[aprssig] time for APRS second generation network?

[Robert Bruninga]

Jason, you are missing two things about APRS:
1) it is a one-to-all traffic system.
2) Real-time data flows outward to one's ALOHA limit
3) Thus there are no LAN boundaries and there are no "routes"
    other than flooding outward.
4) You want to route from LAN to another but this is just not
   APRS.
   a) it assumes you know exactly where you want your pakets to go
       (in that case use a directed path)
   b) Or it assumes you can define for the network so that it knows w
       where you want your packets to go...
   c) or It assumes you can change your desires for a or b at any
      time on the fly...

None of that suits APRS.  Yes, I tried to get the other APRS authors
to accept the definition of "HOME" and each person could
send a packt defining his "HOME" and then let the network
do that routing.  But it was ignored by all other authors...

Remember, with an ALOHA limit of 60 and with 500 stations 
all trying to use the same channel with digis at 10,000 feet
trying to define LANS is an effort in futitility.  In many cases
if not all in SOCAL, one digi covers a aFULL ALOHA lan.

Thus "routing" is meaningless.  Already the channel is
full, there is nothing to route out of the area that wont
add to QRM elsewhere and there is nothing you can
"route" in that wont add QRM here...

Routing made sense back when it took 4 hops to
find 60 people.  But that was 6 years ago...

Bob


>>> Jason Winningham <jdw at eng.uah.edu> 1/5/05 3:02:20 PM >>>

> there is no such thing as "routing" in APRS:

Putting "RELAY,WIDE" in a packet and aliasing digipeaters to respond to

the names RELAY and WIDE it meets the standard definition of source 
routing.  I agree that source routing isn't "real" routing.

My RF LAN consists of all stations that can hear me and all stations I

can hear (my definition).  If a digipeater forwards a packet so that a

station that cannot hear me directly receives that packet then the 
digipeater has routed my packet between two LANs - mine and the other 
station's.

The problem is that our routers (digipeaters) are only capable of 
source routing.  That's a poor way to route a packet, especially in a 
dynamic (mobile, especially cross country) or unknown (SAR, come as you

are) environment.


If APRS uses a network, we should be able to apply some of the basic 
networking terminology to it.  I tend to think in terms of the 7 layer

ISO reference model (even if we don't use all layers).

> 1) APRS is defined as one-to-all information sharing

This statement is either application layer information, or network 
layer addressing information, depending on how you look at it.  It has

nothing directly to do with the underlying network.  It does influence

design decisions, but it does not define lower layers of the network 
(OK, it may define the _interface_ between this layer and the next, but

it does not define the internals of the layers below).

> 2) It is physically impossible to have more than 60 or so
>     users in a single RF domain.

Wouldn't it be nice if the nodes on our network responsible for the 
physical area we see were aware of that fact, and could adapt to it 
dynamically?

> Thus, by definition, there simply is no such thing as "routing"
> on the APRS RF domain

There is no such thing as "real" routing in APRS RF networks now.  
That's my point, and I think that is its biggest weakness.

This is _not_ to say that there _cannot_ be routing in APRS RF 
networks.  If it really is a network, it can be routed.

Using a standard networking protocol layer breakdown, RF is simply the

physical layer.  There's a lot more network above that.  Routing is two

layers up, and doesn't necessarily care what's happening at layer 1.

You _can_ route on an RF network, and the routing model I'm talking 
about is roughly analogous to logical subnetting of multiple IP 
networks on a single LAN.  Right now you can't _practically_ route on 
APRS-RF, simply because there are no routers to perform this function.

>  except in non-routine, unusual circumstances.  Otherwise "routing"
is 
> simply the APRS-IS.

IGates do the only real routing in the global APRS network, but only 
between RF and IS.  Unfortunately, that's not where we need it the 
most.

A real APRS router would:
	- simplify client configuration
	- stop client abuse of the network with excessive hops
	- statically determine how many hops are allowed in its physical
area
	- avoid loops (the ping-pong effect)
	- reduce packet size (no "RELAY,WIDE2-2" to double the size of a
Mic-E 
packet)

in addition, it could:
	- dynamically resize it's definition of "local" to match traffic
to 
capability
	- only transmit packets that the LAN can handle

-Jason
kg4wsv