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Introduction
Overview
Computer requirements
Packet Engine Pro
Configure AGWPE
Download and Install
Basic AGWPE Setup
2 Radio Setup
2 Card Setup
Sound Device Setup
Basic Device Settings
Rename Sound Device
Additional Settings
Using the Tuning Aid
Problems?
Program Behavior
Receiving
Transmitting
Connections
Firewalls
AGWPE Features
AGWPE on a Network
Baud Rates & Modes
Remote Control
TCP/IP Over Radio
Tips and Tricks
Traffic Parameters
Compatible Programs:
Setup Help
Radio Interface
Getting Started
Kits and Pre-assembled
USB SignaLink
Receive Audio Cable
Transmit Audio Cable
PTT (TX Control) Cable
2 Radio Modification
About Packet
Packet Overview
Exchange Modes
TNCs and AGWPE
What
To Do with Packet
Common Frequencies
Frame Headers
Further Reading
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TNCs and AGWPE
On the
Packet Process Overview
page and the
TNC Modes page, we saw how
important the TNC (Terminal Node Controller) is to the packet
process. Just to recap, the TNC:
- packages (assembles) addressing
information and data into a packet frame according to the AX.25
protocol roles -) -- and reverses the process when receiving
- uses its integrated modem to convert the
frame from binary bits to audio tones for transmission -- and
reverses the process when receiving
- employs the AX.25 protocols to establish
"connections" between stations that result in error-free frame
exchanges
- can be programmed to send out periodic beacons
of information
- can be programmed to digipeat (relay) packets
as a service to other stations
- may have a "mail box" to receive and store
messages while the operator is away
So how does AGWPE fit into this picture?
Original Role of AGWPE
As capable as the TNC was, AGWPE's author, George
SV2AGW, saw some limitations and found a way to overcome them. These TNC
limitations included:
- only one computer program at a time could
connect to and receive data from the TNC
- a computer program could only connect to one TNC
at a time
- there was no logic to measure or dynamically
adjust timing and traffic settings
To overcome these limitations, AGWPE relieves the
TNC of using its built-in logic. It does this by putting the TNC in an
operating mode found in most TNCs, called KISS (Keep It Simple
Stupid). When a TNC is put in KISS mode, the modem
of the TNC remains
functional but all the other logic functions of the TNC are turned off
and AGWPE handles them.
Since it is now in control of the packet exchange
process, AGWPE can use its logic to measure packet traffic conditions on
the frequency and make immediate timing changes. And by providing a way
for computer programs to connect to AGWPE rather than the TNC directly,
AGWPE lets many programs use the TNC's modem at the same time.
Another side benefit of AGWPE is it can simplify
the programming work for programmers writing packet programs. Without
AGWPE, programmers had to write code to link to a many different TNCs
(not knowing which TNC the program user would have). With AGWPE, they
can simply link to AGWPE and let AGWPE handle the job of linking to
different TNCs.
AGWPE's Sound Card Mode
The next step in the evolution of AGWPE was to take
over the one remaining major function of the TNC, the modem. This
was done by using the computer's sound card as a modem emulator. Then,
with the radio input and output hooked directly to the computer sound
card and the radio's PTT control handled by a signal sent to a COM or
LPT port, a computer running AGWPE can work directly with the radio and
there is no need for a TNC!
But there are some functions that a TNC does that AGWPE
can not do on its own and so work-arounds were developed:
- Digipeat -- a
special digipeater program linking to AGWPE can be used for this
function
- Personal Mail Box - again a
special messaging program
linking to AGWPE can do this
-
Watch Dog Timer
- a circuit can be added to the PTT cable to prevent continuous,
unwanted transmissions
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