Friday, March 2, 2018

Chapter 2 - 802.11e and WMM

Wireless networks have become the primary method of network connectivity for many organizations. As such they need to be able to handle the various applications that wired networks have evolved to handle over the years. This includes latency sensitive applications such as voice and video. To this end, the 802.11e amendment was written and implemented. It details various MAC procedures to support these various applications that have QoS requirements

802.11e brought with it two new types of STA's - QoS Access Points and QoS Stations. These are pretty straightforward. Basically what it means is that they are AP's or STA's that can support QoS, but can and will act as a normal (non-QoS) AP or STA if they need to.

QoS STA's must support the following:
  • QoS Functions - Obviously
  • Channel Access Rules - With 802.11e came EDCAF which is a new coordination function for channel access and something I'll go into a bit more in depth in a minute
  • Frame Formats and Frame Exchanges
  • Managed Objects

EDCAF - Enhanced Distributed Channel Access Function - 802.11e brought with it an enhancement to DCF to allow for certain priority levels to be applied to certain types of traffic. This allows traffic with a higher priority to be able to take control of the medium before traffic of a lower priority. It doesn't guarantee it, but it makes it more probable.

EDCAF has eight traffic categories, each with a User Priority (UP) from 0 to 7.

The Wi-Fi Alliance decided at some point that they needed to make a certification before the 802.11e standard was fully ratified. So they created the Wireless Multimedia (WMM) certification which was based on the draft version of 802.11e. It is currently in use for VoWiFi devices.

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