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Sorry, ARRL 7th Computer Networking Conference 1988 is no longer available
This proceeding is available on CD-ROM
- Location:
- Columbia, Maryland
- Coordinators:
- Tom Clark, W3IWI
Andre Kesteloot, N4ICK
Dave Tillman, WA4GUD
Jack Colson, W3TMZ
Paul L. Rinaldo, W4RI - Hosted by:
- Johns Hopkins Applied Physics Laboratory ARC
Tucson Amateur Packet Radio Association (TAPR)
Amateur Radio Research and Development Corporation (AMRAD)
Radio Amateur Satellite Corporation (AMSAT)
American Radio Relay League (ARRL)
Abstracts:
7th Computer Networking Conference
October 1, 1988
- A Duplex Packet Radio Repeater Approach to Layer One Efficiency. Part Two
by Scott Avent, N6BGW and Robert Finch, N6CXB - Abstract:
Last year the authors presented the first part of this paper at the
6th conference by presenting related material NOT contained within the
text of the published paper itself. The intent of the verbal
presentation was to spur interest in reading the published paper itself.
This presentation contained a simple mathematical examination of simplex
versus duplex repeater approaches to local area network implementation.
In contrast the paper contained the design goals and basic equipment
approach we implemented in our duplex repeater environment here in
Southern California.
- Formal Description in Estelle of AX.25
by Michel Barbeau, VE2BPM - Abstract:
A protocol description must be precise as possible in
order to avoid multiple subjective and incompatible interpretations by the
different implementers. Natural language (e.g. English) descriptions are a
priori easy to understand but they are i ngeneral ambiguous. It has been
now recognized that formal techniques give rise to more precise and complete
descriptions of software. Estelle is such a formal technique specially
designed for communications protocols. This paper investigate the use of
Estelle for describing AX.25 a link-level protocol for packet-radio.
- International Code Designator for Amateur Radio
by J. Gordon Beattie, Jr., N2DSY and Thomas A. Moulton - Abstract:
Amateur Radio now has an International Code Designator (ICD) assigned by the
International Organization for Standardization (ISO) to identify Amateur Radio
organizations, network components and applications in Open Systems. Open Systems
are defined by the* use of the communications protocols of ISO and the International
Consultive Committee for Telephone and Telegraph (CCITT) and their national
member bodies. The architecture has been defined by these bodies as a model called
the Open Systems Interconnection Reference Model (OSI-RM) to facilitate
communications between applications using different computers and operating systems.
- Amateur Framing Protocol
by J. Gordon Beattie, Jr., N2DSY, Terry Fox, WB4JFI, and Thomas A. Moulton, W2VY - Abstract:
Over the last ten years Amateur Radio packet mode operations have
evolved to the point where there are approximately fifty thousand Radio Amateurs
worldwide using the AX.25 Link Layer Protocol implemented in special computer
interfaces called Terminal Node Controllers (TNCs). During this period many
functional extensions or changes to the protocol have been suggested, but
their use would not conform to the basic AX.25 protocol.
- The authors have identified a common set of protocol capabilities which can be provided in a simple framing sublayer. These capabilities include framing, station identification, bit-error detection, digipeating, and appiication specific options. The Amateur Framing Protocol (AFP) presented in this paper defines a a format and a set of rules to support these functions, while providing an envelope for higher layer protocols such as ARRL AX.25 Link Layer, CCITT Q.921, CCITT Q.931, CCITT X.25, ISO 8208, ISO IP, and US DoD TCP/IP and ARP.
- The authors have identified a common set of protocol capabilities which can be provided in a simple framing sublayer. These capabilities include framing, station identification, bit-error detection, digipeating, and appiication specific options. The Amateur Framing Protocol (AFP) presented in this paper defines a a format and a set of rules to support these functions, while providing an envelope for higher layer protocols such as ARRL AX.25 Link Layer, CCITT Q.921, CCITT Q.931, CCITT X.25, ISO 8208, ISO IP, and US DoD TCP/IP and ARP.
- Amateur Framing Protocol Specification
by J. Gordon Beattie, Jr., N2DSY, Terry Fox, WB4JFI, and Thomas A. Moulton, W2VY - Abstract:
The Amateur Framing Protocol (AFP) is a general purpose data format protocol
for Amateur Radio packet mode communications systems. AFP provides the framework
on which other protocols may be implemented. An AFP frame provides an
envelope to support any form of Logical Link Control protocol which two (or
more) stations wish to use during packet mode operations. The relationship
of AFP to other protocols is shown below.
