Chapter 5_ part3a-2008 - PART 3: 5.4: WIRELESS LAN 1 5.4...

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1 PART 3: PART 3: 5.4: WIRELESS LAN 5.4: WIRELESS LAN
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2 5.4 WIRELESS LAN(802.11) Wireless LANs offer the following productivity, convenience, and cost advantages over traditional wired networks: Mobility : Wireless LAN systems can provide LAN users with access to real-time information anywhere in their organization. Installation Speed and Simplicity : Installing a wireless LAN system can be fast and easy and can eliminate the need to pull cable through walls and ceilings. Installation Flexibility : Wireless technology allows the network to go where wire cannot go. Scalability : Wireless LAN systems can be configured in a variety of topologies to meet the needs of specific applications and installations.
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3 Components of 802.11 LAN Four major physical components: Stations : Networks are built to transfer data between stations. Stations are computing devices with wireless network interfaces (typically battery-operated laptop or handheld computers) Access points (base stations): Frames on an 802.11network must be converted to another type of frame for delivery to the rest of the world. Devices called access points perform the wireless-to-wired bridging function . Wireless medium Access point Station Distribution system
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4 wireless medium : To move frames from station to station, the standard uses a wireless medium (Initially, two radio frequency (RF) physical layers and one infrared physical layer were standardized). Distribution : When several access points are connected to form a large coverage area, they must communicate with each other to track the movements of mobile stations. The distribution system is the logical component of 802.11 used to forward frames to their destination. In most commercial products, the distribution system is the backbone network (mostly Ethernet) used to relay frames between access points.
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5 Access Method The 802.11 MAC layer provides functionality to allow reliable data delivery for the upper layers over the wireless media. The data delivery itself is based on an asynchronous, best-effort, connectionless delivery of MAC layer data. There is no guarantee that the frames will be delivered successfully. The 802.11 MAC protocol is quite different from that of Ethernet due to the inherent complexity of the wireless environment compared to that of a wired system.
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6 No CSMA/CD Wireless LAN cannot implement CSMA/CD for three reasons: Collision detection implies that the station must be able to send data and receive collision signals at the same time. This implies
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Chapter 5_ part3a-2008 - PART 3: 5.4: WIRELESS LAN 1 5.4...

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