During WLPC_EU we had an 802.11ax after-party where we tried to make OFDMA functioning with different vendors AP and we got someone to do OFDMA. But we were kicked out of the meeting room before we got good results.
I have a network at home that does UL ODFMA, but it does not do DL OFDMA.
I have a packet capture of the UL OFDMA transmission and will explain it in this blog.
My previous article was on how to do wireless capturing on a Jetson Nano, with a big external screen connected to either the HDMI or the Display outputs of the Jetson Nano. And with connected external mouse and keyboard
But what if you want to use favorite packet analyzer on your preferred client where you have all your configured filters, profiles, aliases and so on.
The NVIDIA Jetson Nano Developer Kit with Intel AX200NGW WiFi6 chips set is one method to make a WIFi6 client. I have some of these.
Earlier today Francois Verges announced at Twitter a method for capturing 802.11ax frames with this kit. And I wasn’t difficult to trigger.
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.
This is a blog article on 802.11ax uplink OFDMA (UL OFDMA) and the control frames that are involved.
According to the IEEE802.11ax draft 4 the UL OFDMA process look like this
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
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
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
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
The presentation (slides) could be downloaded at this link (pdf)
If someone have constructive feedback I would be grateful
Useful links
Next Pcap-quiz, number 2, is “Fun with Beacons”
In the attached file there are
It is 1000 different parameters to check in a beacon, but we are not going so very deep. Just some basic parameters that are useful to know about
Please, try it
