Packet satellite technology reference sources
RFC 829

Document Type RFC - Unknown (November 1982; No errata)
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Network Working Group                                            V. Cerf
Request for Comments: 829                                          DARPA
                                                           November 1982


                             Vinton G. Cerf
               Defense Advanced Research Projects Agency


This paper describes briefly the packet satellite technology developed
by the Defense Advanced Research Projects Agency and several other
participating organizations in the U.K. and Norway and provides a
biblography of relevant papers for researchers interested in
experimental and operational experience with this dynamic
satellite-sharing technique.


Packet Satellite technology was an outgrowth of early work in packet
switching on multiaccess radio channels carried out at the University of
Hawaii with the support of the Defense Advanced Research Projects Agency
(DARPA).  The primary difference between the earlier packet-switched
ARPANET [1, 2] and the ALOHA system developed at the University of
Hawaii [3] was the concept of multiple transmitters dynamically sharing
a common and directly-accessible radio channel.  In the ARPANET, sources
of traffic inserted packets of data into the network through packet
switches called Interface Message Processors (IMPs).  The IMPs used high
speed point-to-point full-duplex telephone circuits [4] on a
store-and-forward basis.  All packet traffic for a given telephone
circuit was queued, if necessary, in the IMP and transmitted as soon as
the packet reached the head of the queue.  On such full duplex circuits
there is exactly one transmitter and one receiver in each direction.

The ALOHA system, on the other hand, assigned a common transmit channel
frequency to ALL radio terminals.  A computer at the University of
Hawaii received packet bursts from the remote terminals which shared the
"multi-access" channel.  Under the control of a small processor, each
terminal would transmit whenever it had traffic, and would await an
acknowledgement, on another frequency, dedicated to the service host. If
no acknowledgement was received, the terminal processor would transmit
again at a randomly chosen time.  The system operated on the assumption
that no store-and-forward or radio relay was needed.  The University of
Hawaii researchers later demonstrated that the ALOHA concept worked on a
satellite channel linking Hawaii and Nasa-Ames via NASA's ATS-1
satellite [5, 6].  A variety of more elaborate satellite channel
assignment strategies were developed and analyzed in the early 1970's
[7-13, 31].

Cerf                                                            [Page 1]

RFC 829                                                    November 1982
                                              Remote User Telnet Service


In 1973, DARPA began the development of a packet satellite system which
would support the sharing of a common, high speed channel among many
ground stations.  Using an INTELSAT-IV satellite, the Atlantic Packet
Satellite experiment was carried out with the cooperation and support of
the British Post Office, COMSAT Corporation, Linkabit Corporation, and
Bolt Beranek and Newman Corporation, later joined by the Norwegian
Telecommunication Administration and the Norwegian Defense Research
Establishment (NDRE).  Along with University College London and COMSAT
Laboratories, NDRE became one of the major users of the SATNET system.

During 1975-1978, SATNET underwent a broad range of performance
evaluations and tests.  Since 1979, it has served as a stable support
for international experiments and demonstrations of command and control
technology of interest to DARPA, NDRE and the U.K. Royal Signals and
Radar Establishment (RSRE).  Late in 1982, a ground station was added to
connect the German Aeronautics and Space Research Establishment (DFVLR)
into the system.

The early development of SATNET is outlined in [14].  The system design
is documented in [15-22].  Experience with the operation of the SATNET
is reported in [23-24] and experimental results in [25-26].  Potential
services which might be supported by this technology are discussed in

The integration of the packet satellite technology into a larger,
multiple packet network context is discussed in [28-29].  The system is
expected to continue in use to support joint research by DARPA, RSRE,
NDRE, DFVLR and UCL.  DARPA and the U.S. Defense Communications Agency
are experimenting with a 3 megabit/second domestic packet satellite
system to determine whether packetized voice and data services can be
integrated economically using this technology.  DARPA and the U.S. Naval
Electronic Systems Command recently demonstrated a Mobile Access
Terminal Network (MATNET) which uses packet satellite techniques to
support ship-ship and ship-shore communication over a shared FLTSATCOM
satellite channel [30].
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