CS522 F2004 Homework#4:  Protocol Implementation

• You can work on the exercise remotely from home or any machine in the CS Software Lab ENS 149.
• In this exercise,  you are asked to implement the sender of the alternating bit protocol.


• I have implemented the channel and the receiver programs.   They are abrcv.c and channel.c in the ~cs522/project/socket/altbit directory.  Copy ~cs522/project/socket directory using
• cp -r ~cs522/project/socket ~<login>/public_html/cs522/project Assume you have already create cs522/project directory under your public_html directory.
• A template absend.c is created for you.  It handles the command line interface for reading in the domain names and port numbers of the receiver and channel C1. It contains the loop that sends the number of packets to the receiver.  It  also contains the message structure which we will use to send packets to the receiver.

struct Msg {
   struct    sockaddr_in dst;
   struct    sockaddr_in src;
   char    msgtype;
   char    buf[80];
   char   alternating_bit; };
• You need to fill in the declaration of variables for sockets and messages, and the code that implement the sender part of the alternating bit protocol.  Use select system code to implement the time-out and packet reception transitions at states 3 and 6.
• I have included a sample executable absend program in I386 directory.
• For group 1 with last digit of SS#=0,3,6,9. Here is the instruction on how to emulate the alternating bit protocol:
• We are going to run channel C1 on shavano, C2 on sanluis, abrcv (receiver) on redcloud, absend (sender) on wetterhorn.
• We should start C1 and C2 first, then abrcv, finally absend.
• telnet to shavano
• shavano.uccs.edu> cd ~<login>/public_html/cs522/project/socket/altbit/I386

shavano.uccs.edu> channel -d -o
set debug mode on
Channel will lose odd numbered messages. (1,3,5)
socket has port #1537
• telnet to sanluis
• sanluis.uccs.edu> cd ~<login>/public_html/cs522/project/socket/altbit/I386

sanluis.uccs.edu> channel -d -e
set debug mode on
Channel will lose even numbered messages. (2,4,6)
socket has port #1499
• telnet to redcloud
• redcloud.uccs.edu>cd ~<login>/public_html/cs522/project/socket/altbit/I386

redcloud.uccs.edu> abrcv sanluis 1499
C2hostname=sanluis, C2PortNo=1499
socket has port #1226
• telnet to wetterhorn
• The absend command allows -n option which specifies how many packets from upper layer will be sent.
• It takes the domain name and port number of receiver (abrcv) and C1 as required parameter.
• wetterhorn.uccs.edu>cd ~<login>/public_html/cs522/project/socket/altbit/I386

wetterhorn.uccs.edu> absend -n 5 redcloud 1226 shavano 1537
The number of messages to be sent is 1073928917
socket has port #3196
State1: Get New Data=packet 0
State2: Sending -D0
State3: Select timeout...
State7: Resending -D0
State3: Received +A0 msg
State4: Get New Data=packet 1
State5: Sending -D1
State6: Select timeout...
State8: Resending -D1
State6: Select timeout...
State8: Resending -D1
State6: Select timeout...
State8: Resending -D1
State6: Received +A1 msg
State1: Get New Data=packet 2
 
• In your implementation, you are asked to print out the state and the action related to the transition, in a format similar to the above produced by the absend sample program.
• On the receiver, you will see the following output:

redcloud.uccs.edu> abrcv sanluis 1499
C2hostname=sanluis, C2PortNo=1499
socket has port #1226
State1: Received +D0 msg=packet 0
State2: Deliver data=packet 0
State3: Sending A0
State4: Received +D1 msg=packet 1
State5: Deliver data=packet 1
State6: Sending -A1
State1: Received +D1 msg=packet 1 It is duplicate or error!
State8: Resending -A1
State1: Received +D0 msg=packet 2
State2: Deliver data=packet 2
State3: Sending A0
State4: Received +D0 msg=packet 2 It is duplicate or error!
State7: Resending -A0
State4: Received +D1 msg=packet 3
State5: Deliver data=packet 3
• After you compiled your absend.c, repeat the above setup and see if you get the same state transition sequence.
• Repeat the setup except that for Channel C1 use "channel -d "  which does not lose msg, for Channel C2 use "channel -d -o" which loses odd numbered msgs.  Capture the output of the sender and receiver from the first state 1 to the 2nd state 1. Use absend.txt and abrcv.txt as the filenames.
• Question:
• In the above experiments, C1 was started, before the receiver was started. In order for C1 to relay the packets from the sender to receiver, C1 must know the socket (domain name/IP and portno) address of the receiver, but it was started before the receiver, therefore we cannot enter the receiver's portno in the command line for C1.  Same problems for C2 w.r.t. the sender. This is similar to a chicken-egg problem, i.e., which process should we start first.   Discuss how we solve this problem.

