How to pass session variable from aspx page to WCF Service

[ServiceBehavior(InstanceContextMode = InstanceContextMode.PerSession)]
   public class Service1 : IService1
   {
       //bool boolValue = true;
       //string stringValue = "Hello ";
       public string Greet(string words)
       {
           return GreetInternal(words);
       }
       public string Greet2(string words)
       {
           return GreetInternal(words);
       }
       string GreetInternal(string words)
       {
           MySessionState state = (MySessionState)HttpContext.Current.Session["MySessionState"];
           if (state == null) {
               state = new MySessionState();
               HttpContext.Current.Session["MySessionState"] = state;
           }
           int counter = state.Touch();
           return string.Format("[Session '{0}'] You said: {1} (counter: {2})", HttpContext.Current.Session.SessionID, words, counter);
       }

   }
   class MySessionState
   {
       int counter;
       public MySessionState() { }
       public int Counter { get { return this.counter; } }
       public int Touch() { return Interlocked.Increment(ref this.counter); }
   }