[aprssig] Question about 'H-bit' handling and WIDEn-N paths

[Curt, WE7U]

On Fri, 28 Jan 2005, Robert Bruninga wrote:

> For WIDEn-N digipeating the "has-been-digipeated bit is not
> set until WIDEn-0.  THen it is set.

I see "WIDE3*" in the internet stream.  I also see "WIDE2-1*".  That
last one doesn't appear often, so perhaps it is a mistake in some
software or other.

"WIDE3*" is another representation of "WIDE3-0*", as usually an
SSID of zero is not shown in the headers output from a TNC.  If
you're dealing in raw AX.25 frames and/or KISS frames, you'll of
course see the zero.

If you see "WIDEn*" (with a number for the 'n'), it means some digi
digipeated a WIDEn-1 field, set the SSID to 0, and set the
has-been-digipeated flag.

Here's a blurb from the "aprsdigi" man-page at:

http://www.users.cloud9.net/~alan/ham/aprs/old/aprsdigi-2.0/aprsdigi.html


"FLOODING ALIASES

       APRS flooding (WIDEn-n) digipeating works by repeating any
       received packet whose next hop digipeater has  a  flooding
       alias (specified with the -f option), and the SSID is 1 or
       greater.  The SSID is decremented by one, and  the  packet
       is  repeated.   Furthermore,  to prevent broadcast storms,
       recently transmitted packets are remembered for  a  period
       of time specified by the -k option and are not repeated if
       they are heard within that time period.

       Unlike conventional digipeating, in which  the  digipeater
       callsign/alias is flagged as "repeated", the flooding mode
       does not do this.  Once the SSID decrements to zero,  then
       a flooding alias is treated just like any other alias, and
       does get marked as repeated upon transmission."


Another minor note:  You shouldn't ever see "TRACEn-0*", as you'll
see a substitued callsign in that slot instead by that point.
TRACEn-N adds digipeater fields, substituting the actual callsign as
it goes, as well as decrements that last number in the TRACEn-N digi
field.

--
Curt, WE7U.   APRS Client Comparisons: http://www.eskimo.com/~archer
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