Order Tray | Contact Us | Home | SIG Lists

[aprssig] AX.25 'H' flag

Scott Miller scott at opentrac.org
Mon Nov 14 16:57:06 UTC 2005


Argh.  I was just concerned about the language of the spec.  Now my head 
really hurts.  =]  What's wrong with just marking the 'H' bits?  I wrote 
some display code over the weekend (roughly emulating the KPC-3 output) that 
did just that.  Easier than finding the last 'H' bit set, and unambiguous.

Ok, as long as we're at it, is there a specification for the converse mode 
output?

Scott
N1VG
----- Original Message ----- 
From: "Robert Bruninga" <bruninga at usna.edu>
To: <archer at eskimo.com>; <aprs at kd4rdb.com>; <aprssig at lists.tapr.org>
Sent: Monday, November 14, 2005 8:50 AM
Subject: Re: [aprssig] AX.25 'H' flag


THe AEA's use a non-TAPR-2 monitor mode
display standard and they DO show the * for
every digi.  But the TAPR standard only shows
them on the LAST digi heard.   Bob

>>> aprs at kd4rdb.com 11/14/05 11:19 AM >>>
I am indeed talking about the kiss/ax.25 spec...  I used the CONV mode
method of H bit indication... so a little mixing of terms here... but I
did see a difference in the way the kpc3's and pacomms dealt with H bits.

I think Bob said it would be chaotic... and he's right... but it's what
I saw.  Unfortunately, I don't remember which TNC filled up the h bits,
and which on just set the current bit.

wes



Curt, WE7U wrote:
> On Mon, 14 Nov 2005, Wes Johnston wrote:
>
>
>>passing thru a mishmash of digipeaters, you can end up with a packet
>>like this:
>>digi1*,digi2,digi3*,digi4
>>
>>In either of these cases, digi4 should figure out that it's the one
>>supposed to digi next...  This point drove me nuts when I wrote my kiss
>>digipeater years ago.  Best to parse packet paths from the END and work
>>toward the first path element looking for any H flag to be set.  This
>>also plays well with pre-emptive digipeating.
>
>
> Wes, if you're really talking KISS packets (or raw AX.25 packets)
> then you should never see the operation you describe else it's a bug
> in the software in those TNC's and not per spec.  That bit _must_
> get set in order to show that the slot is used up.  Havoc will reign
> otherwise.
>
> For command-mode TNC's then the '*' really can't be relied upon to
> indicate state of each digipeater field.  The most common format
> would be a single asterisk at the last used-up digipeater slot.  The
> other format I know of would be an asterisk for every one from the
> beginning to the last used-up slot, which is more indicative of the
> state of the bit for each slot than the first format.
>
> --
> Curt, WE7U.   APRS Client Comparisons: http://www.eskimo.com/~archer
> "Lotto:    A tax on people who are bad at math." -- unknown
> "Windows:  Microsoft's tax on computer illiterates." -- WE7U
> "The world DOES revolve around me:  I picked the coordinate system!"
>
> _______________________________________________
> aprssig mailing list
> aprssig at lists.tapr.org
> https://lists.tapr.org/cgi-bin/mailman/listinfo/aprssig
>
>
>


_______________________________________________
aprssig mailing list
aprssig at lists.tapr.org
https://lists.tapr.org/cgi-bin/mailman/listinfo/aprssig


_______________________________________________
aprssig mailing list
aprssig at lists.tapr.org
https://lists.tapr.org/cgi-bin/mailman/listinfo/aprssig






More information about the aprssig mailing list