CS 453 Computer Networks

Fall 2026 · Tuesdays & Thursdays · 11:30 AM–12:45 PM · Computer Science Building W150

Application Layer

Course overview

This course provides an introduction to fundamental concepts in the design and implementation of computer networks, their protocols, and applications. Topics to be covered include: overview of network architectures, applications, network programming interfaces (e.g., sockets), transport, congestion, the network data plane (packet forwarding, addressing) and control plane (routing algorithms, software-defined networks, network management), link-layer protocols, local area networks and data center networks, wireless networks, and a bit of network security. Examples will be drawn primarily from the Internet (e.g., TCP, UDP, and IP) protocol suite. There will be five or six written assignments, a couple of programming assignments, several short hands-on labs (that can be done on any Internet-connected PC). We'll have two exams and an optional final.

Class meetings

Tuesdays & Thursdays
11:30 AM–12:45 PM
Computer Science Building W150

Prerequisites

A rudimentary understanding of algorithms (e.g., CMPSCI 311) and operating systems (CMPSCI 377) is required, or you should be willing to pick up elements from those courses as needed. A previous course in computer organization (e.g., CMPSCI 201) is required. You must be able to program in a structured high-level programming language, such as Python.

Materials

Recorded lectures

This course will be taught in person and recorded. You can watch the recordings using Echo360.

Pre-recorded lectures by Prof. Jim Kurose and additional materials are available on the textbook companion site.

PowerPoint slides

The PowerPoint slides used for this class will be posted on Canvas. I will do my best to release the slides before each lecture.

Transport Layer

Communication protocol

We are here to help! Please don’t hesitate to reach out. Here are our protocol guidelines for which channels to use and what to expect.

ChannelPiazza
Expected ACKWithin 1 business day
Urgent flagEmail with “CS453” in subject
RetransmissionFollow up after 24 hours

Use Piazza for questions that may help the class. Use email for urgent matters. Please do not hesitate to follow up if I have not replied within the expected time of one business day. Please include enough context for us to reconstruct the packet.

Network Layer

Route through the semester

This schedule is tentative and may change as the semester unfolds. It is intended to give you the big picture of what we plan to cover and when.

Week 1Sep 8 & 10 · Course foundations

Lecture 1 Course goals and overview. Course mechanics. What is the Internet? What is a protocol?

Lecture 2 The network edge, the network core, and performance: delay, loss, and throughput.

Week 2Sep 15 & 17 · Layering and HTTP

Lecture 3 Performance continued; layering; encapsulation; networks under attack; history.

Lecture 4 Principles of networked applications; the Web and HTTP.

Week 3Sep 22 & 24 · HTTP, DNS, and CDNs

Lecture 5 HTTP continued; e-mail; DNS.

Lecture 6 DNS, video streaming, and content distribution networks.

Week 4Sep 29 & Oct 1 · Sockets and UDP

Lecture 7 Socket programming.

Lecture 8 Introduction to the transport layer; multiplexing and demultiplexing; UDP.

Week 5Oct 6 & 8 · Reliable transport and TCP

Lecture 9 Principles of reliable data transfer.

Lecture 10 Pipelined protocols; TCP connection management and reliable data transfer.

Week 6Oct 13 & 15 · Congestion and network layer

Lecture 11 Principles of congestion control; TCP congestion control.

Lecture 12 Congestion-control futures; introduction to the network layer: forwarding, routing, data plane, and control plane.

Week 7Oct 20 & 22 · Routers and Exam I

Lecture 13 What is inside a router?

In-class Exam I

Week 8Oct 27 & 29 · IP, SDN, and middleboxes

Lecture 14 The Internet Protocol: IPv4 and IPv6.

Lecture 15 Generalized forwarding and SDN; middleboxes.

Week 9Nov 3 & 5 · Election Day and routing algorithms

Election Day · No class

Lecture 16 Link-state and distance-vector routing algorithms.

