[Vk1tac] this is was sent by Geoff Gatward, to fill in a bit more information about APRS and it's possible use from Ginnini

[Neil Pickford]

-------- Original Message --------
Subject: Fw: this is was sent by Geoff Gatward, to fill in a bit more
information about APRS and it's possible use from Ginnini
Date: Fri, 17 Jan 2003 14:46:56 +1100
From: "Mr Gilbert Hughes" <ghughes3@bigpond.com>
To: "Richard Elliott" <richard.elliott@dfat.gov.au>,"Paul Elliot"
<pkbelliot@bigpond.com>, "Paul Bell" <paul.bell@afp.gov.au>,"Neil
Pickford" <neilp@goldweb.com.au>,"Keith Malcolm"
<kmalcolm@tpg.com.au>,"John Woolner" <johnwoolner@auslig.gov.au>,"Mike
Dower" <vk1eng@tpg.com.au>

3rd most recent

Regards
Gilbert Hughes
mailto:ghughes3@bigpond.com

----- Original Message -----
From: "Peter Westerhof" <Peter.Westerhof@aspect.com.au>
To: <ghughes3@bigpond.com>
Sent: Tuesday, 14 January 2003 5:05 PM
Subject: this is was sent by Geoff Gatward, to fill in a bit more
information about APRS and it's possible use from Ginnini


>
> Comments below.....
>
> > 3. An APRS wide has been suggested, however we understand that a
wide
> > coverage store and forward service could do more harm than good if
APRS
> > continues to gain in popularity and more 'wides' are installed.
> >
> > APRS, although using packet protocols (AX.25), albeit in a limited
way, is
> > more about transmitting packets (in a broadcast mode) without
apparently
> much
> > regard to whether they are received anywhere of use. My experience
is that
> > success rates are low, caused again in part by congestion, and
incorrectly
> > aligned transmitters.
>
> Success rates of recieving APRS packets are actually quite high.
Careful
> planning and regulation of WIDE (and RELAY) digipeater locations
results in
> a network that does not become too congested.  Being a broadcast
method of
> transmission actually DECREASES the traffic on a frequency. In a
messaging
> situation, for traditional packet terminal to terminal connection for
one
> packet of text (1-256 chars) we need:
> 1-Connect Frame
> 2-Connect Ack
> 3-Info Frame
> 4-Info Ack
> 5-Disconnect Frame
> 6-Disconnect Ack
>
> Compared to APRS messageing for one packet of text we need
> 1-Broadcast frame
> 2-Ack (when remote station has heard packet)
>
> The broadcast frame is transmitted a maximum of 6 times, and is
cancelled
> upon reciept of an ACK from the recipient.
>
> Position reports are broadcast with no ACK to all monitoring the
channel. If
> a packet is missed by a user, it is no big deal, since the repitition
rates
> of the packets by the sender mean that they will be recieved on their
next
> transmission.
> -Fixed stations transmit once every 30 mins
> -Wx stations once every 20 mins
> -Mobile stations once every 1 min
>
> Also the rate of transmissions from non local users is controlled by
the
> local I-Gate, leaving relitively large holes of dead-air on the
frequency
> for local users (covered by the WIDE) to access the system.
>
> > My though is that wanting to increase the number of WIDE nodes that
are
> heard
> > in a community increases congestion. So whilst simple thinking is
that
> lots of
> > WIDES and RELAYS increase the change of a position report being
heard
> > somewhere usefull, increased traffic causes congestion and decreases
the
> > probability that a position report is not clobbered by another
(hidden)
> > station.
>
> Only one WIDE should be heard by a community - placing a WIDE at RGI
would
> mean the removal of the WIDE and replace it with a RELAY only at RBM,
so
> still only having one WIDE digi
> serving VK1, but also extending the coverage in the network in all
> directions.  Since there are no other WIDE digipeaters planned between
> Canberra and Wagga, and also Canberra to Wollongong, the site at
Ginini
> would be an invaluable asset to the APRS community.
>
> RELAY digipeaters are a slightly different situation, these are only
> required in areas where a mobile station is unable to directly access
the
> WIDE. The number and location of RELAY digis is ideally regulated
locally so
> as to avoid congestion.  In Sydney, we have found that using
appropraitely
> placed RELAY and WIDE digipeaters effectively eliminates around 80% of
> hidden transmitter problems.
> (We have 2 WIDEs that serve East and West Sydney, and one RELAY in an
> eastern hollow area)
>
> Hope that helps a bit.....
>
> Geoff
>
>
>
>
> Regards
>
> Peter
> VK1NPW
>
>
>
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