EWS Push Notification : Notification Service is not getting called from Exchange Server.

I have written 2 web services 1) Subscribing to Exchange Server 2) Notification client

I am able to create subscription to Exchange Server. But from Exchange server my notification client webservice is nt getting called. I am not sure how i am missing out any setting. below is my subscribe code and notification client code.

Subscribe code :

ExchangeService service = new ExchangeService(ExchangeVersion.Exchange2010_SP1);
                service.UseDefaultCredentials = true;
                service.Url = new Uri(exchangeServerurl);
                FolderId parentId= FindFolderIdByDisplayName(service, "Order", WellKnownFolderName.PublicFoldersRoot);
                 pushSubscription = service.SubscribeToPushNotifications(
                            new FolderId[] {FindFolderIdfromRoot(service, "EmpCreatealert", parentId)},
                            new Uri(notificationService)         /* The endpoint of the listener. */,
                            1                              /* Get a status event every 5 minutes if no new events are available. */,
                            null                           /* watermark: null to start a new subscription. */,
                            EventType.NewMail);

Notification client : 

 public class Notification : NotificationServicePortType, INotification 
    {           
        public SendNotificationResponse SendNotification(SendNotificationRequest request)
        {
            log("Enter SendNotification");
            SendNotificationResponse snr = new SendNotificationResponse();
            snr.SendNotificationResult = new SendNotificationResultType();
            snr.SendNotificationResult.SubscriptionStatus = SubscriptionStatusType.OK;
            return snr;
        }

}

Can anyone suggest me what els i should do to get notification client to get called.