[asterisk-users] Redundant PSTN PRI Gateways using Asterisk

[Karl Fife]

On Mon, 1 Sep 2008 22:01:19 -0400, "Michael Melia Jr." said:
> 
> I am looking to implement Asterisk in front of the legacy PBX as the new
> gateway to the PSTN for the company in an effort to begin a slow
> transition to VoIP.  While I am familiar with Asterisk when it comes to
> implementing it as a single box solution for PRI, SIP, voicemail, IVR,
> etc, I get a little confused when you start to separate the functions to
> different boxes for redundancy and scalability.
> 

We're doing something similar, except that we have only 1 PRI.  I too am
partially in new waters with this project, but we've chosen to buy a
RedFone box instead of a complex assortment of PRI cards between MAIN
and FAILOVER and LEGACY PBX's.  We like the choice because it's simple,
highly reliable and gives us lots of flexibility and failover options
(available).  For example:

1 - It means we don't have to any PRI cards for the asterisk servers
themselves--the redfone box wraps the TDM in ethernet frames.  The
Asterisk boxes need no hardware other than their own ethernet cards. 
The Redfone box translates the TDM to TDM over Ethernet (TDMoE).  Now we
can do any *logical* routing we want between Ast1, Ast2 and Legacy
without having to establish *physical* routes and interfaces.
2 - The RedFone box has the PRI interface(s) from the Telco, AND to the
legacy PBX.  The legacy PBX remains essentially unchanged, except that
RF routes the traffic to Ast1 (Ast2 if Ast1 is down), and Asterisk can
decide which call tasks it wants to handle, and which it will route BACK
to the legacy PBX.  If we want migrate a number, service, mailbox, IVR
etc AWAY from the Legacy PBX, we do so easily with a tiny tweak of the
dialplan.  If we move something from away from the legacy system, and it
turns out to have a problem, bug, etc. (not that my dialplans EVER have
problems, but I'm just speaking hypothetically :-) ), I can just send it
back with the same tiny dialplan tweak.  
3 - In an unlikely double-failover scenario, I can leave all of my
legacy IVR trees etc intact on the legacy PBX.  If both Asterisk servers
are down, the customer is routed to the old system.  The customer may
wonder why they're hearing the OLD voiceover artist, instead of the NEW
voiceover artist but at least the call gets handled :-)

This is just another tool to consider.  I would be able to report in
more detail but at this time but it's a work in progress.  If anyone has
a RedFone solution in place and would care to report on (from the
trenches) I'd be interested in hearing your experience. 

-Karl