[aprssig] Tier 2 Status

Steve Dimse steve at dimse.com
Wed Jun 21 20:10:49 CDT 2006

On Jun 21, 2006, at 7:34 PM, Stan - N0YXV wrote:

> If anybody can use the core servers then whats the purpose of  
> Tier2? If the
> Tier1 servers go down we have nothing. If Tier2 goes down we have a  
> backup (Tier
> 1). To do it the other way around wouldn't work. I mean if we crash  
> Tier 1 there
> isn't a Tier 2 to fall back on. Maybe somebody can get the confused  
> look off my
> face.

No, you misunderstand the configuration of the APRS-IS. All the tier  
2 servers are connected to the core servers in one place. Were all  
the core servers to go down, you would have a bunch of non-connected  
tier two servers. This in fact is one of my principle objections to  
tier 2. The user gets little feedback about the connectivity of the  
server they are connected to. For example, say a typical tier 2  
server has some sort of problem with its connection to tier 1. As a  
user, you are connected to a network, but have no idea your APRS  
universe is limited to those people connected to the same server. On  
the other hand, someone using the core is either connected or not, if  
you are connected to a server you are connected to everyone. If you  
are not connected, your program tells you that information.

Granted, it is pretty rare to have a problem with the outgoing  
connection to a tier 2 server, and therefore my second issue is the  
more common one, packets must pass through more hubs to reach users  
that do not happen to share the same hub. Image two stations each  
connected to a hub. If they use tier 2, the odds are only what, 1 out  
of 20?, that they are on the same hub. If they are not, their path is  
tier 2 -> core ->tier 2 at best. If the two tier 2 hubs are not  
connected to the same core hubs (which will be true 2 out of 3  
times), then the path is tier 2 -> core -> core ->tier 2. So the odds  
are 5% one hop, 31.7% 3 hops and 63.3% 4 hops.

With core connections for the two clients, the odds are 33.3% one hop  
and 66.7% two hops.

Which sounds better to you?

The argument for the tier 2 system is usually the core can't support  
the number of connections currently in APRS. As it stands now, that  
is a true statement, but that is simply because the core has not  
attempted to provide that much core capacity, instead the system  
keeps pace just with the number of users on the core. I believe two  
more servers in the core (which would bring the odds to 20% one hop  
and 80% two hops) would be adequate. The core servers do need to be  
on very fat pipes, but servers in such locations are available, every  
time I need a server location I get several good offers from people  
here on the sig.

Steve K4HG

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