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New Member

Voice over IP on a frame relay

We are a Government Department that processes waste water. I have a wan that consists of 2 T1's each T1 is connected to two central but separate monitoring points waste water treatment plants. From these T1's there are 35 56K connections or pump stations. Each 56K connection has two DLCI's one to each T1. This was set up for redundancy due to the nature of our business, some of the 56K connections are monitored by one station and the rest by the second station this division is geographic in nature and is set up that if a line goes down each station could monitor all 35 56K locations if needed.

At 12 of these 56K locations (Pump Stations) I have standard phone service that we pay extra for a line in to the building. Our T1's and 56K's are now dedicated to monitor flows, pump operations, water levels through the use of PLC's. My Goal is to eliminate the twelve phone systems that are limited in their usage to once a day and at this time costly and install Voice Over IP on this system and install phones at all 35 56K locations. These phones do not have to be the type that connect to the outside world just to our monitoring stations that are set up to handle any emergency calls that may come to them. Each phone would have to have the ability to choose the monitoring station the caller would like to converse with.

That said, is all this possible without causing any signal loss from the monitoring system? Would special software be required?



Hall of Fame Super Gold

Re: Voice over IP on a frame relay


yes you can have voice on these low speed circuits, but "barely". Why is that, once you take into consideration rtp overhead, even with a low bit rate codec, voice will take about 24 kbps.

Another possibility would be to run VoFR that takes less bandwidth, but that requires tandem-switching at the hub (don't worry if you're not familiar with the term, I can explain what means if you need).

Anyway, it's doable, what routers do you have at the stations and in the center, chances are these are upgradable to voice interface, another possibility is that you place IP phones in the stations, and with a simple CME router you control them remotely, to all effect you would have virtual pbx that way.

New Member

Re: Voice over IP on a frame relay

Hi and thanks for responding:

If need be I can send the sh ver for all of these.

one of the center routers is a Cisco 4500

The other Center router is a Cisco 1721

there are:

9 Cisco 1721's 2 1841 and 24 1602's

There are also 4 other waste water treatment plants on this frame as 1/4 T1 384K

I don't believe that these plants may be included in the phone system I'm trying to put together. These plants are only populated during the day and at night monitored by the central stations listed above.

The routers at these locations are Cisco 1721, 1602, 1000, and 1841

I think we will be hard pressed to add anything to the 1602's or the 1000 but I don't know!

Most of the above locations have smart jacks provided at the verizon termination points some don't. Just an FYI

Thanks Again


Hall of Fame Super Gold

Re: Voice over IP on a frame relay


none of your routers can be upgrades to have voice interfaces. The 4500 at the center would benefit of become an ISR 38xx, independently from voice or not.

You can the explore the CME approach that I suggested before, with cheap IP phones or ATAs in the branch. If you replace the 4500 with an ISR, that same router can control them as a true PBX. Then you can trunk via voip or pots interface to you corporate PBX and be connected form/to anyway.

Hope this helps, please rate post if it does!