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
About Computer Networks
Networking is taught in layers, and the layers are not an implementation detail — they are the reason the internet could be built at all. Each layer solves one problem and assumes the layer below solved its own, so a browser can request a page without knowing whether the packets travel over fibre or radio.
The consequence worth internalising early is that the network guarantees very little. Packets are lost, duplicated, delayed and reordered as a matter of routine. Nearly every mechanism here — checksums, sequence numbers, acknowledgements, congestion windows — exists to build a reliable stream on top of a medium that offers no such thing.
Because the interesting behaviour is all about timing and ordering, static diagrams tend to hide exactly what matters. A three-way handshake, a CRC catching a flipped bit, a distance-vector table converging hop by hop: these are processes, and they are shown here as processes.
What to know first
- The idea that data can be split into chunks and reassembled
- No hardware knowledge — everything needed is built up here
Where it gets used
- Reading a packet capture and knowing which layer a fault belongs to
- Understanding why latency, not bandwidth, governs how a page feels
- Subnetting a network without reaching for a calculator