[Asterisk-bsd] Modifying DNIS and call capacity question?

[Steve Ames]

Hey. I have an application that I need a solution for and I think Asterisk
fits the bill... checking other opinions to see if you all agree.

What I have... I have incoming calls coming in on SIP (using either g.711 or
g.729) to my network. All incoming DNIS/Called numbers are 10 digits. At
present they are terminating on a Cisco 2651XM. At the Cisco we are using
'num-exp' to map the DNIS on a 1to1 basis from a 10 digit number to a 6
digit number that bears no resemblence to the 10 digit number before sending
the call out (TDM via HDV card) to our PBX. We are hitting capacity
limitations on the Cisco both in terms of the number of calls it will handle
(no big deal, obviosuly we can just get a bigger router) but also in the
number of 1to1 mappings we can do. IOS limites this to 255 and that is just
way too small. We've come up with a lot of clever workarounds but are fast
reaching a point where that just isn't going to work for us anymore.

So.... what I'm looking for is opinions on feasibility and system sizing.
I'll reterminate the incoming calls to the Asterisk system instead. At the
asterisk system I'll want to do the 1to1 mappings and either send them out
via a PRI card or forward the call onward (using SIP) to our gateway router
which has PRI resources.

The questions:

1. Is this doable at all? Everthing I've seen indicates yes but would like
to hear from other people.
2. What would be the maximum number of these 1to1 mappings that I could put
into the ASterisk configuration?
3. How many PRIs can I put into an asterisk server?
4. Is there a formula for calculating simultaneous calls based on codec
(only 711 and 729 are options), RAM, CPU, etc...?

Many thanks.

-Steve