Thank you Garth Jones for you response and advice
sorry for give little info
I have 17 sites one of them is Central managamenet (HQ) and all remaining the same
" managed sites have two database servers and few clients"
the branches connected via IP-VPN 6 MB/s
I make single domain model , and put each branch in distinct OU
also i will deploy SCCM to manage all assets and clients.
but now i'm thinking about design to make it easier in SCCM with AD
Thanks all