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Emergency comms. Was RE: [aprssig] Igates Are A Fair WeatherSolution (was: "Finito")

Dave Baxter dave at emv.co.uk
Tue Aug 30 16:13:32 UTC 2005


Careful Jason, some of us have spent more time in the distributed
communications field (and related industries) at a profesional level as
well as amateurs, than the age of our call's may indicate....

I'm well aware of the layered aproach to packet based data comm's
(Including the transport layer and all it's faults and foibles) and the
inherrent unrelaiblility of the UI system when "pushed".

As someone else on this list earlier pointed out, you can't trust the
"established and tested" infrastructure (RF, 'net or otherwise) in an
emergency.  So, best provide your own, "on the fly"..  

Mobiles (or portables) set up on an overlooking hill, or a safe (if
there is such a thing) high car park or other structure, running as a
node or digi for example.  That's what happens over hear, as the usual
APRS frequency is too full of people who would want to "have a go" but
get in the way...

Read the rest of my post, especialy about the use of CW and the KISS
principle.

Nearly chucking out time hear, may get one more round in if quick!

Cheers...

Dave B.  G0WBX



> -----Original Message-----
> From: aprssig-bounces at lists.tapr.org 
> [mailto:aprssig-bounces at lists.tapr.org] On Behalf Of Jason Winningham
> Sent: Tuesday, August 30, 2005 4:56 PM
> To: TAPR APRS Mailing List
> Subject: Re: Emergency comms. Was RE: [aprssig] Igates Are A 
> Fair WeatherSolution (was: "Finito")
> 
> 
> On Aug 30, 2005, at 10:09 AM, Dave Baxter wrote:
> 
> >> Maybe, but if those 150 to 250 stations are transmitting 
> very often, 
> >> your network is dropping a _lot_ of packets.
> >
> > So what if a lot of packets are being dropped?
> 
> large number of dropped datagrams == overloaded, unreliable network.  
> Introduction to Networks 101.
> 
> >   It's a UI,
> 
> Yes, and two of the assumptions typically made with datagrams 
> are: a) the packet has a very good chance of being delivered, 
> and b) if reliable delivery is absolutely required, delivery 
> confirmation will happen at a higher layer.  In APRS we do 
> _not_ have any sort of confirmed delivery (other than some 
> point to point messaging conversations, a small fraction of 
> the overall traffic), so a reliable APRS network must _not_ 
> drop a large percentage of its packets, else it isn't reliable.
> 
> > Yes, sometimes it doesn't get through, but for "Emergency" use, why 
> > use the normal (busy) frequency anyway?
> 
> Because that's where the tested infrastructure is located?  
> That's where people are actually listening?
> 
> There's FM capture and power settings and antenna factors and 
> mobile flutter and band openings and all sorts of things that 
> affect the RF signal.  Don't forget, however, that when you 
> start talking about a data network you must realize there are 
> several layers to the beast, and the RF layer is maybe 1/4 to 
> 1/7 of the picture you must see when you're building a 
> network with an RF layer 1.
> 
> FM radio is not all there is to APRS.  education, education, 
> and more education etc....  (:
> 
> I have no idea what CW has to do with the discussion at hand, 
> so I'll let it pass.
> 
> > and as for most things PC based, well...
> 
> Right.  Hence my entry into this discussion with the 
> questions about NWS SAME and the usefulness of a non-pc, 
> non-internet means of getting some weather data onto APRS.
> 
> -Jason
> kg4wsv




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