Point-to-Point Protocol (PPP) and Serial Line IP (SLIP) are widely used protocols for carrying IP packets over a serial link. A number of institutions offer dialup PPP and SLIP access to machines that are on the Internet, thus providing IP connectivity to private persons (something that's otherwise hardly affordable).
No hardware modifications are necessary to run PPP or SLIP; you can use any serial port. Since serial port configuration is not specific to TCP/IP networking, we have devoted a separate chapter to this. Please refer to Chapter 4, for more information. We cover PPP in detail in Chapter 8, and SLIP in Chapter 7.