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 […]

For an 802.11 station to send a Contention Free Burst – it needs to negotiate a Block ACK Session for whichever particular Traffic Identifier (tid) class of packets that intends to use the Block ACK mechanism. The frame that are part of the Block ACK mechanism are ADDBA Request    – ADD Block ACK Request – […]

ADDBA response frame format The Frame is shown pictorially below The Category field is set to 3 – indicating Block Ack Block Ack Action field is set to 1 – representing ADDBA Response Dialog token is the same as the non-zero value that is sent in the ADDBA request Status code – indicates whether the […]

After a Block ACK Session is negotiated between an Access Point and a WLAN station connected to the Access Point, the AP and the WLAN station can partake in a Contention Free Burst within the scope of the block ACK session. After the Frame burst is complete, the WLAN station would send a Block ACK […]

DELBA Frame format The DELBA frame is depicted below Fig Courtesy: 802.11 Standard The Category field is set to 3 – indicating Block Ack Block Ack Action field is set to 2 – representing DELBA The DELBA Parameter set contains the below The initiator subfield – indicates who is sending the DELBA frame – the […]