- A Routing Agent for TCP/IP: RFC 1058 Implemented for the KA9Q
Internet Protocol Package
by Albert G. Broscius, N3FCT - Abstract:
The KA9Q Intemet Protocol Package has introduced full TCP/IP internetworking to
the Amateur packet community yet, until now, automatic routing has not been
available within the package. This paper describes an implementation for the KA9Q
package of the DDN Internet standard Routing Information Protocol as specified in RFC 1058.
Proper usage and configuration of this routing code are explained.
- Recommended Power and Antenna Height Guidelines for LAN's and WAN's
by Bob Bruninga, WB4APR - Abstract:
What follows is simply an appeal that we apply
some degree of frequency coordination within the
digital allocations on two meter FM. We have noted
rapid growth in the nASH DC area as shown in figure 1
with over 38 BBS's, 35 DIGI's and a number of
NET/ROMS and TCP/IP nodes spread over the 100 KHz
segments starting at 145.0, 145.5 and 145.6 plus 221
MHz. The nature of packet radio i3 quite forgiving
in accommodating multiple users and a mix of services
on any one frequency. But condoning a total free-
for-all mixture can not possibly result in an
effecient network. The opposite extreme of total
coordination and rule making is restrictive and
abhored by most radio amateurs.
- A Totally Awesome High-Speed Packet Radio I/O Interface for
the IBM PC XT/AT/386 and Macintosh II Computers
by Mike Chepponis, K3MC and Bernie Mans, AA4CG - Abstract:
This paper describes a plug-in card for IBM PC XT/AT/386 compatible
computers or the Apple Macintosh 11 computer. It is designed to handle two 56 kilobit/sec
full-duplex channels via DMA and 10 slow speed (19,200 bits/sec or less) channels
via interrupts without main processor intervention. The board uses an NEC
V40 processor and up to six Zilog 85C30 Serial Communication Controllers, together with
either 256k bytes of DRAM or 1 megabyte of DRAM to omoad the main processor
from low-level interrupt fielding. It communicates with the main processor with an 8k
byte memory window in the IBM version, and directly with Macintosh II main
memory using the Bus Master concept of the NuBus. It is targeted at
replacing existing TNCs in the high-speed networks of the future; special
consideration has been given to the support of TCP/IP. Even the minimum (easily upgradable)
implementation with only one 85C30 outperforms all existing TNCs, relying on
the host PC only for bootstrapping, power, and of course, an effective user interface when
called for.
- AMSAT's MICROSAT/PACSAT Program
by Tom Clark, W3IWI - Abstract:
In 1989 AMSAT-NA plans to launch the first
of a series of low-earth orbit (LEO) satellites dedicated to serving digital
store-and-forward message handling. These satellites
are quite small cubes, approximately 230 cm (9
inches) on a side weighing less than 10 kg
this small size has led to our calling the
project MICROSAT. Despite the small size, the
satellites are crammed with state-of-the-art
electronics. This paper will review the
development program leading to this design and
some of the technical details as well as
describing how the terrestrial user will make
use of the resource. We are planning on the
launch of 4 satellites using MICROSAT
tcchnology into LEO in early 1989, and several
more launches over the next 2 years.
- The DSP Project Update
by Dr. Thomas Clark, W3IWI and Dr. Robert McGwier, N4HY - Abstract:TAPR and AMSAT have signed a formal agreement which
forms a joint project. The purpose is to bring the rapidly
advancing technology and techniques of digital signal pro-
cessing to bear on the communication needs of amateur ra-
dio. The AMSAT-TAPR digital signal processing project
has made steady progress over the past year on both soft-
ware and hardware. Lyle Johnson is leading the hardware
effort in Tuscon and will report on that progress elsewhere
in these proceedings. We will report on work that is on-going to
choose what the second generation DSP unit will look like.
- Digital Radio Networks and Spectrum Management
by Paul A. Flaherty, N9FZX - Abstract:
Spectrum Management is a vital part of amateur radio. Questions of where to
place services in the available spectrum continue to plague frequency
coordinators. This paper contends that multiaccess radio systems should be
allocated in the spectrum below one GigaHertz, and that monoaccess or link
oriented systems be placed above that frequency.
