• Most announcements will be on Piazza.

Class Info

Class: TuTh 2:40–3:55, Science Center 101
Professor: Kevin Webb
Piazza: Q&A Forum
GitHub: Swarthmore GitHub Enterprise
Gradesource: Anonymized Grade Listings
Office hours: W 11:00 AM - Noon, Th Noon - 2:00 PM
Office: Sci 255

Welcome to CS43. 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'll 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:

Required Textbook & Clicker:

Computer Networking: A Top-Down Approach by Kurose and Ross
ISBN: 978-0133594140
We'll be using the seventh edition.

iClicker device: This course will use clickers to facilitate feedback and discussion during class. For many upper level courses including CS43, we are now requiring that students purchase their own clicker for personal use. Clickers may be purchased at the college bookstore or online. You must also register your clicker online.

Goals for the course:

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


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

Sep 05

  Course introduction Lab 1 Audio

Sep 07

  Internet/OSI Models and layering
Reading: 1.1, 1.5

Sep 12

  HTTP and the Web
Reading: 2.2

Sep 14

  Structure, threading, and blocking
Reading: pthreads and Beej 7.1: Blocking

Sep 19

  Network applications and distributed systems
Reading: 2.1
Lab 2 Audio

Sep 21

  Naming and DNS
Reading: 2.4

Sep 26

  Email and SMTP
Reading: 2.3

Sep 28

  BitTorrent, DHTs, and CDNs
Reading: 2.5 - 2.6.3

Oct 03

  Transport services, UDP
Reading: 3.1, 3.3
Lab 3 Audio

Oct 05

  Reliable transport
Reading: 3.4

Oct 10

  Reliable transport in TCP
Reading: 3.5 - 3.5.4

Oct 12

  Reliable transport in TCP (continued) Audio

Oct 17

Fall Break

Oct 19


Oct 24

  Midterm information + Q&A Lab 4 Audio

Oct 26

  Midterm N/A

Oct 31

  Flow and congestion control
Reading: 3.6 (Skip 3.6.1), 3.7

Nov 02

  Network layer introduction
Reading: 4.0 - 4.2.1

Nov 07

Reading: 4.3 - 4.3.3
Lab 5 Audio

Nov 09

Reading: 4.3.4 - 4.3.5, 5.6

Nov 14

  Routing algorithms
Reading: 5.2 + very beginning of 5.3 (before OSPF)

Nov 16

  Routing on the Internet
Reading: 5.3 (from OSPF) - 5.4
Lab 6 Audio

Nov 21

  Traffic management
Reading: 4.2.3 - 4.2.5, 9.5 - "The Leaky Bucket")

Nov 23



Nov 28

  Link layer
Reading: 6.1 - 6.2

Nov 30

  Media access
Reading: 6.3 - 6.3.3
Lab 7 Audio

Dec 05

  Switches and LANs
Reading: 6.4 - 6.4.3

Dec 07

  End-to-end Example Audio

Dec 12

Reading: 1.6, 8.2.0, 8.2.2

Dec 15

Final Exam 9:00 - 12:00 AM, in SCI 199

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 Friday will generally be due by midnight on Thursday 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.

Weekly Lab Sessions
Section 1 Fridays 2:15—3:45 Science Center 256
Section 2 Fridays 4:00—5:30 Science Center 256

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.


Grades will be weighted as follows:
35%Lab assignments (3%, 5%, 5%, 6%, 5%, 5%, 6%)
30%Final Exam
25%Midterm Exam
  5%Reading Quizzes (I will drop your three lowest quizzes.)
  5%Class Participation

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.

How to Succeed in CS 43

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.

Academic Accommodations

If you believe that you need accommodations for a disability, please contact the Office of Student Disability Services (Parrish 113W) or email to arrange an appointment to discuss your needs. As appropriate, the office will issue students with documented disabilities a formal Accommodations Letter. Since accommodations require early planning and are not retroactive, please contact the Office of Student Disability Services as soon as possible. For details about the accommodations process, visit the Student Disability Service website.

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

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

Beej's Guide to Network Programming