Most announcements will be on Piazza.

Class Info

Class: Tuesday/Thursday 2:00 - 03:45PM, Science Center 181

Professor: Vasanta Chaganti
Lecturer: Charlie Kazer

Piazza: Q&A Forum

Grades: Grades will be posted on Piazza, using GradeSource.

Office hours:


Tuesday 10.00 - 11.30 AM

Thursday 4.00 PM - 5.30 PM


Monday 2.30 - 4.30 PM

Friday 11.00 AM - 1.00 PM

Weekly Lab Sessions: Vasanta & Charlie

Section A/C

Wednesday 1.15 - 2.45PM

Clothier 016

Section B/D

Wednesday 3.00 - 4.30PM

Clothier 016

Welcome to CS43, Computer Networks! This course will introduce fundamental ideas in computer networking. The structure of this course may be different from many other CS courses at Swarthmore. We will be using a teaching model called Peer Instruction, which places a strong emphasis on classroom discussion and student interaction.

The course is composed of the following:

  • Readings: The readings serve as a first exposure to new topics, where students learn the basics of the material.

  • Class meetings: The classroom material will cover the difficult concepts and facilitate student discussions.

  • Labs: There are several lab programming assignments (mostly in C) that will explore various aspects of network programming.

  • Exams: There is a midterm exam and a final exam (both closed-book) covering the material in the class meetings and labs.

Required Textbook & Clicker

Computer Networking: A Top-Down Approach by Kurose and Ross. ISBN: 978-0133594140.
We will be using the Seventh Edition.

iClickers: This course will use iClickers to facilitate feedback and discussion during class. For many upper level courses including CS43, clicker will commonly be used in class. Clickers may be purchased at the college bookstore or online. Please register your device as soon as you get it. Registering allows me to give you credit for quizzes and class participation. We will begin using clickers for credit at the start of week 2!

Goals for the course

By the end of the course, we hope that you will have developed the skills to:

  • Classify network functionality into the appropriate abstraction layer.

  • Characterize the behavior of popular network applications and protocols (HTTP, SMTP, DNS, etc.).

  • Construct distributed applications using various concurrency models.

  • Design and analyze network application protocols.

  • Identify the role of transport protocols in providing reliability and high performance.

  • Implement routing algorithms and analyze routing protocols.

  • Compare and contrast switching and forwarding platforms.

  • Test and debug networked applications.


This is a tentative schedule; it may change as we go. You should read the assigned sections before class to prepare for class discussion points. All readings refer to the Kurose and Ross textbook unless otherwise indicated (e.g., there’s a link to some other source).


Sep 03


Course Introduction, Protocols and Layering
Optional Reading: 1.1

No Lab

Sep 05


Layering and HTTP
Reading: 1.1, 1.5, 2.2

Try Telnet!

Lab 1


Sep 10


Reading: 2.2

Sep 12


Socket Programming: Concurrency & Non-blocking I/O
Socket Programming
Read up to Concurrent Servers. Skip section - Host Byte Order to Network Byte Order Conversion.

Lab 2


Sep 17


Socket Programming: Concurrency & Non-blocking I/O
Beej 7.1: Blocking
Concurrency and Non-blocking I/O
Reading: 2.1.1, 2.1.2 and Non-Blocking I/O, select() and epoll()

Sep 19


Network Applications and Distributed Systems
Reading: 2.1.3-2.1.6

Optional Reading:Proof of the CAP Theorem


Sep 24


Naming and DNS
Reading: 2.4
How DNS Works

Optional Reading:
Root Servers in the World
, Benefits of hosting a Root server

Sep 26


Email and SMTP
Reading: 2.3

Lab 3


Oct 01


Reading: 2.5

Oct 03


DHTs and CDNs
Reading: 2.6


Oct 08


Transport Services and UDP
Reading: 3.1, 3.3
UDP Protocol Layer

Oct 10


Lab 4 Protocol Design

Lab 4


Oct 15

Fall break

Oct 17


Oct 22


Oct 24


Reliable Transport
Reading: 3.3, 3.4


Oct 29


Reliable Transport and TCP
Reading: 3.5 - 3.5.4

Oct 31


Flow and Congestion Control
Reading: 3.6 (Skip 3.6.1), 3.7


Nov 05


Network Layer Introduction
Reading: 4.0 - 4.2.1

Optional: Leonard Kleinrock Packet Switching

Lab 5

Nov 07


Reading: 4.3 - 4.3.3


Nov 12


Reading: 4.3.4 - 4.3.5, 5.6

Nov 14


Routing Algorithms
Reading: 5.1 + very beginning of 5.3 (before OSPF)


Nov 19


Routing on the Internet
Reading: 5.3 (from OSPF)

