CHEPPONIS@C.CS.CMU.EDU (12/03/85)
From: Mike Chepponis <Michael.Chepponis@C.CS.CMU.EDU>
Fellow packeteers, I'm posting the following article, taken from "Electronic
Engineering Times" 2 Dec 85, pp 15 and 16 because I think it may be of interest
to you. My editorial comments are enclosed in "{" and "}" characters.
U.K. Develops Combat Packet Switch System
by Roger Wollnough
GREAT MALVERN, England - Packet-switching techniques are being applied to the
transmission of data between combat-net radios in a development project at the
Royal Signals & Radar Establishment (RSRE) here.
The method has been adopted to provide good flexible communications in the
highly hostile and mobile nature of the modern battlefield { ... of the
modern Ham Radio "network"? }. Called packet radio, the program started in
late 1981. It is now entering the design and development stage of a 25-station
pilot system.
This will be carried out in collaboration with British industry. Experimental
field testing is slated for 1988. Packet Radio was designed not simply as a
standalone communications system, but as a building block in the integrated
electronic battlefield of the future.
One aim is to achieve internetworking, so that users of different networks can
communicate easily with each other. { Does this sound familiar? } This is
important in battle situations, where the survivability of communications can
only be assured if the different networks are flexibly interconnnected. { Is
the situation any different for ham networks, especially when we rely on them
for disaster communications? }
The RSRE laboratory has demonstrated packet radio's ability to provide tactical
to strategic communications with other networks. The British Army currently
uses a manpack called Clansman, which provides all the commmunications at the
front line.
Ptarmigan System
Another system, the Ptarmigan battlefield-communications network which is just
entering service, is designed to allow control of mobile and widely dispersed
forces operating over vast distances.
"Ptarmigan has a packet-switch overlay," says Terry Davies of RSRE's Mobile
Communications Division. "There is a need to introduce a system for areas
where only Clansman radio operates. Packet radio does this."
RSRE devised and proved the basic concepts of packet radio on narrow-band
channels.
In a packet-radio network, a number of microprocessor-controlled radio
transceivers - from two to 50 - share a single channel. { Unless, of course,
you're on the US east coast, where between 2 and 2000 stations share the same
channel :-) }
They exchange information over this channel in the form of short bursts,
typically of 100-ms duration. { This is about 12 characters at 1200 baud,
for comparison to ham standards. I do not know if RSRE uses 1200 baud,
however. } A novel feature is that in order to communicate, two users do not
have to be in direct radio contact with each other. { Can you say "digipeater?"
Well, I don't know if they have link-level ACKs or not, but.... }
Packet radio uses a strategy similar to that of passing the ball in a soccer
game.
Any of the units in the network can provide a relaying function, so that the
information gets from source to the destination in a number of discrete hops.
The Challenge
The technical challenge was to develop algorithms which would permit automatic
and efficient relaying, despite the small size of the channel (25 kHz), the
mobility of the users and the possible rapid changes in the radio environment.
In the first stage of the development, finite-state machine-based simulation
techniques were used to develop the channel access, routing and network-
control algorithms, and to characterize their performance under various
conditions. These included rapidly varying traffic loads and rapidly changing
radio connectivities.
Next, RSRE designed and built a small number of prototype packet-radio
stations. These used Clansman 353, a British Army-standard VHF transceiver.
Extensive trials were carried out with the Clansmans, and demonstrations of
interoperability have been given at NATO symposiums.
The third stage, which is just beginning, will be used to transfer the
technology of packet radio to British industry. "By 1990," Davies said,
"packet radio will be capable of providing reliable data communications at VHF
between manpacks, as well as vehicular terminals."
The team assembled at RSRE included experts in signal processing, analog- and
digital-circuit design, error-control coding, protocol design, realtime
computing and network architectures.
The team discovered that the iterative approach to systems design was better
than a simple top-down method. In the iterative approach, prototyping and
experimental realizations are used to validate the system concepts. This
carries much less risk of major system redesign during the production-
development phase. { A lesson here for ham systems? }
{ -Mike, k3mc }
-------leiner@RIACS.ARPA (12/03/85)
From: Barry Leiner <leiner@RIACS.ARPA> For those of you who don't know, Brian Davies of RSRE has been involved in the DARPA internet and packet radio programs for a very long time. Barry ----------
@DCN6.ARPA:mills@dcn6.arpa (12/04/85)
From: mills@dcn6.arpa Folks, "Terry's" name is really Brian. The UK system operates at 16 kbps with rate-1/2 convolutional encoding and QPSK modems over standard VHF radios, so that the station-station rate is 8 kbps. The demo system operates in the 30-50 MHz band using a couple of fixed repeaters and a flock of Land Rovers carrying the radio, modem, controller and power converter. The client protocols include the DoD Internet portocol suite (IP, TCP and Telnet) running in an LSI-11 with video terminal. In a recent demo I had the pleasure of reading my mail on a Fuzzball in my home near Washington, DC, while the driver and I bounced around the Malvern contryside dodging sheep. There were eight nets, including packet-radio, packet-satellite, Ethernet, token-ring and ARPANET technologies between my fingernails and my Fuzzy, which seems to bear testimony that the Internet suite may be in fact sufficiently heroic to hack the flaky paths enjoyed by our fraternity. Dave -------