Packet Basics
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Introduction to Packet Radio
For the GTA West ARES Packet Users

II.  Packet Basics

What is a packet?
Connected packets
Unconnected Packets
Basic Packet Commands and Operations
Talking to your TNC
Connecting to another station
Disconnecting from another station.

 

What is a packet?

For our purposes, a packet is a digital data stream that identifies 

the sending station
the receiving station
how much data is being sent
the data itself. 

(For the more technically inclined, amateur radio packets transmissions adhere to the AX.25 packet protocol.)

Packets can be sent out as "Connected Packets" or as "Unconnected Packets". 

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Connected packets

Most of our activities will involve connected packets. This is where the sender has linked (or connected) to an specific receiving station. Every transmission between these two stations will be acknowledged by the other. Transmissions are always received 100% accurately, or are automatically repeated until they have been received. While connected, both stations ignore all other traffic on the channel. (Note that other unconnected stations can see the data passing between the connected stations, although they aren't taking part in the conversation.)

Unconnected Packets

These are transmissions that are sent out without a specific receiving station. There is no way of knowing if the transmissions are received correctly, or at all. It's like calling CQ on the radio without knowing if any one is listening. Although we won't cover this means of packeting here, there are some circumstances where this is preferable to working in a connected mode.

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Basic Packet Commands and Operations

Talking to your TNC

Your TNC is more than just a modem. It is a type of microcomputer, and as such can receive & interpret commands. Your TNC can be in command mode, converse mode, KISS mode, transparent mode, or host mode. For our purposes, we will deal with command mode & converse mode.

When you first turn it on, your TNC should be in "command mode". This means that anything you type will be interpreted locally by the TNC as a command, and will not be sent over the air. You are in command mode if, whenever you hit the 'Enter" key, the TNC responds with "CMD:". If you don't see the CMD: prompt, you are probably in converse mode. In this case, anything typed is sent over the radio. 

Hint: Typing the sequence "Ctrl-C" will switch your TNC from Converse to command mode. 

Here are some of the basic commands you will use.

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Connecting to another station.

c callsign - The "c" is the abbreviation for "connect". This causes the TNC to initiate a connection to another station. If successful, all subsequent transmissions are between that station and yours only. Once the connection is made, you will see "Connected to callsign" on your screen.

e.g.. (My station is VE3TRJ. I want to connect to VA3PB.) (For all the following examples, what I type is in Blue, what comes from the TNC is in Red, and comments are in Green.)

cmd:
c va3pb 
<-- I type this and hit enter
*** CONNECTED to VA3PB <--my TNC sends me this, saying we are now connected
Hi Paul - You there?<-- I type this, hit enter & it appears on Paul's screen
Yes - what's up? <-- His response
Etc.

The above is an example of a keyboard to keyboard conversation.

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Disconnecting from another station.

Once you have finished your conversation, you need to disconnect. This allows both stations 
to resume monitoring, waiting for another connection.

First, put your TNC in command mode by sending Ctrl-C. This is not sent over the air, but is 
captured by the TNC causing is to switch to command mode. 

Then, type "d" which forces the TNC to disconnect, ending the conversation. This can all be 
done on one line, if you want. 
("Ctrl-C d"). ("d" is the abbreviation for "disconnect".)

cmd:
c va3pb  
*** CONNECTED to VA3PB 
Hi Paul - You there?
Yes - what's up? 
...
OK, gotta go. 73! 
Ctrl-C <-- This puts the TNC into Command mode
cmd: <-- This sends the disconnect command to my TNC.
cmd:*** DISCONNECTED
<-- this comes from the TNC and breaks the connection.

That's it! These are the basic operations that you will use for most of your packeting! Simple, isn't it?

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