Local Area Networks Part 2: Wireless and Virtual LANs

Chapter 10Local Area NetworksPart 2:Wireless and Virtual LANsUnderstand the different transmission techniques used in wireless LANs.Understand the main characteristics of IEEE 802.11 wirelessLANs.Understand the applications of IEEE 802.11.Understand the characteristics of 802.15 LANs and the Bluetooth technology that implements this standard. After reading this chapter, the reader should be able to:OBJECTIVESOBJECTIVES (continued)Understand the applications and rationale for VLANs.Understand the concept of virtual LANs.WIRELESSLANs10.1Figure 10-1ISM bandsFigure 10-2FHSSFigure 10-3DSSSIEEE 802.11:RF LANs10.2Figure 10-4BSSFigure 10-5ESSTechnical Focus: Portable versus MobileIn networking two terms are used to define nonstationary devices: portable and mobile. The term portable means that a device may move from one location to another, but it remains in a fixed place when in use. The term mobile means that the station can move during operation. Technical Focus: Hidden Node ProblemIn a wired Ethernet, when a station sends a frame, every station connected to the shared medium senses (hears) the signal; stations are not hidden (electronically) from each other. On the other hand, in a wireless network, two stations may be separated from each other by a physical barrier (such as a wall). They are hidden (electronically) from each other. In this case, both of these stations may start sending a frame at the same time without sensing the signal coming from the other station. In other words, a collision may occur without either station detecting it. This means that the CSMA/CD access method, which is based on the detection of a collision by the sender, does not work here. Technical Focus: Wireless LAN AddressingThe addressing mechanism in a wireless LAN is more complicated than in a wired LAN. In a wireless LAN a frame may travel from a station to another station in the same BSS, or from a station in one BSS to another station in another BSS.In the second case, the frame journey is made of three trips: from the source station to the AP of the source BSS, from the AP of the source BSS to the AP of the destination BSS, and from the AP of the destination BSS to the destination station.For this reason, a wireless frame has four address fields. IEEE 802.11:INFRARED LANs10.3Figure 10-6Infrared point-to-point LANFigure 10-7Infrared diffused LANIEEE 802.15:BLUETOOTH LANs10.4Figure 10-8PiconetFigure 10-9Scatternet Business Focus: BluetoothBluetooth was named after the king of Denmark, who triedto unite all of the Baltic Region countries (Denmark, Sweden, Norway, and Finland). He united Denmark and Norway, but was killed by his son in 986.VIRTUALLANs10.5Figure 10-10A switch connecting three segmentsFigure 10-11A switch using VLAN softwareFigure 10-12Two switches in a backbone using VLAN software