by Darius Kazemi, May 28 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.

Severe strains

RFC-148 is titled “Comments on RFC #123”. It's authored by Abhay Bhushan of MIT Project MAC, dated May 7th, 1971.

The technical content

This RFC registers a complaint about the Initial Connection Protocol. Recall that byte size varies wildly from computer to computer — the ICP asks that computers send 32-bit bytes during the very initial stages of initial connection. So a server goes:

  1. Listen for a message of byte size 32
  2. On connection, send socket data, using byte size 32
  3. Close this connection
  4. Initialize the long-term connection using byte size B, as requested by the user

The Network Control Program (NCP) running on the PDP-10 at Project MAC has two modes: 36-bit bytes, and 8-bit ASCII bytes where the high bit is always 0. So they can't send arbitrary 32-bit data by stringing together four 8-bit bytes, as they are limited by the high bit of each byte always being zero. And the least common multiple of 36 and 32 is 288, which means they could send 8 36-bit bytes at a time representing a total of 9 32-bit bytes. But that seems unweildy.

Buhshan suggests that the default byte size on connection could be very large, like 72 bits, and use filler bits.


Personally it sounds like Project MAC's NCP could use some tweaking to conform to the initial connection protocol, not the other way around.

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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 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.