Network Working Group
Request for Comments: 22
Vint Cerf
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
    <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

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 ]