rfc907.txt

RFC 相关的技术文档

     RFC 907






                    HOST ACCESS PROTOCOL SPECIFICATION



                                 July 1984








                               prepared for

                 Defense Advanced Research Projects Agency
                           1400 Wilson Boulevard
                         Arlington, Virginia 22209








                                    by

                   Bolt Beranek and Newman Laboratories
                             10 Moulton Street
                      Cambridge, Massachusetts 02238
















     RFC 907                                      Host Access Protocol
     July 1984                                           Specification



     Preface (Status of this Memo)

          This document specifies  the  Host  Access  Protocol  (HAP).
     Although  HAP was originally designed as the network-access level
     protocol for the DARPA/DCA sponsored  Wideband  Packet  Satellite
     Network,  it is intended that it evolve into a standard interface
     between hosts and  packet-switched  satellite  networks  such  as
     SATNET  and  TACNET (aka MATNET) as well as the Wideband Network.
     The HAP specification presented here is a minor revision of,  and
     supercedes,  the  specification  presented  in  Chapter  4 of BBN
     Report No. 4469, the  "PSAT  Technical  Report".   As  such,  the
     details  of  the  current  specification  are  still most closely
     matched to the characteristics if the Wideband Satellite Network.
     Revisions  to  the  specification  in the "PSAT Technical Report"
     include  the  definition  of  three  new  control  message  types
     (Loopback Request, Link Going Down, and NOP), a "Reason" field in
     Restart Request control messages, new Unnumbered Response  codes,
     and  new  values  for  the setup codes used to manage streams and
     groups.

          HAP is an experimental protocol, and  will  undergo  further
     revision as new capabilities are added and/or different satellite
     networks  are  supported.   Implementations  of  HAP  should   be
     performed  in coordination with satellite network development and
     operations personnel.




























     RFC 907                                      Host Access Protocol
     July 1984                                           Specification



                             Table of Contents




     1   Introduction.......................................... 1
     2   Overview.............................................. 3
     3   Datagram Messages..................................... 8
     4   Stream Messages...................................... 14
     5   Flow Control Messages................................ 17
     6   Setup Level Messages................................. 24
     6.1   Stream Setup Messages.............................. 32
     6.2   Group Setup Messages............................... 44
     7   Link Monitoring...................................... 58
     8   Initialization....................................... 62
     9   Loopback Control..................................... 68
     10   Other Control Messages.............................. 72



























                                     i








     RFC 907                                      Host Access Protocol
     July 1984                                           Specification



                                  FIGURES




     DATAGRAM MESSAGE.......................................... 9
     STREAM MESSAGE........................................... 15
     ACCEPTANCE/REFUSAL WORD.................................. 19
     ACCEPTANCE/REFUSAL MESSAGE............................... 21
     UNNUMBERED RESPONSE...................................... 22
     SETUP MESSAGE HEADER..................................... 26
     NOTIFICATION MESSAGE..................................... 29
     SETUP ACKNOWLEDGMENT..................................... 31
     STREAM EXAMPLE........................................... 33
     CREATE STREAM REQUEST.................................... 35
     CREATE STREAM REPLY...................................... 37
     CHANGE STREAM PARAMETERS REQUEST......................... 39
     CHANGE STREAM PARAMETERS REPLY........................... 41
     DELETE STREAM REQUEST.................................... 42
     DELETE STREAM REPLY...................................... 43
     GROUP EXAMPLE............................................ 45
     CREATE GROUP REQUEST..................................... 47
     CREATE GROUP REPLY....................................... 48
     JOIN GROUP REQUEST....................................... 50
     JOIN GROUP REPLY......................................... 52
     LEAVE GROUP REQUEST...................................... 53
     LEAVE GROUP REPLY........................................ 55
     DELETE GROUP REQUEST..................................... 56
     DELETE GROUP REPLY....................................... 57
     STATUS MESSAGE........................................... 59
     HAP LINK RESTART STATE DIAGRAM........................... 64
     RESTART REQUEST.......................................... 65
     RESTART COMPLETE......................................... 67
     LOOPBACK REQUEST......................................... 71
     LINK GOING DOWN.......................................... 73
     NO OPERATION (NOP)....................................... 75








                                    ii








     RFC 907                                      Host Access Protocol
     July 1984                                           Specification



     1  Introduction

          The Host Access Protocol (HAP) specifies the  network-access
     level communication between an arbitrary computer, called a host,
     and a packet-switched satellite network.  The  satellite  network
     provides  message  delivery services for geographically separated
     hosts: Messages containing data which are meaningful to the hosts
     are submitted to the network by an originating (source) host, and
     are passed transparently through  the  network  to  an  indicated
     destination host.  To utilize such services, a host interfaces to
     the satellite network via an access link to a  dedicated  packet-
     switching  computer,  known  as  a  Satellite  Interface  Message
     Processor (Satellite IMP or SIMP).   HAP  defines  the  different
     types  of  control messages and (host-to-host) data messages that
     may be exchanged over the access link connecting  a  host  and  a
     SIMP.   The  protocol establishes formats for these messages, and
     describes procedures for determining when each  type  of  message
     should be transmitted and what it means when one is received.