- Where is My High-Speed RF Part II
by Terry Fox, WB4JFI - Abstract:
In 1986 this author presented a paper at the
5th ARRL Computer Networking Conference in
Orlando, Florida regarding high-speed RF (or more
accurately the lack of it). That paper was meant
to spurn on experimentation in the RF arena of
packet radio. This paper is meant to continue where that
one left off. It seems we have made some
progress, but have also stood stil 1. While the
last statement at first appears contradictory, it
does describe what has happened.
- Proposed AX.25 Level 2 Version 2.0 Changes
by Terry Fox, WB4JFI - Abstract:
This paper is presented to document some of
the major changes proposed over the last four
vears of operation for the AX.25 Level 2 Version 2
Protocol. These changes have been collected by
this author from various sources, and were
recommended by a working group of the ARRL Digital
Committee which met in Juiy of 1988.
- Transmission of IP Datagrams over NET/ROM Networks
by Daniel M. Frank, W9NK - Abstract:
One of the main design goals of the Internet
Protocol was that IP datagrams could be carried
over existing local- and wide-area networks. This
characteristic of IP makes it possible to build so
called "internetworks" out of existing network
facilities. We built support for an existing
Amateur wide area network, NET/ROM, into the KA9Q
TCP/IP package, allowing the use of NET/ROM to
carry IP datagrams, and adding features which make
the KA9Q software useful as a full duplex NET/ROM
packet switch. We have also shown that NET/ROM
may be used as a datagram network only,
independent of its transport and application layer
facilities.
- More and Faster Bits: A Look at Packet Radio's Future
by Bdale Garbee, N3EUA - Abstract:
The biggest problem facing amateur packet radio today is
the inability of the ham community to envision the
breadth of possibilities that exist once higher speed
modems become available. This paper attempts to survey some of
the applications popular in other networking
environments, and comments on their possible use in the
amateur service. In addition, a preliminary report on
work in progress to develop multi-megabit per second
connections on the microwave bands is presented.
- Can We Continue to Ignore Level One?
by Eric S. Gustafson, N7CL - Abstract:
For some reason which I cannot fathom,
there has been a great reluctance to
specify or even to provide guidelines for
the various level 1 issues in the amateur
packet radio system. This reluctance
traces back all the uay to the very early
days of packet radio development. I Sind
this situation very strange indeed since
if level 1 isn't uorking. all the other
levels of the protocol uhich everyone
eeems eager to specify doun to the last
bit position are all irrelevant.
- In this paper I will choose one of the most coneistently botched and yet most easily corrected level 1 parameters, the modem's data carrier detector. I will show how the performance of our present packet systems can be improved by careful consideration of even just this simple level 1 issue.
- In this paper I will choose one of the most coneistently botched and yet most easily corrected level 1 parameters, the modem's data carrier detector. I will show how the performance of our present packet systems can be improved by careful consideration of even just this simple level 1 issue.
- Finger - A User Information Lookup Service
by Michael T. Horne, KA7AX - Abstract:
With the recent explosion in amateur TCP/IP activity, primarily made
possible by the KA9Q Internet Package, the need has arisen for a user
information lookup service. Users on the amateur network can now
retrieve important information about other amateurs through the use
of a new application called fnger. This paper describes finger and its
potential as an important source for information retrieval in the amateur
networking world.
- Big Sky Telegraph and Other Tales
by Dave Hughes WNKV696 - Abstract:
Discussion on implementing packet radio to
provide telecommunication services to schools.
- International Routing Designators
by Lew Jenkins, N6VV, David B. Toth, MD, VE3GYQ and H.N. Hank Oredson, W0RLI - Abstract:
It has become obvious by now that the work-horse of our so-called
packet network is the venerable BBS program. In fact, some will argue
that it has been too successful. Every time that a band-aid is needed
to "fix" the network, it is applied through the various BBS programs.
It is probably fair to say that the maintenance of the forwarding
tables is a drudgery that most sysops could do without. This point also
under-scores a serious problem faced by all networks: ROUTING.
- With the introduction of WORLI V7.00 and support for Hierarchical routing designators, we have an opportunity to improve traffic routing particularly for international traffic. Since N6VV is at the present time responsible for traffic to Asia and the Pacific, and occasionally Europe and Africa, he has implemented some Hierarchical routing designators which will assist him in international routing.
