CS158A - Computer Networks
Project 2: Sliding Window Protocol Simulation
Due Date: Mar 21, 2008 (11:59 PM)
Instructor: Praveen Yalagandula
Spring 2008
 

The goal of this programming assignment is to simulate the sliding window protocol discussed in the
class (Section 2.5.2 of the textbook). Similar to Project 1, you will implement a server and a client programs
where the client program can be invoked to request a file from the server. The key difference between Project
1 and this project is to use a sliding window protocol for communication between the server and the client.
To test the sliding window protocol, you will also simulate packet losses.

Server:

 The server program should start on a port specified as a command-line argument and listen for
connections from clients. When a connection from a client is established, server should read a string from
the client. This string will be the name of the file that the client is interested in. Server should check in the
file directory, specified as a command line argument, to see if the requested file exits. If a file exists, server
should respond to the client with a string “SUCCESS” followed by the contents of the file. If no file exists
with the requested name, then the server should respond with the following failure message string—“NO
SUCH FILE EXISTS”.
Server should use the sliding window protocol to send the file contents to the client. Server should
fragment the contents into small frames of size, FrameSize. Server should use a sliding window size specified
as command-line argument and use a loss probability specified on command-line to simulate packet losses
on the outgoing packets.

Server should support the following arguments:

• -p <portNumber>: The port number at which server will listen
• -d <dirName>: Directory name where files will be located
• -F <FrameSize>: Payload size in each frame
• -w <SenderWindowSize>: Sliding window size at the server
• -l <LossProbability>: A float value to denote the packet loss probability
• -t <timeout>: Timeout value in seconds
   

So, one should be able to start a server listening on port number 5678, serving files in directory “./testDir”,
with frame sizes of 100, with sender window size of 10, and loss probability of 1 in every 10 packets as follows:

$> ./server -p 5678 -d ./testDir -F 100 -w 10 -l 0.1

Client:

 The client program should take command-line arguments to denote a server’s name and server’s
port number that it will connect to, and a string denoting the name of the file it will request from the server.
If the client obtains the file successfully, it should create a file with name specified above in the local directory
and write the contents into that file. Remember to remove “SUCCESS” string at the start of the contents
received from the server. Also client program should accept command-line arguments for specifying frame
size, receiving window size, and a loss probability. Similar to server, client should use the loss probability
specified on the command-line to simulate packet losses only on the outgoing packets.

The client program should support the following arguments:

• -s <servername>: Name of the machine where server is located. If you are running server and client on a same host, you can specify “localhost” as the server name.
• -p <serverport>: Port number where server is running
• -f <fileNameToRequest>: Name of the file to download
• -F <FrameSize>: Payload size in each frame
• -w <ReceiverWindowSize>: Sliding window size at the receiver
• -l <LossProbability>: A float value to denote the packet loss probability.

You should be able to start a client to connect to the server started in the example above, to request a file testFile while using frame size of 100 and a receiver window size of 10 and loss probability of 1 in every 20 packets as follows:

$> ./client -s localhost -p 5678 -f testFile -F 100 -w 10 -l 0.05

Important Notes:

• You can use C, C++, or Java for this programming assignment.
• Your server and client programs should also print out the following after a successful file transfer: total number of packets dropped and total number of packets sent and received.
• Submit all your submission files as a single zip file (gzip is fine too). You should also include a README
  file describing how to compile your programs and how to execute server and client programs.
• Write-up to submit along with the submission: (1) Description of how you implemented the sliding
  window protocol including description of the fields in each of the frame, (2) Run your program for
  transferring different sized files (1KB, 10KB, 100KB, 1MB, 10MB, 100MB) for different frame sizes (1B,
  10B, 100B, 1KB, 10KB) and report how many frames are transmitted for different loss probabilities at
  server and destination (0.001, 0.002, 0.004, 0.008, 0.01, 0.02, 0.08, 0.1, 0.2, 0.4). Present both tabulated
  data and with graphs for few cases (e.g., number of frames transmitted from server vs. loss probability
  for different frame sizes for 100MB file).
• Due on Mar 11, 2008: A short description of how you are making progress on this project: should
  include pseudocode of your server and client programs and frame format.
• You can use the code given in Section 2.5.2 of the text book for this assignment. [Code from the book]