RFC 1221 (rfc1221) - Page 1 of 68

Host Access Protocol (HAP) specification: Version 2

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Network Working Group                                          W. Edmond
Request for Comments: 1221                                           BBN
Updates: RFC 907                                              April 1991


          Host Access Protocol (HAP) Specification - Version 2

Status of this Memo

   This memo describes the Host Access Protocol implemented in the
   Terrestrial Wideband Network (TWBNET).  It obsoletes most but not all
   of RFC 907.  This memo provides information for the Internet
   community.  It does not specify an Internet standard.  Distribution
   of this memo is unlimited.

Preface

   This memo specifies the Host Access Protocol (HAP).  HAP is a Network
   layer (OSI Layer 3 lower) access protocol that was first implemented
   about a decade ago for the DARPA/DCA sponsored Wideband Packet
   Satellite Network (WBNET), the precursor of the current Terrestrial
   Wideband Network (TWBNET).  This version of the specification
   obsoletes references [1] and [2] in addition to most of RFC 907.

   HAP is a developmental protocol, and will be revised as new
   capabilities are added and unused features are eliminated or revised.
   One reason that HAP is being revised now is that, unlike the original
   WBNET's satellite channel, the TWBNET's T1 fiber links are not a
   broadcast medium.  This has prompted some changes to the protocol
   that will permit greater efficiency in a mesh topology network.
   Another cause of revision is the need to make HAP able to support a
   variety of OSI layer 3 upper protocols, such as DECNET Phase V, ST,
   and CLNP, where before only Internet Protocol (IP) was used.
   Appendix B describes how backward compatibility with the older IP-
   only version of HAP is achieved.  A third cause of protocol changes
   is the desire to simplify interaction between ST2 protocol (RFC 1190)
   agents and the TWBNET.  This has mainly affected the way certain
   setup errors are handled.  These changes are expected to be backward
   compatible.  Appendix A describes two capabilities that may be added
   to HAP in the future.

   One of the protocol enhancements, "Group Streams", described in
   reference [2] has been eliminated.  There are no known applications
   that use the feature.  As described in Appendix A, a new mechanism,
   to be called "shared streams", capable of providing equivalent
   capabilities will be implemented if needed.  Changes in [2] that have
   been retained include various query/reply control messages that
   permit a host to determine what resources it owns (mostly useful for



Edmond
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