- With the introduction of WORLI V7.00 and support for Hierarchical routing designators, we have an opportunity to improve traffic routing particularly for international traffic. Since N6VV is at the present time responsible for traffic to Asia and the Pacific, and occasionally Europe and Africa, he has implemented some Hierarchical routing designators which will assist him in international routing.
- AX.25 Packet Radio Communications Using Meteor Scatter Propagation
by Thomas Johansson, SM5IXE - Abstract:
Meteor scatter propagation is commonly used in modern
commercial and military digital
communications. This traffic preferably takes place in the frequency range 30 to 50
MHz, where the reflectivity and duration of the meteor trails are the best. Meteor scatter
links exhibit very reliable communication, even during periods of low meteor trail
occurrence [2]. Among radio amateurs digital meteor burst communication has been discussed for many
years. Despite this, no experiments on amateur basis have (to the knowledge of the
author) been performed in Sweden or elsewhere in the world. During the past two years
several amateurs have reported the random appearance of AX.25 packets from very
distant stations. The propagation of these packets can only be explained by meteor scatter
reflections. This supports the idea to exploit these reflections for packet radio links.
The following paper reports on the realization and results of an initial experiment with
packet radio communication using meteor scatter propagation in the 144 MHz amateur
radio band. The tests were carried out during the meteor shower Geminides in the midst
of December 1987.
- The AMSAT/TAPR DSP 1 Project: Hardware Design
by Lyle V. Johnson, WA7GXD - Abstract:
This paper is intended to provide a design overview of
the DSP 1 hardware configuration, sponsored by TAPR/AMSAT joint development
project.
- MICROSAT Project - Flight CPU Hardware
by Lyle V. Johnson, WA7GXD and Charles L. Green, N0ADI - Abstract:
This paper focuses on the design of the flight computer
hardware and outlines some of its capabilities.
- RADIX 95: Binary to Text Data Conversion for Packet Radio
by James G. Jones, WD5IVD and Gerald A. Knezek, KB5EWV - Abstract:
Binary files can prove to be difficult to
transfer over the current amateur packet
radio network. Radix 95 provides a way
to convert data such as compiled
programs or graphic images to printable
ASCII characters and allow their transfer
in Converse Mode. Radix 95 (base 95) iS
a simple variable length encoding
scheme which offers greater efficiency
than is available with conventional fixed-length encoding procedures.
- Amateur TCP/IP: An Update
by Phil R. Karn, KA9Q - Abstract:
Amateur radio use of the DARPA Inter-net protocols
("TCP/IP") has grown from a
paper proposal during the "protocol wars" of
several years ago to a well-established reality
today. Because the TCP/IP software is free and
available to radio amateurs and all other noncommercial
users, it is hard to say exactly how
many are using it. One rough estimate is the
number of Internet addresses that have been
assigned from the "network 44" block for amateur
packet radio: about 1,000 amateurs in
several dozen countries. The package has also
gained considerable popularity outside of amateur
radio, especially in universities.
- With the popularity of TCP/IP on amateur radio has come another most welcome development: the appearance of others making substantial contributions to the software effort by creating new features and enhancing existing ones. Several of these contributors have documented their work in other papers in these proceedings, and any other potential contributors are also encouraged to do so. In this paper I will review the TCP/IP developments and experiments of the past year. Although I will mention several contributors by name, the project has grown much too large for this to be an exhaustive list; I hope no one will feel slighted if they are accidentally omitted.
- In this paper I will also comment on some of the lessons learned so far, and then discuss possible directions for the future. As expected, much has been learned about the operational aspects of true computer networking on amateur packet radio. We've also learned quite a bit about coordinating the development of a com- plex software package when volunteers all over the world are involved.
- With the popularity of TCP/IP on amateur radio has come another most welcome development: the appearance of others making substantial contributions to the software effort by creating new features and enhancing existing ones. Several of these contributors have documented their work in other papers in these proceedings, and any other potential contributors are also encouraged to do so. In this paper I will review the TCP/IP developments and experiments of the past year. Although I will mention several contributors by name, the project has grown much too large for this to be an exhaustive list; I hope no one will feel slighted if they are accidentally omitted.
