Computer Networks
How computers actually talk to each other, built up from first principles: wires and radio waves, addresses, routing, reliability, and the web itself. Every idea is explained with a simple picture first, then the real math behind it.
Written byRohan Sharma
Foundations of Networking
4 lessons- 8 min read
What is a network, really?
Why computers need to talk to each other at all, and the one simple idea sitting underneath every network you have ever used.
- 9 min read
Protocols and the layered model
Why network software is built like a set of nested envelopes, and how the OSI and TCP/IP models describe it.
- 8 min read
Circuit switching, packet switching, and the virtual circuit compromise
A deeper look at the three ways to move data through a network, including the middle-ground idea most students forget: virtual circuits.
- 9 min read
Bits, bytes, and how devices get addresses
A gentle path from counting on your fingers to binary numbers, and why every device needs both a MAC address and an IP address.
Foundations of Networking Quiz
10 questions
Physical Layer & Signals
3 lessons- 8 min read
How bits become wires, light, and radio waves
What is physically happening inside a cable or through the air when a computer sends a 0 or a 1.
- 8 min read
Bandwidth, latency, and throughput
The three numbers that actually decide whether your internet "feels fast," and the math connecting all three.
- 11 min read
Noise, errors, and how we catch them
Why bits flip during transmission, and the simple math (parity and checksums) used to catch it before it causes real damage.
Physical Layer & Signals Quiz
9 questions
Data Link Layer
6 lessons- 9 min read
Framing techniques and CRC, the real error-detection workhorse
How a receiver knows exactly where one frame ends and the next begins, and the polynomial division trick (CRC) that catches errors far better than a simple checksum.
- 8 min read
Frames, switches, and how a local network delivers mail
How raw bits get organized into frames, and why a switch is smarter than just a shared wire.
- 7 min read
Sharing the wire without everyone talking at once
What happens when two devices try to send at the exact same instant, and the simple rules (CSMA/CD and CSMA/CA) that stop it from becoming chaos.
- 9 min read
ALOHA and token passing: two more ways to share the channel
The classic Medium Access Control numericals — pure ALOHA, slotted ALOHA, and token passing — worked through step by step with the actual efficiency formulas.
- 7 min read
ARP, or how a device finds its neighbor's fingerprint
The knock-on-every-door trick your computer uses to translate an IP address into a MAC address before it can send anything.
- 8 min read
Bridges, and how Ethernet segments get joined without chaos
How a bridge grows a network beyond one shared segment, and the spanning tree trick that stops bridges from looping a frame forever.
Data Link Layer Quiz
14 questions
Network Layer & Routing
6 lessons- 10 min read
IP addresses and the math of subnetting
How one IP address is split into a "network part" and a "host part," and the binary math behind subnet masks and CIDR notation.
- 8 min read
IP fragmentation, when a packet is too big for the road
What happens when a packet is larger than a link can carry, and the math behind how IP splits it into smaller pieces and reassembles them.
- 9 min read
How routers find a path across the internet
What a router actually does with every packet, and how routing tables and simple shortest-path math decide which way traffic flows.
- 10 min read
Flooding, distance vector, and link state routing compared
Three real strategies routers use to learn the network's shape: shout to everyone, gossip with neighbors, or build a full map.
- 8 min read
DHCP and ICMP: the IP layer's helper protocols
How a device gets its own IP address automatically, and how the network reports problems back using ICMP (the protocol behind ping and traceroute).
- 8 min read
NAT, and why we ran out of IP addresses
Why your entire household shares one public IP address, and how IPv6 was designed to make address scarcity a permanently solved problem.
Network Layer & Routing Quiz
15 questions
Transport Layer
5 lessons- 8 min read
Ports, and the choice between TCP and UDP
How one IP address serves hundreds of programs at once, and the fundamental trade-off between reliable TCP and fast, careless UDP.
- 9 min read
The three-way handshake and how TCP stays reliable
Why TCP shakes hands before talking, and the sequence number math it uses to guarantee nothing gets lost or reordered.
- 11 min read
Stop-and-Wait, Go-Back-N, and Selective Repeat: the classic ARQ numericals
How reliable delivery actually gets implemented step by step, with the exact efficiency formulas and worked numericals for all three sliding window strategies.
- 9 min read
Flow control and congestion control
How TCP avoids drowning a slow receiver, and how it avoids drowning the network itself, using two related but different windows.
- 7 min read
Sockets, where your code actually meets the network
The programming-level handle that turns everything this course has covered into a few lines of actual code.
Transport Layer Quiz
14 questions
Application Layer & The Web
4 lessons- 8 min read
DNS, the internet's phonebook
How typing a name like google.com turns into an actual IP address, through a surprisingly simple chain of questions.
- 9 min read
HTTP, and everything that happens when you load a webpage
The request-response conversation your browser has with a server, and exactly which layers from this whole course get used along the way.
- 7 min read
FTP, and why file transfer got its own dedicated protocol
Why FTP uses two separate connections at once, and what problem that unusual design was actually built to solve.
- 7 min read
Email and the other quiet protocols running the internet
How email actually travels between providers, and a tour of the other application-layer protocols working behind the scenes.
Application Layer & The Web Quiz
8 questions
Wireless, Security & Performance
3 lessons- 10 min read
Encryption and how HTTPS keeps a connection private
Why plain HTTP is like a postcard anyone can read, and the clever math (public-key cryptography) that lets two strangers agree on a secret key in public.
- 8 min read
Firewalls, and the attacks they defend against
How a firewall decides what traffic to let through, and simple explanations of DoS attacks, spoofing, and man-in-the-middle attacks.
- 8 min read
Wi-Fi standards and real-world network performance
What those Wi-Fi generation names actually mean, and how to reason about why your real speed never quite matches the number on the box.
Wireless, Security & Performance Quiz
7 questions
Assessments
8 quizzesFoundations of Networking Quiz
Foundations of Networking · 10 questions
Physical Layer & Signals Quiz
Physical Layer & Signals · 9 questions
Data Link Layer Quiz
Data Link Layer · 14 questions
Network Layer & Routing Quiz
Network Layer & Routing · 15 questions
Transport Layer Quiz
Transport Layer · 14 questions
Application Layer & The Web Quiz
Application Layer & The Web · 8 questions
Wireless, Security & Performance Quiz
Wireless, Security & Performance · 7 questions
Computer Networks Final Assessment
Final assessment · 24 questions