Packet protocols like IP or IPX rely upon the receiver host knowing
where the start and end of each packet are in the data stream. The
mechanism used to mark and detect the start and end of packets is
called delimitation. The Ethernet protocol
manages this mechanism in a LAN environment, and the SLIP and PPP protocols
manage it for serial communications lines.
The comparatively low cost of low-speed dialup modems and telephone circuits
has made the serial line IP protocols immensely popular, especially for
providing connectivity to end users of the Internet. The hardware required
to run SLIP or PPP is simple and readily available. All that is required is
a modem and a serial port equipped with a FIFO buffer.
The SLIP protocol is very simple to implement and at one time was the more
common of the two. Today almost everyone uses the PPP protocol instead. The
PPP protocol adds a host of sophisticated features that contribute to its
popularity today, and we'll look at the most important of these later.
Linux supports kernel-based drivers for both SLIP and PPP. The drivers
have both been around for some time and are stable and reliable. In
this chapter and the next, we'll discuss both protocols and how to