by Darius Kazemi, May 1 2019

In 2019 I'm reading one RFC a day in chronological order starting from the very first one. More on this project here. There is a table of contents for all my RFC posts.

On-line operators

RFC-121 is titled “Network On-line Operators” and authored by Mark Krilanovich of the Computer Research Lab at UCSB. It's dated April 21st, 1971, the same day as RFC-119 and RFC-120.

The technical content

This document is similar to RFCs 119 and 120 in that it documents an interface to the network that is “higher level” (more abstract and ideally easier to use) than the Network Control Program (NCP). In particular this document defines commands that a user of the UCSB On-Line System can enter in order to connect to remote hosts on the ARPANET.


It makes sense that RFCs 119, 120, and 121 were published together as they are all documentation for what seems like the exact same system, but implemented in three different programming environments.

Further reading

This brief guide to the Culler-Fried On-Line System (eventually just called the “On-Line System”) is worth a read. It's important to note that “on-line” did not mean “on the internet” back then, because again, there was no internet! “On-line” simply meant that you were directly interfacing with a computer through an interactive terminal of some kind. A personal computer today, with no internet attached to it, would still be considered “on-line” by 1969 standards.

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About me

I'm Darius Kazemi. I'm an independent technologist and artist. I do a lot of work on the decentralized web with both ActivityPub and the Dat Project. You can support my work via my Patreon.