Wimax standards and Security The Wimax

QoS of Wireless LAN and 802.11e

Like Ethernet, WLAN (802.11) is a connectionless service. However, the bottle- neck of WLAN is the transmission media (i.e., the radio frequency spectrum) rather than the network device. As a result, the QoS schemes discussed for Ethernet, IP, and ATM do not apply to WLAN. The 802.11 standard supports two access methods—distributed coordination function (DCF) and point coordination function (PCF) [5]. The PCF operation requires the wireless

access point (WAP) to function as a central control point that polls each wireless client at a regular interval. A wireless client is allowed for data trans- mission only when it is polled. The WAP could implement a QoS scheme that polls real-time applications more often than nonreal-time applications. Although PCF has the capability to support a QoS scheme, PCF is not sup- ported by most vendors. As a result, a new QoS scheme is proposed by the IEEE 802.11e working group (which is still a draft). 802.11e specifies a new access method, extended DCF (EDCF), which uses different interframe gap (IFG) and contention windows (CW) for differentiated services. A real-time service will have a shorter CW and IFG while a nonreal-time service will have a longer CW and IFG. As a result, a real-time application will have a higher probability of accessing the media. Experimental results of EDCF are mixed

[6] and few vendors are supporting the draft standard, yet.



4.3 IEEE 802.16

1. 
   Basic Operation
   

The IEEE 802.16 standard supports two network architectures—P2MP mode and mesh mode. The mesh mode is an optional architecture and the discus- sion of QoS performance and scheduling of the mesh mode can be found in Ref. 7. This chapter focuses on the QoS performance and scheduling of the P2MP mode and its network architecture is illustrated in Figure 4.2. The

Subscriber LAN