4.2BSD/usr/doc/net/3.t

.nr H2 1
.ds RH Goals
.NH
\s+2Goals\s0
.PP
The networking system was designed with the goal of supporting
multiple \fIprotocol families\fP and addressing styles.  This required
information to be ``hidden'' in common data structures which
could be manipulated by all the pieces of the system, but which
required interpretation only by the protocols which ``controlled''
it.  The system described here attempts to minimize
the use of shared data structures to those kept by a suite of
protocols (a \fIprotocol family\fP), and those used for rendezvous
between ``synchronous'' and ``asynchronous'' portions of the
system (e.g. queues of data packets are filled at interrupt
time and emptied based on user requests).
.PP
A major goal of the system was to provide a framework within
which new protocols and hardware could be easily be supported.
To this end, a great deal of effort has been extended to
create utility routines which hide many of the more
complex and/or hardware dependent chores of networking.
Later sections describe the utility routines and the underlying
data structures they manipulate.
.ds RH "Address representation
.bp