VOIP Business setup with asterisk

Hi All Expert,

I want to setup a new VOIP business using asterisk. The requirement is as below:

Asterisk Server 1----------|
| My central
Asterisk Server 2----------| ----SIP Call Forward—> [Asterisk Server]–Trunk–>Call route to any Number
| Billing and Charging
Asterisk Server 3----------| +

can any one guide how to use my central asterisk server from other asterisk server and route to other part of the word. I mean call establish to any phone. For the call establish to out world…what SIP need to use? Or i need to install digisum cards on my central asterisk server or what?

Target is 20,000 Concurrent call. How concurrent call Asterisk 11.4 can handle?

Please cooperate for any information…or any link or diagram.

Thanks! in advance.

You should move this to job forum.

Thanks! I have posted in the job forum as you suggested.