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Data Communication EDA344, DIT420 Description of Lab 1 and Optional Programming HTTP Assignment

Introduction to Wireshark, a tool for analyzing internet traffic. Learn about ethical considerations and gain insight into HTTP messages and processes.

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Data Communication EDA344, DIT420 Description of Lab 1 and Optional Programming HTTP Assignment

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  1. Data Communication EDA344, DIT420Description of Lab 1 and Optional Programming HTTP Assignment Aras Atalar Prajith R G 24/01/2018

  2. Overview • Lab 1 (Compulsory): WIRESHARK lab • General Description • Programming Assignment (Optional): Multi-threaded Web Server • What to do and how to do it • HTTP messages • Processes and threads DataCommunication'18

  3. Lab 1 (Compulsory): WIRESHARK lab • Get insight into Internet traffic through the WIRESHARKtool  • Beware of ethical considerations! E.g. it is inappropriate to use this and similar tools outside the lab environment. DataCommunication'18

  4. WIRESHARK Lab: Important Deadlines • Jan 29: Study and submit in ping-pong the preparatory assignment. ** ONLY after this submission, you can get an invitation to the lab and book a timeslot.  Accept the invitation & book lab-slot in ping-pong ** • Feb 5, 6: Labs @ Lindholmen. Study and get a printed copy of the manual for this lab and get the printed copy along when coming to lab • Feb 12: Submit Lab Report in ping-pong DataCommunication'18

  5. Accepting the invitation • When an invitation is sent to you, you will also be notified by mail to your mail-id. • You should log-in to your ping-pong account and go to the invitations (On top menu : Tools -> Invitations). • Check the current invitations and click on the link 'Book me on event' to book yourself for the event.  DataCommunication'18

  6. Focus on the labs now DataCommunication'18

  7. WIRESHARK Lab • Download WIRESHARK and install it in your machine • Follow the preparation notes for the lab to get familiar with WIRESHARK . • Try the lab instruction manual yourself and there will be help during the lab session. DataCommunication'18

  8. application (www browser, email client) packet analyzer application OS Transport (TCP/UDP) Network (IP) Link (Ethernet) Physical packet capture (pcap) copy of all Ethernet frames sent/received [Computer Networking : A TOP DOWN APPROACH, 7th Edition, Kurose, Ross] DataCommunication'18

  9. Programming Assignment (Optional):Multi-threaded Web Server • Implement a multi-threaded webserver following the HTTP RFC specifications • Successful completion gives extra credit if you pass the March 2018 exam DataCommunication'18

  10. Programming Assignment: Important Deadlines • Study the assignment description. Work on the assignment. For support with questions consult the Freuently-Asked-Questions Document • Jan 31, Feb 14: Join the Q&A sessions  • Feb 21: Present your solution at the demo session • Feb 28: Submit your code in ping-pong system DataCommunication'18

  11. Multi-threaded Web Server • The task: • Write a small Web server that supports a subset of the HTTP 1.0 specifications • The server should • be able to handle simultaneous requests • implement the HTTP methods GET and HEAD • handle and respond to invalid requests • Include Date:, Server:, Content-Type: and Content-Length: headers in all responses. Last-Modified: should be included where appropriate. DataCommunication'18

  12. Multi-threaded Web Server • Hints • Read the textbook • an example: simple Web server that does not handle simultaneous requests (Section 2.7, 2.9, 5th edition) • To handle concurrent requests • One way is to create a thread for each request • Java tutorial Writing a Client/Server pair • Check course assignments page for hints DataCommunication'18

  13. http message format: request ASCII (human-readable format; try telnet to www server, port 80) request line (GET, POST, HEAD commands) GET /somedir/page.html HTTP/1.0 Host: www.someschool.edu Connection: close User-agent: Mozilla/4.0 Accept: text/html, image/gif,image/jpeg Accept-language:fr (extra carriage return + line feed) header lines Carriage return, line feed indicates end of message DataCommunication'18

  14. http request message: general format DataCommunication'18

  15. http message format: response status line (protocol status code status phrase) HTTP/1.0 200 OK Date: Thu, 06 Aug 1998 12:00:15 GMT Server: Apache/1.3.0 (Unix) Last-Modified: Mon, 22 Jun 1998 …... Content-Length: 6821 Content-Type: text/html data data data data data ... header lines data, e.g., requested html file DataCommunication'18

  16. http response status codes In first line in server->client response message. A few sample codes: 200 OK • request succeeded, requested object later in this message 301 Moved Permanently • requested object moved, new location specified later in this message (Location:) 400 Bad Request • request message not understood by server 404 Not Found • requested document not found on this server 505 HTTP Version Not Supported DataCommunication'18

  17. Java Concurrency Support class MessagePrinter implements Runnable { protected String msg_; The message to print protected PrintStream out_; The place to print it MessagePrinter(String msg, PrintStream out) { out_ = out; msg_ = msg; } public void run() { out_.print(msg_); // display the message } } DataCommunication'18

  18. Sequential Version class SequentialPrinter { public static void main(String[] args) { MessagePrinter mpHello = new MessagePrinter("Hello\n", System.out); MessagePrinter mpGoodbye = new MessagePrinter("Goodbye\n", System.out); mpHello.run(); mpGoodbye.run(); } } DataCommunication'18

  19. MultiThreaded Version class ConcurrentPrinter { public static void main(String[] args) { MessagePrinter mpHello = new MessagePrinter("Hello\n", System.out); MessagePrinter mpGoodbye = new MessagePrinter("Goodbye\n", System.out); Thread tHello = new Thread(mpHello); Thread tGoodbye = new Thread(mpGoodbye); tHello.start(); tGoodbye.start(); } } DataCommunication'18

  20. Different types of servers • Single process/thread do forever accept client connection process all client requests close connection • One thread per connection do forever accept client connection create a new thread to process requests DataCommunication'18

  21. application application socket controlled by app developer process process transport transport controlled by OS network network link Internet link physical physical Socket programming • goal: learn how to build client/server applications that communicate using sockets • socket: door between application process and end-end-transport protocol DataCommunication'18

  22. Socket programming Two socket types for two transport services: • UDP: unreliable datagram • TCP: reliable, byte stream-oriented TCP Client Socket: Socket TCP Server Socket: ServerSocket We will see examples in our skeleton code DataCommunication'18

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