- Cellular Area Coverage Transport Networks
by Donald V. Lemke, WB9MJN - Abstract:
With the advent of level 3 software
becoming widely available to Ham Packet Radio, a
complete rethink of transport radio
systems can lead to greater thruput improvements.
This paper details a cellular area
coverage transport system. Designed to be collision-free,
and not significantly effected by modem lock-up times,
this radio system would have thruput equivalent to modem
data rate.
-
9600 Baud Packet Radio Modem Design
by James Miller, BSc, G3RUH - Abstract:
The theoretical minimum audio bandwidth required to send 9600 baud binary
data is 4800 Hz. Since a typical NBFM radio has an unfiltered response
from zero some 8 kHz, transmission of 9600 baud binary data is perfectly
possible though it. This paper describes a successful implementation.
- ARES/Data: A Packet-Radio Database for Emergency Communications
by W.E. Moerner, WN6I and David Palmer, N6KL - Abstract:
ARES/Data is a multiple connect
specialized bulletin board system tailored to store
and retrieve basic information about people, places
or things during an emergency. The program is a
generalized form of the FINDER program (Family
Information Database for Emergency Responders)
written by David Palmer, N6KL and W. E.
Moerner, WN6I. Although ARES/Data allows
access to the database via packet radio, the program
can also operate stand-alone without the need for
packet radio hardware. The actual operating mode
is chosen by the system operator when the
ARES/Data program is started.
- ARES/Data is a system which allows collection and organization of information during a widespread emergency that overloads normal communications channels. The program is designed to be flexible, so that it can be used without change for both small and large disasters to organize information about victims, evacuees, locations, or even ham radio operators.
- With alternate power sources and their own frequencies, Amateur Radio Emergency Service (ARES) operators can provide the ARES/Data service without tying up critical communications channels or relying on commercial power.
- ARES/Data is a system which allows collection and organization of information during a widespread emergency that overloads normal communications channels. The program is designed to be flexible, so that it can be used without change for both small and large disasters to organize information about victims, evacuees, locations, or even ham radio operators.
- PACSAT Software
by Harold Price, NK6K and Robert McGwier, N4HY - Abstract:
The evolving structure of the Microsat system software is discussed.
With a launch services agreement in
hand, several "Pacsats" should be in orbit in 1989; they
will have more memory and a more complex suite of system and
application programs than any amateur spacecraft
launched to date.
- Overview of ARRL Digital Committee Proposals for Enhancing
the AX.25 Protocols into Revision 2.1
by Eric L. Scace, K3NA - Abstract:
A working group within the ARRL Digital Committee has been evaluating
enhancements and other proposals for
improving AX.25. This paper summarizes the most significant items which are
being proposed. You are invited to
comment on these proposals. Comments are desired so that any final
recommendations by the Committee will benefit from
the broadest possible input.
- Introducing System Description Language for AX.25 and Related Protocols
by Eric L. Scace, K3NA - Abstract:
This paper is part of a series of papers which provide
extended finite state machine representations for AX.25 and
related protocols. The state machines are depicted using state description
language (SDL) graphic conventions from the
Z.100 series of Recommendations developed by the International Telegraph and
Telephone Consultative Committee (CCITT)
of the Intemational Telecommunications Union (ITU). An extended finite state
machine representation of a communications
protocol such as AX.25 avoids the ambiguities associated with prose
descriptions. These descriptions also compel the
protocol designer to confront many of the error scenarios which arise on a
communications path, and simplify the
implementor's task of producing correct solutions which will interwork with
solutions created by others.
- This particular paper introduces the SDL symbols and explains other general aspects of SDL diagrams. It also lays out an organization of extended finite state machines which, together, perform the AX.25 link layer protocol, handle multiple simultaneous links, interact with the radio transmitter and receiver, and accomodate large data units sent by the application.
- This particular paper introduces the SDL symbols and explains other general aspects of SDL diagrams. It also lays out an organization of extended finite state machines which, together, perform the AX.25 link layer protocol, handle multiple simultaneous links, interact with the radio transmitter and receiver, and accomodate large data units sent by the application.
