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[aprssig] APRX aprs-is filtering

Keith VE7GDH ve7gdh at rac.ca
Fri Aug 6 17:29:53 UTC 2010

Jaye KE6SLS wrote...

> When I set up my local aprx tx-gate, I was very concerned about being
> flooded with packets (reading several manuals, aprs-is seemed ominous.

It isn't really all that ominous, but a bit of reading wouldn't hurt. Your IGate
shouldn't flood the APRS frequency unless you tell it to.

> However, my experience with the aprs-is servers has been remarkably
> calm and useful without so much as a single filter in use. From time to
> time, the server will chuck a random non-local packet at my gateway, but
> it isn't too far--usually within 200-300 miles from this qth.

Some servers apply a default filter. Others will send you nothing if you
ask for nothing. I would really recommend that you read FILTER.TXT
and not just hope that the server that you connect to applies a default
filter, especially as you say that you are using rotate.aprs2.net:14580.
> This is my config server setting:
> # APRS-IS server name and portnumber.
> server    rotate.aprs.net    14580

That will connect you to any of a number of servers around the world.
You would be better off selecting the server closest to you and having
noam.aprs2.net:14580 as your "backup" server. Of course, I am assuming
that you can specify more than one server.

> I have logged onto these servers and learned that I am far from being
> the only one using these servers without the use of filtering of any kind
> regardless of client I-gate software used.  

It appears that we are talking about KE6SLS-3. It is currently connected
to THIRD. This is one of the core servers, not one of the tier 2 servers.
Unfortunately, the status page just shows that port 14580 is a filtered port.
It doesn't state if a default filter is applied. It's too bad that not all server
operators keep the status page up-to-date. While port 14580 is the standard
port for a filtered feed, the status page should really indicate if a default
filter will be applied to that port.


> There must be more to the story. I assume that the aprs-is servers are aware 
> of my location and will only send useful packets to my gate and automatically 
> suppress (filter) non-related packets that are beyond my service area?  

As I mentioned above, some servers apply a default filter. I wouldn't consider
it wise to depend on that especially when you are using rotate.aprs.net:14580.

> So far, I'm very pleased that I haven't had to worry about my station bombing 
> the local APRS frequency!  

 Even if you were getting a "full feed" from the whole world, you wouldn't be
"bombing" the local APRS frequency... unless you had the software misconfigured
to gate some or all of what you were receiving from the server to RF. You should
only gate specific things to RF plus APRS messages to local stations. Even though
an IGate shouldn't automatically gate everything it is getting from the APRS-IS to
RF (a total disaster) you should read up on filters and only get from the server
what you want to get. This will conserve server bandwidth (whether someone is
paying for it or if it's being donated) and will conserve your own bandwidth.
It will also mean that the IGate computer won't have to work as hard if you are
only getting from the server what you want to get.

73 es cul - Keith VE7GDH
"I may be lost, but I know exactly where I am!"

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