[OpenSER-Users] Help with Setup

Hi, I need to configure my ser / openser in such a way that these sites should be able to call each other : Site A -> 01113, 01114 Site B -> 02113, 02114 Site C -> 03113, 03114 User in Site A (Dial 02113 or 03113) --------> SER / OpenSER --------> User in Site B or Site C and they should be able to call within site : User in Site A (Call 114) ----------> SER / OpenSER ---------> User in Site A here 01, 02, 03 are my site code so site code is only needed when users want to call between sites. If they are calling within same site no need to dial site id. please advise and give some links. Thanks, arun