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TCP/IP Sockets in Java: Practical Guide for Programmers. Kenneth L. Calvert Michael J. Donahoo. Computer Chat. How do we make computers talk? How are they interconnected? Internet Protocol (IP). Internet Protocol (IP). Datagram (packet) protocol Best-effort service Loss Reordering

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TCP/IP Sockets in Java: Practical Guide for Programmers


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    1. TCP/IP Sockets in Java: Practical Guide for Programmers Kenneth L. Calvert Michael J. Donahoo

    2. Computer Chat • How do we make computers talk? • How are they interconnected? Internet Protocol (IP)

    3. Internet Protocol (IP) • Datagram (packet) protocol • Best-effort service • Loss • Reordering • Duplication • Delay • Host-to-host delivery

    4. IP Address • 32-bit identifier • Dotted-quad: 192.118.56.25 • www.mkp.com -> 167.208.101.28 • Identifies a host interface (not a host) 192.18.22.13 209.134.16.123

    5. Transport Protocols Best-effort not sufficient! • Add services on top of IP • User Datagram Protocol (UDP) • Data checksum • Best-effort • Transmission Control Protocol (TCP) • Data checksum • Reliable byte-stream delivery • Flow and congestion control

    6. Ports Identifying the ultimate destination • IP addresses identify hosts • Host has many applications • Ports (16-bit identifier) Application WWW E-mail Telnet Port 80 25 23 192.18.22.13

    7. Sockets • Identified by protocol and local/remote address/port • Applications may refer to many sockets

    8. Clients and Servers • Client: Initiates the connection • Server: Passively waits to respond Server: Jane Client: Bob “Hi, Bob. I’m Jane” “Hi. I’m Bob.” “Nice to meet you, Jane.”

    9. Client Create a TCP socket Communicate Close the connection Server Create a TCP socket Repeatedly: Accept new connection Communicate Close the connection TCP Client/Server Interaction Server starts by getting ready to receive client connections…

    10. Client Create a TCP socket Communicate Close the connection Server Create a TCP socket Repeatedly: Accept new connection Communicate Close the connection TCP Client/Server Interaction ServerSocket servSock = new ServerSocket(servPort);

    11. Client Create a TCP socket Communicate Close the connection Server Create a TCP socket Repeatedly: Accept new connection Communicate Close the connection TCP Client/Server Interaction for (;;) { Socket clntSock = servSock.accept();

    12. Client Create a TCP socket Communicate Close the connection Server Create a TCP socket Repeatedly: Accept new connection Communicate Close the connection TCP Client/Server Interaction Server is now blocked waiting for connection from a client

    13. Client Create a TCP socket Communicate Close the connection Server Create a TCP socket Repeatedly: Accept new connection Communicate Close the connection TCP Client/Server Interaction Later, a client decides to talk to the server…

    14. Client Create a TCP socket Communicate Close the connection Server Create a TCP socket Repeatedly: Accept new connection Communicate Close the connection TCP Client/Server Interaction Socket socket = new Socket(server, servPort);

    15. Client Create a TCP socket Communicate Close the connection Server Create a TCP socket Repeatedly: Accept new connection Communicate Close the connection TCP Client/Server Interaction OutputStream out = socket.getOutputStream(); out.write(byteBuffer);

    16. Client Create a TCP socket Communicate Close the connection Server Create a TCP socket Repeatedly: Accept new connection Communicate Close the connection TCP Client/Server Interaction Socket clntSock = servSock.accept();

    17. Client Create a TCP socket Communicate Close the connection Server Create a TCP socket Repeatedly: Accept new connection Communicate Close the connection TCP Client/Server Interaction InputStream in = clntSock.getInputStream(); recvMsgSize = in.read(byteBuffer);

    18. Client Create a TCP socket Establish connection Communicate Close the connection Server Create a TCP socket Bind socket to a port Set socket to listen Repeatedly: Accept new connection Communicate Close the connection TCP Client/Server Interaction close(sock); close(clntSocket)

    19. Client out.write(“Hello Bob”) in.read() -> “Hi Jane” Server in.read() -> “Hello ” in.read() -> “Bob” out.write(“Hi ”) out.write(“Jane”) TCP Tidbits • Client knows server address and port • No correlation between send() and recv()

    20. Client out.write(string) while (not received entire string) in.read(buffer) out.write(buffer) close(socket) Server in.read(buffer) while(client has not closed connection) out.write(buffer) in.read(buffer) close(client socket) Closing a Connection • close() used to delimit communication • Analogous to EOF

    21. Constructing Messages …beyond simple strings

    22. TCP/IP Byte Transport • TCP/IP protocols transports bytes • Application protocol provides semantics Application Application byte stream byte stream Here are some bytes. I don’t know what they mean. I’ll pass these to the app. It knows what to do. TCP/IP TCP/IP

    23. Application Protocol • Encode information in bytes • Sender and receiver must agree on semantics • Data encoding • Primitive types: strings, integers, and etc. • Composed types: message with fields

    24. 0 77 0 111 0 109 0 10 Primitive Types • String • Character encoding: ASCII, Unicode, UTF • Delimit: length vs. termination character M o m \n 3 77 111 109

    25. Primitive Types • Integer • Strings of character encoded decimal digits • Advantage: 1. Human readable 2. Arbitrary size • Disadvantage: 1. Inefficient 2. Arithmetic manipulation 49 55 57 57 56 55 48 10 ‘1’ ‘7’ ‘9’ ‘9’ ‘8’ ‘7’ ‘0’ \n

    26. Primitive Types • Integer • Native representation • Network byte order (Big-Endian) • Use for multi-byte, binary data exchange • htonl(), htons(), ntohl(), ntohs() Little-Endian 0 0 92 246 4-byte two’s-complement integer 23,798 Big-Endian 246 92 0 0

    27. Message Composition • Message composed of fields • Fixed-length fields • Variable-length fields