WHAT IS A PACKET NETWORK
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   A local area packet radio network (LAN) consists of a net
control station and a number of individual operators. The net
control station is sometimes referred to as the "station node"
and the individual stations as "terminal nodes". The net may also
contain a digital repeater or "digipeater", which may be the net
control station or a separate repeater station. The repeater
station may be a single-frequency simplex repeater which re-
transmits any correctly received packets, or it can be "normal"
split frequency repeater.

   As operators sign on to the net, they are recognized by the
net control and given net address codes. An operator desiring to
start a QSO with another net station will subsequently have his
transmissions addressed to that station. Any operator may choose
to have his TNC receive all transmissions, rather than just those
addressed to his station. Of course, the TNC will only acknowledge
those transmissions intended for that station. The operator whose
station is functioning as net control participates in exactly the
same way as other operators. The net control functions are taked
care of automatically by his TNC.

   As more packet radio LAN's become active, there will be the
possibility of link stations with access to two distinct LAN's.
These stations can be members of both nets and serve as communic-
ations links thorugh which packets originating in one net can be
funneled to an addressee in the other net.

   A more sophisticated possibility is that of a "gateway"
station, which will be a specialized station having access to some
long-distance mode of communications. The gateway station will
reformat packets with another layer of protocol containing inter-
network linking information and transmit it to another gateway
station in a distant LAN. Three possibilities are being explored
for long-distance links.

   TERRACON will be a high-speed ground-based linking system
utilizing UHF and/or microwave relays. It could potentially
handle most long-distance packet radio communications in the
United States and Canada. It will probably be a few years before
TERRACON is0implemented as a useful system, and somewhat longer
before the continent is linked.

   AMICON will be a satellite-based network utilizing one of the
special-services channels on the AMSAT Phase III-B satellite.
AMICON will allow intercontinental linking and contact with
isolated areas not accessible to TERRACON. High data rate exper-
iments are being planned for the 23cm uplink/70cm downlink (mode
L) translator. There are also plans for a packet radio digital
repeater aboard the AMSAT Phase III-C satellite.

   SKIPCON is AMRAD's projected HF network of LAN gateway
stations. The nature of HF propagation will require slower data
rates (75 to 600 baud) and error correction as well as error
detection protocol. SKIPCON experiments have been conducted
since the end of 1981.