RFC22 - Host-host control message formats

Network Working Group Vint Cerf
Request for Comments: 22 UCLA
October 17, 1969

Host-Host Control Message Formats

NWG/RFC11 has been modified at UCLA; and will be republished. In
the meantime, it seems important to report a new control message
format which does not use 7-bit ASCII character mode of transmission.

All Host-Host control messages consist of sequences of 8-bit bytes of
the form:

It is reasonable to transmit more than one control message in any
given packet, although this is not mandatory.

Presently, 9 control messages have been defined by UCLA these are
given in the table below along with their parameters. The
interpretation is given from the point of view of the transmitting
host. ("L" or "Li" mean Link#, and are binary values.)

Control byte Parameter Interpretation

<0> <L> Please establish primary connection;
our output link # is L

<1> <L,> <L2> Please establish auxiliary connection
parallel to our primary output link L.
The auxiliary output link is L2.

<2> <L1> <L2> DK primary. Your primary output link
to us was L; our primary output link
to you is L2.

<3> <L1> <L2> OK auxiliary. Your auxiliary output
link is Li, our auxiliary output link
is L2.

<4> <L> Not OK primary. We cannot establish a
primary connection. Your primary
output link number was L.

<5> <Li> <L2> Not OK auxiliary. We cannot establish
an auxiliary connection. Your primary
output link no was L2.

<6> <L> Please stop transmitting over link
number L. This is called the CEASE
directive.

<7> <L> We are CLOSING our output link number
L. You may get this message before
the last message arrives over this
link since control messages are higher
priority than regular data messages.

<8> <L> UNCEASE: that is, you may resume
transmitting over output link number
L.

Each control message is embedded in the appropriate message structure
e.g.:

<-------------32 bits --------------->
| HEADER |
|____________________________________|
| | | | |
| mark | l | <L1> | <L2> |
|______|_______|___________|_________|
| | |
| checksum | Padding |
|_________________|__________________|
typical control message (please
establish auxiliary link #L2
parallel to our primary link #l)

The header for all HOST-HOST control messages is given below:

0 3 4 7 8 9 10 14 LINK# 24 31
_______________________________________________________________
| | | | | |////////////////|
| FLAGS | TYPE | H | SITE | 00000001 |////////////////|
|_______|______|_____|_______|_______________|________________|

where FLAGS - 0000
TYPE - 0000 (regular message)
H - host #(0-3) at SITE (usually 0 for single HOST sites)
SITE - Site #
LINK# - 00000001 (HOST-HOST control link)

[ This RFCwas put into machine readable form for entry ]
[ into the online RFCarchives by Alison De La Cruz 12/00 ]