[aprssig] APRS CSMA Settings

Robert Bruninga bruninga at usna.edu
Tue May 20 13:04:57 EDT 2014

You are correct.  Digis (not on balloons or aircraft or the mountains
surrounding LA) should wait for the channel to clear (not carrier squelch,
but data-clear) and then transmit immediately (Dwait=0) whereas all other
stations should have a Dwait... (hummh... of what??? What is the default?
I hope it is not zero for every TNC out of the box?)


-----Original Message-----
From: aprssig-bounces at tapr.org [mailto:aprssig-bounces at tapr.org] On Behalf
Of Lynn W. Deffenbaugh (Mr)
Sent: Tuesday, May 20, 2014 12:14 PM
To: TAPR APRS Mailing List
Subject: Re: [aprssig] APRS CSMA Settings

On 5/19/2014 3:53 PM, Kenneth Finnegan wrote:
> the competing CSMA
> behaviors are:
> 1. None. Transmit as soon as you have traffic 1a. Time slotting.
> Transmit during your allocated time slot (seconds since top of hour
> modulus beacon interval).
> 2. DWait. Wait for a specific period of quiet time before transmitting
> any pending traffic 3. P-persistent. Randomly transmit during a quiet
> time slot.
> Deaf trackers obviously must follow the first algorithm.
> Reading the archives, it seems that Bob, et. al usually promotes no
> CSMA (algorithm 1) for digipeaters as well, due to:

I used to think this as well because of some confusion in the words.
Bob says that digipeaters should not wait before repeating a packet, but I
have had him clarify that statement to mean that they should have a DWAIT
of ZERO, but SHOULD wait for a clear channel before transmitting anything.

Bob, if I still have the worng (sic) please correct me.

Lynn (D) - KJ4ERJ - Author of APRSISCE for Windows Mobile and Win32

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