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designing a wireless network phần 5

, trong mỗi lớp là một loạt các địa chỉ dành cho riêng địa chỉ addresses.The tin như sau:rong nhiều trường hợp, các địa chỉ này được dành riêng cho các thiết bị đó sẽ không được gửi hoặc nhận được lưu lượng truy cập bên ngoài mạng riêng của mình. | Identifying Evolving Wireless Technologies and Standards Chapter 4 133 QoS is the key to the added functionality with 802.11e. It provides the functionality required to accommodate time-sensitive applications such as video and audio. QoS includes queuing traffic shaping tools and scheduling.These characteristics allow priority of traffic. For example data traffic is not time sensitive and therefore has a lower priority than applications like streaming video.With these enhancements wireless networking has evolved to meet the demands of today s users. Developing WLANs through the 802.11 Architecture The 802.11 architecture can best be described as a series of interconnected cells and consists of the following the wireless device or station the access point AP the wireless medium the distribution system DS the basic service set BSS the extended service set ESS and station and distribution services. All of these working together providing a seamless mesh gives wireless devices the ability to roam around the WLAN looking for all intents and purposes like a wired device. The Basic Service Set The core of the IEEE 802.11 standard is the basic service set BSS . As you can see in Figure 4.7 this model is made up of one or more wireless devices communicating with a single Access Point AP in a Figure 4.7 Basic Service Set www.syngress.com 134 Chapter 4 Identifying Evolving Wireless Technologies and Standards single radio cell. If there are no connections back to a wired network this is called an independent basic service set. If there is no access point in the wireless network it is referred to as an ad-hoc network. This means that all wireless communications is transmitted directly between the members of the ad-hoc network. Figure 4.8 describes a basic ad-hoc network. Figure 4.8 Ad-Hoc Network When the BSS has a connection to the wired network via an AP it is called an infrastructure BSS. As you can see in the model shown in Figure 4.9 the AP bridges the gap between the .