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Counseling Astrology Advice | Tarot Advice | Parenting Dating Advice | Love Advice | Divorce Advice Legal Advice | Debt Advice | Career Advice W IRELESS N ETWORK S ECURITY 3-9 Although this section of the document focuses on the IEEE 802.11 WLAN standard, it is important to note that several other WLAN technologies and standards are available from which consumers may choose, including HiperLAN and HomeRF. For information on the European Telecommunications Standards Institute (ETSI) developed HiperLAN, visit the HiperLAN Alliance site. 10 For more information on HomeRF, visit the HomeRF Working Group site. 11 This document does not address those technologies. 3.1.2 Frequency and Data Rates IEEE developed the 802.11 standards to provide wireless networking technology like the wired Ethernet that has been available for many years. The IEEE 802.11a standard is the most widely adopted member of the 802.11 WLAN family. It operates in the licensed 5 GHz band using OFDM technology. The popular 802.11b standard operates in the unlicensed 2.4 GHz2.5 GHz Industrial, Scientific, and Medical (ISM) frequency band using a direct sequence spread-spectrum technology. The ISM band has become popular for wireless communications because it is available worldwide. The 802.11b WLAN technology permits transmission speeds of up to 11 Mbits per second. This makes it considerably faster than the original IEEE 802.11 standard (that sends data at up to 2 Mbps) and slightly faster than standard Ethernet. A summary of the various 802.11 standards is provided in Appendix D. 3.1.3 802.11 Architecture The IEEE 802.11 standard permits devices to establish either peer-to-peer (P2P) networks or networks based on fixed access points (AP) with which mobile nodes can communicate. Hence, the standard defines two basic network topologies: the infrastructure network and the ad hoc network. The infrastructure network is meant to extend the range of the wired LAN to wireless cells. A laptop or other mobile device may move from cell to cell (from AP to AP) while maintaining access to the resources of the LAN. A cell is the area covered by an AP and is called a "basic service set" (BSS). The collection of all cells of an infrastructure network is called an extended service set (ESS). This first topology is useful for providing wireless coverage of building or campus areas. By deploying multiple APs with overlapping coverage areas, organizations can achieve broad network coverage. WLAN technology can be used to replace wired LANs totally and to extend LAN infrastructure. A WLAN environment has wireless client stations that use radio modems to communicate to an AP. The client stations are generally equipped with a wireless network interface card (NIC) that consists of the radio transceiver and the logic to interact with the client machine and software. An AP comprises essentially a radio transceiver on one side and a bridge to the wired backbone on the other. The AP, a stationary device that is part of the wired infrastructure, is analogous to a cell-site (base station) in cellular communications. All communications between the client stations and between clients and the wired network go through the AP. The basic topology of a WLAN is depicted in Figure 3-1. 10 For more information see the HiperLAN Alliance site http:///www.hiperlan.com. 11 For more information see the HomeRF Working Group site http://www.homeRF.org. |
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