Re: Airport Extreme Cards and Airbears

Here's a blurb from Macosxhints.com about what "interference
robustness" does -- Greg

-----
 From http://forums.macosxhints.com/archive/index.php/t-25762.html:

"I posted this question to alt.internet.wireless, and got a useful
response from Jeff Liebermann. there, who seems to know something about
microwave communication. Thanks, Jeff!

Although Apple doesn't seem to want to tell anyone about interference
robustness, Orinoco (Lucent), who contributed strongly to Airport design
(I think Airport at one time used their PMCIA card) is willing to help
us. See

http://www.orinocowireless.com/support/techbulletins/TB-035.pdf

The answer is that Orinoco provided a settable option in their PMCIA to
give robustness against microwave ovens. We believe that this option is
the one that Apple calls "interference robustness". The key to this
option is that microwave ovens have a strong periodic component to their
radiated power. For 60Hz ovens, at least,, they spend 8.3ms radiating
strongly, and 8.3ms being quiet, out of a 16.6ms period. Now, if a PMCIA
sees interference, it'll slow down the transmission more and more. At
some point, the packet size takes longer than 8.3ms to get out, and such
long packets will get whacked every single time (at least by a 60Hz
oven) - not just occasionally. What the option does, I think, is to
prevent the PMCIA from ever backing off to packet sizes that are longer
than this. Clever. Basically keep the PMCIA from shooting itself in the
foot as it valiantly tries to keep up.

The bottom line is that the option shouldn't make much of a difference
unless ACK failures are common. That's when packet management becomes an
issue. For truly random noise sources, in fact, keeping this option off
may be the best noise mitigation strategy. So my guess is that turning
it on to kill 2.4GHz telephone noise or rogue wifi router noise might
actually be disadvantageous. But do what works."

Beth Muramoto wrote:
> Mike,
>
> I hadn't tried this so I will give it a go. The user I want to test it
> on is gone for the weekend, but I'll try to catch him and give this a
> shot when he gets back. Couldn't hurt. Thanks for the suggestion.
>
> Beth
>
>
> At 11:21 AM -0700 10/14/04, Mike Hunter wrote:
>
>> On Oct 14, "To Beth Muramoto" wrote:
>>
>>> On Oct 13, "Beth Muramoto" wrote:
>>>
>>> > I didn't know who to email about this in CNS so forgive this post if
>>> > it should go elsewhere. If anyone knows who I should direct this,
>>> > please let me know, but another reason for posting this is to find
>>> > out if others are experiencing the same problem.
>>> >
>>> > We've had 3 iBooks with the Airport Extreme card both pre-installed
>>> > and manually installed where they were not able see Airbears in
>>> > Tolman Hall. We even tested on the second floor where there are 2
>>> > antennas (one in 2515 and one in the Ed-Psych Library) and Airbears
>>> > was not detected. On one of the iBooks, we did test the card by
>>> > creating a network on an iMac that we have in a lab here that has an
>>> > older Airport card and was connecting wirelessly. That iMac was
>>> > detected by the iBook. We also put the laptop on the same table that
>>> > the iMac with the older Airport card was on and there was no signal
>>> > to the iBook, but the iMac was detecting both Airbears and another
>>> > wireless network.
>>> >
>>> > Does anyone know if there is a compatibility/connectivity issue with
>>> > the Airport Extreme cards and Airbears? Or has anyone experienced
>>> > similar problems as well?
>>> >
>>> > Any suggestions are welcome and appreciated.
>>>
>>> Have you tried turning off "Interface Robustness" on the ibooks? Rumor
>>> has it that can affect signal strength issues.
>>
>>
>> Specifically, my GF came back with:
>>
>> Interverence Robustness does influence ability to connect
>> to airbears. Sometimes it makes the connection
>> better, sometimes worse. Hm...
>>
>> That wishy-washy answer is what I get for dealing with users directly!
>>
>> I tend to think Fred A. is correct that it's a vendor interaction issue.
>>
>> Mike

-- 
Greg Paschall -- gregp@ssl.berkeley.edu
SSL Network & IT Manager
Space Sciences Lab - University of California at Berkeley
Room 230 -- (510) 643-6907 -- Fax: (510) 643-7629
AST:7731^29u18e3
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