CS 462 – Sliding Window Protocols
This can be divided into two phases:
1. Reliable communication between two processes, e.g., A and B, with error-handling using the
Internet Checksum or the CRC checksum algorithm.
2. Sliding window protocols, e.g., Go-Back-N (GBN), and Selective Repeat (SR).
The project must be implemented with the C++/C language. You may use the ACE or Boost framework or
any available networking APIs.
Remember that we are doing this in software and that you should introduce situational errors to test the
correctness of your implementation. This means that you must have the ability to force packets to be out
of sequence, lost, damaged, and/or simulate lost acknowledgement packets. Situational errors can be
randomly generated or user-specified (described later).
As you progress, you will notice that other minor details not mentioned in this document may be
required. This is to simulate a real-world environment where a customer initially provides as much
information as possible for you to get started. As you start your design, you have questions. You contact the
customer to get more information. It is therefore expected that you visit my office for questions.
There are two types of Internet sockets, stream sockets and datagram sockets. Most of you have used the
stream sockets in your Operating Systems class. Stream sockets are reliable sockets, i.e., frames received
are always in the order they are sent. Since this project requires the implementation of data link protocols,
you must use datagram sockets. Datagram sockets are also known as connectionless sockets. As a
consequence, packets sent may be received out of order when datagram sockets are used.
Provide a design document to describe your implementation. Describe and justify your design decisions.
Your design must have the ability to do an ftp any (one) client to any (one) server. As extra credit, having
your program do multiple clients to multiple servers is encouraged, Examples of this are: single client to
multiple servers, multiple clients to one server, multiple clients to multiple servers simultaneously.
In designing your program, you should discuss the pros and cons of the following design issues:
1. The protocol to be used.
2. The size of your packet.
3. Frame format, i.e., type of header information you want to keep.
4. Sequence numbers (do not use infinite sequence numbers)
5. Error detection (use the CRC algorithm). Is this a reasonable algorithm to use?
6. The size of your sliding window.
7. The time-out interval (static or dynamically determined).
8. How to implement timeouts.
As we proceed to cover each of the appropriate topics throughout the semester, more information will
be given regarding details of the implementation.
You will be asked to demo your project. Hence, it is important to capture as much information as possible
of your run.
Use the md5 hash utility to check the integrity of the files you have transferred over, i.e., the file at the
source must have the same md5 hash value as the one at the destination. To use the md5 hash on our
$ md5sum random.txt
Design a simple (text-based or graphical) UI for your program. The user should be prompted to select
the protocol to be demonstrated, i.e., Stop and Wait, Go-Back-N, or Selective Repeat.
The user should subsequently be prompted for parameter values for the selected protocol simulation.
For example, the user should be prompted for either default values (determined by the designer) or user-
defined values to be entered. The following, at a minimum, must be prompted for:
(a) Type of protocol: GBN or SR.
(b) Size of packet
(c) Timeout interval (user-specified or ping-calculated)
(d) Size of sliding window
(e) Range of sequence numbers
(d) Situational Errors (none, randomly generated, or user-specified, i.e., drop packets 2, 4, 5, lose
acks 11, etc.)
Your output should provide enough information for me when you demo your project. There should be
a separate area where all the necessary information is logged and printed on the screen.
The user should be able to specify a server host for the file transfers. At a minimum, you should be able
to transfer one file.
File Transfer Phase:
You will be required to open two windows, one for the client and one for the server. Information should
be available from both windows that show the protocol in action. The information provided in the client
(sender) window should include, but not limited to:
• Packet sequence number of packet sent.
• Packet (sequence number) that timed out
• Packet that was re-transmitted.
• All packets in the current window.
• Acks received.
• Which packets are damaged, .i.e., deliberately trigger a
checksum error on the receiver side.
Packet 3 Re-transmitted.
Session successfully terminated
Number of original packets sent: xxxx
Number of retransmitted packets: xxxx
Total elapsed time: xxxx
Total throughput (Mbps): xxxx
Effective throughput: xxxx
You MUST strictly follow the format specifications for both sender and receiver shown below.
Packet 0 received
Ack 0 sent
Current window =  and WS = 1 for GBN
Packet 1 received
Current window = 
Last packet seq# received:xxxx
Number of original packets received: xxxx
Number of retransmitted packets received: xxxx
Information to be provided by the receiver:
• Packets (sequence number) received.
• Damaged packet(s) (checksum error should match corresponding
damaged packet from sender window).
• Packets in the current receiver window. o Packets (duplicated) that are discarded.
• Ack packets that are sent.
• Frames arriving out of order should be re-sequenced before assembly.
Example of output on the sender side:
Note: Remember relationship between sequence numbers (SN) and window size (WS).
Example below has SN = 32 and WS = 8.
Packet 0 sent
Packet 1 sent
Ack 0 received
Current window = [1, 2, 3, 4, 5, 6, 7, 8]
Ack 1 received
Current window = [2, 3, 4, 5, 6, 7, 8, 9]
Packet 3 *****Timed Out *****
Example of output on the receiver side:
Stress Test Files
You can create a test file of 2G using the dd command:
dd if=/dev/urandom of=/tmp/1Gtestfile iflag=fullblock bs=500M count=4
You should first check /tmp to make sure that a 1G file exists. If someone else had created it, use
that one instead of creating another huge file.
1. Create a folder with both your email names, e.g., stark_lannister_proj.
2. Put all .cc files (no executables) and a README under the folder.
3. The naming of all .cc files must adhere to the naming convention used in the naming of
your folder, e.g.,
(a) stark_lannister _main.cc
(b) stark_lannister _slidingwdw.cc
(c) stark_lannister _packet.h, etc.
4. DO NOT zip or tar any file under that folder.
5. Submit folder to the W drive as is.
6. Submit hardcopies of the design document, lab cover page, and honor code (downloadable from
462 home page) in class.
7. Schedule a demo.
CS 462 – Computer Networks Project Cover Page
1. Include a copy of your source code, a design document (if required), and a sample run
2. Fill in the table of contents including the names of routines and the corresponding pages.
3. Indicate the status of your program by checking one of the boxes.
4. Submit the assignment at the beginning of the class on the due date.
Program Status: (check one box)
□ Program runs with user-defined test cases. □ Program runs with some errors.
□ Program compiles and runs with no output. □ Program does not compile.
List only major modules
that are typically more
than 50 lines of code
S & W Testing
Design (Data Struc/Alg) (Fast/Slow/Molasses) / 30
Stress test (memory leaks, seg faults, etc.) / 30
Correctness / 30
Lab Total / 90
Specs Compliant / 10
Project Total / 100 学霸联盟