Connect multiple site with asterisk

can any one tell me how we can connect multiple site with asterisk. please send me the architecture design, helping materials or if one have small project application please send it to me.

suppose there are 2 sites in same City on different Locations and 3 are on different Sites.
on each there are approximately 50 users.

Connections between servers for the purposes of making / receiving calls are done across VoIP trunks, generally. This means you’re going to be building SIP and/or IAX2 trunks between them across whatever data network you have available. There should be some guidance on connecting Asterisk servers together in the book here: