1. RFC 0829
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].


The development of Packet Satellite technology has involved many
institutions and individuals, but special credit for the successful
realization of the SATNET and its successor systems must be given to Dr.
Robert E. Kahn, Director, Information Processing Techniques Office,
DARPA, for his continuous support and technical contributions throughout
the development and maturation of this technology.

Cerf                                                            [Page 2]
RFC 829                                                    November 1982
                                              Remote User Telnet Service


1.  L.G. Roberts and B.D. Wessler, "Computer Network Development to
Achieve Resource Sharing," Spring Joint Computer Conference, AFIPS
Proceedings, Vol. 36, 1970, pp. 543-549.

2.  R.E. Kahn, "Resource Sharing Computer Networks," Proceedings of the
IEEE, Vol. 60, No. 11, November 1972, pp. 1397-1407.

3.  N. Abramson, "The Aloha System - Another Alternative for Computer
Communications," AFIPS Conference Proceedings, Vol. 36, 1970, pp.

4.  F.E. Heart, et al, "The Interface Message Processor of the ARPA
Computer Network, Spring Joint Computer Conference, AFIPS Proceedings,
1970, pp. 551-567.

5.  R. Binder, et al, "Aloha Packet Broadcasting--a retrospect," AFIPS
Conference Proceedings, National Computer Conference, 1975, pp. 203-215.

6.  N. Abramson and F. Kuo, Editors, Computer Communication Networks,
Prentice Hall, Englewood Cliffs, N.J., 1973.

7.  L. Kleinrock and S. Lam, "Packet Switching in a Slotted Satellite
Channel," AFIPS Conference Proceedings, NCC, 1973, pp. 703-710.

8.  L. Kleinrock and F. Tobagi, "Random Access Techniques for Data
Transmission over Packet Switched Radio Channels," AFIPS Conference
Proceedings, NCC, 1975, pp. 187-201.

9.  L. Kleinrock and S.S. Lam, "Packet Switching in a Multiaccess
Broadcast Channel:  Performance Evaluation," IEEE Transactions on
Communication, Vol. COM-23, 1975, pp. 410-423.

10.  L.G. Roberts, "Aloha Packet System with and without Slots and
Capture," ACM SIGCOMM, Computer Communication Review, Vol 5, No. 2,
April 1975.

11.  S.S. Lam and L. Kleinrock, "Packet Switching in a Multi-access
Broadcast Channel:  Dynamic Control Procedures," IEEE Transactions on
Communication, Vol Com-23, September, 1975.

12.  L.G. Roberts, "Dynamic Allocation of Satellite Capacity through
Packet Reservation," AFIPS Conference Proceedings, NCC, 1973, pp.

13.  N. Abramson, "Packet Switching with Satellites," AFIPS Conference
Proceedings, NCC, 1973, pp. 695-702.

Cerf                                                            [Page 3]
RFC 829                                                    November 1982
                                              Remote User Telnet Service

14.  R.E. Kahn, "The Introduction of Packet Satellite Communications,"
National Telecommunications Conference, Nov. 1979, p. 45.1.1-45.1.8.

15.  I.M. Jacobs, et al, "CPODA - A Demand Assignment Protocol for
SATNET," Fifth Data Communications Symposium, Snowbird, Utah, 1977.

16.  I.M. Jacobs, et.al, "General Purpose Satellite Networks,"
Proceedings IEEE, Vol 66, No. 11, November 1978, pp. 1448-1467.

17.  I.M. Jacobs, et al, "Packet Satellite Network Design Issues,"
Proceedings, NTC, November 1979.

18.  L. Palmer, J. Kaiser, S. Rothschild and D. Mills, "SATNET Packet
Data Transmission," COMSAT Technical Review, Volume 12, No. 1, Spring
1982, pp. 181-212.

19.  Weissler, et al, "Synchronization and Multiple Access Protocol in
the Initial Satellite IMP," COMPCON, September 1978.

20.  Hsu and Lee, "Channel Scheduling Snychronization for the PODA
Protocol," ICC, June 1978.

21.  E. Killian and R. Binder, "Control Issues in a PODA Voice/Data
Satellite Network," ICC, June 1980.

22.  C. Heegaard, J. Heller and A. Viterbi, "A Microprocessor-based PSK
Modem for Packet Transmission over Satellite Channels," IEEE
Transactions on Communications, COM-26, No. 5, May 1978, pp. 552-564.

23.  P. Cudhea, D. McNeill, D. Mills, "SATNET Operations," AIAA 9th
Communications Satellite Systems Conference, Collection of Technical
Papers, 1982, pp. 100-105.

24.  D.A. McNeill, et al, "SATNET Monitoring and Control," Proceedings
of the NTC, November 1979.

25.  P.T. Kirstein, et al, "SATNET Applications Activities," Proceedings
of the NTC, November 1979.

26.  W.W. Chu, et al, "Experimental Results on the Packet Satellite
Network," Proceedings of the NTC, November 1979.

27.  E.V. Hoversten and H. L. Van Trees, "International Broadcast Packet
Satellite Services," ICCC Conference Proceedings, Kyoto, Japan,
September 1978.

28.  V.G. Cerf and R.E. Kahn, "A Protocol for Packet Network
Intercommunication," IEEE Trans. on Comm., Vol. COM-23, May 1974, pp.

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RFC 829                                                    November 1982
                                              Remote User Telnet Service

29.  V.G. Cerf and P.T. Kirstein, "Issues in Packet Network
Interconnection," IEEE Proceedings, Vol. 66, No. 11, Nov 1978, pp.

30.  L. Evenchik, D. McNeill, R.P. Rice, F. Deckelman, et al, "MATNET,
an Experimental Navy Shipboard Satellite Communications Network, "IEEE
INFOCOM 82 Proceedings, March, 1982.

31.  M.L. Molle and L. Kleinrock, "Analysis of Concentrated ALOHA
Satellite Links," Sixth Data Communications Symposium, Nov 27-29, 1979,
pp. 87-95.

Cerf                                                            [Page 5]
  1. RFC 0829