http://unity3d.com/support/resources/unite-presentations/developing-mult...
ISSUES FACED :
LAG
Delays created by server or client congestion. Decrease server load / improve performance
Latency
Delays created by network transport time. Solve by prediction and clever game design
Connectivity
Client is unable to communicate/ connection drops. NAT punchthrough but also clever game design
All clients and server will be always be slightly out of sync with each other.
UNITY Networking :
RPC ->
RPC calls and state synch
RPC Buffer - holds states within the game / tracks history of physical happenings within the game. permanent effects
State Synchronisation ->
Unity Master Server Source Code available in order build your own master server