Lab 6

Nov 21


Net Neutrality, Internet Policy
Guide to Net Neutrality


Nov 26


Traffic Management
Reading:5.4, 4.2.3 - 4.2.5

Nov 28


Link Layer
Reading: 9.5 - "The Leaky Bucket", 6.1


Dec 03


Media Access
Reading:6.2, 6.3-6.3.3

Lab 7

Dec 05


Switches and LANs
Reading: 6.4 - 6.4.3


Dec 10


End-to-End Example Reading: D.Clark-The Design Philosophy of the DARPA Internet Procotols

Dec 13

Finals Week: Exam Dates - TBA

Lab Policy

This course features regular lab assignments that account for the largest component of your course grade. Lab attendance is required by all students, unless you have already completed and submitted the lab assignment for the week. Additionally, the CS labs are open 24 hours a day, 7 days a week for you to use for CS43 lab assignments. While you must attend the lab session for which you are registered, you may optionally attend additional lab sessions, provided space is available. In case of space constraints, students registered for the lab will have seating priority.

Lab assignments will typically be assigned during the lab sections on Wednesday will generally be due by midnight on Tuesday 1-2 weeks later. You are strongly encouraged to start early!

Even if you do not fully complete an assignment, you should submit what you have done to receive partial credit.

Lab Partnerships

For this course, there will be 1 individual lab, and 6 paired labs. You may choose your own lab partner for each lab, there will be a piazza post to record your choice the week before the lab is out. If you have not chosen a lab partner by Tuesday before lab, I will assign a lab partner for you. You may only partner with the same person for up to 4 labs.

Working with Partners: For partnered lab assignments, you should follow these guidelines:

  • The expectation is that you and your partner are working together side by side in the lab for most, if not all, of the time you work on partnered lab assignments. You and your partner should work on all aspects of the project together: initial top-down design, incremental testing and debugging, and final testing and code review.

  • If you are pair programming, where one of you types and one of you watches and assists, then you should swap roles periodically, taking turns doing each part. There may be short periods of time where you each go off and implement some small part independently. However, you should frequently come back together, talk through your changes, push and pull each other’s code from the git repository, and test your merged code together.

  • You should not delete or significantly alter code written by your partner when he or she is not present. If there is a problem in the code, then meet together to resolve it. If there is any issue with the partnership, please contact Vasanta or Charlie.

Partnerships where partners work mostly independently rarely work out well and rarely result in complete, correct and robust solutions. Partnerships where partners work side-by-side for all or most of the time tend to work out very well.

You and your partner are both equally responsible for initiating scheduling times when you can meet to work together, and for making time available in your schedule for working together.

Accessing the CS labs after hours

  • You can use your ID to gain access to the computer labs at nights and on the weekends. Just wave your ID over the onecard reader next to the lab doors. When the green light goes on, just push on the door handle to get in (the door knob will not turn). If you have issues with the door locks, send an email to If the building is locked, you can use your ID to enter the door between Martin and Cornell library. For this class, your ID will give you access to the labs in rooms SCI 238, 240, 256, and Clothier basement.

Absence / Assignment Extension Policy

To help with cases of minor illnesses, athletic conflicts, or other short-term time limitations, we will drop your three lowest reading quizzes and participation grades. You are still responsible for the material, and you should review any missed materials via the class recordings as soon as you can.

All students start the course with two "late assignment days" to be used at your discretion, with no questions asked. To use your extra time, you must email your professor after you have completed the lab and pushed to your repository. You do not need to inform anyone ahead of time. When you use late time, you should still expect to work on the newly-released lab during the following lab section meeting. The professor will always prioritize answering questions related to the current lab assignment.

Your late days will be counted at the granularity of full days and will be tracked on a per-student (NOT per-partnership) basis. That is, if you turn in an assignment five minutes after the deadline, it counts as using one day. For partnered labs, using a late day counts towards the late days for each partner. In the rare cases in which only one partner has unused late days, that partner’s late days may be used, barring a consistent pattern of abuse.

If you feel that you need an extension on an assignment or that you are unable to attend class for two or more meetings due to a medical condition (e.g., extended illness, concussion, hospitalization) or other emergency, you must contact the dean’s office and your instructors. Faculty will coordinate with the deans to determine and provide the appropriate accommodations. Note that for illnesses, the College’s medical excuse policy, states that you must be seen and diagnosed by the Worth Health Center if you would like them to contact your class dean with corroborating medical information.


Grades will be weighted as follows:


Lab assignments (3%, 5%, 5%, 6%, 5%, 5%, 6%)


Final Exam


Midterm Exam


Class participation & Lab attendance

How to Succeed in CS 43

  • Attend class.
    In class, we will cover new topics and dig into the more challenging details of the material. Class discussions are a critical part of the learning process, as these exercises give you immediate experience with the material we are covering. Also, we will have class participation points, so you need to be present!

