[Vk1tac] APRS Spec

[Owen Duffy]

All,

Peter Westerhof wrote:
> Howdy everybody, attached is a PDF, this is the APRS spec and contains
> information on the difference between RELAY and WIDE..

Under the heading "Generic digipeating" the APRS Spec V1.01 offers the 
following description / recommendation:

"1. RELAY — Every VHF APRS TNC is assumed to have an alias of
RELAY, so that anyone can use it as a digipeater at any time."

(My observation is that the majority of stations here (fixed and mobile) 
have a UNPROTO path that starts the VIA list with RELAY, and so would 
use any RELAYs that hear their 'direct' transmission.)

If every station with a TNC active on the channel was configured for 
RELAY as assumed in the spec, there would be a gross increase in traffic 
from low lying stations and an increased probability of collision 
leading to reduced probability that position reports would be received 
successfully at the WIDE.

I noted in a recent email to Gil the following:
"RELAYs and WIDEs appear to be deployed in an ad-hoc fashion. For 
example, ... I watched the channel here in Canberra for an hour and 
observed only one mobile active (although stationery) transmitting 
position reports every 50 seconds, which I received reliably at a 
distance of 24Km. The position reports were reliably repeated by three 
RELAY stations that were located within 4Km of the mobile, and the WIDE 
on Black Mountain. In all, I received 5 copies of the position reports. 
I don't understand the value of three RELAYs (over one or none) in such 
close proximity."

I would have though the last thing that we need is 20 RELAYs in town! I 
don't think that is your intention Peter, but the APRS Spec V1.01 
doesn't really give much configuration advice about service levels, 
traffic policies, network topology and in respect of RELAYs, might 
encourage excessive deployment.


Owen

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