[aprssig] time for APRS second generation network?

[Robert Bruninga]

>>> Jason Winningham <jdw at eng.uah.edu> 1/6/05 11:43:42 AM >>>
>I haven't studied the 9600 baud backbone system, but...
>I can't see how that will help local nodes reliably send and 
>receive data amongst themselves.  

Its works just like the APRS-IS.  Everything from up to 8
ALOHA areas all goes in to the 9600 buad UHF backbone:
* Anyone who wants to see EVERYTHING tunes in UHF at 9600
* Any directed packets from one LAN to another are just like
  on APRS-IS, the receiving LAN-gate sees the packet on
  the backbone for someone in his area and then brings it 
  back to its local 1200 baud user.

>as far as I can tell the 9600 baud backbone can 
>improve send to outside, can improve receive from outside, 
>or you can make your network bigger. 

Yes, anything beyond your ALOHA limit (about 60 users or so)
is "outside" and since your channel is saturated already
you can not bring anything else in unless it is a message
specifically targeted from one station to one other station.

> If you improve send OR receive but not both, 
>you have an asymmetric data flow and someone is not 
>getting the whole picture.  

Yep, that's the whole point.  It is impossible to make "the
big picture" on 1200 baud RF bigger than about 60 users. 
ANything beyond that has to be point-to-point (messages 
only).  But with the UHF backbone concept, anyone with 
a UHF receiver and a 9600 baud TNC (Any Kenwood D7 
or D700) can then tune in the UHF side and see all 8 area 
LANS or about 480 stations which should cover an area 
like LA.

This system rocks!

1)  It is really very simple, 
2) uses nothing but what we have on hand
3) is only a two-tier system
4) operates crossband full duplex for maximum throughput
5) Any fixed station with 9600 baud can see up to 400 stations
    in the greater local area on RF
6) Mobiles and HT users at 1200 baud see no change
    but can work more reliably because of less QRM

Its a win-win.  I think it is ideal for the LA basin.
One 9600 baud feed from the High site could
see "everything"...  And the investment is all done
at one site.  Done.!

Bob


Bob


If you make your network bigger, well, it's already too big.

As far as I can tell, the only way for 9600 baud to improve "A tactical

real-time local ad-hoc network for
digital communications among everyone..." is for _all_ nodes to switch

to 9600 baud.

> Im just saying that we MUST fix this level 2 saturation
> problem first.

I'm not saying we shouldn't do anything now, or that there's anything 
wrong with the work being done now.  I'm proposing the next step, which

is to get a layer 3 with some smarts because we are currently 
demonstrating that layer 2 cannot do enough, especially the layer 2 we

have now.

>   and the smarter infrastructure cant do a
> anything about that.

Sorry, but that statement is wrong.  I began my first message with an 
example of a real network that had everything on a single layer 2 
ethernet, but no layer 3.  Doing nothing more than adding layer 3 
(replacing some layer 2 devices with layer 3 routers) improved that 
network orders of magnitude.  The same basic networking principle _can_

improve the APRS network.

Because of the nature of our physical layer we cannot see same same 
"orders of magnitude" improvement, but we CAN:

- simplify user configuration
- adjust the local segments of the network to handle traffic 
appropriate to the local network load
- reduce duplicate repeats
- reduce path lengths, both number of hops and physical packet size

>  And I just want to un-confuse
> users.

Yes, and I think it should be whether they want it or not; that is, let

the network infrastructure make decisions to benefit the whole network

rather than being at the mercy of any ignorant or malicious user due to

this archaic source routing scheme we use now.

> The bottom line is we MUST cut path length and
> high-digi coverage

Right, but these are two completely separate issues.  Nothing we do at

layer 2 or above can have a useful impact with a very badly configured

layer 1, like a digi antenna that can see the entire northern 
hemisphere.

In a nutshell:  yes, there is a problem, yes New N-n helps if everyone

plays, but what are you going to do next time, when New N-n has reached

its limit?

-Jason
kg4wsv