Exercise 2: Communicate with a Java GUI ABWPlot program

• In this exercise, we will write a simple program, measure.c, that sends simulated bandwidth date with timestamp to a Java GUI program called ABWPlot that plots the results. First we will run a test program called testPlot that interacts with ABWPlot. Then we will discuss how to write the measure.c program.

Run ABWPlot and testPlot programs.

• The Java GUI program is already written for you. It is located in ~cs522/project/socket/ABWPlot.
• login to one of assigned CS Unix machines.
• In your home directory, create a cs522 subdirectory. If you already have it, skip this step.
• "cp -r ~cs522/project/socket/ ~<login>/cs522" copy the socket directory to your cs522 directory.
• login to the PCs in the lab using your UFP account. or using your PC at home with dialup link on.
• Download the files in ~cs522/project/socket/ABWPlot to a local directory.
• Run ABWPlot by "java ABWPlot" You will see the following java window shows up without the curve.
  
• ABWPlot will print out the port number of the socket it listens to, normally it is 9001. Assume here you are login to blanca. It is better to sit in front of the console of the machine to run this experiment.
• If you see the following error msg, that means your classmate is using ABWPlot on the same machine. Try to run ABWPlot on a PC in the lab and use netstat to find out its IP address.
  "blanca.uccs.edu> java ABWPlot
  java.net.BindException: Address already in use"
• Login to your assigned CS Unix machine, say redcloud.
• run "~<login>/cs522/socket/ABWPlot/testPlot -d 128.198.168.21 9001"
  Here assume 128.198.168.32 is the IP address of the PC running ABWPlot.
• testPlot is the kind of program you need to write. You will observe the msgs on the console similar to the following
  redcloud.uccs.edu> testPlot -d 128.198.168.21 9001
  turn on debug mode.
  The receiver's host name is 128.198.168.21, port_no=9001
  socket has port #33334
  packet 0 id=1 time=1033595144.938120, bw=8000000
  packet 1 id=1 time=1033595146.948898, bw=7985012
  packet 2 id=1 time=1033595148.958685, bw=7940199
  packet 3 id=1 time=1033595150.968469, bw=7866009
  packet 4 id=1 time=1033595152.978257, bw=7763182
  packet 5 id=1 time=1033595154.988042, bw=7632747
  packet 6 id=1 time=1033595156.997826, bw=7476006
  packet 7 id=1 time=1033595159.7612, bw=7294526
  packet 8 id=1 time=1033595161.17397, bw=7090120
  packet 9 id=1 time=1033595163.27183, bw=6864829
  packet 10 id=1 time=1033595165.36968, bw=6620906
  packet 11 id=1 time=1033595167.46754, bw=6360788
  
• The ABWPlot will receive the msg and display as point/curve on its screen similar to the above screendump.

Write measure.c program.

• The ABWPlot accepts the datagram with structure data defined as below:
  struct MSG {
         int id;
         struct timeval tv;
         int bw;
  } msg;
• Your measure.c program will be similar to idgs.c but instead of sending character string data, it sends out a structured MSG data defined above.
• You can reuse idgs.c for setting up the socket and command line processing.
• Measure.c will set msg.id to your SS# % 2. (Either one or zero). Same for all packets.
• After set up the socket address, the program will go through a loop like this
  
• for (i=0; i<n; i++) {
       (void) gettimeofday(&msg.tv, 0);
       msg.bw = 1000000*cos(0.1*i)+5000000;

       if (debug)
           printf("packet %d id=%d time=%d.%d, bw=%d\n",
                      i, msg.id, msg.tv.tv_sec, msg.tv.tv_usec, msg.bw);

       if (sendto(#######) < 0)
              perror("sending datagram message");
       sleep(2);
  }
  

• 
  
• You can substitute the bandwidth expression 1000000*cos(0.1*i)+5000000;
  with others. Here 1000000 is bandwidth variation range; 5000000 is the baseline bandwidth.
• The ABWPlot allows you to change the bandwidth display range.
• After editing the program, compile it with
  cc -o measure measure.c -lm
• Run the experiment with ABWPlot and measure.
• After the curve is displayed, hit alt-PrintScreen to get a copy of ABWPlot window image and go to MS Word and hit control-v to paste the image from clipboard to the document. You can also save it as PNG or .JPG using photoeditor.
• Turn in that as part of your hw4ex2.
• mail the answer and the following urls to chow@cs.uccs.edu:


http://cs.uccs.edu/~<login>/cs522/project/socket/altbit/absend.c
http://cs.uccs.edu/~<login>/cs522/project/socket/altbit/absend.txt
http://cs.uccs.edu/~<login>/cs522/project/socket/altbit/abrcv.txt http://cs.uccs.edu/~<login>/cs522/project/socket/altbit/abrcv.txt


http://cs.uccs.edu/~<login>/cs522/project/socket/ABWPlot/measure.c

http://cs.uccs.edu/~<login>/cs522/project/socket/ABWPlot/screendump.png or .doc (this contains the image of screendump).