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Network Working Group                                          Vint CerfRequest for Comments: 22                                            UCLA                                                        October 17, 1969Host-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.Cerf                                                            [Page 1]

RFC 22             Host-Host Control Message Formats        October 1969    <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 ]Cerf                                                            [Page 2]