Analog Solutions

Answered Question
Jun 26th, 2008

We are about to move our equipment to a co-location site. The biggest issue are our analog phone lines. We have 5 T1's for voice(analog only) These T1's go to a CSU/DSU then to a PBX then are broken do to single phone lines that plug into a phone server that answers to an extension. I was wondering if there is anyway to do this process with one of the Cisco IAD's without the PBX. The phone cards on the server are loop start and have a circular hunt group.

Thanks for any advice.

I have this problem too.
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Correct Answer by Paolo Bevilacqua about 8 years 7 months ago

You can use 4 x IAD2430-24FXS (slightly reduced model).

You also need the rj-21 cable to split lines to an RJ-11 patch panel.

Nothing else should be required beside a switch to connect.

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Overall Rating: 5 (2 ratings)
Paolo Bevilacqua Thu, 06/26/2008 - 05:52

Hi, any ISR router with FXS ports would do that. This assuming the phone server has FXO ports.

You can also interface the router between T1's and PBX if you want, eventually you can eliminate the PBX as the router can do that job also.

jameswils Thu, 06/26/2008 - 05:55

Hmmm. I have a cisco 2851 ISR. How man analog lines can the router support? My phone servers hold 80 analog lines. And what modules or interfaces would I need to support this?

Paolo Bevilacqua Thu, 06/26/2008 - 05:59

Please confirm if has to be FXS ports. You can use high-density VG-248 for this. But like the phone server can have T1 as well you can interface with that more easily.

Have to say I may have not understood why you have to do that so perhaps explaining in more detail what you need to to and what does what now and after move, to propose a solution.

jameswils Thu, 06/26/2008 - 06:05

When we move we do not want to move the PBX it is an old Ericcson That is on it's last leg basically. How do I tell if The ports on the phone servers are FXO/FXS? Sorry I'm new to the telephony side of networking. I do know that I can plug a regular phone line into the phone server and it will answer to that extension. The reason we are keeping the analog phone cards in the phone server is because the digital cards are just out of the budget right now. So basically we have a couple of 800 numbers that point to the phone servers and if one port is busy it will flow over to the next port and so on.

Paolo Bevilacqua Thu, 06/26/2008 - 06:29

You phone server has FXO and would interface to a voice gateway with a lot of FXS ports. These are quite expensive all well.

Now if I understand correctly, currently you use the PBX to convert T1 to analog for a phone server that handles a bunch of calls.

You have to move now, what you need to move and where ?

Also what the phone server actually does ? There are many solutions from cisco that could possibly replace it.

jameswils Thu, 06/26/2008 - 07:01

Yes the PBX in converting the T1 to analog.

We need to move all our mission critical servers. The phone servers don't do anything but answer the call so no configuration is needed on the phone servers.

Paolo Bevilacqua Thu, 06/26/2008 - 07:06

Ok, so assuming the phone server talks to the mission critical servers, seems like the only thing you've to do is an IP data network between old and new location, and not touch the phone part ?

jameswils Thu, 06/26/2008 - 07:10

No, we are moving the phone servers as well. The whole reason is we don't want to be tied to this location. So I just need a total solution for the new site without the use of a PBX. So basically need something that can covert the T1's to analog with hunt group capability at the new site for the phone servers.

jameswils Thu, 06/26/2008 - 09:13

Also keep in mind the phone servers are currently answering on 80 analog lines. Will the router support this or will I have to purchase multiple devices?

Paolo Bevilacqua Thu, 06/26/2008 - 13:06

Hi, what you need is kind of expensive when done as VoIP, that is a Router with 5 x T1 voice T1s + 2 x VG248.

If you cannot place T1 cards on the phone server directly, you can look at using 5 access banks, that does the digital to analog conversion. A reputable vendor is Carrier Access, but there are others. This might a bit cheaper that the Cisco solution above.

jameswils Thu, 06/26/2008 - 14:02

I currently have 4xVWIC2-2MFT-T1/E1 in the router now. Will this work? So how would the router pass the analog traffic to the VG248?

Paolo Bevilacqua Thu, 06/26/2008 - 14:18

You also need a minimum of 2 x PVDM2-48, or 1 x PVDM2-64 and 1 x PVDM2-32, to cover 4 x T1 DSP resources. You can do "show diag" to see what you've in the router currently.

If you have a 3845 router, you can also host 2 x EVM-HD expanded each to 24 FXS ports, thus using a single additional VG248.

Router would pass traffic to the VG as VoIP, using codec g711u for the best voice quality. The VG248 supports SCCP and you would be able to control the ports from the router with a CME configuration.

If at a later time you want to migrate the application from the phone server, there are cisco application platforms for "contact center" that allow you to create custom call flow, interact with databases, etc. This would let you eliminate the VG248 also.

As an appreciation to those providing answers, please rate usewf posts with the scrollbox below!/

jameswils Thu, 06/26/2008 - 14:30

I did a show diag But I don't see anything referring to a PVDM2 chip.

So basically the router and the VG248's would need to be on their on Vlan or connected through a xover cable?

Paolo Bevilacqua Thu, 06/26/2008 - 14:34


Without the PVDM2 modules, you cannot process voice calls on the T1 interfaces.

Thanks for the appreciation and good luck!

jameswils Thu, 06/26/2008 - 14:43

So I wouldn't be able to use the Cisco IAD 2430 for this? Also is CME seperate software that needs to be purchased?

Paolo Bevilacqua Thu, 06/26/2008 - 14:56

The IAD2432-24FXS had 24 ports and you would need four of them plus a VWIC card for each one. That would not require CME as there is no SCCP support in the IAD.

There is a separate license for CME. The functionality itself is embedded in all voice images.

I still believe that the cheapest an simplest solution would be to get T1 interfaces for the phone server to connect it directly to PSTN.

All the cisco solution we have discussed so far are quite expensive.

jameswils Thu, 06/26/2008 - 15:04

But in this scenario I would only need to purchase the 4xIAD2432-24FXS and the 2xPVDM2-48 because I aleady have 4 VWIC's correct? Would I need any other accessories? ie. cables?

Correct Answer
Paolo Bevilacqua Thu, 06/26/2008 - 15:26

You can use 4 x IAD2430-24FXS (slightly reduced model).

You also need the rj-21 cable to split lines to an RJ-11 patch panel.

Nothing else should be required beside a switch to connect.


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