How does a computer differentiate between ad-hoc and infrastructure networks?

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. 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.

Thanks, StandardGreen

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The information is in IEEE 802.11-1999 specs found at:

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:

The info is in the probe response frame (which also supplies the SSID) as in 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:

A more simplified list of frame types can be found at:

Reply to
Jeff Liebermann

Good afternoon,

Can somebody recommend a good "wireless sniffer" to see what's running in my neighborhood? I'm running XP SP2. I'm currently using "Netstumbler" as it shows my wi-fi S/N ratio. Is NetStumbler good enough?

TIA for your time,

Reply to
Curt Christianson

I like it. This link below also shows a neat device that I use. Of course a spectrum analyzer and protocol analyzer is also reccomended. But these high priced devices are not needed for casual use.

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Sorry, Posted here in error. Will start a new thread.

Reply to
Curt Christianson

Thank you Dana--even though this post got accidently mixed in with this thread. I'm somewhat of a NG veteran, and should know better. I'll check out your link.

Thanks again,

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