Off Premise Extension for CallManagers

Answered Question
Jun 9th, 2008
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I work for a hospital. We have extended our Avaya Definity switch to several private practice doctor's office. This allows the doctor's office to have a single phone they can call directly into any hospital extension.


Does anyone have any experience setting this up on with a CallManager or with Cisco routers. I'm not quite sure where to start.

Correct Answer by paolo bevilacqua about 8 years 10 months ago

Hi, yes to both your questions.


To have CM see the line like a "physical phone", you configure the FXS port in SCCP mode, thing for which I can give you the link once you decide to go that direction. You could also use an ATA that has two FXS ports.


In any case it is important that you find out which exact type of line is that, like a "dry pair" or OPX with loop current, etc. This to avoid purchasing the wrong hardware.


Note that in most cases provisioning such a line is more expensive in terms of time and HW, than an IP phone over VPN.


Hope this helps, please rate post if it does!

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paolo bevilacqua Mon, 06/09/2008 - 11:07
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What is the exact type of line installed at doctor's office ? A regular pots, a leased line, or what ?


With Cisco equipment this type of things is usually done with voip over a VPN, but even for legacy configuration, what the others do, cisco does as well.

zebranutz80 Mon, 06/09/2008 - 11:54
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This line was installed close to 15 years ago and there is noone working here still that has first hand knowledge. I'm a little sketchy on all the details. I beleive it is a leased line. Our telco provider refers to the circuit as an OPX (Off Premise Extension) Line.


The doctor's phone is a standard 2500 series phone plugged into the wall. I am assuming the wall jack is run directly to the NetPop.

paolo bevilacqua Mon, 06/09/2008 - 11:59
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You should check which exact card type is installed for this line on the PBX, in order to choose one for a cisco router that would replicate that. Quite possibly, it will be a normal FXS.


However as mentioned before the "new world" approach would be to use an IP phone via VPN router and broadband. That would save the recurring dedicated line cost and give all the added features.


Hope this helps, please rate post if it does!



zebranutz80 Mon, 06/09/2008 - 13:08
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I agree with your VPN comment. However, many of the private practice doctors do not have an IT staff and we do not support their network equipment.


So does the FXS card supply the doctor's office phone with dial-tone? Does our CallManager see this as a physical phone? We do not use MGCP.

Correct Answer
paolo bevilacqua Mon, 06/09/2008 - 13:17
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Hi, yes to both your questions.


To have CM see the line like a "physical phone", you configure the FXS port in SCCP mode, thing for which I can give you the link once you decide to go that direction. You could also use an ATA that has two FXS ports.


In any case it is important that you find out which exact type of line is that, like a "dry pair" or OPX with loop current, etc. This to avoid purchasing the wrong hardware.


Note that in most cases provisioning such a line is more expensive in terms of time and HW, than an IP phone over VPN.


Hope this helps, please rate post if it does!

zebranutz80 Mon, 06/09/2008 - 13:31
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Thank you very much for answering all my questions. If you wouldn't mind, please send me the link for configuring the FXS port.


I am fairly sure the line type is OPX, but I will be sure to verify before moving forward.



Rob Huffman Mon, 06/09/2008 - 13:59
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Hi Thomas,


Just to add a note to the great info from Paolo, these OPX lines are most likely "conditioned" circuits not "dry pairs". You should make sure to engage the Telco prior to cutting these over and open a work order in case this line conditioning needs to be tweaked/adjusted for the new FXS Equipment.


Hope this helps!

Rob

Rob Huffman Mon, 06/09/2008 - 14:32
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No worries Thomas :) Good luck on the changeover!


Rob

Abhijit.Das Tue, 06/10/2008 - 03:57
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Rob,

Hope that you are doing good friend.

What is a "conditioned" circuit & what's a "dry pair"?


Take care,

Abhijit.

Rob Huffman Tue, 06/10/2008 - 04:27
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Hi Abhijit,


Life is good here :) Hopefully this finds you well. Here is a simplified look;


A "Dry Pair" is just a plain old Copper pair of wires from point A to point B.


A "Conditioned Line" will be properly engineered by the Telco to provide Impedence matching, amplification to overcome low talk battery / loop current and/or boost Ring Voltage. Generally OPX Lines require some sort of intervention or "Conditioning" to be pushed from the CPE (Customer Premise Equipment) to the Far End or OPX location.


Hope this helps buddy!

Rob

Abhijit.Das Tue, 06/10/2008 - 04:54
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hey Rob nice to hear from you buddy!! I am doing good. So this "conditioning" is to match all parameters in the remote PBX, correct?


take care,

Abhijit.

Rob Huffman Tue, 06/10/2008 - 05:18
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Hey Abhijit,


The Line Conditioning could be described as "assisting" the PBX in this case. We must think that a FXS port can only push the signal so far (let's say 2km for this example) but the Doctors office is 25km away. How can we push this circuit the additional 23km??


We must use equipment located along the path (usually in the Telco CO) to boost to signal for both the initial setup (Ring Voltage) and the actual Transmit/Receive of voice conversations. The matching or equalization is to make sure the voice sounds right. Not like it's a million km away or like the person is yelling in your ear.


I hope this makes sense good friend :)

Rob

Abhijit.Das Tue, 06/10/2008 - 05:57
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Rob,

Yeah this definitely makes a lot of sense, even to me!!

Thanks for your help. Have a nice day.


Take care,

Abhijit.

Abhijit.Das Tue, 06/10/2008 - 05:21
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hey Rob nice to hear from you buddy!! I am doing good. So this "conditioning" is to match all parameters in the remote PBX, correct?


take care,

Abhijit.

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