Apple Training Series: Mac OS X Support Essentials v10.6: A Guide to Supporting and Troubleshooting Mac OS X v10.6 Snow Leopard

PPP is a standard protocol for connecting a computer to the Internet, usually with a dial-up modem.

PPP provides error-checking features.

PPP sends the computer's TCP/IP packets to a server, which puts packets onto the Internet.

PPP can be configured in Network preferences and Internet Connect.

Resources for PPP are found in /System/Library/ModemScripts.