“*Guest Post* How Stuff Works – Frame Aggregation and Block ACKs”

This is a guest post for Xirrus employee, Douglas Haider. I have been in contact with Douglas ever since he started his blog. We both agreed that he could guest blog on HipTech101. Douglas blogs under the name “WiFi Jedi“. I have previously promoted his blog and if you haven’t seen it already, you can check it out at http://wifijedi.wordpress.com

“Greetings to the subscribers and readers of HipTech101! As advertised, I am the WiFi Jedi, and I have a blog about wireless networking and security located at http://wifijedi.wordpress.com In my blog, I have a series of posts called “How Stuff Works”. I have posted several times on technical improvements related to 802.11n and thought that I would continue that format here. For this post, I would like to discuss frame aggregation and block acknowledgement.

In normal 802.11 operation, each directed data and management must be acknowledged. This ACK takes the form of a 14 byte packet. This is shown in the top row of the graphic.

802.11n MAC Improvements

With frame aggregation, up to 64 MSDUs (MAC Serivce Data Units – essentialy layer 2 frames) can be sent at one time. This “super” fram has one physical layer header, then data frames (each with their own MAC header). Once all the data has been sent, a block acknowledgement is sent. This is shown in the bottom row of the graphic.

This is more efficient for several reasons. First, a physical layer header does not have to be transmitted for each data frame. Second, the block acknowledgement is much shorter than 64 separate ACKs. Third, there are far fewer interframe spaces as all the data is aggregated into one burst and all the acknowledgements are bundled together. Block Acknowledgements are also used under 802.11e Quality of Service.

Check out my blog at http://wifijedi.wordpress.com to see additional posts in my “How Stuff Works” series to include MIMO antennas, Spatial Multiplexing, and Channel Bonding.”

Expect more guest post to come!

Pizza Scissors

This has got to be one of my favorite inventions! I am a pizza lover and this just speaks to me. For $20, this lifts the pizza and slices it to the size that you desire. Dirty your hands and mess up the cheese no more!

Engineering Codes

This is pure comedy. I guess only engineers can decode this and figure out the phone number. The fact that it has 3 missing tags makes me chuckle. Lets just hope that this is not a random problem someone found on the internet!