PPP

In networking, Point-to-Point Protocol[https://en.wikipedia.org/wiki/Point-to-Point_Protocol ] is a protocol meant to be run between network devices, rather than hosts, which can be used to handle authentication, encryption, compression, loop detection.

It was/is seen used on serial cables, acoustic modems, trunk lines, cellular telephones, some specialized radio links, ISDN, some fiber optic links, and if you include derivatives PPPoE and PPPoA, also DOCSIS style cable, and DSL style broadband. Particularly at the start of that list it is used as a data link protocol, distinguishing packets where the line itself doesn't do that for you(verify).

In GPS positioning, Precise Point Positioning is one way of improving precision