[aprssig] I almost understand WIDEn-N

[Keith VE7GDH]

Joseph NE3R

> WIDEn-N, I understand what the second N is for, I think. Basically
> after each digi the value of N goes down by one. What is the purpose
> of the first n?
> 
> I'm curious what the difference would be between WIDE2-2 or WIDE3-2.

Just some additional comments to Herb's reply... I see you have already got 
NE3R on the air, but it must be rather lonely in the middle of the Pacific - 
hi! http://map.findu.com/NE3R. If you had multiple stations running under 
your callsign, each would be made unique by a different SSID. (Ummm... 
secondary station identifier??) When you use NE3R the implied SSID is -0, 
but "dash zero" isn't used. You could have up to 15 other stations running 
as NE3R-1, NE3R-2 etc. That SSID doesn't change. When specifying a digi path 
e.g. WIDE2-2 the "WIDE2" is an alias. The "-2" is an SSID, but with a 
special function. When your beacon goes through a digipeater, it decrements 
the SSID to indicate how many "hops" are left. When it gets to zero,
it isn't digipeated any more. A path of WIDE7-7 (not recommended!) 
would indicate that you wanted go be digipeated seven times and that none of 
the hops had (so far) been used up. However, in the real world (at least in 
North America) seven hops would be unrealistic and anything more than two 
(or three) hops would be considered QRM. APRS is after all for "local" use 
and trying to propagate a beacon via 7 WIDEn-N digis would be very bad 
practice unless you had some kind of an emergeny going on. Someone could use 
a really stupid path of WIDE2-7 and (if not stopped by up-to-date digis that 
try and trap such paths) could potentially go on and get 7 hops even though 
it starts out by saying that the user really wanted two hops. Stupid paths 
would of course be more than frowned upon! I'm just trying to give a further 
example of what the n-N means. The first number is actually part of the 
alias and indicates the desired number of hops via digipeaters. The second 
one (really an SSID) indicates how many hops are left and does get 
decremented by one each time it goes through a digipeater.

In your example of WIDE2-2, you would be requesting two hops and one are 
used up yet. In WIDE3-2 you were presumably requesting three hops by 
starting out as WIDE3-3 and the first hop had already been used up by going 
via a digipeater and it spat it out the other side as WIDE3-2 and the next 
digi it went through would decrement it to WIDE3-1 and after one more digi, 
it would be down to zero (WIDE3-0) and any other WIDEn-N digis that heard it 
wouldn't take any action.

Again, the recommended path in North America is WIDE1-1,WIDE2-1 for mobiles. 
Any "home fill-in" digi that responds to WIDE1-1 will act on it. If heard 
direct by a WIDEn-N digi, it will also act on it. Paths are used 
sequentially, so after the WIDE1-1 has been used up, it would get one 
additional hop from any WIDEn-N digi that heard the request for WIDE2-1. The 
reason home stations shouldn't use WIDE1-1 is that presumably they have 
better antennas and a good path to an adjacent WIDEn-N digi and don't need 
any additional help from a fill-in digi. A few (very few) places will need 
more than two hops to make it to a specific place... e.g. to an IGate. It's 
up to the individual to use a sensible path.

If WinAPRS doesn't fill your needs, don't forget that UI-View is available 
at www.ui-view.org.

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