SLIP Operation
Dialup IP servers frequently offer SLIP service through special user accounts. After logging in to such an account, you are not dropped into the common shell; instead, a program or shell script is executed that enables the server’s SLIP driver for the serial line and configures the appropriate network interface. Then you have to do the same at your end of the link.
On some operating systems, the SLIP driver is a user-space program;
under Linux, it is part of the kernel, which makes it a lot faster.
This speed requires, however, that the serial line be converted to the
SLIP mode explicitly. This conversion is done by means of a special
tty line discipline, SLIPDISC. While the tty is in normal line
discipline (DISC0), it exchanges data only with user processes, using
the normal read(2) and
write(2) calls, and the SLIP driver is unable to
write to or read from the tty. In SLIPDISC, the roles are reversed:
now any user-space processes are blocked from writing to or reading
from the tty, while all data coming in on the serial port is passed
directly to the SLIP driver.
The SLIP driver itself understands a number of variations on the SLIP protocol. Apart from ordinary SLIP, it also understands CSLIP, which performs the so-called Van Jacobson header compression (described in RFC-1144) on outgoing IP packets. This compression improves throughput for interactive sessions noticeably. There are also six-bit versions for each of these protocols.
A simple way to convert ...
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