Amateur Radio Today - Free and Open Source Software

epeater-must be used, Unfortunately,
this is still rare--due mostly to
cost.
Hi erarchic al Addressi ng A
scheme which allows stations that
forward packet messages to easily
decode the final destination of the
message. A hierarchical address
runs from specific (callsign) to general
(continental region). We don't yet
Include planet in a hierarchical address.
Internet An enormous Ethernet
network with tens of thousands of
government, educational, and commercial
computers connected. The
resources of the lntemet are used by
amateurs running TCP/IP to create
'wcrmnores' that route transmissions
originating on radio through the landline
Intemers high capacity network.
This makes It possible to connect almost
Instantly from the US to Australia,
for examp le, and end up on the
local Aussie AX.25 network.
KAnode A proprietary networking
scheme found in Kantronics TNCs, it
is similar to NetROM networlling.
LAN
Local Area Networks are
groups of nodes-usually user terminals,
like packet steucns-cmat are
connected in such a way as to directly
share the networll channel. In Ihe
case of packet, LAN nodes are those
slations which directly participate in
the CSMA/CD sharing of a frequency.
This is distinct from WANs (Wide
Area Networks) which are used to
connecl LANs together. The ensurelion
is rot necessarily tied to geagraphy-a
LAN could just as easily cover
more area than a WAN-but to architecture.
The interaction of LANs
on a WAN is similar to the interaction
of nodes on a LAN. See: Backbone.
MAX FRA ME An important TNC
parameter that determines the number
of outstanding (unacknowledged)
frames that will be allowed. This
number should be lowered on busy
or noisy channels; high values of
MAXFRAME In these cases will
cause a reduction in throughput.
Mode m From MODulate-DEModulate,
a modem is a piece of hardware
that converts digital information
into analog signals in the audio frequency
range to permit their transmission
over VOice channels. In a
TNC, the modem is the subsystem
which is connected to the radio. Most
TNCs are delivered with 1200 baud
modems but permit the connection of
other, faster modems to the digital
section that handles the AX,25 protocol.
Multimode A box which can operate
not only as a TNC, but also as
a terminal unit (TU) lor RTTY, AM­
TOR, FAX, etc. The exact capabilities
of multimode units vary from manufacturer
to manufacturer. Multimode
units are-of ccurse-c-oonstderabty
more expensive than simple TNCs,
but are worth considering if the extra
functionality is interesting to you,
NetROM An automatic networking
scheme that is stored on an
EPROM (Electrically Programmable
Read-Only Memory}-also known as
a ROM, hence the name. NetROM
nodes constantly exchange information
about other NetROM nodes that
can be heard and worked from their
location. Use rs connecting to
Ne tRO M nodes can get a list of
reachable nodes and connect to
them, avoiding the time-outs and other
limitations of digipeaters.
Packet The general name given
to amateur computer nefworking via
radio, it is derived Irom the use 01 data
"packets" to provide data integrity.
See: AX.25; Frame.
PACLEN An important TNC parameter
wh ich determines the
length-in characters-of an I
Frame. Larger values will increase
throughpuf on quiet channels by reducing
overhead, but will drastically
reduce efficiency on channels thai require
retries. The default size is usually
128.
PACTOR An experimental mode
for HF digital communications, oeveroped
in Germany. It takes the best
parts of packet and AMTOR and
combines them into an excellent system
for the condi tions found on tne
HF bands. Its legality lor use by US
hams is questionable, given the ambiguity
01 the rules concerning digital
modes. There is hope, however, that
this will change.
PBBS A Packet Bulletin Board
System is a computer program which
allows amateurs to exchange messages
and provides automatic store
and forward facilities for bulletins and
messages a ddressed to distant
hams. It Is similar to a land-line
BBS-like FIDO and other systems
that forward messages.
Protocol A set of rules that specify
the structure of transmitted data
and handshaking (signaling used to
communicate over a oata channel). A
protocol is something like the rules
used on voice repeaters to prevent
confusion and Interference, fhough
much more formal since computer
programs don't think. See AX.25;
TCPfIP.
Retry A request for re-transmission
of a damaged frame, or the refransmission
of the frame. See: Error
ceiecton and Correction.
Ro s e Yet another networking
scheme prevalent in the eastern half
of the US. It has some fechnical merif
and wide support.
RTTY Radio Teletype Is the original
form of digital communication via
radio. In its original form it uses a
simple 5-bit code called Baudot
(Baw'-doe) which allows for trensmssron
of only upper case letters and
the figures 0-9. See: Baud.
Serial Port A communications
port found on a computer or terminal.
Serial ports and other serial devices
send and receive their data as a
string of bits, one alter the other. This
is opposed to a parallel port, which
transm its two or more bits in parallel.
Serial ports a re tne most common
connections to TNCs afld other communications
devices.
SLOTTIME An important TNC parerneter
that works in conjunction
wifh the PERSIST parameter to more
thoroughly randomize attempts to acquire
the channel. On busy channels,
it is important that transmissions occur
at highly random intervals after
the channel is quiet, to avoid collisions.
SLOTTIME and PERSIST
work like this:
SLOTTIME specifies the amount
of time the TNC will wait before qenerating
a random number between 0
and 255, which will be used by PER­
SIST.
PERSIST se ts tne threshold (0­
255) which will be checked against
the random number each time SLOT­
TIME specifies one should be generated.
The exact settings of these values
is a matter of LAN management and
should be determined by a technical
committee of the local packet organizanon.
SSID A Secondary stancn Identifier
is a number following the callsign
tnat allows a station to have
multiple connections active without
cotuston of the packet address.
SSIDs up to and including 15 are
valid. An SSID of 15 is usually attached
to a user's cali when they are
being heard through a network node
like a NetROM node.
TCPIlP Transport Control Protocolflnternet
Protocol is the protocol
used on the Internet. It is me closest
thing to the universal solvent of the
nelworlling world, and is being adopted
by amateurs as an alternative to
AX.25. While il has some distinct
tecrmtcet advantages, it is much
more difficult to get running than a
TNC-based AX.25 station. A suite of
software, including Phil Karns'
(KA9Q) implementation of the utilities
needed to run TCPflP, can be found
on many BBSs. The best way to get
started in TCPflP is to find someone
already running it.
Terminal Emulation Using a
computer program to emulate a
dumb ferminal. Digital's VT series is
the most common choice.
Th eNet Another automatic networlling
scheme, similar to NetROM.
See: NetROM .
TNC A Terminal Node Controller
is a box containing a modem and the
"brains" to run AX.25 protocol. Because
of the intelligence built in, it
needs only to have a terminal and radio
connected to work. Some sottware
implementations of TNC intelligence
are available for use with inexpensive
modems.
TNC Parameters
Sellings used
by the TNC to determine how it will
behave. Because of varying channel
conditions, there is no single "ideal"
set of values. Other things like callsign
and text messages are also
in the set of parameters, See:
MAXFRAME; PACLEN; SLOTTtMfi"",
WAN See: LAN. III
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73 Amateur Radio Today· November, 1992 63