WPA stands for Wireless Protected Access. The WPA standard was introduced by the Wi-Fi Alliance. The WPA standard introduced TKIP (Temporal Key integrity Protocol) as an advancement on WEP to provide better security. WPA also introduced upper layer user authentication for 802.11 devices. Two methods for user authentication were described Pre-shared Key (EAPOL Handshake) 802.1X […]

For reference – the interested reader can look at AES Encyption frame format and the AES Encapsulation process in the below articles AES Encryption Mechanism AES Encapsulation The AES decapsulation process is shown below FIG Courtesy: 802.11 Standard Some description of the parameters TK – AES Temporal Key – obtained during EAPOL handshake PN – […]

DCF or Distributed Co-ordination Function was the initial Access mechanism introduced by the 802.11 standard’s body. The mechanism defined how different 802.11 stations need to compete in order to gain access to the transmission (air) medium for transmitting a packet. The DCF mechanism is a carrier sense multiple access and collision avoidance (CSMA/CA) mechanism and […]

An example Back-off mechanism is depicted pictorially below FIG COURTESY: IEEE Std 802.11-2012TM (section 9.3.4.3) The figure depicts 5 802.11 stations trying to compete for the air medium using DCF mechanism Station A has the transmitting right at the beginning – all the other stations back-off for the duration of transmission by Station A and […]

The EDCA Parameter Set Information Element provides the access category information to the WLAN station. The EDCA Parameter set is not used widely in the real world but the WMM Parameter set element is used instead. The reason for the use of the WMM Parameter set element is that the WMM standard was ratified and […]

The below diagram depicts the timing relations for different time intervals in DCF FIG Courtesy : 802.11 Standard Point Coordination Function (PCF)

The reader can refer the Part 1 of the article here  — <EDCA (WMM) Information Elements – part 1> Continuing from the previous article — the QoS information element is shown below The U-APSD bit indicates if Unscheduled Power Save Delivery is supported for the Access category The Parameter set count is a counter value […]

The Point Coordination Function was another media access mechanism that is described in the 802.11 WLAN standard. In the PCF mechanism, the Access Point would function as a Point Coordinator. The time for which the Access Point would control the medium was termed as the Contention Free Period (CFP). The Access Point can place the […]

The DCF Physical carrier sense/Virtual carrier sense/ Contention window back-off allow different stations to synchronize usage of the air medium. However, the one drawback of the DCF mechanism was that it was a fair mechanism for all Application level user priorities. It treated all user application priorities at the same priority. This caused packet loss […]

As was seen in the previous article <Understanding Packet User Priority>, the IP header incorporates a Differentiated Services Code Point (DSCP) field which provides the packet priority. Another level of priority was introduced in the 802.1p standard which featured a 3 bit priority field in the Ethernet header. The 802.1p standard was merged into the […]