Due: See class webpage.

• Assignment: Reliable Transfer with Stop-and-Go Protocol using UDP
  In this project, you will implement the Stop-and-Wait protocol to enable reliable file transfer between the send and recv programs unreliable UDP sockets.

  You will write and turn in two programs:

  send.c The send program takes 4 arguments: send filename hostname port# timeout and will send the file filename to the socket address (hostname, port#) The parameter timeout specifies the timeout value in milli-seconds used in the stop-and-wait protocol Requirement: The send program must exit after receiving the acknowledge for its last packet transmission Example: send myFile lab1a 8000 5000 will send the file myFile in the working directory to lab1a at port 8000 using stop-and-wait with timeout value 5000 msec (= 5 sec) recv.c: The recv program takes 2 arguments: recv filename port# and will receive lines of text of port port# and save the lines of text in the file filename Comment: The recv program does not need to exit. You need to kill the recv program using control-C when you see the send program has exited

  The communication using UDP ports is unreliable.

  You must implement the stop-and-wait protocol in the sender (send.c) and receiver recv.c) to make the communication (= packet transmissions) reliable

  ---

  ---

  ---

  ---

• Packet structure used in your network programs
  • Use the following struct data type in the communication between send.c and recv.c:

    struct Packet { int done; // contain 0 if not done, contains 1 if done int seqNo; // The seqNo used in Stop-And-Wait char line[1000]; // The next line in the text file };

  ---

  ---

  ---

  ---

• Structure of the sender send.c
  • The sender send.c will open the input file and read the input file one line at a time and send the line to the destination

    Here's is the pseudo code of send.c:

    1. create an UDP socket s 2. bind socket s to a port of the localport 3. open input file FILE *fp = fopen( argv[1], "r"); // CS450 ? 4. read until file is exhausted: char buf[1000]; while ( ( fscanf(fp, "%s\n", buf) > 0 ) { ... } 5. Send the line in buf[ ] in a packet (struct Packet) to the destination using the Stop-and-Wait algorithm Set the done variable in the Packet struct to 0 for these packets ! That means: send the packet wait for an ACK if ( ACK not received before timeout ) repeat the send and wait !!! 6. When the file is completely sent, send a Packet with done = 1 and wait for the ACK When ACK is received, the sender will exit

    Consult the online nodes on the Stop-and-Wait protocol for details: click here

  ---

  ---

  ---

  ---

• Structure of the receiver recv.c
  • The receiver will created a UDP socket on the specific port and write all the lines received on the port to an output file

    ---

  • The pseudo code for recv.c is:

    1. create a UDP scoket s 2. bind socket to the specified (local) port # in command argument 3. open output file: FILE *fp = fopen( argv[1], "w" ); // CS450 ? 4. loop and receive packets: while ( true ) { receive packet P; write the line in packet P to file IF packet is new You write the line with this call: fprintf( fp, "%s\n", line-in-packet ); if packet P contains done = 1 then close the file (use: fclose(fp)) You will need to implement the Stop-and-wait ACK scheme here }

    The receiver wil never exit (that's because the ACK messages sent by the receiver can be lost.

    If the receiver exits after sending the ACK for the done = 1 message and this ACK message is lost, then:

    The sender will keep sending the done = 1 message and will never receive an ACK from the receiver (because the receiver has exited !!!)

  ---

  ---

  ---

  ---

• Dropping packets
  • Because you will be running the program in lab machines that are connected by a highly reliable LAN, there will be no opportunity to let you find errors in your code if you do have bugs in the Stop-and-Wait algorithm.

    So I have rigged "sento( )" function to perform "artificial" packet dropping. I have provided a special library libcs455.a in the directory /home/cs455001/lib that you must link into your code.

    You must compile your send.c and recv.c programs as follows:

    gcc -o send send.c -L/home/cs455001/lib -lcs455 gcc -o recv recv.c -L/home/cs455001/lib -lcs455

    When you compile a UDP network program in the above manner, the sendto( ) function will exhibit the unreliable send behavior more frequently

    After compiling using the above commands, you can test your send and recv programs on 2 lab machines

    Example:

    Run the receiver on lab1a: lab1a: cd ~/tmp lab1a: ~/cs455/recv output 8000 Run the sender on lab1b: lab1b: cd ~/tmp lab1b: create a text file "data" (with gedit) - enter some lines and save lab1b: ~/cs455/send data lab1a 8000 1000

    The sender will exit when it finish transmitting. When you see the sender exit, kill the receiver with control-C

    Compare the files data and output and they must be identical (use cat output to show the file content)

    You can use this command to compare the content of 2 text files:

    diff file1 file2

    If the diff report nothing, then the files file1 and file2 are identical

  ---

  ---

  ---

  ---

• Warning
  • Be careful if you run your tests inside your CS455 project directory where you store your program files !!!

    Because:

    The receiver will create an output file If you use a filename like recv.c for your receiver, then you will overwrite your project !!!

  ---

  ---

  ---

  ---

• Network program examples discussed in class
  • You can start your project using the UDP sender and UDP receiver discussed in class

  • I have put the source code of the UDP sender and UDP receiver discussed in class here:

    /home/cs455001/Handouts/udp/sender.c /home/cs455001/Handouts/udp/receiver.c

    ---

  • You can experience the unreliable communication of UDP by running the sender and receiver:

    To compile: gcc -o sender sender.c -L/home/cs455001/lib -lcs455 gcc -o receiver receiver.c -L/home/cs455001/lib -lcs455

    Run the sender and receiver as follows:

    On lab2a: receiver 8000 // Receiver uses port 8000 to recv data On lab1a: sender lab2a 8000 // Sender will send data to (lab2a, 8000)

  ---

  ---

  ---

  ---

• Test files you can use to transfer
  • I have 2 text file that you can use to test your program:

    /home/cs455001/Handouts/udp/Test.small /home/cs455001/Handouts/udp/Test.large

    ---

  • When you finish your program, you can test the send/recv programs using:

    On labX: recv output 8000 // Run recv on labX using port 8000 On labY: send /home/cs455001/Handouts/udp/Test.small labX 8000 5000

    When the send program exists, type conrol-C to kill the recv program

    Then use the diff command to check difference between the input file and the received file:

    cat output // Show content of received file cat /home/cs455001/Handouts/udp/Test.small // Show input file diff output /home/cs455001/Handouts/udp/Test.small // Check difference // between input and output

    If you pass the small file test, try the program on the large file.

  ---

  ---

  ---

  ---

• Turnin
  • Turn in your send.c and recv.c programs using these commands

    /home/cs455001/turnin send.c udp-1 /home/cs455001/turnin recv.c udp-2

  ---

  ---

  ---

  ---

• Extension request
  • To request an extension for the UDP network programming project, use the following command:

    /home/cs455001/req-ext udp