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Community Member

FXO Backup

Hi All,

I have a customer that would like to use 2x FXO card as backup to there ISDN

My simple thinking would be to use a H323 GW trunk the FXO and ISDN and use the preference command to make use that the ISDN is always tried as a first choice. Unless there is an advantage in using MGCP with Route list, Route Groups... ?

The customer has also added two more requirements which are not meet by the above solution

1) They would like the FXO lines to be used only when the ISDN is down

2) When the FXO is been used, 3 designated phone's get priority over all others

The first requirement I don't think can be done. The second I am not sure. Any ideas, suggestions?




Re: FXO Backup

Hi Alexis,

1. The redundancy you're asking about can be done with Route Lists/Route Groups.

2. This would be done with MLPP. I've really only worked with MLPP on IP phone to IP phone calls and on T1 CAS/PRI links. I imagine it still works for FXOs, but this is mainly a military deployment feature. It assigns priority to phone users and allows for those users when they press a special access code, to kick other users off circuits.



Community Member

Re: FXO Backup

Hi Nick,

Thanks for the information. I should have stated in my original post that the E1 and FXO are both installed on the same gateway. I know with an H323 you simply point the CM to it and then use it within the Route Group. That's why I was going to trunk the E1 and FXO and use the preference command to provide redundancy.

I don't have any experience with MGCP. If I used this protocol then would I be able to select the end points of the Gateway within a Route Group?

Also dose MLPP works with Single Number reach?

Thanks again for the help


Community Member

Re: FXO Backup

i think i may have found the answer to at least one of the Q


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