CWNA guide to wireless LANs 2nd ch02

CWNA Guide to Wireless LANs, Second Edition Chapter Two Wireless LAN Devices and Standards Objectives • List WLAN devices and describe their basic functions • Explain the different types of communication standards and why standards are important • List the three major wireless standards and regulatory agencies and their functions • Describe the different IEEE WLAN standards CWNA Guide to Wireless LANs, Second Edit WLAN Devices: Wireless Network Interface Card • Network interface card (NIC): Connects computer to network so that it can send and receive data • Wireless NICs perform same function, but without wires • When wireless NICs transmit: – Change computer’s internal data from parallel to serial transmission – Divide data into packets and attach sending and receiving computer’s address – Determine when to send packet – Transmit packet CWNA Guide to Wireless LANs, Second Edit WLAN Devices: Wireless Network Interface Card (continued) Figure 2-1: Network interface card for a wired network CWNA Guide to Wireless LANs, Second Edit WLAN Devices: Wireless Network Interface Card (continued) Figure 2-2: Wireless NICs for desktop computers: (a) PCI network interface card, (b) standalone USB device, (c) USB key fob CWNA Guide to Wireless LANs, Second Edit WLAN Devices: Wireless Network Interface Card (continued) Figure 2-3: Wireless NICs for laptop computers: (a) CardBus card; (b) Mini PCI card CWNA Guide to Wireless LANs, Second Edit WLAN Devices: Wireless Network Interface Card (continued) • For smaller devices, several options: – CardBus or Type II PC Card • May require a sled – CompactFlash (CF) card: Consists of small circuit board containing flash memory chips and dedicated controller chip • Small and consume little power – SDIO (Secure Digital I/O) or SDIO NOW! Card: Provides high-speed data input/output with low power consumption CWNA Guide to Wireless LANs, Second Edit WLAN Devices: Wireless Network Interface Card (continued) • A movement towards integrating wireless NICs – Would eliminate need for external wireless NICs • Software drivers necessary to allow wireless NIC and operating system (OS) to interface – Windows XP and PDA OSs have built-in drivers CWNA Guide to Wireless LANs, Second Edit WLAN Devices: Access Point • Three major parts: – Antenna and radio transmitter/receiver – RJ-45 wired network interface – Special bridging software • To interface wireless devices to other devices • Two basic function: – Base station for wireless network – Bridge between wireless and wired networks CWNA Guide to Wireless LANs, Second Edit WLAN Devices: Access Point (continued) Figure 2-6: An access point acts as a bridge between the wireless network and a wired network CWNA Guide to Wireless LANs, Second Edit 10 FCC: Regulating the Radio Frequency Spectrum (continued) Table 2-3: Common radio frequency bands CWNA Guide to Wireless LANs, Second Edit 32 FCC: Regulating the Radio Frequency Spectrum (continued) • Two unregulated bands used for WLANs • Industrial, Scientific, and Medical (ISM) band • Unlicensed National Information Infrastructure (U-NII) band: Intended for devices that provide short-range, high-speed wireless digital communications • Negative features of unregulated bands: – Devices from different vendors may attempt to use same frequency • Can cause interference and unpredictability CWNA Guide to Wireless LANs, Second Edit 33 FCC: Regulating the Radio Frequency Spectrum (continued) Table 2-4: Unlicensed bands CWNA Guide to Wireless LANs, Second Edit 34 Types of Wireless LANs • Since late 1990s, IEEE has approved four standards for wireless LANs: – – – – IEEE 802.11 IEEE 802.11b IEEE 802.11a IEEE 802.11g • IEEE 802.11n expected to be approved by 2006 HA! CWNA Guide to Wireless LANs, Second Edit 35 IEEE 802.11 • Specified that wireless transmission could take place via infrared (IR) or radio signals • Infrared Transmissions: – Can send data by the intensity of the infrared light wave – Light spectrum: All types of light – Infrared light: Can be used for wireless