Network problem

[tinomudaishe]

i have a network which consists of a windows 2003 domain controller and about 90 client computers on this domain controller.the domain controller also hosts the microsoft exchange server.users on the network are intermitently disconnected and reconnected after a short period.WHAT CAN BE THE CAUSE OF THIS INTERMITENT DISCONECTION FROM THE NETWORK? PLEASE HELP

 

[eibgrad]

wire or wireless?