rfc907.txt

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             +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
     0-5     |            DATAGRAM MESSAGE HEADER            |
             +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
     6-N     |          <OPTIONAL INTERNET HEADER>           |
             +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
     N+1     |      SETUP TYPE       |      SETUP CODE       |
             +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
     N+2     |                 SETUP CHECKSUM                |
             +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
     N+3     |                   SETUP  ID                   |
             +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+


                      Figure 6 . SETUP MESSAGE HEADER



     0-5        Datagram Message Header.  Each  setup  message  begins
                with the six word datagram message header (see Section
                3).

     6-N        Internet  Header  (Optional).   These   fields,   when
                present, conform to the DoD Standard Internet Protocol
                (IP). The Internet header size  is  a  minimum  of  10
                words  but  can  be  longer  depending  on  the use of
                optional  IP   facilities.    (Internet   notification
                messages are not supported.)

     N+1[8-15]  Setup Type.  This field determines the type  of  setup
                message.

                     0 = Acknowledgment
                     1 = Request
                     2 = Reply
                     3 = Notification

     N+1[0-7]   Setup Code.  For requests,  this field identifies  the



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     RFC 907                                      Host Access Protocol
     July 1984                                           Specification



                Request Type.

                     1 = Create group address
                     2 = Delete group address
                     3 = Join group
                     4 = Leave group
                     5 = Create stream
                     6 = Delete stream
                     7 = Change stream parameters
                     8 = Reserved

                For Replies, this field provides the Reply Code.  Some
                of  the  Reply  Codes  can  be  returned  to any setup
                request and others are request specific.

                     0 = Group or stream created
                     1 = Group or stream deleted
                     2 = Group joined
                     3 = Group left
                     4 = Stream changed
                     5 = Reserved
                     6 = Bad request type
                     7 = Reserved
                     8 = Network trouble
                     9 = Bad key
                    10 = Group address/stream ID nonexistent
                    11 = Not member of group/creator of stream
                    12 = Stream priority not being accepted
                    13 = Reserved
                    14 = Reserved
                    15 = Illegal interval
                    16 = Reserved
                    17 = Insufficient network resources
                    18 = Requested bandwidth too large
                    19 = Reserved
                    20 = Reserved
                    21 = Maximum messages per slot not consistent with
                         slot size
                    22 = Reply lost in network
                    23 = Illegal reliability value




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     RFC 907                                      Host Access Protocol
     July 1984                                           Specification



                For   Notifications,   this   field    contains    the
                Notification Type.

                     0 = Stream suspended
                     1 = Stream resumed
                     2 = Stream deleted
                     3 = Group deleted by host
                     4 = Group deleted by SIMP
                     5 = All streams deleted
                     6 = All groups deleted

                For   Acknowledgments,   this   field   contains   the
                Acknowledgment Type.

                     0 = Reply acknowledgment
                     1 = Notification acknowledgment

     N+2[0-15]  Setup Checksum.  The checksum covers the  three  setup
                message  header  words and the setup message body data
                words.  Setups received with  bad  checksums  must  be
                discarded.

     N+3[0-15]  Setup ID.  This field  is  assigned  by  the  host  to
                uniquely  identify  outstanding  requests (Request ID)
                and  by  the  service  host   to   uniquely   identify
                outstanding notifications (Notification ID).


















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     RFC 907                                      Host Access Protocol
     July 1984                                           Specification






              15 14 13 12 11 10  9  8  7  6  5  4  3  2  1  0
             +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
     0-5     |            DATAGRAM MESSAGE HEADER            |
             +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
      6      |           3           |   NOTIFICATION TYPE   |
             +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
      7      |                 SETUP CHECKSUM                |
             +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
      8      |                 NOTIFICATION ID               |
             +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
      9      |                NOTIFICATION INFO              |
             +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+


                      Figure 7 . NOTIFICATION MESSAGE



     0-5         Datagram Message Header (see Section 3).

       6[8-15]   Setup Type = 3 (Notification).

       6[0-7]    Notification Type.

                      0 = Stream suspended
                      1 = Stream resumed
                      2 = Stream deleted
                      3 = Group deleted by host
                      4 = Group deleted by SIMP
                      5 = All streams deleted
                      6 = All groups deleted

       7[0-15]   Setup Checksum. Covers words 6-9.

       8[0-15]   Notification ID.

       9[0-15]   Notification Information.  This  field  contains  the
                 16-bit   group   address  in  the  case  of  a  group



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     RFC 907                                      Host Access Protocol
     July 1984                                           Specification



                 notification (types 3 and  4)  and  the  10-bit  host
                 stream  ID  (right justified) in the case of a stream
                 notification (types 0-2).  This  field  is  zero  for
                 Notification  Types  5  and  6,  which pertain to ALL
                 streams and groups, respectively.







































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     RFC 907                                      Host Access Protocol
     July 1984                                           Specification






              15 14 13 12 11 10  9  8  7  6  5  4  3  2  1  0
             +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
     0-5     |            DATAGRAM MESSAGE HEADER            |
             +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
      6      |           0           |        ACK TYPE       |
             +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
      7      |                 SETUP CHECKSUM                |
             +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
      8      |                   SETUP  ID                   |
             +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+


                      Figure 8 . SETUP ACKNOWLEDGMENT



     0-5         Datagram Message Header.

       6[8-15]   Setup Type = 0 (Acknowledgment).

       6[0-7]    Acknowledgment Type.

                     0 = Reply acknowledgment
                     1 = Notification acknowledgment

       7[0-15]   Setup Checksum.  Covers words 6-8.

       8[0-15]   Setup  ID.   This  is  either  a  Request  ID  or   a
                 Notification ID.












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     RFC 907                                      Host Access Protocol
     July 1984                                           Specification



     6.1  Stream Setup Messages

          Hosts use  streams to support high duty  cycle  applications
     and   applications   requiring   a   one  satellite  hop  network
     transmission delay.  Host streams must be set  up  before  stream
     data messages can flow.  The stream setup messages defined by HAP
     are Create Stream Request, Create  Stream  Reply,  Delete  Stream
     Request,  Delete  Stream Reply, Change Stream Parameters Request,
     and Change Stream Parameters Reply.  The use of these messages is
     illustrated  in  the scenario of exchanges between a host and its
     local SIMP shown in Figure 9 where the host establishes a stream,
     sends  some data, modifies the stream characteristics, sends some
     more data, and finally closes down the stream.

          It is worthwhile noting that the setup exchanges in Figure 9
     are  completely  between  the host originating the stream and its
     local SIMP.  Other SIMPs and hosts are essentially unaware of the
     existence   of   the  stream.   Stream  messages  received  by  a
     destination  host  are,  therefore,  processed   identically   to
     datagram  messages.   (All SIMPs must, of course, be aware of the
     channel allocation associated with a  host  stream  in  order  to
     perform  satellite  channel  scheduling.)   Not  illustrated, but
     implicit in this  scenario,  are  the  optional  A/R  indications
     associated with each of the stream setup messages.




















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     RFC 907                                      Host Access Protocol
     July 1984                                           Specification






                                              Host       SIMP

             Create Stream Request                ------>
             Create Stream Reply                  <------
             Reply Acknowledgment                 ------>
             Stream Message                       ------>
                  .
                  .
             Stream Message                       ------>
             Change Stream Parameters Request     ------>
             Change Stream Parameters Reply       <------
             Reply Acknowledgment                 ------>
             Stream Message                       ------>
                  .
                  .
             Stream Message                       ------>
             Delete Stream Request                ------>
             Delete Stream Reply                  <------
             Reply Acknowledgmen