slides for last Thursdays meeting

[Hal Feinstein]

I  put slides for last thrusdays meeting on 802.11 up on the web.  These 
can be found at:

http://www.black-arts.org/~hal/802.11.ppt

these are power point slides.  One thing I wanted to mention is that 
while the standard
for 802.11 is very concise, vendors have made a lot of their own 
tactical choices either through oversight,
error or deliberate omission, in hopes of  creating a more flexible 
product. In other words, knowing the
standard does not get you all the way to knowing what a specific 
802.11device is capable of doing.
Some examples are in Thursday nights talk: The slides I put up on the 
web talk about a contention free period
where polling is used.  This is actually optional and is not widely 
implemented.  The RTS-CTS
four way handshake to overcome hidden transmitters seems likewise  to be 
implemented in
a variety of way.  I have seen it on over the air traffic a few times 
and some literature
states that some vendors turn it on when packets containing over a 1000 
bytes are transmitted.
However, I don't think the criteria for use is very consistent over the 
field of vendors.  Vendors
have also pumped up a number of "after standard" "killer features" of 
their own devising that
may or maynot conform to the strict letter of the standard..   There is, 
for example, the
802.11g  "afterburner technique" for bursting multiple short
packets within a conventional data transfer to avoid the high overhead 
of handshaking for each one.
Lastly,  there is a lot of very interesting innovation is going on under 
the 802.11n hood including the revolutionary MIMO technology that 
utilizes multipath rays as simultaneous independent  communications paths.
Another interesting technology is channel bonding that binds two 
side-by-side channels into a single wider channel supporting a 
correspodning larger data
rate.  --h