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Problems
Help Date:
21 June 2004
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Editing Port Properties: TNC
Commands (Parameters)
On the Properties screen for any radio port
(TNCs, modems, sound cards), there is a second
tab entitled TNC
Commands. Selecting that tab brings
up a screen where you can edit various timing
parameters.
Your most important decision is
to
choose who will set the TNC's traffic
flow parameters: you or the program?
Program Adjusts Parameters -
this is the default choice and provides a valuable feature: PE Pro monitors the
packet traffic level and will automatically adjust all TNC
traffic flow parameters
every two minutes to match traffic level. Hint: Use the
Port Activity screen
to see the current traffic level and the current program settings.
Note:
The
'on air' baud rate field below this radio
button is no longer used
by the program.
If
you choose "program adjusts parameters", the five parameters
that deal with traffic flow will be 'grayed-out' and inaccessible, as will the
Default 1200
and Default 9600
buttons. You will only be able to adjust a few parameters (see
Parameters information below) and the screen will look like this (default values for all fields are
shown): 
Let me adjust Parameters -
this choice lets you alter the five traffic flow parameters: Persist, SlotTime, MaxFrame, Retries, Frack, RespTime,
and Check Every (see Parameters
information below).
You should only make this choice if the program is
not handling the timing parameters to your satisfaction and you
understand channel traffic symptoms and the intended affect of each parameter.
The screen will look like this (default values for
all fields are shown) :

Parameters -
Here is more information about each of the parameters:
- Persist - works with the SlotTime parameter to determine the frequency of
transmissions. SlotTime sets the time between slots (transmission
opportunities). Persist sets the odds (the number of times in 255) that PE
Pro will actually transmit when a slot come up. Use lower Persist numbers during heavy
traffic (so PE Pro misses some turns and lets other stations transmit). Try
higher numbers if traffic is light (PE Pro will transmit at most slots).
Persist can be from 1 to 255. Default is 128 (50%) for 1200 baud; 190
(75%) for 9600 baud.
- SlotTime
-
works with the Persist parameter to determine the frequency of
transmissions. After detecting a clear channel, the SlotTime is the
time in 10 milliseconds that PE Pro waits for the next slot (transmission
opportunity). The Persist parameter sets the odds that a transmission
will actually be made at that slot. Default is 10 for 1200 baud; 5 for 9600
baud.
- MaxFrame:
the number of packets (frames) of unacknowledged packets that can be
outstanding at one time. When MaxFrame is reached, PE Pro will stop
sending packets and wait for an acknowledgement from the other station that
ALL packets were received. If traffic is light, use a higher MaxFrame
-- packets will get through more quickly. If traffic is heavy, use a lower
value. Otherwise, a lost frame will result in a request from the receiving
station to re-send ALL frames after the lost frame. This adds traffic to the
channel. The maximum MaxFrame value is 7.
- Retries:
if a packet is not acknowledged by the receiving station, PE Pro will re-send
the packet up to the maximum number specified by Retries. After that, the
connection with the other station is assumed to be broken and it is closed.
Default is 10 for 1200 baud; 15 for 9600 baud..
- Frack:
increment to wait for an acknowledgement from the other station before
re-sending the packet. Allow more time if you have more
VIA stations in your packet address path. Default is 10 for 1200 baud; 8 for
9600 baud.
- RespTime:
the minimum delay to wait after a clear channel before sending an
acknowledgement packet. This delay helps ensure all the sending station's
frames have been sent. Increments of 100 milliseconds. Default is 5 for 1200
baud; 3 for 9600 baud. Increase this if
your ACK packets may be colliding with the other station's last info packets.
- Check Every:
the amount of time to wait after hearing nothing from a 'connected' station
before sending a 'check' ("are you still there?") frame. Default is 180 (3
minutes) for 1200 baud; 120 (2 minutes) for 9600 baud.
Note: PacLen,
the number of characters to place in each packet, is determined by
your application program, not PE Pro. PE Pro can sent 255 characters per packet. If traffic is
light (collision risk is low), you can send more characters per packet and
exchanges will be quicker. If traffic is heavy, use less characters per packet
because shorter packets will have a better chance of getting through without
collision. This means the need for retries will be less and exchanges will be
quicker in heavy traffic situations. Other TNC parameters -
You can adjust these parameters, even if PE Pro is automatically adjusting the
timing parameters
above.
- DAMA Slave
- check this if you are working with DAMA stations. It will put the
port in DAMA mode when it detects that the station you have connected to is a DAMA node
or BBS (DAMA Master). DAMA is common only in Germany/Europe. DAMA replaces SlotTime and Persist timing.
- EAX25 Decoding
- if there another station is operating
in EAX25 mode, then checking this box will allow you to monitor its traffic correctly. EAx25 is not a standard protocol and many
stations don't support it. Incorrectly activating EAX25 decoding could result in
problems.
- TXDelay
- the time in 10ths of a millisecond between when the PTT circuit is
activated and packet data is sent. This delay gives your radio's transmitter
time to come up to full power and gives the receiving radio time to switch
from 'transmit' to 'receive'. A minimum delay increases traffic flow, but too
little delay may result in the loss of the beginning of the packet and thus
retries and decreased traffic flow. The default is 35 for 1200 baud; 20 for
9600 baud.
Older radios may need a bit more; newer radios may need 15 or less.
- TXTail
- the time in 10ths of
milliseconds between the end of packet data and the closing of the PTT circuit.
Only needed on some modems. Can be set to zero for most TNCs. Default is 4.
- Soft DCD
- DCD is Data Carrier Detect. Some TNCs/modems must rely entirely on
the radio's squelch to sense when there is a carrier/packet on the air
(hardware DCD). If your radio does this, leave this unchecked. Other TNCs
have software logic to detect when there is a carrier/packet in the noise,
so you can leave the radio squelch open (software DCD). In fact, many TNCs
are designed to run open squelch and use soft DCD automatically. Still other
TNCs/modems let you choose which method to use. Check mark this box this if you want
software DCD. The relative signal-to-noise threshold amount to the right can
be changed. The default is 64.
- Full Duplex
- default is OFF, which means PE Pro uses the DCD signal to determine
when the frequency is clear and when to acknowledge packets. When turned
ON, PE Pro ignores the DCD signal and sends acknowledgements
immediately; may be useful in split frequency operations such as through
satellites or when doing loop-back tests, but only if both stations are
operating full duplex.
- Default 1200
Button - will set all the parameters to PE Pro's default settings
for 1200 baud 'on air' packet.
- Default 9600
Button - will set all the parameters to PE Pro's default settings
for 9600 baud 'on air' packet.
Go to TNC Properties Help
page
Go to Sound Card
Properties Help page
Copyright 2004 SV2AGW George Rossopoulos
. All rights reserved.
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