Computed here
Carries computed results with the working and the starting numbers shown
Part 2 · Cables and waves
The ceiling of a channel — a number nobody gets pastIn 1948 someone proved that every channel has a ceiling computable from its width and its noise, and that no coding scheme can ever cross it
Part 2 · Cables and waves
Wi-Fi — a radio that cannot hear itselfEverything that separates Wi-Fi from Ethernet follows from one fact of physics, and the measured speed on a laptop that never moved swung by almost seven times
Part 2 · Cables and waves
Cellular networks — the invention was not mobilityMobile radiotelephones existed thirty years before cellular. What cellular added was reusing the same frequencies, and that is pure geometry you can compute
Part 3 · Inside one network
Topology — the drawing and the realityTextbooks draw bus, ring, star and mesh, but every network you buy today is physically a star, and how it behaves depends on the box in the middle
Part 4 · Across networks
Routing — what the gateway actually does nextNineteen articles on this site mention routes, and none explained how a router decides. This one answers with a single rule you can measure on your own machine
Part 7 · Boundaries and filtering
Firewalls — the last matching rule winsA firewall does not decide what is safe, it decides what matches a rule — and the packet filter shipping with macOS defaults to pass, not block
Part 7 · Boundaries and filtering
Stateful and stateless — what a firewall remembers, and what remembering costsA stateful firewall runs its own state machine alongside the endpoints, invents a connection for UDP where none exists, and pays three prices for the privilege
Part 8 · Out to the wider world
Switching — why the internet wonA network has two choices, reserve the path first or send piece by piece and find the way — and the ones that lost did not lose by being worse, while ATM paid for its 53-byte cell forever