in this case, you would have two OpenSIPS boxes and two FreeSwitch boxes. The easiest scenario would be to run them in active/standby mode, so that only one box is handling the calls, and the other one starts acting only when it realizes that the master box is gone.

Here is one of possible examples:

http://wiki.freeswitch.org/wiki/Enterprise_deployment_OpenSIPS

There are also some scenarios for active/active redundancy, but that requires much more engineering efforts.

From: D'Arcy Cain <darcy@Vex.Net>
To: FreeSWITCH Users Help <freeswitch-users@lists.freeswitch.org>
Cc: Stanislav Sinyagin <ssinyagin@yahoo.com>
Sent: Sunday, September 23, 2012 10:07 PM
Subject: Re: [Freeswitch-users] Some questions from a relative newbie

On Sun, 23 Sep 2012 11:24:59 -0700 (PDT)
Stanislav Sinyagin <ssinyagin@yahoo.com> wrote:

> by the way, do you consider running a fault-tolerant service with
> OpenSIPS/Kamailio/Repro as a border controller and two FreeSWITCH boxes
> behind?

Thanks. I have added that to my reading list. However, I am not sure
how useful that scenario would be. Doesn't the OpenSIPS router just
become my new point of failure? If I add another box I can get my
provider to fail over to it. That makes them the point of failure but
they already are so I kind of depend on them not to go down anyway.

--
D'Arcy J.M. Cain
System Administrator, Vex.Net
http://www.Vex.Net/ IM:darcy@Vex.Net