by Darius Kazemi, Jan 18 2019
RFC-18 is another short Vint Cerf RFC from September 1969. Here is the whole thing:
It is suggested that link 1 be used for the HOST-HOST control link and link 0 be used for IMP-IMP control.
This will facilitate communication between Hosts and reduce delays due to interference with IMP-IMP communications.
If you'll recall, link 0 has been reserved for control communications like the initial handshake between HOSTs. But IMPs need to talk to each other too, and this proposes that IMPs coordinate over link 0, HOSTs coordinate over link 1. So HOST traffic wouldn't get in the way of IMPs coordinating with each other, I guess.