased circuit is completely different than a OPX. They are configured differntly.

 

[phonman123]

Don't forget, when you are using a OPX you are using the extension of the OPX to "Power" the circuit. When you remove it and connect you must have something to power it. One or the other modems. Plain and simple.

 

[bradcarter]

Phanman123,

This is exactly what I thought. My 2 Multitech modems can connect with each other with a simple RJ11 cable between them. I figured I could put one of these modems at each end of the OPX circuit and have it work but it didn't. I had my coworker at the other end of the circuit and he can see the voltage when I have the PBX hooked up but can't see anything when the modems were plugged in. You post helped confirm what I was trying to do so it now sounds like I need to look into the modems to see what is wrong.

Thanks,

Brad

 

[SYQUEST]

Analogue modems use a carrier to communicate on a voice path, they are usually 4-wire but can be 2-wire for 1/2 duplex operation. If the modems you have are of this type they will not work on an OPS circuit because there is NO audio path without loop current and ringing to signal the station, like a phone going offhook on the station end. I'm surprised anybody is trying to use this type of setup today, unless it is some older equipment that requires a serial connection(s). If 2-wire will work for you, you need to order a 2-wire analogue point-to-point data ckt from your service provider. If cost is a problem, then I would return the Multitech lease line modems for a pair of dialup modems and use the Definity & the OPS as it is and just call the modems thru the PBX. Then the only time the connection would be down is if the PBX crashed or you had a power failure.

Hope this helps!

....JIM....

 

[jerryreeve]

If you provide -48VDC talk battery across the pairs on one end you probably will find that the modems are good to go in a back to back mode. the talk battery is (as noted above) what the actual voice rides over and what droves the signal from end-to-end. you can up a test setup using 5 9vdc batteries to test the feasability of this.

JerryReeve
Communications Systems Int'l
com-sys.com

 

[exverizon]

You said it works when connected directly together (rj11 mounting cord), so if that cord were, say, 500 feet between buildings the only difference would be length. That introduces slight attenuation, but I doubt there would be enough to degrade the signal. An off-prem extension just uses a copper pair--like the cord--so the issue is the condition of the pair it's on. Since it normally carries voice traffic, marginal conditions in the pair are probably not heard. But for data, the tolerances are more stringent. Have the pair tested for leaky faults (shorts and grounds), or swap pairs if another is available. By the way, your coworker won't see voltage on the line with the modem because there isn't any. It's just a termination device, like a phone. It can be detected with a VOM.

 

[SYQUEST]

Hi exverizon,

That is not necessarily the case. If the OPS ckt is going thru the CO, it probably has a DLL(dial long line) or loop extender/voice repeater on the pair. That could preclude any VF getting thru from one end to the other without loop current. Most TELCOs design OPS with equipment even on some short loops just to be safe and the nature of these analog beasts...

Hope this helps!

....JIM....

 

[hdingman]

True DC copper continuity is rare on an OPX unless you specifically request it, but the DLL makes it appear like continuity. Try putting clean 48VDC (Talk or "A" Battery) on one end, and a choke at the other end for DC current draw. Hi-pass on each end to the modems. It might work, it might not. Bottom line, check the line requirements for the modems against the OPX specification, and if necessary order a change. It's probably easier and a lot more reliable than trying to make do with a kludge.

Howard

 

[NCBrit]

Is it a local call? Obviously the OPX was required for voice, but why can't you just rent a line at the remote office and dial the modem at the main office?

 

[SYQUEST]

There are a variety of reasons why we use OPS & OPX. For example, to control access both in & out, same system presence, feature access & use, physical line access & appearance(OPX), answering service, cost, and functionality.

In some areas of the US business lines are measured on local calls for the duration of the call. Hence as long as the connection is up the meter is running! With an OPS there is no meter!

In this case the company already had existing facilities they are trying to utilize for an application, but they ordered the wrong type of modems.

Hope this helps!

....JIM....