          The term "Interface Message  Processor"  originates  in  the
     ARPANET, where it refers to the ARPANET's packet-switching nodes.
     SIMPs differ from ARPANET IMPs in that SIMPs form a  network  via
     connections  to a common multiaccess/broadcast satellite channel,
     whereas ARPANET IMPs are interconnected  by  dedicated  point-to-
     point   terrestrial   communications   lines.   This  fundamental
     difference between  satellite-based  and  ARPANET-style  networks
     results in different mechanisms for the delivery of messages from
     source  to   destination   hosts   and   for   internal   network
     coordination.   Additionally,  satellite  networks  tend to offer
     different type of service options to their connected  hosts  than
     do  ARPANET-style  networks.   These  options are included in the
     Host Access Protocol presented here.

          Several types of Satellite IMPs have  been  developed  on  a
     variety  of processors for the support of three different packet-
     switched satellite networks.  The original SIMP was  employed  in
     the Atlantic Packet Satellite Network (SATNET).  It was developed
     from one of the models of ARPANET IMP, and was implemented  on  a
     Honeywell  316  minicomputer.   The  316  SIMPs were succeeded in
     SATNET by  SIMPs  based  on  BBN  C/30  Communications  Processor
     hardware.   The  C/30 SIMPs have also been employed in the Mobile



                                     1








     RFC 907                                      Host Access Protocol
     July 1984                                           Specification



     Access Terminal Network (MATNET).  The SATNET  and  MATNET  SIMPs
     implement  a  network-access  level protocol known as Host/SATNET
     Protocol.  Host/SATNET Protocol is the precursor to  HAP  and  is
     documented  in  Internet  Experiment  Note  (IEN)  No.  192.  The
     Wideband  Satellite  Network,  like  SATNET,  has  undergone   an
     evolution  in  the development of its SIMP hardware and software.
     The original Wideband Network  SIMP  is  known  as  the  Pluribus
     Satellite  IMP,  or  PSAT,  having  been  implemented  on the BBN
     Pluribus Multiprocessor.  Its successor, the BSAT,  is  based  on
     the  BBN  Butterfly  Multiprocessor.   Both the PSAT and the BSAT
     communicate with their connected network hosts via HAP.

          Section 2 presents an  overview  of  HAP.   Details  of  HAP
     formats and message exchange procedures are contained in Sections
     3  through  10.   Further  explanation  of  many  of  the  topics
     addressed  in  this  HAP specification can be found in BBN Report
     No. 4469, the "PSAT Technical Report".

          The protocol used to provide sufficiently  reliable  message
     exchange  over the host-SIMP link is assumed to be transparent to
     the network-access protocol defined in this  document.   Examples
     of  such  link-level protocols are ARPANET 1822 local and distant
     host, ARPANET VDH protocol, and HDLC.





















                                     2








     RFC 907                                      Host Access Protocol
     July 1984                                           Specification



     2  Overview

          HAP can  be  characterized  as  a  full  duplex  nonreliable
     protocol  with  an optional flow control mechanism.  HAP messages
     flow simultaneously in both directions between the SIMP  and  the
     host.  Transmission is nonreliable in the sense that the protocol
     does not provide any guarantee of error-free sequenced  delivery.
     To  the  extent that this functionality is required on the access
     link  (e.g.,  non-collocated  SIMP  and  host  operating  over  a
     communication  circuit),  it  must be supported by the link-level
     protocol  below  HAP.   The  flow  control   mechanism   operates
     independently in each direction except that enabling or disabling
     the mechanism applies to both sides of the interface.

          HAP  supports  host-to-host  communication  in   two   modes
     corresponding  to  the  two  types of HAP data messages, datagram
     messages and stream messages.  Each type of message can be up  to
     approximately  16K bits in length.  Datagram messages provide the
     basic transmission service in the  satellite  network.   Datagram
     messages transmitted by a host experience a nominal two satellite
     hop end-to-end network delay. (Note that this delay, of about 0.6
     sec  excluding  access  link  delay,  is associated with datagram
     transmission between hosts on different SIMPs.  The  transmission
     delay  between  hosts  on  the  same  SIMP  will  be much smaller
     assuming the destination is not a group address.  See  Section  3
     and  6.2.)  A  datagram control header, passed to the SIMP by the
     host along with message text, determines the  processing  of  the
     message  within the satellite network independent of any previous
     exchanges.

          Stream  messages  provide  a   one   satellite   hop   delay
     (approximately  0.3  sec)  for  volatile traffic, such as speech,
     which  cannot  tolerate  the  delay  associated   with   datagram
     transmission.   Hosts  may  also use streams to support high duty
     cycle applications which require  guaranteed  channel  bandwidth.
     Host  streams are established by a setup message exchange between
     the host and the network prior to the commencement of data  flow.
     Although  established host streams can have their characteristics
     modified by subsequent setup messages while they are in use,  the
     fixed  allocation  properties  of  streams  relative to datagrams
     impose rather strict requirements on the source  of  the  traffic



                                     3








     RFC 907                                      Host Access Protocol
     July 1984                                           Specification



     using  the stream.  Stream traffic arrivals must match the stream
     allocation  both  in  interarrival  time  and  message  size   if
     reasonable efficiency is to be achieved.  The characteristics and
     use of datagrams and streams are described in detail in  Sections
     3 and 4 of this document.

          Both datagram  and  stream  transmission  in  the  satellite
     network  use  logical  addressing.   Each  host on the network is