[MLB-WIRELESS] So how does this routing bit work?

[Bryce Letcher]

I've seen plenty of discussions about network configuration, bandwidth
requirements, scalability, routing etc. but I must have missed something. I
don't understand. Possibly I'm dumb (but I don't think so :) )

In a simple wired network if point A sends a packet to point X all points on
the network receive the packet, and point X accepts the packet. All points
receive the packet because they are all within range of point A. (and yeah
there is a hub in the network to connect the points)

In a mixed wired LAN with wireless interface as is used by many companies,
there is an AP and a number of nodes that talk to the AP. Yes the nodes can
talk directly together IF they are within range of each other. The AP
bridges between the LAN and the node connection and also retransmits the
packets received on both the wireless and LAN interfaces.


If we look at a routed wired lan system, point A can send a packet addressed
to point X and when a router picks up the packet, it "knows" which port to
re-transmit the packet on to reach point X. Now that's a big statement. The
router KNOWS because it's been programmed or configured. The router also
RE-TRANSMITS the packet on the correct port. This implies router has at
least 2 PORTS.

If we look at the wireless network being built here, we have a lot of nodes,
some within range of each other and some a number of hops removed.

How do the nodes that at several hops away from the origin ever get the
packet?

I do not see any means of routing buy a node.

Now someone will pipe up and say, easy! Just have 2 nodes (IE 2 ports), and
route between them. And yes I can do that, BUT we now need to look at
topology. In the wired system above where routing is used the two segments
are isolated, except for the router. In a wireless system however, isolation
is only achieved by directional antennas, and then not totally. Why does
this matter? Well if I use 2 ad hoc nodes (A & B) in the same box and route
from A to B, when B transmits the packet, A WILL pick it up and it will the
routed to B again. This is just like a loop. Hang on! It is a loop. The
packet will have the potential to circulate endlessly and tie up all the
bandwidth.

Surely this means that everybody needs to run an AP which has a filter to
prevent exactly this occurring?


Over to you guys for comments.

rgds,
Bryce


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