Ask : asterisk sizing and capacity

Dear all experts,

need advice to design solution using Asterisk.
now, I plan IVR using Asterisk, and the capacity is 500 call concurrent.
the planning is only for IVR/Auto Attendant and connected to another IP PABX using SIP Protocol.

need your advice for :

  • how many server hardware for this requirements
  • server specification (RAM, processor) ?

cak phi