transmissions • Invisible – Emitter: Device that transmits a signal – Detector: Device that receives a signal CWNA Guide to Wireless LANs, Second Edit 36 IEEE 802.11 (continued) Figure 2-13: Directed transmission CWNA Guide to Wireless LANs, Second Edit 37 IEEE 802.11 (continued) Figure 2-14: Diffused transmission CWNA Guide to Wireless LANs, Second Edit 38 IEEE 802.11 (continued) • Infrared Transmissions (continued): – Advantages: • Does not interfere with other communications signals • Not affected by other signals • Does not penetrate walls – Disadvantages: • • • • Lack of mobility Limited range Confined to indoor use Slow transmission speed CWNA Guide to Wireless LANs, Second Edit 39 IEEE 802.11 (continued) • Radio Wave Transmissions: – Radio waves can penetrate through objects • Provides mobility – Radio waves travel longer distances – Can be used indoors and outdoors – Radio waves can travel at much higher speeds than infrared transmissions – IEEE 802.11 standard outlining radio wave transmissions has become preferred method for wireless LANs CWNA Guide to Wireless LANs, Second Edit 40 IEEE 802.11b • 802.11 standard’s Mbps bandwidth not sufficient for most network applications • 802.11b amendment added two higher speeds (5.5 Mbps and 11 Mbps) to original 802.11 standard – Uses ISM band • Supports wireless devices up to 115 meters (375 feet) apart – Radio waves decrease in power over distance – 802.11b standard specifies that, when devices out of range to transmit at 11 Mbps, devices drop transmission speed to 5.5 Mbps CWNA Guide to Wireless LANs, Second Edit 41 IEEE 802.11a • IEEE 802.11a standard specifies maximum rated speed of 54 Mbps – Also supports 48, 36, 24, 18, 12, 9,and Mbps transmissions using U-NII band • 802.11a and 802.11b published at same time – 802.11a came to market later due to technical issues and high production cost • Range of 802.11a is less than that of 802.11b CWNA Guide to Wireless LANs, Second Edit 42 IEEE 802.11g • Effort to combine best features of 802.11a and 802.11b – Data transfer rates to 54 Mbps – Support devices up to 115 meters apart • 802.11g standard specifies that devices operate entirely in ISM frequency CWNA Guide to Wireless LANs, Second Edit 43 Projected IEEE 802.11n • Currently in evaluation stage • Top speed of 802.11n standard will be anywhere from 100 Mbps to 500 Mbps • Ratification may not occur until 2006 – Devices based on standard may appear prior to that • 802.11 pre-N CWNA Guide to Wireless LANs, Second Edit 44 Summary • Wireless LAN devices are in many respects similar to those found in a wired network; the main difference is that wireless devices use an antenna or other means to send and receive signals instead of a wired connection • An access point (AP) is both the base station for the wireless network and a bridge to connect the wireless network with the wired network • A remote wireless bridge is a wireless device designed to connect two or more wired or wireless networks together CWNA Guide to Wireless LANs, Second Edit 45 Summary (continued) • Standards ensure that devices from one vendor will interoperate with those from other vendors, and create competition between vendors • There are three regulatory bodies that play a major role in wireless LAN technology: the IEEE, the WiFi Alliance, and the FCC • There currently are three standards or types of wireless LANs: IEEE 802.11b, IEEE 802.11a, and IEEE 802.11g CWNA Guide to Wireless LANs, Second Edit 46 ... interference CWNA Guide to Wireless LANs, Second Edit 12 WLAN Devices: Remote Wireless Bridge (continued) Figure 2-8: Point -to- point remote wireless bridge CWNA Guide to Wireless LANs, Second... miles transmitting Mbps CWNA Guide to Wireless LANs, Second Edit 15 WLAN Devices: Remote Wireless Bridge (continued) Figure 2-10: Root and non-root modes CWNA Guide to Wireless LANs, Second Edit 16... fob CWNA Guide to Wireless LANs, Second Edit WLAN Devices: Wireless Network Interface Card (continued) Figure 2-3: Wireless NICs for laptop computers: (a) CardBus card; (b) Mini PCI card CWNA Guide