I have in my short WiFi life thought when an 802.11 station (WiFi) does carrier detect it would detect all parts of an ongoing frame transmission on the channel and defer its own transmission because of that. But it seems my understanding has been wrong.

The last week’s online discussions has open my eyes to another look at the protocol and the importance of detecting the 802.11 preamble.

In this article I will write about the uniqueness of the 802.11 preamble, how important it is to detect it and how long it travels

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Please, set your mind into an 802.11 station and think about what happens during the start of an 802.11 frame reception.
In the preamble there is a field called L-SIGNAL and one of the subfields is called Rate. If the rate indicates 6mbs the rest of the frame could be any of the available PHY types in the 802.11 standards.
In the 5GHz band, it could be either a non-HT, HT, VHT, HE SU, HE MU, MU Trigger-based, or HE ER frame format.
How will you differentiate between those types of frame formats, and receive and process it correctly?

No clue, read this article

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A WiFi Ghost frame is a term widely used in the WiFi community lately. It is not a part of the 802.11 standard, it is just a term many uses.

Some say it is a frame the receiver don’t hear, other say the receiver don’t understand. Both are wrong.

So what is it?. I will try to explain.

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Andrew McHale wrote a blog last week on “Will we be able to capture 802.11ax frames“. Since I was mentioned in it, I have to answer. I jump straight to the core and if you need some background, read Andrews blog

I will in this article try to explain some aspect regarding 802.11ax ODFMA wireless capturing, and suggest how it could be done in the future

 

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Some days ago I helped my son when he complained about slow wifi in his rented apartment in Lisboa. To do this we used iOS app Airport to visualize the network.

I thought this process could be documented in a blog

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With the introduction of 802.11ax and the newly released frequency band for 802.11 transmission in the 6GHz band (WiFi6E) there have been talks about allowing only 802.11ax frame formats in WiFi6E. A week ago Jim Vajda (@jimvajda) released a blog article on “Whats Different About 802.11ax in 6Ghz“. This article concluded with the use of 802.11a, or non-HT, frame format for some types of control and management frames, and 802.11ax (HE) frame format for the rest.

In this article, I will describe airtime consumption for those two frame formats and show where 802.11a/non-HT frame formats consume less airtime than 802.11ax/HE frame format.

This article is only regarding airtime consumption for single user frame types. Multi-user frame types in 802.11ax/HE solve other issues. 

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In our eagerness to learn new stuff all the time it is sometimes useful to have the basic WiFi knowledge repeated.

I do, approximately once a year, listen or look through some webinars/podcasts/presentations which are available online. This is nice to do when I’m driving between locations.

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I made a Kahoot challenge last week. But because of different subscription models only 20 could attend. The winner in that challenge had 8 correct answers out of 10 questions.

I make this blog with the same challenge so everyone who wishes can test themself.

First is the 10 question, each with 4 options.
Then the same 10 questions with the correct answers, and some explanation

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In Wireshark version 3.2.1 for Windows, there is a field where the value of the Rate and the Length subfield from the Legacy Signal field in the Physical header is shown for 802.11ax aggregated frames

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Let us use this and have some fun.

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802.11 Frame Aggregation is the technology in WiFi that enables the sender/transmitter to “pack” together several frames and send them in one frame transmission, a TXOP.

I will in this case study drill down in a frame capture and interpret the different parts of an 802.11ax aggregated frame transmission, both a single-user transmission (OFDM) and a multi-user transmission (OFDMA).

The wireless capture I use in this case study contains two-level aggregation, where A-MSDU is sent inside an A-MPDU.
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