PSN End-to-End functional specification
RFC - Unknown
(March 1986; No errata)
||RFC Editor Note
RFC 979 (Unknown)
||Send notices to
Network Working Group Andrew G. Malis
Request for Comments: 979 BBN Communications Corp.
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.
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
Section three contains the new EE's functional specification. It
describes the services provided to the various types of hosts that
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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".
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
The new EE has an adjustable window facility instead of the old
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