showstack

The layer model, as a lookup

Where each thing indexed on this site sits, and what it therefore can and cannot do. The network explainer has the animated version and the reasoning.

Two things worth reading off this. DMX512 has no layers above 1 and 2 at all, which is why it cannot be routed, addressed or acknowledged — every limitation follows from that row. And a protocol at layer 7 inherits every property of the layers under it, which is why “is it on the network?” is a different question from “can the switch see it?”

Serial bus rates

Signalling rates for the buses that turn up in a rack, so a spec sheet can be read against what the cable can actually carry. Usable throughput is always lower — encoding overhead, protocol overhead, and in the case of USB a shared bus.

Bits and bytes are the trap here: a 10 Gbit/s link moves at most 1.25 GB/s before overhead, and GT/s is not Gbit/s — PCIe transfers carry encoding, so gen 3 at 8 GT/s yields about 7.88 Gbit/s of payload per lane. The storage calculator works in bytes; the numbers above are in bits.

Analog vs digital — and what it changes per department

An analog signal represents its value directly as a continuously variable voltage, current or light level — every metre of cable, every connector and every amplifier stage adds a little noise and loss that cannot be undone. A digital signal encodes the value as discrete symbols; as long as the receiver can still tell the symbols apart, it can be regenerated bit-perfect at every hop, which is why digital chains tolerate long runs and many hops that would visibly degrade an analog one — and why, past their rated distance, digital links tend to fail hard (the "cliff effect") rather than gracefully.