For most of a century the telephone network knew who was talking. A call reserved a physical path and held it: two identified endpoints, a start time, a route, an explicit hang-up. By the late 1970s the signaling layer underneath tracked all of that well enough to bill you by the second. The relationship between two people talking was something the network itself maintained.

Donald Davies, working on data communication in Britain in the mid-1960s, kept circling the waste in that arrangement. An hour on the line during which almost nothing is transmitted still occupies the circuit. Computers talk in bursts; reserving a lane for silence is expensive.

Data networks took the bits and left the rest. They got resilience, cheap components, and room for applications nobody had to clear in advance.

But the knowledge was useful, so it was rebuilt one layer up — cookies, tokens, session identifiers — by every application separately. It was also rebuilt outside the rules the phone network operated under. Common carriage, wiretap statutes, and audited billing records governed what a switch was allowed to know. Nothing comparable moved with it.