From: pierre@ecs.umass.edu
Newsgroups: comp.bbs.misc
Subject: Info Post on Packet Radio.
Date: 3 Sep 92 17:09:08 GMT



Posted by Xyzzy Markany Tesseract Plugh on 08.10.92: 15.19
Xyzzy@ai.mit.edu or DanielD@(vax2.)hofstra.edu
Mind Itself > /dev/null == A Mind Itself goes nowhere 

Packet Radio

Packet radio is a form of amateur radio communications combining radios with 
modems. Packet radio uses the features of TCP/IP or AX.25, but using RF signals
instead of telephone or dedicated wires.

To use packet radio, you must have a valid amateur radio license or an 
excellent forgery <grin>. In all seriousness, however, the FCC 
_does_crack_down_ on people who obviously don't know what they are doing.  Once
you have a radio license, you must get a VHF radio. Some radios are well suited
for this purpose; others are not. Usually, because people are really starting 
to get into packet radio a lot because of the new NO-CODE radio class, many 
radios proudly bear the label 'good for packet radio'. Don't worry, 
you _can_ believe that. <:-)>.

You will also need a device called a TNC (terminal node controller). The best 
one is PK-232 (a good one is made by AEA); two other standards are the TNC1 and
TNC2.  It connects directly to the 232 port and your radio. The TNC is used to 
control the input and output to and from the radio waves. It is in charge of 
assembling the actual frames of data. Another item you may or may not need is 
a packet radio terminal program. Although you may use a regular program such as
Smartcom or Procomm, this will put you through the needless pain of learning 
all of the TNC system commands. The alternative is getting a packet terminal 
program that acts as a front end to the TNC. Many good shareware programs have 
been written for this purpose. If you get a PK-232, there is a shareware 
program called PK232com, which is what I use and it supports packet, morse, 
baudot, RTTY, etc. (Morse, baudot, and RTTY are other forms of non-vocal 
communication; you don't have to know Morse code to converse in it!)

How Packet Works

Packet radio originated in the late 1970s, when radio amateurs in Canada 
decided that the marriage of the radio and the computer would be a Good Thing. 
At that time, a standard for communications was decided on, but it was soon 
seen that this format was too limiting to be supportive of many people in the 
long term. As hams in the United States got involved in this aspect of radio, 
amateurs got togehter and decided on a new, improved format. It was decided 
that the new protocol should take after the popular X.25 format. The new format
for radio was named AX.25. This format, still in use, defines the way TNCs 
pass information between them. Each TNC, when it sends a block of information, 
sends first a header block (sometimes called a supervisory block), then a data 
block, then an end block.

Header Block
The header block is used only when on a frequency being used by many people. 
(This will usually be the case. However, if you have found a certain person 
with whom you wish to chat or exchange files without being in contact with the 
rest of the radio network, it is consindered good equiette to move off 
frequency so as not to clog the airwaves. When off frequency, header blocks are
not needed as there is only one place where your files are going.) This header 
block contains, among other items, your call sign, supervisory information such
as error codes, and addressing information (where you are talking to).

Data Block
The data block contains the actual data that you are sending.

End Block
The end block tells the other computers that you are done. Sometimes, the end 
block is not used because the data block contains a fixed amount of 
information. However, it is good because it can contain a checksum to make sure
everything was sent correctly.

The header block serves a very important purpose; in most cases many hundreds 
of stations will be using the same frequency. This is good. Each and every of 
those stations, if configured properly, can act as an intelligent digipeater. 
When you send a packet of information to a certain address, you send it out in 
all directions. Then, when another station recieves it, it compares the address
with a list in memory and, if it is closer to the target address than others 
in the vicinity, it will rebroadcast this packet. (These lists are updated on 
powerup by checking what signs are being transmitted.) You yourself will also 
be acting as a digipeater for others. (This can be disabled, but there is no 
real advantage to doing so.) In this manner, you can transmit around the world,
although if the frequency is crowded, there can be so many packets bouncing 
around that it may take almost a second for your packet to reach its target.

Use
Packet radio is a great way to communicate with other radio operators. Like 
morse and RTTY, there is a better chance of your message getting through than 
with voice, because it is a completely binary format. However, it is better 
than others because if there is a single mistake made in transmitting your 
packet, the recieving station will ask for a retransmittance. In this way, no 
matter how bad the conditions eventually a error-free packet will get through.
There are many people out there using Packet, (150000+) and each wants to talk 
to you. There are even computers out there called PBBSs, which are the radio 
equivelent of telephone BBSs, and the packet equivelent of radio repeater clubs.

Beyond (before?) Packet
Many TNCs are also capable of transmitting and recieving morse, baudot, and 
RTTY. The TNC will detect the speed and copy code to normal characters on your 
screen and vice versa; you don't need to know a letter of code. This will 
usually work perfectly as many others will also be transmitting and recieving 
morse with a computer, so there will be no timing errors. You can also 
transmit baudot and RTTY, although these are not as popular.

The New Standard
Although AX.25 is still widely used, an emerging standard in the packet radio 
networks is the TCP/IP protocol used in the Internet (THE net). The TCP/IP is 
considerably more complex (and accurate) than the AX.25 standard, and will 
probably be the standard in a few years. It is important to buy a TNC that 
supports this.

Bad Idea
There are many programs going around called things like "Poor Man's TNC" and 
"SofTNC". These are supposidly software TNCs. They work, but very slowly, and 
you will soon be seen as an impediment to the network because your link will 
slow every packet sent through you to a crawl. Get a REAL TNC.

Radio and Phones; what's the link?
Some PBBSs, for a fee, will patch through your transmission to a telephone 
line, enabling your radio to be connected to various services. This is very 
useful if you need to access an online service while in the middle of nowhere.

Conclusion
Packet Radio is good.

d8-<
-- 

	Again this was posted on my bbs, I do not use packet and don't think I
will.  2 technical at the moment. Hope this is informative to all who read it. 
I made sure his addresses were in the header.


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 <   Michael R. Pierre       Pierre@ecs.umass.edu                             >
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