Sending One Message to Multiple Instances of Same Application

Above is a system
Scenario is: System receives different SMS on GSM Modems.. Modem Server reads that message from Modems. If Modem server finds particular format message then it will notify all user terminals, Now the problem that what kind of communication protocol do i need to use..
Multiple instances of same application are running on different user terminals, so all the running terminals should be notified when particular type of text message receive on GSM Modems..
What King of communication i need between terminals and Modem Server???
Terminals and Modem Server are connected through LAN...