Help needed in receiving two consecutive msges from SIP Ser in UDP server!

Question

Hi everyone,
I am Mitul Gogoi,from Assam,North-east part of India.
I am writing a SIP proxy server,which is simly a UDP server and which will sit between the Client(X-Lite softphone) and Brekeke SIP Server and just receive and send messages.
Client---------------->My UDP Server-------------------------->SIP Server (This is for requests)
again,
SIP Server---------->My UDP Server-------------------------->Client (This is for responses)
(couldnot draw the arrows together)
My server will receive any msg coming from Client in port 7000 from Client and My server will send the msg to SIP Server to its IP address and port 5060.So, I just wanted to change the port number to which Client will send msges;i.e. instead of earlier port 5060,it will now send to port 7000.
The msg sending and receiving scenerio:
1.The first msg from Client is received by My Server.
2.My server sends the msg to SIP Server.
3.My server then waits for response from SIP server.
4.One msg comes to My server and received successfully. and it closes the socket.
5.This msg is sent to Client.
6.Second msg comes from SIP server to My server.But My server is unable to receive this second msg.maybe because My server closes the socket to receive the next msg.
I am using ResponseHandler Thread in main which will listen to any msges that may come from SIP server to My server.
My question is :
Is it not possible to receive two consecutive msg from SIP server ?
If one msg comes,it then closes the socket.
My code for sending and receiving :
udpClSocket = new DatagramSocket();
packet = new DatagramPacket(buf, buf.length,InetAddress.getByName(server), port);
udpClSocket.send(packet);//it will send to SIP Server as well as Client,by changing the server and port
byte resbuf[] = new byte[msgSize];
packet = new DatagramPacket(resbuf, resbuf.length);
udpClSocket.receive(packet);//it will receive msg from SIP server only
packet = null;
udpClSocket.close();
The first msg comes to My server successfully,but the second msg is not being received.
I have tried in so many ways,such as taking two different ports :one for receiving for Client and My server ,and another port for My server and SIP server.
If anyone can help me in this ,then I will be highly grateful.
regards,
Mitul

Answer 1

Why? Throw all this code away, and use the NIST reference implementation of JAIN-SIP. They've done all the hard work for you. All you have to do to write a stateless proxy is a little mild header processing.
Thank you ejp for your reply.Mine is a Outbound SIP proxy server,which uses a port other than default 5060 SIP server port.The client will REGISTER SIP server via my server.and moreover,I want to build my own server at least once for learning purpose.
maybe because My server closes the socket to receive the next msg.
Why?
I donot know why.may be I am very new to network programming or did not do much research in networking.But,my code should work;couldn't find out any fault.
Here is my code:
package com.ef;
import java.net.DatagramPacket;
import java.net.DatagramSocket;
import java.net.InetAddress;
import java.util.Date;
* It sends UDP packets to following destinations-
* 1. SIP Server
* 2. SIP UACs
public class OBUDPClient extends Thread {
     private DatagramSocket udpClSocket;
     private DatagramPacket packet;
     private String server = "192.168.1.2";//IP of Brekeke SIP server
     private int port = 5060;
//SIP Message Size
     private int msgSize = 2048;
     private byte buf[];
     private boolean serFlag = true;
     private OBMessage m;
     * Send Request to SIP Server
     * @param in_packet
     * @throws Exception
     public OBUDPClient(DatagramPacket in_packet) throws Exception{
          super("Client-"+String.valueOf((new Date()).getTime()));
          this.buf = in_packet.getData();
          m = new OBMessage();
          * Keep track of IP and Port of the source of this packet. Response
          * from SIP Server will be redirected to this IP and Port
          m.setTargetIP(in_packet.getAddress().getHostAddress());
          m.setTargetPort(in_packet.getPort());
          start();
     * Send Request to SIP UAC (). This constructor gets call from OBResponseHandler.java
     * @param server
     * @param port
     * @param buf
     * @throws Exception
     public OBUDPClient(String server, int port, byte buf[]) throws Exception{
          super(String.valueOf((new Date()).getTime()));
          this.server = server;
          this.port = port;
          this.buf = buf;
          serFlag = false;
          start();
     public void run(){
          try{
          System.out.println("OBUDPClient Redirecting packet");
          udpClSocket = new DatagramSocket();
          //Send Request
          packet = new DatagramPacket(buf, buf.length,InetAddress.getByName(server), port);
          udpClSocket.send(packet);
          //Receive Response
          byte resbuf[] = new byte[msgSize];
          packet = new DatagramPacket(resbuf, resbuf.length);
          udpClSocket.receive(packet); //could not receive two consecutive msg from SIP server
          if(serFlag){
          * If request is sent to SIP Server we are interested for the
          * response otherwise not
          System.out.println("<----------------Handle Response----------------->");
     System.out.println("++++++++++++++++++++++++++++++++++++++++++++++++++");
     System.out.println("Response from SIP Server: "+new String(packet.getData()).trim());
     System.out.println("++++++++++++++++++++++++++++++++++++++++++++++++++");
     //Read SIP reseponse sent by SIP Server
     m.setMessage(new String(packet.getData()).trim());
     //Store the Response message in Queue
     OBMain.q.push(m);
     }catch(Exception ex){
     ex.printStackTrace();
     packet = null;
     udpClSocket.close();
Note:Everything starts from the Client.First,Client makes a REGISTER request;it is passed through Outbound server to SIP server.Then,SIP server responds with 100 Trying;this is received successfully by my outbound server and sent to Client.Then,again,SIP server responds with 200 OK;this is not received by my outbound server;hence cannot reach Client,as a result of which Registration fails.
regards,
mitul