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rfc:rfc22

Network Working Group Vint Cerf Request for Comments: 22 UCLA

                                                      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.

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]

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