When two systems are physically connected, through a telephone line, it is typically referred to as a point-to-point connection or link. Support for TCP/IP Point-to-Point Protocol (PPP) is included on your IBM i systemas part of the Wide Area Network (WAN) connectivity.
The primary reason for connecting a remote host to the IBM i system by using a PPP link is for the purpose of exchanging data between locations. In addition, the Point-to-Point Protocol is commonly used as a means for connecting a computer to the Internet. PPP is an Internet standard and is the most widely used connection protocol among Internet Service Providers (ISP).
Layer Two Tunneling Protocol (L2TP) is also supported and is known as 'Virtual PPP'. Whereas PPP only allows you to run over a 'PPP line', L2TP allows you to run PPP traffic over any given physical interface supported by TCP/IP. By using L2TP tunneling in conjunction with IP-SEC, you can send, route, and receive data.
For more information visit PPP on the IBM i Information Center.