[OZAPRS] APRS 'idea' ? - needs some clarification

Ray Wells vk2tv at exemail.com.au
Sat Feb 2 14:18:34 EST 2013

I'm also unclear about what Paul was asking. I can, however, make 
comment on a couple of points Ben mentioned.

1. With regard to the amount of traffic from IS to RF, when I was 
attempting to gather interest in aprs in my area (Kempsey) around 6 
years ago, I chose to feed aprs from the IS to a quiet, local RF 
channel, 144.900, my BBS channel with just one user. That 1k2 
transmitter RARELY stopped transmitting and would occasionally exceed 
the watch dog timer timeout in the TNC, and that was with just vk2, vk3 
and vk4 stations being sent from the IS. Keep in mind that there was 
MUCH less aprs activity back then there is now. I was the only station 
in NSW between the latitude of Newcastle (350km to the south) and the 
latitude of the vk2/vk4 border (a similar distance to the north). Maybe 
one day I'll dabble with a 9k6 70cm channel to see what it can do.

2. If anyone on this list was into packet radio around its peak in the 
late 80s/early 90s they'll be very aware of the dreaded hidden 
transmitter problem that results from many stations sharing a common 
frequency. The greater the number of well-sited transmitters that exist, 
the more hidden transmitters you have, resulting in a reduced chance to 
get packets to their destination. Connected mode packet had the 
advantage of stations retransmitting a packet if a response (ACK, RR, 
RNR) was not received. Unconnected (UI) packet (read APRS) does not have 
that advantage and a lost packet is lost forever.

Ray vk2tv

On 02/02/13 13:32, Ben VK2BEN wrote:
> HI Paul,
> I think there is a profound question in your message below, but some 
> clarification is required to give you a satisfactory answer.
> After rephrasing your entire question in a couple of different ways 
> here in my head, I think I may have deduced what you might be asking:
> Are you suggesting that, instead of multiple stations (by which you 
> might mean "digipeaters"?) re-transmitting all APRS packets that it 
> hears over the air, or gathers from an Internet Gateway ("iGate") in a 
> given area; that only "one" station should do this and cover a really 
> large geographical area?
> Well, actually that how digipeaters work in any case, so I am still 
> not sure that I fully understand your proposal from the start. Digi's 
> will re-transmit what they hear - within the limits set by their 
> Wide-n parameters - and IS (Internet) to RF (Radio) gateways (iGate) 
> are generally not encouraged [perhaps even strongly discouraged? I am 
> open to correction here]  due to the massive amount of data with which 
> they could potentially flood the RF channel.
> Digi's are strategically placed to cover large areas [and to stretch 
> the VHF network out to sparsely populated areas and even link such 
> scattered areas back to the network if there are no Internet links at 
> the regional areas]  and to repeat APRS posits to mobile and fixed 
> users of that network who may not have received the originating signal 
> (which is usually a lower-powered mobile transmitter with limited LoS 
> range). Fill-in Digi's are set up in blind spots, or as links between 
> service areas, that might not be covered by the regional Digipeater. 
> These can be given limited range (path, as well as RF power) so as not 
> to fill the channel with redundant data. Thus, I think that the short 
> answer is no; we cannot realistically remove large numbers of 
> Digipeaters in order to reduce traffic on the APRS channel. It would 
> not solve many problems. Especially here in Australia, where the 
> frequency can hardly be described as 'overloaded' ;-)
>  As for reducing the amount of traffic on the frequency in a given 
> geographical region; this would become a moot point because the same 
> amount of APRS data would still need to be transmitted to service that 
> area all at once with a single transmission. But instead of several 
> short bursts of repeated data coming from a group of well-managed 
> digipeater sites, it sounds like we might end up with really long (and 
> perhaps more susceptible to interference and errors?) transmissions 
> carrying all sorts of position data that might not be wholly relevant 
> to the users in that specific area. Currently, Digi's are dispersed so 
> as not to cover the same areas as each other, nor with too much 
> overlap. At the same time, protocols are in place (within the TNCs) to 
> disallow indiscriminate repeating of data and thus unending loops of 
> repeated data.
> I think there is a fine balance between covering all areas well with 
> as few digipeaters as possible, whilst at the same time filling in 
> valleys and great open spaces with the required positioning data. The 
> way the system works right now is pretty darned good. And after 
> reading thru parts of the aprs.org website, I am surprised that 
> anybody can understand it at all :-P
> Paul, I apologize if I have extrapolated far more from your brief 
> proposal than you might have intended, but it seemed necessary to 
> clarify a few things before approaching what you appeared to be 
> asking. Hopefully I didn't veer off the track too far?
> 73,
> Ben vk2ben
>>> Hi there all,
>>> Its been a while from my last post, I have an idea. I have no idea 
>>> if this
>>> has been implemented anywhere in the world but this idea could be done.
>>> I have been thinking about the way that the APRS network works, now 
>>> I might
>>> be wrong with fully understanding the network but this is my idea.
>>> All the sites are Receive getting data from the mobiles and passing 
>>> it on to
>>> a main internet link as per normal and the remote sites passing the
>>> information as per normal.
>>> The main difference is with a single area transmitter what gathers 
>>> data and
>>> what is coming from the internet is transmitted from a single site.
>>> Of course as you move away from possible single site receiving maybe 
>>> another
>>> site could pick up the slack with another internet to RF gateway, there
>>> might be another way of doing it, this I feel could reduce the 
>>> traffic by
>>> 25% - 33%.
>>> Cheers and 73s'
>>> Paul
>>> VK5VCO
>>> *****************************
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