how to make the asynchronus methods in wcf

hi,

i am developing the method in wcf as asynchronous but they can't work i am use

[OperationContract]
    int add(int x,int y);
    [OperationContract(AsyncPattern = true)]
    IAsyncResult Beginadd(int x,int y,AsyncCallback callback,object state);
   
    int Endadd(int x, int y, IAsyncResult result);

but it will not work if you have any resources plz provide me any link also