[Cu-wireless] Re: Are we making things too hard on ourselves?

[Paul Kennedy]

[
    I get the digest of this list, so I don't know whether anyone
    has talked about this before.  Apologies if this has already
    been covered.
]

niteshad at whopper.de wrote:
> I was just thinking about our conversation at the last
> meeting regarding ways to get cheap wireless routers,
> which ultimately terminated in the decision to look into
> the University Auction in Springfield.  We decided that we
> needed something with an 802.11b card, an RJ-45 Ethernet port
> and the ability to do routing, well, isn't that exactly the
> definition of a Wireless Access Point?

Unfortunately, no.  Here's part of the difference.  In most
"apartment network" setups, the only thing that needs to be
done is "routing" like this:

       [Node A]-| ....  
                       .
       [Node B]-|  .... . |-[ HOST Z ]---->[modem]----[Internet at large]
                       .
       [Node C]-| ....  


Host Z acts as a fairly rudimentary router (and possibly Network
Address Translation, or NAT box).  In this simple network, the
decisions that host Z has to make are fairly simple: did the
transmission come in on the wireless port side?  does this next
packet need to go out on the wireless side or the wired side?
Host Z is really acting as a gateway.

Consider the mishmash below (dashed lines represent links,
wired or wireless, it doesn't really matter).

                       B-----C-----D---[Internet]
                      /      |      \
                     /       |       \ 
    [Internet]---- A         E--------F
                     \       |       / 
                      \      |      /
                       G-----H-----J---[Internet]

Nodes A, D and J have links to the Internet.  Where do packets
coming from E go?  Do they go E-C-D or E-F-J or E-H-J or E-F-D?
With real routers, we could pick amongst various routing
protocols to find what works best for the collection of nodes
that we'll end up having (as well as being resilient in the
face of node/link failure).

As a side note to the network junkies, my guess is that we'll
probably end up running something related to OSPF since it is a
link state protocol (instead of a distance vector protocol with
their associated problems).  I have no idea of the consensus
of the group.

So the real problem with trying to use just a wireless access
point is that you are most likely _not_ getting a true router.
A true router should be able to deal with network loops (as
in the case above) as well as deal with things like nodes or
links going down (as might happen with a community network).

I hope that I've not caused any confusion and hopefully even
helped :)

Paul


-- 
Paul A. Kennedy    "I don't use VI unless I need to resort to 'paper tape'"
pakenned at uiuc.edu                                    --Brynnen Owen 98/9/11