by Darius Kazemi, September 20 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.

Long distances

RFC-263 is titled “'Very Distant' Host Interface”. It's authored by Alex McKenzie of BBN and dated December 17, 1971.

The technical content

Recap time: the ARPANET consists of host computers conencted to Interface Message Processors (IMPs). Each IMP is its own computer that is sort of like combination routers and modems that connect you to a network of all the other IMPs. Physically speaking, this means that a host site, like UCLA, would have an IMP installed on site, and any network-enabled computers would be hooked up to the IMP via wires.

The IMPs are pretty close to the computers they serve. The wired connections are usually not more than 2,000 feet long. The (simplified) reason for this short distance is that the longer your wires are, the more chance there is of interference and other natural phenomena to introduce errors in your transmission.

In this RFC, McKenzie presents a design for a longer-distance connection that meets these criteria:

The connection will use something called a cyclic redundancy check (CRC). I'm not an expert in this stuff but it seems to me like a souped-up checksum, and like a checksum it's used for error detection. The IMP will retransmit messages where errors are detected.

The host computer's Network Control Program (or perhaps some specialized hardware) will need to provide the same level of CRC and retransmission functionality.

The design is preliminary but this RFC is a kind of early warning to the Network Working Group that these changes are in the works and comments are, well, requested.

How to follow this blog

You can subscribe to this blog's RSS feed or if you're on a federated ActivityPub social network like Mastodon or Pleroma you can search for the user “@365-rfcs@write.as” and follow it there.

About me

I'm Darius Kazemi. I'm an independent technologist and artist. I do a lot of work on the decentralized web with ActivityPub, including a Node.js reference implementation, an RSS-to-ActivityPub converter, and a fork of Mastodon, called Hometown. You can support my work via my Patreon.