PSN End-to-End functional specification
RFC 979

Document Type RFC - Unknown (March 1986; No errata)
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Network Working Group                                    Andrew G. Malis
Request for Comments: 979                       BBN Communications Corp.
                                                              March 1986

                PSN END-TO-END FUNCTIONAL SPECIFICATION

Status of this Memo

   This memo is an updated version of BBN Report 5775, "End-to-End
   Functional Specification".  It has been updated to reflect changes
   since that report was written, and is being distributed in this form
   to provide information to the ARPA-Internet community about this
   work.  The changes described in this memo will affect AHIP (1822
   LH/DH/HDH) and X.25 hosts directly connected to BBNCC PSNs.
   Information concerning the schedule for deployment of this version of
   the PSN software (Release 7.0) in the ARPANET and the MILNET can be
   obtained from DCA.  Distribution of this memo is unlimited.

1  Introduction

   This memo contains the functional specification for the new BBNCC PSN
   End-to-End (EE) protocol and module (PSN stands for Packet Switch
   node, and has previously been known as the IMP).  The EE module is
   that portion of the PSN code which is responsible for maintaining EE
   connections that reliably deliver data across the network, and for
   handling the packet level (level 3) interactions with the hosts.  The
   EE protocol is the peer protocol used between EE modules to create,
   maintain, and close connections. The new EE is being developed in
   order to correct a number of deficiencies in the old EE, to improve
   its performance and overall throughput, and to better equip the PSN
   to support its current and anticipated host population.

   The initial version of the new EE is being fielded in PSN Release
   7.0.  Both the old and new EEs are resident in the PSN code, and each
   PSN may run either the old or the new EE (but not both) at any time,
   under the control of the Network Operations Center (NOC).  The NOC
   has facilities for switching individual PSNs or the entire network
   between the old and new EEs.  When the old EE is running, PSN 7.0's
   functionality is equivalent to that provided by PSN 6.0, and the
   differences listed in this memo do not apply.  Hosts on PSNs running
   the old EE cannot interoperate with hosts on PSNs running the new EE.

   There are two additional sections following this introduction.
   Section two describes the motivation and goals driving the new EE
   project.

   Section three contains the new EE's functional specification.  It
   describes the services provided to the various types of hosts that

Malis                                                           [Page 1]



RFC 979                                                       March 1986
PSN End-to-End Functional Specification

   are supported by the PSN, the addressing capabilities that it makes
   available, the functionality required for the peer protocol, and the
   performance goals for the new EE.

   Two notes concerning terminology are required.  Throughout this
   document, the units of information sent from one host to another are
   referred to as "messages", and the units into which these messages
   are fragmented for transmission through the subnetwork are referred
   to as "subnet packets" or just "packets".  This differs from X.25's
   terminology; X.25 "packets" are actually messages.  Also, in this
   report the term "AHIP" is used to refer to the ARPANET Host-IMP
   Protocol described in BBN Report 1822, "Specifications for the
   Interconnection of a Host and an IMP".

2  Motivation

   The old EE was developed almost a decade ago, in the early days of
   packet-switching technology.  This part of the PSN has remained
   stable for eight years, while the environment within which the
   technology operates has changed dramatically.  At the time the old EE
   was developed, it was used in only one network, the ARPANET.  There
   are now many PSN-based networks, some of which are grouped into
   internets.  Originally, AHIP was the only host interface protocol,
   with NCP above it.  The use of X.25 is now rapidly increasing, and
   TCP/IP has replaced NCP.

   This section describes the needs for more flexibility and increases
   in some of the limits of the old EE, and lists the goals which this
   new design should meet.

   2.1  Benefits of a New EE

      Network growth and the changing network environment make improved
      performance, in terms of increasing the PSN's throughput, an
      important goal for the new EE.  The new EE reduces protocol
      traffic overhead, thereby making more efficient use of network
      line bandwidth and transit PSN processing power.

      The new EE provides a set of network transport services which are
      appropriate for both the AHIP and X.25 host interfaces, unlike the
      old EE, which is highly optimized for and tightly tied to the AHIP
      host interface.

      The new EE has an adjustable window facility instead of the old
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