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Old 09-04-2007, 11:01 PM
Jeff Liebermann
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Default Re: How does a computer differentiate between ad-hoc and infrastructure networks?

On Tue, 04 Sep 2007 20:25:17 -0000, StandardGreen
<StandardGreen@gmail.com> wrote:

>When I look at available wireless networks, Windows XP differentiates
>between the WLAN and any nearby ad-hoc networks. How? I'm assuming
>that there is some kind of identifying bit in the packets.


The information is in IEEE 802.11-1999 specs found at:
<http://standards.ieee.org/getieee802/802.11.html>
Section 5.6 explains the difference between AdHoc and Infrastructure
modes. The problem is that the IEEE calls them IBSS (adhoc) and ESS
(infrastructure) modes. A client bridge is also known as an STA.
Reading IEEE specs turns my brain to mush. Therefore, I suggest you
digest the technobabble and acronyms in small bites.

Also see:
<http://grouper.ieee.org/groups/802/11/Tutorial/>

The info is in the probe response frame (which also supplies the SSID)
as in 7.2.3.9. Specifically, it's in the IBSS (adhoc) Parameter Set.
If it's an ESS (infrastructure) access point that's responding, the
field is blank.

It might be helpful if you try a wireless sniffer and looked at the
packets involved. See Wireshark at:
<http://www.wireshark.com>

>Furthermore, to those that know the answer to the question, where do
>you learn this? I'd like to find your sources so I can get tips on
>finding this stuff out for myself.


A more simplified list of frame types can be found at:
<http://www.wi-fiplanet.com/tutorials/article.php/1447501>

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