Computer Networks
Networking is easiest to believe when you can see the packet. These topics animate a single message as it is framed, addressed, routed, acknowledged and reassembled.
Start from the beginning →13 topics you can watch now, 12 still to come.
Foundations
What a network is before any of it is layered, and the one design decision everything else follows from.
- What is a Computer Network?Start here. Two machines, one wire, and the four problems that appear the moment you add a third.
- Circuit vs Packet SwitchingThe choice the internet made, shown as the same three conversations sharing one link two different ways.
- LAN, MAN and WAN
- Network topologies
The layered model
Why a network is built in layers, and what each one adds to your message.
- OSI and TCP/IP LayersSeven layers against four — including the two OSI layers nobody ever implemented.
- Encapsulation of One MessageFollow five bytes down four layers, across the wire, and back up the other side.
- Delay, bandwidth and RTT
Link layer
Getting a frame across one hop reliably, over a wire that loses things.
- CRC Step by StepBinary long division with XOR instead of subtraction — and why the remainder catches every burst error.
- Stop-and-WaitOne frame at a time. Simple, correct, and mostly spent waiting — plus the duplicate that explains sequence numbers.
- Go-Back-NOne frame is lost, two intact ones are thrown away, and six frames cost nine transmissions.
- Selective RepeatThe same loss as Go-Back-N, but the receiver buffers — so it costs seven transmissions instead of nine.
- Framing and error detection
- CSMA/CD and CSMA/CA
Network layer
Finding a path across many hops, and addressing the far end.
- IPv4 Addressing and SubnettingMove the boundary between network and host bits, and watch subnets double as hosts halve.
- Distance Vector RoutingTell your neighbours what you know — then watch count-to-infinity happen when a link fails.
- Link State and DijkstraEvery router holds the whole map and computes its own shortest-path tree.
- Longest prefix match
- NAT and fragmentation
Transport layer
Turning a best-effort network into a connection two programs can trust.
- UDP vs TCP
- Sliding window flow control
- Congestion control: slow start to CUBIC
Application layer
The protocols you actually use, sitting on top of all of it.
- HTTP/1.1 vs HTTP/2
- TLS handshake