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>From: steve@matt.ksu.ksu.edu (Steve Schallehn)
>Newsgroups: rec.radio.amateur.packet
>Subject: packet radio FAQ part 1 of 3
>Message-ID: <1991Jul10.122926.25174@maverick.ksu.ksu.edu>
>Date: 10 Jul 91 12:29:26 GMT
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Frequently Asked Questions
for
Amateur Packet Radio
Part 1 of 3

Version 1.0
9 Jul 1991

This document is for unlimited distribution.

Please send corrections and additions to Steve Schallehn
(steve@matt.ksu.ksu.edu).  This posting will be made on a monthly
basis, posted to rec.radio.amateur.packet.




1.0 Basic Packet Radio Information . . . . . . . . . . . . . .  1
     1.1 What is packet radio? . . . . . . . . . . . . . . . .  1
     1.2 What is amateur radio?. . . . . . . . . . . . . . . .  2
     1.3 Why packet over other digital modes:  . . . . . . . .  2
     1.4 What elements make up a packet station? . . . . . . .  2
          A TNC (Terminal Node Controller) . . . . . . . . . .  2
          Computer or Terminal . . . . . . . . . . . . . . . .  3
          A radio  . . . . . . . . . . . . . . . . . . . . . .  3
     1.5 What do you mean we can all use the same channel? . .  3
     1.6 What is AX.25 ? . . . . . . . . . . . . . . . . . . .  3
     1.7 Definitions:  Commonly used terms in Amateur Packet
          Radio. . . . . . . . . . . . . . . . . . . . . . . .  3



1.0 Basic Packet Radio Information


1.1 What is packet radio?

Packet radio is digital communications via amateur radio.  Packet
radio takes any digital data stream and sends that via radio to
another amateur radio station.  Packet radio is so named because
it sends the data in small burst, or packets.


1.2 What is amateur radio?

Amateur Radio is individuals using specified radio frequencies
for personal enjoyment, experimentation, and the continuation of
the radio art.  Amateur radio operators must be licensed by their
government.  In the United States, the Federal Communications
Commission issues amateur radio licenses.  Normally, a test on
operating practices, radio theory, and in some cases morse code
proficiency test is administered.  Amateur radio is not to be
used for commercial purposes.  Also, amateur radio operators are
restricted from using profanity and using amateur radio for
illegal purposes.

For more information on Amateur Radio in general, see the monthly
frequently asked questions posting in rec.radio.amateur.misc.


1.3 Why packet over other digital modes:

Packet has one great advantage over other digital modes :
automatic operation.  Packet TNC's are very advanced as far as
automatic control go.  Just simply connect to the other station,
type in your message, and it is sent automatically.  Any packet
TNC can be used a packet relay station, or a digipeater.  This
allows for greater range by stringing several stations in a row.
On HF, this allows for contacts with stations normally not in
propagation range.

Packet radio provides error free transmissions because of built
in error detection schemes.  If a packet is received, it will be
correct.

Also, on VHF/UHF packet, packet operators are allowed to operate
in automatic control mode.  This means that you can leave your
packet station on constantly.  Other users can connect to you at
any time they wish to see if you are home.  Some TNC's even have
Personal BBS's (sometimes called mailboxes) so other amateurs can
leave you messages if you are not at home.

Another advantage of packet over other modes is the ability for
many users to be able to simultaneously use the same frequency
simultaneously.


1.4 What elements make up a packet station?

A TNC (Terminal Node Controller)
A TNC contains a modem to decode the audio signals into digital
signals.  It also contains a micro-computer handle to convert the
digital signals into text that can be sent over a RS-232 port to
the computer.  The CPU also handles the protocol overhead of the
packet station.  When you send data, it takes the text, puts
error checking on it (CRC) and also puts it in an envelope for
sending.  When receiving a signal, it takes it out of the
envelope, and sends the message to the computer.

Computer or Terminal
This is the user interface.  A computer running a terminal
program or just a dumb terminal can be used.  For computers, any
phone modem communications program can be adapted for packet use
or customized packet radio programs are available.

A radio
For 1200 baud operation (normal user access), a standard voice
radio can be used.  For UHF or VHF packet, Narrow band FM is
used, normally on simplex channels.  For HF packet, 300 baud data
is used over single side band modulation.




1.5 What do you mean we can all use the same channel?

Packet radio uses a protocol called AX.25.  AX.25 specifies
channel access (ability to transmit on the channel) to be handled
by CSCA/CD ?????? (Carrier Sense Collision Avoidance / Collision
Detect)  If you need to transmit, your TNC monitors the channel
to see if someone else is transmitting.  If no one else is
transmitting, then the radio keys up and the TNC sends it's
packet.  All the other stations hear the packet and do not
transmit until you are done.  Unfortunately, 2 stations could
accidentally transmit at the same time.  This is called a
collision.  If a collision occurs, neither TNC will receive a
reply back from the last packet it sent.  Each TNC will wait a
random amount of time and then retransmit the packet again.


1.6 What is AX.25 ?

AX.25 (Amateur X.25) is the communications protocol used for
packet radio.  A protocol is a standard for how two computer
systems are to communicate with each other, somewhat analogous to
using business format when writing a business letter.  AX.25 was
developed in the 1970's and based of the wired network protocol
X.25.  Because of the difference in the transport medium (radios
vs wires) and because of different addressing schemes, X.25 was
modified.  AX.25 also included a digipeater field to allow other
stations to automatically repeat packets to extend the range of
transmitters.  One advantage of AX.25 is that every packet sent
contains the senders and recipients amateur radio callsign, thus
providing identification with every transmission.

1.7 Definitions:  Commonly used terms in Amateur Packet Radio

HDLC :  (High-Level Data Link Control Procedures) A standard for
high level link control. (ISO 3309)

AX.25 : Amateur X.25 protocol.  The basis of most packet systems.
See section 1.6.

TAPR : Tucson Amateur packet Radio.  Was the first group to
create a packet radio TNC using AX.25.  Soon a TAPR TNC became
cloned by many others.  TAPR continues development of packet
radio equipment.

digipeater : A packet radio station used for repeating packets.
See section 3.3.1 for more information.

digi : Short name for a digipeater

NET/ROM : A scheme for packet radio networking.  See section
3.3.3 for more information.

TCP/IP : Transmission Control Protocol/Internet Protocol.  A set
of utility programs used over AX.25.  See sections 3.2 for more
information.

KA9Q NOS : (KA9Q Network Operating System)  A TCP/IP program
originally developed by Phil Karn, KA9Q.  Currently there are
many different versions available.  See section 3.2 for more
information.

NODE : A network node.  Often a network node running NET/ROM.

KA-Node : A simple networking scheme developed by Kantronics.
See section 3.3.2 for more info.

CSCA/CD ???? : Carrier Sense Collision Avoidance / Collision
Detect.

TNC : Terminal Node Controller.  See section 1.4 for more
information.

AMPR : An abbreviation for Amateur Packet Radio.

44 net : The class A network designator for TCP/IP amateur packet
radio.  All numerical TCP/IP addresses are in the format of
44.xxx.xxx.xxx.

ampr.org : The organization recognized on Internet for amateur
packet radio TCP/IP.
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