TCP/IP Communication Latency too big

Question

I have a simple application sending 500 byte messages to a server and recieved the resoinse with the similar saize of message(for testing purpose we do not do any manupulation of the message. It is simple recieve and reply) . Both apps a Java, but I somehow see the roundtrip of 1,7 msec, wchich seems to be quite high for what it is doing.
one machine is LINUX REDHAT Ver4., and the other is SUN Opteron box with Solaris10. JDK1.6 is used.
Does anybody have any way to improve the latency at all?
By the way, the message is already sent and recieves using 'NO TCP DELAY' set on.
Thank you very much for your advaice.
H

Answer 1

Test programs below; around 0.7 ms for one way is what I get too. You have your network speed and your computers' ability process interrupts.
You may want to look into ways to bunch up several requests into one network packet. (Yeah, TCP/IP is not a packet protocol, but if you need to get the last bit of performance you may need to consider stuff like packet issues and NIC interrupts.) Do another test first: stream a few megabytes one way in large write sizes; that's your baseline upper limit for what you can transfer by bunching up requests and replies. In olden days this test would be done using FTP, but I guess FTP servers are getting less common for security reasons.
public class TimePingPongServer
    static final int SIZE = 500;
    public static void main(String args[])
     throws Exception
        ServerSocket serverSocket = new ServerSocket(6666);
     while (true) {
         System.out.println("waiting for connections");
         Socket socket = serverSocket.accept();
         System.out.println("got connection");
         OutputStream out = socket.getOutputStream();
         InputStream in = socket.getInputStream();
         int size = TimePingPongServer.SIZE;
         byte buf[] = new byte[size];
         while (true) {
          if (!readFully(in, buf, 0, TimePingPongServer.SIZE)) {
              System.out.println("got EOF");
              break;
          out.write(buf, 0, size);
         socket.close();
    public static boolean readFully(InputStream in, byte buf[], int pos, int len)
        throws IOException
        int got_total = 0;
        while (got_total < len) {
            int got = in.read(buf, pos + got_total, len - got_total);
            if (got == -1) {
                if (got_total == 0)
                    return false;
                throw new EOFException("FileUtil.readFully: end of file; expected " +
                                       len + " bytes, got only " + got_total);
            got_total += got;
        return true;
import java.net.*;
import java.io.*;
public class TimePingPongClient
    public static void main(String args[])
     throws Exception
     System.out.println("connecting");
     Socket socket = new Socket(args[0], 6666);
     socket.setTcpNoDelay(true);
     OutputStream out = socket.getOutputStream();
     InputStream in = socket.getInputStream();
     System.out.println("connected");
     int packets = 0;
     int modulo = 10000;
     long start = System.currentTimeMillis();
     byte buf[] = new byte[TimePingPongServer.SIZE];
     while (true) {
         out.write(buf);
         if (!TimePingPongServer.readFully(in, buf, 0, TimePingPongServer.SIZE)) {
          System.out.println("got EOF");
          break;
         if (++packets % modulo == 0) {
          long end = System.currentTimeMillis();
          long time = end - start;
          System.out.println(modulo + " pingpongs in " + time + " ms; " +
                       (2.0 * time / modulo) + " ms/message");
          if (packets % (modulo * 20) == 0) {
              socket.close();
              break;
          start = end;
}