SLIP is an asynchronous serial line protocol developed for running TCP/IP
over serial communications lines in a point-to-point configuration. SLIP
was developed to transmit IP packets over low-speed, sometimes noisy,
asynchronous communications lines where error recovery and an efficient
line protocol is needed. A new, serial, line protocol named "PPP" is
replacing SLIP. PPP uses an even more efficient means of establishing a
point-to-point IP connection.
MacTCP 1.0.2 has hooks for different third-party link-layer modules. This
helps the development of interfaces to SLIP, PPP, and any other link layer,
like broadband, X.25, FDDI, and so on. Apple does not provide support in
MacTCP for SLIP or any other serial line protocol. These have to come from
third-party developers.