- AX.25 Data Link State Machine
by Eric L. Scace, K3NA - Abstract:
This paper is part of a series of papers which provide extended finite state
machine representations for AX.25 and
related protocols. The state machines are depicted using state description
language (SDL) graphic conventions from the
Z.100 series of Recommendations developed by the International Telegraph and
Telephone Consultative Committee (CCITT)
of the Intemational Telecommunications Union (ITU). An extended finite state
machine representation of a communications
protocol such as AX.25 avoids the ambiguities associated with prose
descriptions. These descriptions also compel the
protocol designer to confront many of the error scenarios which arise on a
communications path, and simplify the
implementor's task of producing conect solutions which will interwork with
solutions created by others.
- This particular paper describes an extended finite state machine which executes the data link procedures between two stations.
- This particular paper describes an extended finite state machine which executes the data link procedures between two stations.
- AX.25 Link Multiplexor State Machine
by Eric L. Scace, K3NA - Abstract:
This paper is part of a series of papers which provide extended finite state
machine representations for AX.25 and
related protocols. The state machines are depicted using state description
language (SDL) graphic conventions from the
Z.100 series of Recommendations developed by the International Telegraph and
Telephone Consultative Committee (CCITT)
of the International Tdecommunications Union ~TU). An extended fnite state
machine representation of a communications
protocol such as AX.25 avoids the unbiguities associated with prose
descriptions. These descriptions also compell the
protocol designer to confront many of the error scenarios which uise on a
communications path, und simplify the
implementor's task of producing conect solutions which wiU interwork with
solutions created by others.
- This particular paper describes an extended finite state machine which supports multiple simultaneous AX.25 links. "Link" here embraces both AX.25 connections (established between two stations with the SABM command) and connectionless operation between two stations (using UI frumes exclusively). The main responsibilities of the link multiplexor SDL machine are to insure that each link has a fair and equal opportunity to access the radio channel, und to handle incoming frames which require digipeating.
- This particular paper describes an extended finite state machine which supports multiple simultaneous AX.25 links. "Link" here embraces both AX.25 connections (established between two stations with the SABM command) and connectionless operation between two stations (using UI frumes exclusively). The main responsibilities of the link multiplexor SDL machine are to insure that each link has a fair and equal opportunity to access the radio channel, und to handle incoming frames which require digipeating.
- Simplex Physical Layer State Machine by
Eric L. Scace, K3NA - Abstract:
This paper is part of a series of papers which provide extended finite state
machine representations for AX.25 and
related protocols. The state machines are depicted using state description
language (SDL) graphic conventions from the
Z.100 series of Recommendations developed by the International Telegraph and
Telephone Consultative Committee (CCITT)
of the International Tdecommunications Union ~TU). An extended fnite state
machine representation of a communications
protocol such as AX.25 avoids the unbiguities associated with prose
descriptions. These descriptions also compell the
protocol designer to confront many of the error scenarios which uise on a
communications path, und simplify the
implementor's task of producing conect solutions which wiU interwork with
solutions created by others.
- This particular paper describes an extended finite state machine suitanle for use on shared simplex radio channels; such channles represent the vast majority of environments where AX.25 is employed today. A sister paper describes a similar machine suitable for use on full-duplex channels.
- This particular paper describes an extended finite state machine suitanle for use on shared simplex radio channels; such channles represent the vast majority of environments where AX.25 is employed today. A sister paper describes a similar machine suitable for use on full-duplex channels.
- A Brief Note Proposing Non-Aloha Access Techniques for PACSATs
by Jeff W. Ward, G0/K8KA - Abstract:
Carrier-sense multiple-access (CSMA), as used in most terrestrial packet
radio networks, is
not efficient for low-Earth orbiting store-and-forward packet satellites
(PACSATs). This note
describes a simple time-division multiple-access protocol for PACSATs. A
procedure is
proposed for eariy experiments on the UoSAT-D Packet Communications
Experiment (PCE)
transponder, using AX.25 as the link protocol with satellite-controlled TDMA
arbitration.
- The UoSat-D Packet Communications Experiment
by Jeff Ward, G0/K8KA - Abstract:
This paper describes the Packet Communications Experiment (PCE), which will be the
primary payload on the UoSAT-D satellite. UoSAT-D is to be launched in 1989, along with
several other Amateur PACSATs. The PCE design will be based on results of the
UoSAT-OSCAR-11 Digital Communications Experiment, using an 80C186, 512 kbytes
program RAM and 4 Mbytes message-storage RAM. It will be an open-access Amateur Radio
PACSAT messaging system.
