Request for Comments: 22
October 17, 1969
Host-Host Control Message Formats
NWG/RFC 11 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:
<control byte> <parameter byte l> ... <parameter byte n>
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 RFC was put into machine readable form for entry ] [ into the online RFC archives by Alison De La Cruz 12/00 ]