C#

private void OnReceive(IAsyncResult ar)
        {
            IPEndPoint ipeSender = new IPEndPoint(IPAddress.Any, 0);
            EndPoint epSender = (EndPoint)ipeSender;

            try
            {
                serverSocket.EndReceiveFrom(ar, ref epSender);

                //Transform the array of bytes received from the user into an
                //intelligent form of object Data
                Data msgReceived = new Data(byteData);

                ipeSender = epSender as IPEndPoint;

                // Processing the message which is received

                byte[] message = new byte[<<ACK size>>];
                // Frames the ACK

                serverSocket.BeginSendTo(message, 0, message.Length, SocketFlags.None, epSender,
                    new AsyncCallback(OnSend), epSender); // epSender holds the sender Endpoint.

                byteData = new byte[40];
                serverSocket.BeginReceiveFrom(byteData, 0, byteData.Length, SocketFlags.None, ref epServerSender,
                    new AsyncCallback(OnReceive), epServerSender); // epServerSender holds the server IP and port.
            }
            catch (Exception ex)
            {
                byteData = new byte[40];
                serverSocket.BeginReceiveFrom(byteData, 0, byteData.Length,
                    SocketFlags.None, ref epServerSender, new AsyncCallback(OnReceive), epServerSender);
                    // error is thrown in the above statement
                }
            }
        }