Wi-Fi Quality of Service(QoS) - Wi-Fi

What is Wi-Fi Quality of Service(QoS)?

With the adoption of the IEEE 802.11e standard, there are plans to include quality of service (QoS) capabilities in WiFi technology. There are two operating modes in 802.11e standard, anyone can be used to improve service for voice -

  • WiFi Multimedia Extensions (WME) − Mandatory
  • WiFi Scheduled Multimedia (WSM) − Optional

WiFi Multimedia Extensions (WME)

WiFi Multimedia Extensions uses a protocol called Enhanced Multimedia Distributed Control Access (EDCA). The protocol is considered as an extension of an enhanced version of the Distributed Control Function (DCF) defined in the original 802.11 MAC.

EDCA will define eight levels of access priority to the shared wireless channel in the enhanced version. The EDCA access is a contention-based protocol that engages a set of waiting intervals and back-off timers modeled to avoid collisions. However, with DCF all stations use the same values and hence have the same priority for transmitting on the channel.

Different access priorities are assigned a different range of waiting intervals and back-off counters with EDCA. Shorter intervals are assigned to transmissions with higher access priority. We have a packet-bursting mode that permits an access point or a mobile station to reserve the channel and send 3- to 5-packets in a sequence.

WiFi Scheduled Multimedia (WSM)

It is considered optional and it provides true consistent delay services. It operates like the less used Point Control Function (PCF) defined with the original 802.11 MAC.

The access point broadcasts a control message that causes all the stations to consider the channel as busy and not attempt to transmit. During that interval, the access point polls each station that is defined for time sensitive service.

Devices need to send a traffic profile describing latency, bandwidth and jitter requirements to use the WSM. Suppose the access point do not have enough resources to meet the traffic profile, it will return a busy signal.

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