Media Gateway for fail over

Hello - I am using Asterisk in my business and have a few remote sites. Currently each site has their own trixbox for phones. All of these sites are on a WAN, so I would like to have each site point to the main site over the WAN for phone calls to save money, however, I don’t want to do this without having some kind of fail over in the event the WAN at the main site goes down for some reason.

Can you help me think of ways to setup either the phones with alt. proxy or some kind Media Gateway to setup this redundancy?

I have a couple of POTS lines at each remote site so the if the WAN links are down, the PBX automatically routes the calls to the PSTN. It even has some logic to convert internal numbers to DID for dialing on the PSTN.

I also have it setup so we can contact the remote based on the backup trunk numbers.

You could do something similar with a SIP provider, but if the remote site’s Internet was down as well, that option would not work.

POTS lines may be a bit more expensive, but because of the nature of the business, it is worth having the backup on alternat facilities.