ARPA Network Functional Specifications
A handwritten May 1969 specification covering error checks, host-to-host links, and how two hosts open a connection.
Deloche, G., "ARPA Network Functional Specifications", RFC 8, DOI 10.17487/RFC0008, May 1969, <https://www.rfc-editor.org/info/rfc8>.
@misc{rfc8,
series = {Request for Comments},
number = 8,
howpublished = {RFC 8},
publisher = {RFC Editor},
doi = {10.17487/RFC0008},
url = {https://www.rfc-editor.org/info/rfc8},
author = {G. Deloche},
title = {{ARPA Network Functional Specifications}},
year = 1969,
month = may,
} RFC text
This text was converted from the RFC Editor's PDF edition and may contain conversion errors; the layout is approximate. The PDF is the reference copy.
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Title: ARPA Network Functional Specifica.tions
Author: G. Deloche
Insta.llation: University of Cal i forni a at Los Angeles
Date: 5 May 1969
Networ-k l'iorki.ng Group Request foT. Comnerrt : 8
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On this page
§1Transmission Checking
The note names two kinds of transmission checking. Between IMPs, a cyclic checksum is computed and checked by the BBN hardware. Between hosts, a special 16-bit checksum is computed and checked by the host programs.
For the host checksum a message is broken into 1152-bit pieces, an end-around carry sum is calculated for each piece, and the pieces are combined with increasing weights (the sum of the first piece, plus twice the sum of the second, plus four times the sum of the third, and so on). The 16-bit result sits just after the marking of the host heading. The author says this also guards against bad host-to-IMP or IMP-to-host transmission and against IMP packet number inversion, and gives a small worked end-around carry example.
It is like counting the pieces in a puzzle box twice, once when it is packed and once when it arrives, to check nothing fell out.
§2Links Between Two Hosts
Thirty-two links are possible between two hosts, and each is viewed as full duplex. Link 0 is a control link, used for connection requests and status of any kind. The other 31 serve either as teletype-like connections or as file transmission connections.
A teletype-like connection carries ASCII characters, the remote host generates the echoes and looks for break or interrupt control characters, and the transmission is slow.
Think of 32 phone lines between two houses. One is only for saying who is going to call whom, and the rest carry chats or big deliveries.
§3Functional Software Specifications
The note splits host software into three parts. The user program is an application such as the NLS program at SRI. It is viewed as a local control part (the user interface) and a hard part (the application), and the local control program could be sent to another host, written in a Decode Encode Language called DEL, so that only program data crosses the link.
The network program multiplexes outgoing messages and distributes incoming ones, runs link initiation, builds the host message heading, computes and checks the host-host checksum, receives RFNM control messages and supervises the handler. The transmission handler is initiated by the network program or by the I/O interrupt, controls the channel hardware unit and is very short.
There is a person who does the job, a manager who sorts the mail and checks it, and a small driver who runs the van.
§4Establishing a Link
The general procedure is to establish a teletype-like link to the remote host in a pre-log-in state, send and receive characters, then set up a file-like link in parallel, which both host user programs must do, and send over it.
In the example, a user at UCLA wants NLS at SRI. The network program selects an open link, for example 25, sends a message over link 0 requesting a connection on link 25, and waits for an acceptance over link 0. If both sides try the same link at once, the one with the higher priority prevails; the author suggests priority be exactly the host identification number.
You first ring the front desk line to ask for a room number, wait for a yes, then use that room. If two people ask for the same room at once, the one with the higher number wins.