Examples of org.jnetpcap.protocol.tcpip.Tcp$SACK

org.jnetpcap.protocol.tcpip.Tcp
TCP may experience poor performance when multiple packets are lost from one window of data. With the limited information available from cumulative acknowledgments, a TCP sender can only learn about a single lost packet per round trip time. An aggressive sender could choose to retransmit packets early, but such retransmitted segments may have already been successfully received.
SACK is a strategy which corrects this behavior in the face of multiple dropped segments. With selective acknowledgments, the data receiver can inform the sender about all segments that have arrived successfully, so the sender need retransmit only the segments that have actually been lost.

The SACK option is to be sent by a data receiver to inform the data sender of non-contiguous blocks of data that have been received and queued. The data receiver awaits the receipt of data (perhaps by means of retransmissions) to fill the gaps in sequence space between received blocks. When missing segments are received, the data receiver acknowledges the data normally by advancing the left window edge in the Acknowledgement Number Field of the TCP header. The SACK option does not change the meaning of the Acknowledgement Number field.

This note defines an extension of the SACK option for TCP. RFC 2018 specified the use of the SACK option for acknowledging out-of-sequence data not covered by TCP's cumulative acknowledgement field. This note extends RFC 2018 by specifying the use of the SACK option for acknowledging duplicate packets. This note suggests that when duplicate packets are received, the first block of the SACK option field can be used to report the sequence numbers of the packet that triggered the acknowledgement. This extension to the SACK option allows the TCP sender to infer the order of packets received at the receiver, allowing the sender to infer when it has unnecessarily retransmitted a packet. A TCP sender could then use this information for more robust operation in an environment of reordered packets, ACK loss, packet replication, and/or early retransmit timeouts.
@author Mark Bednarczyk @author Sly Technologies, Inc.


    InetAddress dst = InetAddress.getByName("201.1.1.1");
    InetAddress src = InetAddress.getByName("192.168.1.1");


    Ip4 ip = packet.getHeader(new Ip4());
    Tcp tcp = packet.getHeader(new Tcp());


    ip.destination(dst.getAddress());
    ip.source(src.getAddress());


    ip.checksum(ip.calculateChecksum());
    tcp.checksum(tcp.calculateChecksum());
    packet.scan(Ethernet.ID);


    System.out.println(packet);
    List<PcapIf> alldevs = new ArrayList<PcapIf>(); // Will be filled with NICs
    StringBuilder errbuf = new StringBuilder(); // For any error msgs

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    assertNotNull(errbuf.toString(), pcap);


    pcap.loop(Pcap.LOOP_INFINATE, new PcapPacketHandler<String>() {
      Ip4 ip = new Ip4();


      Tcp tcp = new Tcp();


      // public void nextPacket(PcapHeader header, JBuffer buffer, String user)
      // {
      public void nextPacket(PcapPacket packet, String user) {


        if (packet.hasHeader(tcp) == false) {
          return;
        }


        // PcapPacket packet = new PcapPacket(header, buffer);


        long f = packet.getFrameNumber();
        assertTrue("#" + f, packet.hasHeader(ip));


        final int crc =
            Checksum.pseudoTcp(packet, ip.getOffset(), tcp.getOffset());


        if (crc != 0 && tcp.checksum() != crc) {
          System.out.println(tcp);
          System.out.printf("#%d: tcp.crc=%x computed=%x\n", f, tcp.checksum(),
              crc);
          // System.out.println(ip.toHexdump());
          // System.out.println(tcp.toHexdump());
          System.exit(0);
        }

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    assertNotNull(errbuf.toString(), pcap);


    pcap.loop(Pcap.LOOP_INFINATE, new PcapPacketHandler<String>() {
      Ip6 ip = new Ip6();


      Tcp tcp = new Tcp();


      public void nextPacket(PcapPacket packet, String user) {


        if (packet.hasHeader(tcp) == false) {
          return;
        }


        // PcapPacket packet = new PcapPacket(header, buffer);


        long f = packet.getFrameNumber();
        assertTrue("#" + f, packet.hasHeader(ip));


        assertTrue("Frame #" + f, tcp.isChecksumValid());
      }


    }, null);
  }

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   */
  public void testTcpOptions() {
    JPacket packet = TestUtils.getPcapPacket(SMALL_IMAP, 1 - 1);
    System.out.println(packet.toString());
    
    Tcp tcp = packet.getHeader(new Tcp());
    Tcp.Timestamp ts = new Tcp.Timestamp();
    
    if (tcp.hasSubHeader(ts)) {
      System.out.printf("tsval=%d tsecr=%d%n", ts.tsval(), ts.tsecr());
    }
  }

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    long pid = sig.getPid();
    ProcMem pm = new ProcMem();
    long base = 0;
    final PcapPacket packet = new PcapPacket(JMemory.POINTER);
    int loop = 0;
    final Tcp tcp = new Tcp();


    final JBufferHandler<Object> handler = new JBufferHandler<Object>() {


      public void nextPacket(PcapHeader header, JBuffer buffer, Object user) {

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    ProcMem pm = new ProcMem();
    long base = 0;


    final PcapPacket packet = new PcapPacket(JMemory.POINTER);
    final PcapPacket.State state = packet.getState();
    final Tcp tcp = new Tcp();
    // final TcpScanner tcpScanner = new TcpScanner();


    final ByteBuffer byteBuffer = ByteBuffer.allocate(8 * 1024);


    final ReferenceQueue<PcapPacket> refQueue =

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org.jnetpcap.packet.TestForMemoryLeaks

org.jnetpcap.protocol.TestTcpIp

org.jnetpcap.TestTransmitter

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