RFC 979 (rfc979) - Page 2 of 15

PSN End-to-End functional specification

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
      EE's fixed window of eight outstanding messages between any host
      pair.  The old EE applies this limit to all traffic between a pair
      of hosts; it has no notion of multiple independent channels or


Malis