diff -r c4e03315035c -r c375286d1a1c Interface/Interface.cs
--- a/Interface/Interface.cs	Thu Aug 14 18:37:23 2014 +0200
+++ b/Interface/Interface.cs	Fri Aug 15 10:20:01 2014 +0200
@@ -9,8 +9,9 @@
 
 namespace SharpDisplayInterface
 {
-
-    [ServiceContract(CallbackContract = typeof(IDisplayServiceCallback))]
+    
+    [ServiceContract(   CallbackContract = typeof(IDisplayServiceCallback),
+                        SessionMode = SessionMode.Required)]
     public interface IDisplayService
     {
         [OperationContract(IsOneWay = true)]