An introduction to fundamental concepts of computer networks and widely used networking technologies. Topics include application protocol design; principles of congestion and error control protocols; network routing; local, wireless, and access networks; network security; and networking programming. The Internet suite of protocols will be discussed in depth. Students will learn about conventional and state-of-the-art computer networks through problem sets and programming projects. More...

Credits 4
  • CS 231 - Data Structures and Algorithms
  • CS 232 - Computer Organization
  • Or permission of the instructor
Semester Spring 2021
Time Zone All the times on this webpage refer to EST.
Date Time, Location TR 9:30 - 10:45 am,
Davis 301
Instructor Ying Li
Office: Davis 111
In-person Course

CS331 in Spring 2021 adopts the in-person model, allowing in-person students to participate in the class.

However, due to the uncertainty of the pandemic situation, we may have to have some remote lectures, e.g., the first three days of the semester, Feb. 10 to Feb. 12. When we have to switch to the remote model, please join the class using the Zoom link provided here (Colby IP Needed). Please mute yourself after joining the class. If you have questions to ask, please unmute yourself or type your quesiton in the chatbox. I will check the chatbox when it's appropriate.

The in-person lecture will not be recorded, but the remote lectures will be recorded and posted on the course website. If you have to miss a lecture for any reason, please let me know in advance. I'm happy to work with you and direct you to read the lecture notes for the classes you missed. Do not hesitate to come to my office hours or email me if you have any questions.

Please wear a mask during the 75-minute class when we meet in person. It will protect everyone in the classroom, including yourself.

Although we've been through the pandemic for almost a year, I believe many of us are still trying very hard to get used to the new normal, and the process is not easy nor pleasure. Please do not hesitate to share your experience/suggestions/thoughts/comments with me whenever you want. We need to work together to make everyone feel comfortable in this class during this challenging period.

Ying's Office Hours

MTWR 2:30 - 4:00 pm or by appointment

I will be waiting for you over Zoom 2:30 - 4:00 pm Monday through Thursday. You can find the Zoom link for my office hours from here (Colby IP Needed). I look forward to meeting you during my office hours. We can solve your questions together or talk about any topics you are interested in. If you want to meet outside of my office hours, please email me to make an appointment. Don't hesitate to contact to me if you have any questions. I'll do my best to reply to your email in a timely manner and help you in any way I can.

Course Goals
  1. Students demonstrate an understanding of the fundamental concepts of computer networks and widely-used networking technologies.
  2. Students demonstrate an understanding of the Internet suite of protocols.
  3. Students demonstrate an ability to utilize the commonly used networking tools.
  4. Students demonstrate an ability to analyze the network performance.
  5. Students present methods, algorithms, results, and designs in an organized and competently written manner.
Grading The course grade will be determined as follows:
  • Projects: 55%
  • Two midterms: 20%
  • Final Exam: 15%
  • Class Participation: 10%

This course has five projects helping you practice the knowledge you learned in class. Every project has two parts: a problem set and a programming assignment.

These projects are usually assigned on Tuesdays. The usual deadline is the midnight of the second Tuesday after the project is assigned.

You are strongly encouraged to work in groups of two on the projects through the semester, which will help you understand the course contents better and let you get the most out of the projects. If you prefer working individually, feel free to do so. Please let me know whether you will work individually or not and who will be your partner by the Friday of the second week of class (Feb. 19, 2021).

If you decide to work with a partner, both team members should actively participate in the projects. The two midterms and the final exam are individual work and rely on how well you know the concepts.

You are expected to email me your projects. The subject of your email should follow this format CS331 Spring2021 Proj# -- Your Name or CS331 Spring2021 Proj# -- Your Name and Your Partner's Name if you work with a partner. (e.g., CS331 Spring2021 Proj1 -- Ying Li or CS331 Spring2021 Proj1 -- Ying Li and Toto).

An email submission should have three attachments, a pdf file for your the problem set solution, an archive for your source code, and a pdf writing report for your programming assignment. Please follow the submission instructions to submit your projects. If you work with a partner, only one team member should submit the project.

Projects are graded based on a 30 point scale. Late projects will receive a maximum score of 26/30, so handing in something on the due date is generally better than handing in a complete assignment late.

As you all have busy schedules, you may have one four-day extensions you can use at your discretion over the course of the semester, excepting only the final project. That means you may choose to hand in one of the projects on Saturday instead of Tuesday. Please email Ying and let her know that you are taking your extension before the deadline.


Midterms are an opportunity for you to show me your understanding of the course. I will assign a mock exam a week before each midterm for you to practice. You don't need to submit your mock exams. But, I strongly encourage you to try them before we discuss them in class.

Two midterms will be on Tuesday, March 23 and Tuesday, April 27. The midterms are take-home exams and will be assigned on Moodle. Each exam should take you about 1-hour, and you have two days finish it and submit your solution to Moodle. You can find the midterms via this Moodle link.

