Mobile Devices and Wi-Fi – AirHeads Session Review

In this blog post I’ll be reviewing a session from the latest AirHeads by Peter Thornycroft.

This session covered some great information about the current state of Wi-Fi clients. How they act, and how we might best go about designing our Wireless LANs to take advantage of client device behavior.

You can find the full session presentation at this URL.

Client Behaviors

At Home

When a Wi-Fi client device is at your home, it is sharing a single access point along with all other devices in your house. It has no need to look around for other access points. It has it’s connection to the Internet and is quite happy. It will also continue to stay connected to the same access point until it drops off completely. Thinking there is only one access point in the home.

In the Enterprise

The client device has many access points to choose from, all with the same SSID – offering seamless roaming and handoff from access point to access point. The device needs to constantly scan for other access points – the thought is there is always a better AP to connect with. The benefits of this model are higher data rates, devices use less airtime, better battery life, and less co-channel contention for limited frequency.

Which of these two client behaviors are mobile smartphones and tablets designed for? Most want a ‘Give me more battery life, and keep me connected’ is the overriding design.

Because of this desire to save battery life above all else, many devices find an access point, then stop probing in an attempt to keep RF Tx to a minimum when no data is flowing. When in fact the Wi-Fi radio uses far less energy than the CPU, or Display, or background tasks.

Location Awareness

Wi-Fi chip manufacturers are just now starting to add features and functionality into their chips to allow for much more accurate location tracking. Using 802.11k and 802.11mc we can get Wi-Fi only location accuracy down to less than a meter. But both the clients and access points need to support more than mere RSSI, but also the Round Trip Time with precise timestamps down to the nanosecond.

Leaning Toward 5GHz Frequencies

This has been a long time coming, but we are finally seeing client device developers putting more and more bias toward 5GHz. Including DFS support – all Apple devices since iPhone 4s and many newer Androids now have this built in. Allowing us to take advantage of the extra frequencies available to WLAN designers in the DFS channels.

Hotspot 2.0

This new type of association process, also called ‘Passpoint’ –(stupid name IMHO) has the potential to change the way clients connect to access points. Though the spec has been around since mid 2012, we are only lately seeing service providers starting to add this to their offerings. Public-facing vendors should put this as a top priority.

Outmoded Handover Processes

The currently used model of packet transfers and decision algorithms has been around for over a decade. It is slow, inefficient and takes a lot of time and packet transfers in order to work properly.

Mobile Devices and Wi-Fi – AirHeads-current-model

The IEEE has been working on protocols to help alleviate some of the inefficiencies in the older roaming model.


  • Neighbor Report from AP to Client
  • Channel Report from AP to Client
  • Beacon Report from Client to AP


  • BSS Transition Management from AP to Client


  • Fast Transition by Client

All of these together have been rolled up into 802.11-2012, 2014.

Mobile Devices and Wi-Fi – AirHeads-model-1

Compare the new transition handover using 802.11k

Mobile Devices and Wi-Fi – AirHeads -model-2

If you are involved in Wireless LANs – you know how much client behavior affects your network. Please take the time to check out Peter’s great presentation from Aruba Airheads online for more details.