Replication

Peer-to-peer replication: http://msdn.microsoft.com/en-us/library/ms151196(v=sql.120).aspx

Merge replication:  http://msdn.microsoft.com/en-us/library/ms152746.aspx

Replication Identity columns:  http://www.replicationanswers.com/p2pidentities.asp

How to setup peer-to-peer replication:

 https://www.youtube.com/watch?v=Ld_bwHe8kcQ 

http://technet.microsoft.com/en-us/library/ms152536%28v=sql.105%29.aspx

Handle error/conflict:

http://www.replicationanswers.com/P2PHandlingConflictsAndErrors.asp 

 

useful articles:

http://www.codeproject.com/Articles/715550/SQL-Server-Replication-Step-by-Step