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FXO for analog PBX



Please let me know if I can connect 2 analoge PBXs which have 6 line for CO and 24 line for internal use in 2 locations connected with a PPP (64kbps) with a router (e.g. 1761) with 4 FXO port and when a user from a location wants to dial a user in another location just pick up the analoge phone, dialing 2 digits (e.g. 25) and hear the tone of another PBX and then dials the number and reach to the colleague.

Is this config possible for analoge PBX?


8 Replies 8


I'm trying to understand what you're wanting to do. Regarding "hear the tone of another PBX"; are you wanting the local analog phone that is behind your local pbx to hear a pbx dial tone that is across the wan? Do you mind drawing up a topology of your question, so that I can better understand the question?


Erik Hoehne


Here is what I would recomend, I have set this up at several installations and it works well. The only difference would be that the ones that I have setup had more than 64K between sites but that is still doable so long as you keep the traffic on that link well regulated.

Anyhow. At each site install a VIC-2FXO and a VIC-2FXS into your 1760. You can use the higer density modules if you need more paths. Tie the FXOs to analog station ports on your PBX and the FXSs to analog CO ports. This may seem backwards but it is correct. Cisco's FXS is expecting to provide dialtone and the analog CO ports on the PBX are expecting to receive dial tone. Depending on what you are using for call processing ITS/CCME/CCM configure your gateway and your route pattern, etc. You will also need to be able to somehow access those fxs ports for outbound calls. You could have direct line access buttons on your phones and instruct users that when calling the remote site the must use lines 7 and 8 as an example. You could also setup a line pool code for these new lines.

Now when site A wants to call Site B, they dial whatever you wish them to dial. You do whatever translations you may wish prior to sending the call. Here is how the call flow works. User at site A accesses the line either by hitting a line button or dialing the line pool code. This grabs the analog line tied to one of the FXs ports on the router. The call is then sent over the 64K link. The router at Site B then uses one of the FXO ports to pass the call to an analog station port on the other PBX. To the PBX at site B it will appear as though someone pickedu picked up an analog station and dialed a local extension.

Hope this helps. If you need any further clarification on this let me know and I will try to clear it up further for you.

Dear Tony,

Thanks alot for your email. By analog PBX I mean a PBX which has no E1 like KX-TA624-4 from panasonic which has 3-6 CO lines and 8-24 extensions.

By dialing 9 , each user can dial outside. I want to setup 4 FXO for each side and when a user dial 6 can get the tone of another PBX and if he wants can dial an extension to reach the other user or dial 9 and then 7 digits for a destination out of company but in that city.

Is it possible?

I am not familiar with that pbx. Can it accomodate analog stations? If so then what I described in the last message will work. The FXS ports on the router will connect to CO ports on the PBX, the FXO will connect to analog station ports on the PBX. As to grabbing dialtone from the remote site that will work as well so long as you have your route lists and patterns setup correctly. You will have to think about that carefully when you do the configurations. Let's say that you want to dial 123-456-7890 which is a local call from the remote. You will need to know if the remote side needs the area code or not, and do they need to dial an access number for an outside line. Lets say that they do not need to dail the area code but dial 8 for an outside line. You would need to drop the 6 and the area code from the string dialed at your local site and then prepend an 8 so the remote side knows that you are trying to access an outside line there.

So you need to create a route pattern allowing this call to be routed. You would also need a translation pattern that would strip the 6 and the area code and then prepend the 8 before presenting the call to the pbx on the remote side.

I hope that this is reasonably clear. I know myself route patterns, route lists, route groups, and translation patterns were hard to get a grasp on. Having worked with keysystems and pbx in the past it took a while to relearn new terms and what these new terms matched to in my old world. Hey who am I kidding, I am still learning about these things every day and probably will continue to for years to come.

If you need more clarification let me know, I'll try to clear up any questions you might have.

I think that maybe there is no CM or CME here, they are just looking to do standard voip toll bypass type of config, although your way looks like a great way to work that into a network with IP phones! I think this person is just looking to allow analog phones at one PBX dial an access code, get sent across the WAN and get dial tone from the other PBX, to then either dial a local ext on that PBX, or dial their (the remote location's) outside line access code, and dial out into the remote local area. So they would hook the 4 fxo ports up to station ports at each end, have pots dial peers for each port on each side, and have them plar over to a port at the other side. Have an h323 dial peer pointing across to the other side. Phone user at side A picks up phone and dials number for far side access, the PBX A rings the station port, it picks up and calls side B, matched digits are stripped, PBX B goes off hook and gives dial tone, and phone A can dial whatever he wants. The only problem here is with FXO on both sides, disconnect supervision can be a big problem.

Mary Beth

You could very well be right. Now that you have mentioned this I have looked back at the original post and don't see any mention of CCM or CCME. You are also very right about the disconnect supervision issue. Your solution can be done, but as you mention disconnect will very likely be an issue to contend with. Guess if there is no CCM or CCME in this design, it comes down to a couple of decisions. Do you simply nail up connections between the PBXs and deal with resetting the FXOs when they don't disconnect, or do some research and see if the savings in toll bypass would justify the purchase of either CCM or CCME. Myself I like the second option. You will end up with a better intigration, more features and then when you hit your upgrade cycle for your pbx's you already have a portion of your IPT solution in place and can start transitioning to full IPT.


i work with the UC520 which is connecetd to 3 cisco IP phones. the cisco ip phone 7911 hasn't a button to define for CO line so how can i configure the line pool code for CO line knowing that i use the CCA for configuration. Thanks 

raghda chakchouk wrote:


i work with the UC520 which is connecetd to 3 cisco IP phones. the cisco ip phone 7911 hasn't a button to define for CO line so how can i configure the line pool code for CO line knowing that i use the CCA for configuration. Thanks 

Wrong forum, post in "small business voice - UC500".

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