Timothy Murphy wrote:
> What exactly is the difference between an Access Point
> and an ordinary, eg PCMCIA, WiFi card?
Hardware wise there is little difference. Form factor, packaging and
antennas are the main differences. Early APs actually used cards for
their wireless transmitter that were no/little different from the cards
used in laptops.
> I mean, what is the difference in the way they function?
As transceivers, there is no essential difference. An AP has
additional duties and greater workload than a laptop card and must
provide its own processor and memory. APs are not "end user" devices
but are better thought of as network devices akin to switches.
WiFi cards in your laptop or USB port or plug-in cards of a desktop are
the wireless equivalent of ethernet NICs. They provide access to the
wireless medium rather than the wired medium of ethernet.
> Does the Access Point send out different packets
> when responding to a client?
The wireless medium gives new meaning to the words "broadcast medium"
as originally applied to ethernet. It is a _very_ complex (set of)
protocol(s) that is broadly similar to ethernet but that, due to the
medium, requires more intensive access control and traffic management.
Because of the "network" role of the AP, it does indeed send different
packet _types_ than client stations (and vise versa). APs are
responsible for providing their clients _access_ to the airwarves, to
other clients, and (optionally) to an attached ethernet wired network.
Think computerized "air traffic controller". Both APs and clients must
understand the whole protocol in order to "fit into" a wireless
network. Clients using an AP are said to use infrastruture or managed
mode.
But laptops with wireless cards have tranceivers so they should be able
to talk to each other directly, right? Right. These are said to be
using ad-hoc mode, ie., a "temporary" collection of computers
communicating directly with each other. They must share the burdens of
keeping things working right, including many of the services provided
by an AP.
> Is there anywhere online (or at O'Reilly)
> where this is explained?
I've not found a one-stop article, report, or tutorial that covers the
basics of WiFi satisfactorially. The more you look into it, the more
questions arise, and the need for clarifications and distinctions grows
exponentially. About all you can do is use google and pick and choose
on your own in order to answer _your_ questions.
You might start with this -- or a similar -- google search:
wireless home network tutorial
http://www.google.com/search?num=50&...twork+tutorial
Wireless home networking can get pretty complicated today but is more
likely to provide less technical explanations to get you started with
the basics. After that, you should have enough terms under your belt
to google till you drop.
cheers,
prg
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