RFC 829 (rfc829) - Page 1 of 5

Packet satellite technology reference sources

Network Working Group                                            V. Cerf
Request for Comments: 829                                          DARPA
                                                           November 1982



             PACKET SATELLITE TECHNOLOGY REFERENCE SOURCES


                             Vinton G. Cerf
               Defense Advanced Research Projects Agency

ABSTRACT

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.

INTRODUCTION

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