1.8 BSD Networking History
The sockets API originated with the 4.2BSD
system, released in 1983. Figure 1.15 shows the development of the various
BSD releases, noting the major TCP/IP developments. A few changes
to the sockets API also took place in 1990 with the 4.3BSD Reno
release, when the OSI protocols went into the BSD kernel.
The path down the figure from 4.2BSD through
4.4BSD shows the releases from the Computer Systems Research Group
(CSRG) at Berkeley, which required the recipient to already have a
source code license for Unix. But all the networking code, both the
kernel support (such as the TCP/IP and Unix domain protocol stacks
and the socket interface), along with the applications (such as the
Telnet and FTP clients and servers), were developed independently
from the AT&T-derived Unix code. Therefore, starting in 1989,
Berkeley provided the first of the BSD networking releases, which
contained all the networking code and various other pieces of the
BSD system that were not constrained by the Unix source code
license requirement. These releases were "publicly available" and
eventually became available by anonymous FTP to anyone.
The final releases from Berkeley were
4.4BSD-Lite in 1994 and 4.4BSD-Lite2 in 1995. We note that these
two releases were then used as the base for other systems: BSD/OS,
FreeBSD, NetBSD, and OpenBSD, most of which are still being
actively developed and enhanced. More information on the various
BSD releases, and on the history of the various Unix systems in
general, can be found in Chapter 01 of [McKusick et al. 1996].
Many Unix systems started with some version of
the BSD networking code, including the sockets API, and we refer to
these implementations as Berkeley-derived
implementations. Many commercial versions of Unix are based
on System V Release 4 (SVR4). Some of these versions have
Berkeley-derived networking code (e.g., UnixWare 2.x), while the
networking code in other SVR4 systems has been independently
derived (e.g., Solaris 2.x). We also note that Linux, a popular,
freely available implementation of Unix, does not fit into the Berkeley-derived
classification: Its networking code and sockets API were developed
from scratch.
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