Week 10Nov 10 & 12 · Routing protocols and link layer

Lecture 17 Routing protocols: OSPF and BGP.

Lecture 18 Introduction to the link layer; error detection and correction; multiple-access protocols.

Veterans Day holiday

Week 11Nov 17 & 19 · TBA and switched LANs

Topic TBA

Lecture 19 Cable networks (DOCSIS); switched LANs.

Week 12Nov 24 · Wednesday schedule and Thanksgiving break

Wednesday schedule · No CS453 class

Thanksgiving break

Week 13Dec 1 & 3 · Data centers and wireless

Lecture 20 Data-center networking; retrospective: a day in the life of a web-page request.

Lecture 21 The wireless channel; Wi-Fi and Bluetooth.

Week 14Dec 8 & 10 · 4G/5G and Exam II

Lecture 22 4G/5G networks.

In-class Exam II

Week 15Dec 15 · It’s time to say goodbye!

Lecture 23 Course wrap-up.

Link Layer

Grading frame

Each component contributes a field to the final frame. No single packet determines the whole transmission.

Assignment deadlines: Every assignment has a due date and is due at 11:59 PM EDT on that date.

15%

Written homework

Five or six weekly, open-book assignments completed through Canvas.

15%

Wireshark labs

Near-weekly packet-analysis labs completed on your own laptop and submitted through Canvas.

20%

Programming assignments

Two assignments in a high-level language such as Python, Java, or C, submitted through Gradescope.

15%

Midterm Exam I

Covers approximately the first half of the course. See the schedule for the exam date.

15%

Midterm Exam II

Covers only the second half of the course and is held near the end of the semester.

20%

Optional final exam*

This comprehensive exam covers the entire course. You may keep your provisional grade or take the final; it can only improve your course grade.

*How the optional final works: The optional final is comprehensive and covers the entire course. After the other coursework is complete, you will receive a provisional grade based on the components above excluding the final. You may accept that grade or take the final exam, which is weighted at 20% relative to the other components. Your final course grade will be the higher of the two calculations.

Physical Layer

Our course policies

Extension

Every deadline comes with an automatic, no-penalty, one-day extension. After that, the credit you receive decreases by 10% for each additional day late. If you need more time for an assignment, please reach out to the instructor. We are very willing to accommodate exceptional circumstances, but we do need you to communicate with us.

Academic honesty policy

Copying programs, written homework, or exam answers is not permitted. Working as a team on an individual written or programming assignment is also not permitted. You are welcome to discuss concepts and assignment questions with other students, but the work you submit must be substantially your own.

A student found violating this policy will receive, as an informal resolution, a grade of 0 on the assignment. A subsequent violation will result in a failing grade for the course. If you are struggling with an assignment or a deadline, please contact the instructor or a TA. We will bend over backwards to help, but we will not tolerate cheating. Please read the UMass Academic Honesty Policy.

AI policy

We are okay with you using AI tools to help clarify concepts, explore examples, and debug code you have written. However, please do not use AI to generate assignment solutions or write the code for you. The purpose of these assignments is to help you understand the course content and develop your own problem-solving and programming skills. Outsourcing that work may save time today, but it can quietly create gaps that make later assignments, exams, interviews, and future courses much harder. If you feel that you need to use AI because you are running out of time, please reach out to us instead. We really want you to learn, and we will do our best to help you find a workable path forward. When in doubt, ask us whether a particular use is appropriate.

Accessibility

Please contact Disability Services and the instructor early so that accommodations can be arranged smoothly.

Well-being

Your well-being matters more than any single assignment. Sometimes life takes an unexpected turn, and none of us needs extra stress piled on top of that. If something is affecting your ability to participate or meet a deadline, please do not hesitate to reach out. You do not need to share more than you are comfortable sharing, but please communicate with us so we can help identify a reasonable path forward. We care about both your learning and your well-being, and we want you to be successful in this course.

Changes to the syllabus

The schedule may evolve. Important changes will be announced in class and posted on Canvas.