  • Read the material before you come to class.
    Don’t worry about total comprehension, but at least get a feel for what we will be covering that week. If you have some understanding of the material coming into class, it will be easier for you to ask questions during class, rather than later when help may not be available.

  • Ask questions if you don’t understand.
    This means both during class and while doing lab assignments. This class continually builds on previous material, so if you don’t understand something one week, it will continue to be a problem the next week, and the week after that, and so on. If you need help, ask your classmates (make sure you have read the "Academic Integrity" section below first), post on Piazza, or come talk with me or Charlie Kazer during my office hours.

  • Start the lab assignments early.
    I realize this one is not always easy to do, but if you can get in the habit of doing this, you will be much better off. If you get stuck early (i.e., not two hours before it is due), there will be time to look for help. In addition, if you start early enough, you can take a break, go do something else, and come back later. I find I always have at least a few new ideas when I come back to a problem after a break. If you wait until the last minute, you can’t do this.

  • Practice, practice, practice.
    The only effective way to learn the material and pass the quizzes and exams is to consistently do the labs. Finish all of the assigned programs (and do some extras, for fun!). Even if you don’t get them done on time, they will still help you learn the material.

  • Seek help early and often.
    Because course material builds on previous material, it is essential to your success in this class that you keep up with the course material. If you are having difficulty with a programming assignment, if you didn’t follow something covered in class, if you feel you need some extra help understanding or practicing some of the course material, or if you just want to discuss something from a class, an assignment, or the text, please come to my office hours.

  • Attend CS43 Labs.
    Lab Attendance is required, and the labs constitute the largest portion of your grade. You should be there!

Academic Integrity

Academic honesty is required in all your work. Under no circumstances may you hand in work done with (or by) someone else under your own name. Your code should never be shared with anyone; you may not examine or use code belonging to someone else, nor may you let anyone else look at or make a copy of your code. This includes, but is not limited to, obtaining solutions from students who previously took the course or code that can be found online. You may not share solutions after the due date of the assignment or make them publicly available anywhere (e.g. public GitHub repository).

Discussing ideas and approaches to problems with others on a general level is fine (in fact, we encourage you to discuss general strategies with each other), but you should never read anyone else’s code or let anyone else read your code. All code you submit must be your own with the following permissible exceptions: code distributed in class, code found in the course text book, and code worked on with an assigned partner. In these cases, you should always include detailed comments that indicates on which parts of the assignment you received help, and what your sources were.

Failure to abide by these rules constitutes academic dishonesty and will lead to a hearing of the College Judiciary Committee. According to the Faculty Handbook:

"Because plagiarism is considered to be so serious a transgression, it is the opinion of the faculty that for the first offense, failure in the course and, as appropriate, suspension for a semester or deprivation of the degree in that year is suitable; for a second offense, the penalty should normally be expulsion."

The spirit of this policy applies to all course work, including code, homework solutions (e.g., proofs, analysis, written reports), and exams. Please contact me if you have any questions about what is permissible in this course.

Exam Integrity

Students must strictly adhere to the following policy, which applies to all exams taken in a Computer Science course at Swarthmore:

Exam takers must place all non-essential items at the front of the room (or other designated area). Unless otherwise permitted, students may not have any electronic devices or course materials in their possession during the entirety of the exam. This includes cell phones, tablets, laptops, smart watches, course notes, articles and books, among others. These items should be placed at the front of the room near the proctor. If you need to leave the room during the exam, you must obtain permission from an instructor first. Any non-permitted discussion or aide in regards to exam material will result in immediate forfeiture of the exam and a report to the College Judiciary Committee. Please discuss any concerns or accommodations with your instructor prior to starting the exam.

Academic Accommodations

If you believe you need accommodations for a disability or a chronic medical condition, please contact Student Disability Services (Parrish 113W, 123W) via e-mail at studentdisabilityservices at to arrange an appointment to discuss your needs. As appropriate, the office will issue students with documented disabilities or medical conditions a formal Accommodations Letter. Since accommodations require early planning and are not retroactive, please contact Student Disability Services as soon as possible. For details about the accommodations process, visit the Student Disability Services website.

To receive an accommodation for a course activity you must have an official Accommodations Letter and you need to meet with me to work out the details of your accommodation at least two weeks prior to any activity requiring accommodations.

You are also welcome to contact me, privately to discuss your academic needs. However, all disability-related accommodations must be arranged, in advance, through Student Disability Services

Networks Resources

Links that are related to the course may be posted here. If you have suggestions for links, let me know.