RFC 89 from January 1971 is interesting:
While awaiting the completion of an interim network
control program
(INCP) for the MIT MAC Dynamic Modeling/Computer Graphics PDP-6/10
System (MITDG), we were able to achieve a number of 'historic moments
in networking' worthy of some comment.
Our experiments were run on the MITDG PDP-6/10 using
what we have
affectionately called our 'interim interim NCP' (IINCP).
MITDG runs the MAC Incompatible Time-sharing System
(ITS)
At MITDG are a PDP-6/10 Time-sharing System
https://tools.ietf.org/rfc/rfc89.txt