Each midterm may be made up when a prior request is made or there is a documented health issue. Please contact me immediately in the event of illness and other unforeseen circumstances, we will work out accommodations.

You are expected to take the midterms individually. Please be responsible for yourself.

Final Exam

The final exam will be oral, and you are expected to finish it individually. Exam details will be given in the last class. There are no make-ups for the final exam.

Class Participation

You are expected to attend every lecture and actively join the class discussions. Class discussion is a vital part of the learning experience. A good class discussion needs your contribution.

If you must miss a class, please email me in advance. I'm happy to work with you and direct you to the lecture notes and coursework.

Lecture notes will be posted in the Notes section of this webpage few hours after the class. If we have to switch to the remote model, video recordings will be posted in the Notes section too.

Participation also includes coming to my office hours or sending me emails for help. Don’t hesitate to come to my office hours or email me. I'm happy to help if you let me know your questions.


There is no required textbook for this course. You are encourage to read the lecture notes. All lecture notes will be posted in the Notes section of the webpage.

The following textbook is recommended if you are interested in consulting an additional resource.

James F. Kurose and Keith W. Ross: Computer Networking: A Top-Down Approach, Seventh Edition, Pearson, 2016, ISBN 978-0-13-359414-0.
How to succeed

Projects: Start working on the projects as early as possible. Ask me for help if you need. Talk with your peers about the course concepts.

Midterms: Study for the midterms by doing the mock exams and reviewing the relevant topics in the lecture notes. You are strongly encouraged to try out the mock exams before we discuss the solutions in class.

Final Exam: Learn at least two of the topics we discussed in class well enough during the semester and let yourself feel comfortable talk about these topics. Start working on the exam early after it's assigned.

Participation: Be active in class, asking questions and joining discussions. Come to my office hours. Ask Ying for help if you have questions.

Collaboration, Academic honesty

This policy applies to anyone you work with other than your partner.

Computer science, both academically and professionally, is a collaborative discipline. In any collaboration, however, all parties are expected to make their own contributions and to generously credit the contributions of others. In our class, therefore, collaboration on homework and programming assignments is encouraged, but you as an individual are responsible for understanding all the material in the assignment and doing your own work. Always strive to do your best, give generous credit to others, start early, and seek help early from both your professors and classmates.

The following rules are intended to help you get the most out of your education and to clarify the line between honest and dishonest work. We reserve the right to ask you to verbally explain the reasoning behind any answer or code that you turn in and to modify your project grade based on your answers. It is vitally important that you turn in work that is your own. We do use automated plagiarism detection software, so please be sure to abide by these, rather minimal, rules. Reports of academic dishonesty are handled by an academic review board and a finding of academic dishonesty may result in significant sanctions. For more details on Colby's Academic Integrity policies and procedures, see

  • If you have had a substantive discussion of any programming project with a classmate, then be sure to cite them in your write-up. If you are unsure of what constitutes "substantive", then ask me or err on the side of caution. As one rule of thumb, if you see more than 10 lines of someone else's code, then you should cite them. You will not be penalized for working together.
  • You must not copy answers or code from another student either by hand or electronically. Another way to think about it is that you should be talking English with one another, not program languages.
The Colby Affirmation

Colby College is a community dedicated to learning and committed to the growth and well-being of all its members.

As a community devoted to intellectual growth, we value academic integrity. We agree to take ownership of our academic work, to submit only work that is our own, to fully acknowledge the research and ideas of others in our work, and to abide by the instructions and regulations governing academic work established by the faculty.

As a community built on respect for ourselves, each other, and our physical environment, we recognize the diversity of people who have gathered here and that genuine inclusivity requires active, honest, and compassionate engagement with one another. We agree to respect each other, to honor community expectations, and to comply with College policies.

As a member of this community, I pledge to hold myself and others accountable to these values. More ...

Title IX Statement

Colby College prohibits and will not tolerate sexual misconduct or gender-based discrimination of any kind. Colby is legally obligated to investigate sexual misconduct (including, but not limited to sexual assault and sexual harassment).

If you wish to speak confidentially about an incident of sexual misconduct, please contact Colby Counseling Services (207-859-4490) or the Director of the Gender and Sexual Diversity Program, Emily Schusterbauer (207-859-4093).

Students should be aware that faculty members are considered responsible employees; as such, if you disclose an incident of sexual misconduct to a faculty member, they have an obligation to report it to Colby's Title IX Coordinator. "Disclosure" may include communication in-person, via email/phone/text, or through class assignments.

To learn more about sexual misconduct or report an incident, visit

Religious Holidays

Colby College supports the religious practices of students, faculty, and staff, but we don't always know which people will observe which holidays. Since I need to plan course activities in advance, I need to know in advance, if you need to miss a class or have a deadline adjusted in order to observe a holiday. Please notify me by email at least 14 days in advance of any religious holiday that will affect your ability to participate in this course.

© 2021 Ying Li. Page last modified: 01/31/2021