[aprssig] RADIO paths in APRS Servers

[Randy Love]

There is nothing the the APRS spec that says you cannot direct a
packet via a given path. Most digi continue to digi via their call or
other unique identify ( such as HOTSPR or MTMAG ) along with the
generic digi alias of WIDE. If configured properly, a digi will insert
it's call or special alias in place of the WIDEn-N that it uses. But,
this does not occur in all instances as the digi operator is the one
who decides whether call substitution on a digi's packet occurs or
not.

Taking a look at a recent packet for my mobile station WF5X-9:
 WF5X-9>APOT2A,W8FSM-3,VE3KSR*,WIDE3-1,qAR,KC2HWB:!/8vF59NF#>D!G/A=000746
12.4V 57F

We can determine this:
The path used is WIDE3-3 ( this is considered abusive in some areas )
and the first two hops of this packet went thru W8FSM-3 and VE3KSR,
leaving one more hop ( WIDE3-1 ). This was ported into the APRS-IS by
KC2HWB after being hear from VE3KSR ( that why it has a * after it ).

The problem is that depending on where you are and how the digi op
configures his digi, you may not get this substitution. The best way
to determine a specific path is to observe the local network and
determine which stations are where and available by their posting to
the APRS network. Ideally, you would want to look at it via RF from
your location to see what is available to you.

The reason of the generic alias WIDE and now WIDEn-N is so that as a
mobile travels, it does not need to reconfigure for the local area.
Since APRS is an unconnected network, the need to hard wire digi names
is more of a hinderance than help. Unlike connected mode packet, where
you have to take the same path each time, APRS can digi via different
routes on each packet to get to the same location. Use of a generic
alias facilitates this functionality that helps make ARPS flexible in
message and information delivery.

73,
Randy
WF5X


On Fri, Aug 7, 2009 at 9:42 AM, Andrew Rich
(Home)<vk4tec at tech-software.net> wrote:
> When I started in Ham Radio we had digis that only had a callsign
>
> I could quite happilly direct a packet "via" a chain of digis I knew to get
> to a friend.
>
> Then came the advent of Alias - or a generic call that digis could adopt so
> you could drive around and hit any one of them.
>
> I just hope in the "noise" of progress, we don't do away with the ability to
> be able to discern what digis , or more importantly, have the ability to
> pick, which digis we go via.
>
>
> ----------------------------------------------------------
> Andrew Rich
> Amateur Radio Callsign VK4TEC
> email: vk4tec at tech-software.net
> web: www.tech-software.net
> ----- Original Message ----- From: "Steve Dimse" <steve at dimse.com>
> To: "TAPR APRS Mailing List" <aprssig at tapr.org>
> Sent: Friday, August 07, 2009 10:15 PM
> Subject: Re: [aprssig] RADIO paths in APRS Servers
>
>
>>
>> On Aug 7, 2009, at 12:02 AM, Pete Loveall AE5PL Lists wrote:
>>
>>> APRS servers and IGates do -not- strip the RF path on packets gated
>>> from RF to APRS-IS.
>>
>> But some of the other things he talks about are true. The path
>> statement of a packet cannot tell you the RF path, nor can it tell you
>> the Internet path. There are usually some pieces of information that
>> can be gleaned, but the complete path rarely appears, and you can
>> never rely on it. This is intentional. The focus of APRS is getting
>> the data where it belongs; the RF and Internet networks are designed
>> to accomplish the transport, not to provide a traceback.
>>
>> This is the reason findU, the APRS IS, and the RF network provide
>> limited information about propagation and network configuration. When
>> you hear someone making claims for producing network maps or analysis,
>> look closely at the assumptions being made, they are often not valid.
>>
>> Steve K4HG
>>
>>
>> _______________________________________________
>> aprssig mailing list
>> aprssig at tapr.org
>> https://www.tapr.org/cgi-bin/mailman/listinfo/aprssig
>
>
> --------------------------------------------------------------------------------
>
>
>
> No virus found in this incoming message.
> Checked by AVG - www.avg.com
> Version: 8.5.392 / Virus Database: 270.13.45/2286 - Release Date: 08/06/09
> 18:17:00
>
>
> _______________________________________________
> aprssig mailing list
> aprssig at tapr.org
> https://www.tapr.org/cgi-bin/mailman/listinfo/aprssig
>