Making Things Talk

THE TOOLS 19

Serial protocols like RS-232, USB, and IEEE 1394 (also

known as FireWire and i.Link) connect computers to

printers, hard drives, keyboards, mice, and other periph-

eral devices. Network protocols like Ethernet and TCP/IP

connect multiple computers to each other through

network hubs, routers, and switches. A communications

protocol usually defines the rate at which messages are

exchanged, the arrangement of data in the messages, and

the grammar of the exchange. If it’s a protocol for physical

objects, it will also specify the electrical characteristics,

and sometimes even the physical shape of the connectors.

Protocols don’t specify what happens between objects,

however. The commands to make an object do something

rely on protocols in the same way that clear instructions

rely on good grammar. You can’t give good instructions if

you can’t form a good sentence.

One thing that all communications protocols share, from

the simplest chip-to-chip message to the most complex

network architecture, is this: it’s all about pulses of energy.

Digital devices exchange information by sending timed

pulses of energy across a shared connection. The USB

connection from your mouse to your computer uses

two wires for transmission and reception, sending timed

pulses of electrical energy across those wires. Likewise,

wired network connections are made up of timed pulses of

electrical energy ...