Only a brief description of HCF is provided here. The interested reader can refer the 802.11-2012 or the 802.11-2016 standard. In the EDCF mechanism seen previously – it was seen that all stations contend for the medium and the station that wins contention normally is allowed to transmit. The Hybrid co-ordination function combined features of Point […]

The current article attempts to explain how a partial virtual Bitmap is computed with an example – refer <Understanding Traffic Indication Map> to understand the TIM Element before going through this article. Consider that an 802.11 Station with Association ID 26 has unicast data buffered and no other station has buffered unicast data at the […]

The PS-POLL Mechanism is the Legacy Power save mechanism. The following article tries to explain the same. As the name suggests PS-POLL stands for Power Save Polling. The Access point uses the TIM information element to indicate to the station that there is  unicast data buffered for the WLAN station at the Access Point. The […]

The Access Point will maintain the following for Power management stations and to handle buffered traffic for U-APSD The Access Point will maintain the power management status of each connected station. It will also maintain the per Access Category U-APSD status for each connected WMM Station If the 802.11 WMM station is in power save […]

Unscheduled automatic Power Save delivery (U-APSD) is a mechanism which allows an 802.11 station to wake up when the 802.11 station wants to wake up and ping the Access Point to send buffered unicast data packets meant for it. The Power saving mechanism is good in cases such as VoWLAN connections wherein a voice packet […]

The interested reader can refer <WMM Unscheduled Automatic Power Save Delivery (U-APSD)> as a precursor to this article. In Delivery enabled U-APSD – the station will wake up on its own volition. When the 802.11 Station wakes up (possibly to send a packet), it sends a trigger frame to the Access point. The Trigger frame […]

In Trigger enabled U-APSD mechanism – the 802.11 station needs to send a trigger frame to de-queue a single frame and send more trigger frames to obtain the remaining data packets that are buffered at the access point. The trigger frame that is sent out is normally a PS-POLL frame and the mechanism is the […]

If the 802.11 Station desires to change some Access Categories to be just Trigger enabled or to make other Access Categories as just Delivery enabled – then the mechanism employed by the 802.11 Station is the ADDTS action frame. The Traffic Stream (TS) setup has a lot of parameters and the current article only tries […]

The 802.11 standards body introduced Quality of Service via Task-Group 802.11e. The 802.11e standard introduced the concept of prioritized Traffic and Transmit Opportunities (TXOPs). The Transmit Opportunity for a Station meant that the 802.11 transmitting station would be allocated a particular time period (relative to the QoS access category) for the transmission rather than having […]

In addition to the TXOP mechanism (you can refer TXOP mechanism here)- to further enhance MAC efficiency, the 802.11e standard introduced clubbing all the ACKs for the different data packets sent in a TXOP in one go via a single packet. This packet was termed as a Block ACK (BACK) frame. The Block-ACK frame can […]