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 ]