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[aprssig] distributed findu possible ?

Rick Green rtg at aapsc.com
Sat Aug 9 22:15:42 UTC 2008


On Sat, 9 Aug 2008, Michael Conrad wrote:

> The user interface should be web-based (like findu, aprs.fi, ...). The position report
> script could be redirect the user to the responsible node.
   You've mentioned this several times, but never spell out a 
mechanism, protocol, etc. to carry it out.  It's not that simple!

> Like written above, there are about 30 APRS records per second, coming from less then 15000
> unique APRS stations and producing 120000 APRS records per hour.
>
> If we have a distributed system consisting of 100 peers (nodes) in average each peer
> is responsible for 150 stations or 1200 APRS records per hour. This will result in 0.3
> APRS records per second (or 1 APRS records per 3 seconds) or 2.5 MB data per day.
> With a 48h history, each peers has to store 5 MB APRS data.
>
> If such a system has the same user load like findu (2 mio pages), each peer has to perform
> 20000 pages per day (15 page request per minute). This should be no problem for a cheap
> root server, even a small pc connected via dsl could eventually handle this.
>
   Your numbers are simply the division of the whole APRS-IS by the number 
of nodes.  You don't take into consideration the effort it will take to 
exchange index information with each of the other nodes.  Exactly how will 
a node know where to re-direct a query??  And considering your example of 
100 nodes, 99% of all queries will have to be re-directed, so at a 
minimum, you'll have to double your numbers, since the typical query will 
have to be issued twice, once to your local node, and again to the 
'responsible' node.
   As for the coordination of indices, do you propose that each node make a 
periodic connection with every other node?  How will a node 'discover' the 
identities of its peers?  Remember, you claimed this would be 
self-organizing, didn't you?  Will it also be self-healing, when a single 
node drops offline for any number of reasons?  How will you manage data 
redundancy?  Will it be robust, and impervious to attacks by 'imposter' 
nodes that make false claims of reception of specific callsigns?  Or do 
you propose a single central server that will maintain a worldwide index, 
which would violate your ad-hoc self-organizing principle?

-- 
Rick Green, N8BJX

"Those who would give up essential Liberty, to purchase a little
temporary Safety, deserve neither Liberty nor Safety."
                                   -Benjamin Franklin





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