Does my network do both DL and UL OFDMA?

I have tested the new 802.11ax standard lately and I have suspected that the downlink data frames don’t do Multi User OFDMA (DL OFDMA). I have also sent a question regarding this to some WiFi experts, but no one has answered. So, let us use Wireshark and Sidekick to dive into it.

This test is done with public available devices and software. I have not dived into release notes for each device. This is an article where I use Wireshark and Sidekick to examine how things work.

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HE MU-RTS and CTS deep-dive

The second powerpoint series in my deep dive into the HE/802.11ax protocol is about the Multi User Request to Send (MU-RTS) and Clear to Send (CTS) process.

MU-RTS is one of the new Trigger Frames in the HE process and will be used instead of the legacy RTS.

I’ve have rewritten the slides some times while I have discovered new items during my interpreting of the IEEE802.11ax draft, so the coherence of the slides could have been better.
If I have interpreted it wrong, please tell it to me

My lab is consisting of Cisco equipment and Cisco have not implemented this functionality yet, so nothing is tested in real life.

I hope it useful

 

MU-RTS_CTS_final

Cisco 9800 CL and AP in FlexConnect

 

Last week I got one of my colleagues to install Vmware Workstation and Cisco Catalyst 9800 CL at one of my clients and after 24 hours of configuring and troubleshooting, I finally made it works with APs in FlexConnect mode.

Ciscos documentation on Catalyst 9800 CL and APs in FlexConnect mode is not perfect and I had a lot of challenges during configuration. I have therefore made this recipe for myself and anyone else

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OFDM, HT and VHT PHY cheat sheet

I mentioned in my latest blogarticle that I have read the book “Next Generation Wireless LANs” second edition from Eldad Perahia and Robert Stacy. This is fantastic book that goes way beyonds study material for the CWAP-certification .

To memorize this bit-by-bit stuff I have made myself a ODFM, HT and VHT PHY cheat sheet

Remark: This is a 50% product and in A3 format.

Constructive feedback are welcome

Downloadable file (pdf): OFDM, HT and VHT PHY Reference cheat sheets

ODFM, HT and VHT PHY reference cheat sheets

 

DL MU OFDMA bit-by-bit

There are a lot of blogs, podcast and videos at the internet explaining 802.11ax at a high level. And some have done testing with 802.11ax compatible devices. But I have not found anyone that explains 802.11ax at a deep level. So why not me

The last year, since I bought the Perahia and Staceys book “Next Generation Wireless LANs”, I have been interested in the PHY-level of 802.11. And to go deep at 802.11ax I had to buy the 802.11ax, Draft 4.0.
There are so many new topics in the 802.11ax technologies so I had to make usecases for some of the topics and I have choosen the MU OFDMA process. This first blogarticle, in a series of articles, are about the frame where the AP sends data down to stations that needs data, the DL MU OFDMA frame. This frame is sent in i HE MU PPDU format, one of the four different frame formats in the 802.11ax standard.

Later on I will cover other aspect of the MU OFMDA process, like the MU-RTS/CTS process, the uplink OFDMA (UL MU OFDMA) process and the Acknowledgement process

Nothing of this is testet in real world, it’s picked out of the 802.11ax draft

DL MU OFDMA
DL MU OFDMA is the process where the AP sends data down to several stations that need/want data in a parallell process. In this slides I have used a example where four stations receives data in parallell. The AP have, before it starts to send data, decided how it should allocate its RUs.

A overview of this frame (PPDU) is like this

DL OFDMA transmission overview

The presentation (slides) could be downloaded at this link (pdf)

DL OFDMA, bit-by-bit

If someone have constructive feedback I would be grateful

Useful links

  • Cleartosend 802.11ax podcast-series,  link
  • David Colemans presentation at WLPC_US 2019, link
  • Wifininjas, link
  • IEEE 802.11ax draft 4.0 ($400), link