BBN TCP Vax-Unix

By 1979 the basic TCP/IP specification had been finalised and in
1980 the US Department of Defence decided to make it its standard
inter-networking protocol; Arpanet users were directed to switch over
from NCP to TCP/IP on January 1st 1983 ('flag day'). A good half dozen
interoperable research implementations existed (for an example see
BBN-V6 http://minnie.tuhs.org/cgi-bin/utree.pl?file=BBN-V6/tcp), but no
production quality reference implementation. DARPA contracted with BBN
to write such a reference implementation for 4BSD Unix.

In January 1981 the design was ready (documented in IEN168
https://www.rfc-editor.org/ien/ien168.txt) and coding proceeded. In
parallel several loose ends in the TCP/IP specifications were tied in
(for example, ICMP replaced GGP as the control message protocol) and
these specification changes were back integrated into the code base. In
November 1981 a beta distribution tape that overlaid on 4.1BSD was
ready. The network API was very similar to that of the earlier NCP Unix
(see SRI-NOSC http://minnie.tuhs.org/cgi-bin/utree.pl?file=SRI-NOSC). With
DARPA funding, the code was further developed and maintained into the
early 90’s.

Next to networking extensions to the kernel, the beta distribution tape
contains several user programs such as clients and servers for Telnet
and FTP. It also contains a mail system based on a precursor to SMTP,
called MTP https://tools.ietf.org/html/rfc772. MTP shows the transition
of mail from a feature of FTP to an independent protocol.

Separately, DARPA contracted in 1981 with Berkeley’s CSRG to develop
4.2BSD and to integrate this reference implementation with it. As such,
it became the starting point for 4.1a BSD. This beta distribution tape
comes from the CSRG archives.