[aprssig] WIDEn-N 'Decay Sequence'

[VE7GDH]

Anders KI4IWX wrote...

> Ooops, sorry: ki4iwx :)

Thanks - nice to have a callsign entered in case you want someone to look at 
what you are beaconing or check something!

> So here the definition of a "home fill-in digi" is one where it
> hears the packet, rebroadcasts it without any processing, and has
> as (one of) it's alias, "WIDE1". (Or would it be sufficient for
> it to have a "WIDE" alias?)

No. WIDE is not the same as WIDE1-1. It is the same as WIDE-0. One of the 
problems with APRS as it was up until about a year and a half ago was there 
was no "dupe checking" for the now obsolete RELAY or just plain WIDE. Modern 
WIDE1-1 digs will do some processing... to insert their callsign to indicate 
which digipeater it went through. Less intelligent digis will unfortunately 
not insert their callsign. For the record... RELAY, WIDE, TRACE and TRACEn-N 
are considered obsolete in North America. TRACEn-N is still used in other 
places in the world. Just to add a bit of confusion, modern WIDEn-N digis 
act like TRACEn-N was designed to work. Current up-to-date WIDEn-N 
digipeaters in North America always insert their callsign so you can "trace" 
what path it took to get to where it was heard.

> Ahh, so with a "VE7XYZ,WIDE2-2" path, the ONLY way 'out' would
> be for the packet to be bounced by the station with an alias of
> VE7XYZ, and then outward. Would I assume that if VE7XYZ acted
> upon my packet because I had VE7XYZ in my path, that it would

Actually VE7XYZ would be a legitimate callsign in BC, not an alias, but you 
get the idea. If your path is DIGI1,DIGI2 and DIGI1 didn't hear you, DIGI2 
would not respond even if it heard you. The "DIGI1" could be a digi that 
responds to WIDE1-1, one with an alias of BIGMTN or a callsign with or 
without an SSID tagged on the end... although if none is shown, it's really 
zero.

> Ahh, so not only is the path order sequential, but a 'proper'
> WIDEn-N digipeater will only act on the first thing in the
> path string? So it would be like this:
>
> WIDE1-1,WIDE2-1 (original)
> WIDE1-0,WIDE2-1 (re-broadcast #1)
> WIDE2-0 (re-broadcast #2)
>
> (Assuming that there were digis with aliases WIDE1 and WIDE2
> to pick up the signals.)

You've got it! If you were a fixed station, you could use a path of VE7XYZ 
(if there was a digi using that callsign and it could hear you) followed by 
WIDE2-1 and it would go out (after being digi'd by VE7XYZ) by any WIDEn-N 
digi that could hear it. This wouldn't be suitable for mobile stations. The 
beauty of WIDE1-1,WIDE2-1 is that it works (almost) everywhere. There are 
still "holdouts" that still respond to RELAY and WIDE, but they are 
hopefully disappearing soon. Except for a few places that haven't updated 
their digipeater settings yet, you can go anywhere in North America and have 
a reasonable chance of being heard and digipeated. You don't have to keep 
stopping and changing your digi path as you travel. No knowledge is needed 
of the callsigns of the digipeaters being used. Even the WIDEn-N digis 
respond to WIDE1-1, so if you are in a location where it's difficult to hit 
a WIDEn-N digi and there are WIDE1-1 digis present, they can help you out in 
getting to the usually higher elevation WIDEn-N digi.

If you were surrounded by several high elevation WIDEn-N digis, and you 
wanted your beacon to propagated in a certain direction, instead of using 
WIDE2-2, you could e.g. specify the exact callsign or alias of one of the 
digi and another one. An alternative would be to use WIDE2-1,DIGI2 and allow 
all WIDEn-N digis that could hear you to respond plus DIGI2 (a specific 
callsign-SSID or alias off in a particular direction) to try and ensure 
propagation in that particular direction.

> Can I infer from your example that, in general, large/high
> digis have an alias of WIDE2, while smaller/more local will
> have an alias of WIDE1?

Usually, large/high digis respond to WIDEn-N - not just WIDE2-N. Some digis 
will "trap" paths like WIDE7-7 and give them one hop. Others will refuse to 
respond to WIDE7-7 or WIDE6-6 etc. These are usually in areas where the 
digis are close to high-density areas where trying to "DX" like that would 
be harmful. APRS has evolved. Going back a few years (and before I was 
involved with it) long paths were often used. As more and more people 
started to participate, it quickly became apparent that things fell apart 
when "abusive" paths were still used.

> Now, why have I not seen any examples of a path with "WIDE2-3",
> which would seem to indicate three hops from a WIDE2 aliased digi?
> Answer A is "Because you don't need that many hops, silly!", but I'm
>wondering why it seems that the SSID is never higher than the (desired
> max) hop number?

WIDE2-3 should not be used. The WIDEn is supposed to indicate the desired 
number of hops. The N on the end tells the WIDEn-N digi how many hops 
haven't been used up yet. Some digis would trap WIDE2-3 and either give you 
one hop or just not respond to it. Others (most) would act the same as if 
you had used WIDE3-3 but with some mis-information going along for the ride.

> "Just because I don't know where I am doesn't mean I don't know where to 
> go!"

Ah... but with a GPS, you should have a pretty good idea where you are! Just 
start worrying when other people start trying to tell you where to go. Using 
an abusive path of (bad e.g.) WIDE7-7,WIDE7-7,WIDE7-7 might produce those 
results! I think you are off to a good start. You have asked all the right 
questions and have a nice radio to play with. Have fun with it!

I just sent a message to KI4IWX which you used more recently than KI4IWX-14. 
You may or may not receive it depending on whether your local IGate sends it 
out to you and a few other variables.

73 es cul - Keith VE7GDH
--
"I may be lost, but I know exactly where I am!"