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Upgrading and Repairing PCs |
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Wireless Network StandardsVarious forms of wireless networks using either radio or IR (infrared) have been developed over the years, but until recently, the benefits of a wireless network (no wires to pull or holes to drill) were outweighed by the lack of standards and relatively slow speed. In conventional Ethernet networks, you can use various brands of NICs, hubs, and switches without any problems, as long as each device corresponds to the same Ethernet standard. Even though early forms of wireless networking were much slower than wired networks and often were single-vendor proprietary solutions, today's newest wireless networks offer speeds comparable to or faster than 10BASE-T wired networks and offer multivendor mix-and-match equipment sources. Prices have also dropped dramatically, making wireless networking an increasingly appealing alternative to traditional wired network solutions. The most common forms of wireless networking in the United States and Canada are built around various versions of the IEEE 802.11 wireless Ethernet standards, including IEEE 802.11b, IEEE 802.11a, and the newer IEEE 802.11g standard. Wi-Fi (Wireless Fidelity) is a logo and term given to any IEEE 802.11 wireless network product that is certified to conform to specific interoperability standards. Wi-Fi Certification comes from the Wi-Fi Alliance, a nonprofit international trade organization that tests 802.11-based wireless equipment to ensure it meets the Wi-Fi standard. To wear the Wi-Fi logo, an 802.11 networking product must pass specific compatibility and performance tests, which ensure that the product will work with all other manufacturers' Wi-Fi equipment on the market. This certification arose from the fact that certain ambiguities in the 802.11 standards allowed for potential problems with interoperability between devices. By purchasing only devices bearing the Wi-Fi logo, you ensure that they will work together and not fall into loopholes in the standards. The Bluetooth standard for short-range wireless networking is designed to complement, rather than rival, IEEE 802.11-based wireless networks. In Europe, HiperLAN, which has performance and frequency usage similar to that of 802.11a, is the wireless networking standard. The widespread popularity of IEEE 802.11-based wireless networks has led to the abandonment of other types of wireless networking, including RadioLAN and HomeRF. RadioLAN now markets long-range antennas that work with 802.11a-based wireless networks.
Wi-Fi—A Standard Upon a StandardWhen the first 802.11b networking products appeared, compatibility problems existed due to certain aspects of the 802.11 standards being ambiguous or leaving loopholes. A group of companies formed an alliance designed to ensure that their products would work together, eliminating any ambiguities or loopholes in the standards. This was originally known as the Wireless Ethernet Compatibility Alliance (WECA) but is now known simply as the Wi-Fi Alliance (www.wi-fi.org). The term Wi-Fi is now used to refer to any IEEE 802.11 wireless network products that have passed the Wi-Fi Alliance certification tests. Currently, the alliance has certified 802.11b, 802.11a, and dual-band (a/b) products. It is also working on certification standards for the newer 802.11g products.
Table 20.9 provides an overview of 802.11-compliant networks.
Although you are likely to see retail products identified by their Wi-Fi band designations as in Table 20.9, in this book I will normally use the IEEE designations.
Figure 20.24 shows the labels used by the Wi-Fi Alliance on 11Mbps, 54Mbps, and dual-band equipment along with the name of the official IEEE standard for each type of product. Figure 20.24. The Wi-Fi Alliance's certification labels for Wi-Fi-compliant 802.11b hardware (top), 802.11a hardware (middle), and dual-band 802.11b/a hardware (bottom).
IEEE 802.11b—11Mbps Wi-FiIEEE 802.11b (Wi-Fi 2.4GHz band–compliant) wireless networks run at a maximum speed of 11Mbps, about the same as 10BASE-T Ethernet (the original version of IEEE 802.11 supported data rates up to 2Mbps only). Other data rates supported by 802.11b include 1Mbps, 2Mbps, and 5.5Mbps. 802.11b networks can connect to conventional Ethernet networks or be used as independent networks, similar to other wireless networks. Wireless networks running 802.11b hardware use the same 2.4GHz spectrum that many portable phones, wireless speakers, security devices, microwave ovens, and the Bluetooth short-range networking products use. Although the increasing use of these products is a potential source of interference, the short range of wireless networks (indoor ranges up to 300 feet and outdoor ranges up to 1,500 feet, varying by product) minimizes the practical risks. Many devices use a spread-spectrum method of connecting with other products to minimize potential interference. Although 802.11b supports a maximum speed of 11Mbps, that top speed is seldom reached in practice, and speed varies by distance. Most 802.11b hardware is designed to run at four speeds, using three different data-encoding methods depending on the speed range:
As distances change and signal strength increases or decreases, 802.11b hardware switches to the most suitable data-encoding method. The overhead required to track and change signaling methods, along with the additional overhead required when security features are enabled, helps explain why wireless hardware throughput is lower than the rated speed. Figure 20.25 is a simplified diagram showing how speed is reduced with distance. Figures given are for best-case situations—building design and antenna positioning can also reduce speed and signal strength, even at relatively short distances. Figure 20.25. At short distances, 802.11b devices can connect at top speed (up to 11Mbps). However, as distance increases, speed decreases because the signal strength is reduced.
IEEE 802.11a—Wi-Fi in the 5GHz BandThe second flavor of Wi-Fi is the wireless network known officially as IEEE 802.11a. 802.11a uses the 5GHz frequency band, which allows for much higher speeds (up to 54Mbps) and helps avoid interference from devices that cause interference with lower-frequency 802.11b networks. Although real-world 802.11a hardware seldom, if ever, reaches that speed (almost five times that of 802.11b), 802.11a maintains relatively high speeds at both short and relatively long distances. For example, in a typical office floor layout, the real-world throughput (always slower than rated speed due to security and signaling overhead) of a typical 802.11b device at 100 feet might drop to about 5Mbps, whereas a typical 802.11a device at the same distance could have a throughput of around 15Mbps. At a distance of about 50 feet, 802.11a real-world throughput can be four times faster than 802.11b. 802.11a has a shorter maximum distance than 802.11b, but you get your data much faster. Given the difference in throughput, especially at long distances, why not skip 802.11b altogether? In a single word, frequency. By using the 5GHz frequency instead of the 2.4GHz frequency used by 802.11b, standard 802.11a hardware cuts itself off from the already vast 802.11b universe, including the growing number of public and semi-public 802.11b wireless Internet connections (called hot spots) showing up in cafes, airports, hotels, and business campuses. The current solution for maximum flexibility is to use dual-band hardware. As Figure 20.24 demonstrated earlier in this chapter, the Wi-Fi Alliance is encouraging the manufacture of dual-band hardware through its certification program. Dual-band hardware can work with either 802.11a or 802.11b networks, enabling you to move from an 802.11b wireless network at home or at Starbucks to a faster 802.11a office network. 802.11g—A Compatible 54Mbps StandardIEEE 802.11g, also known to some as Wireless-G, is a promising newcomer that combines compatibility with 802.11b with the speed of 802.11a at longer distances at a price only slightly higher than 802.11b hardware. The final 802.11g standard was ratified in mid-2003, although many network vendors were already rushing products based on the draft 802.11g standard to market before the final standard was approved. Although 802.11g promises to connect seamlessly with existing 802.11b hardware, early 802.11g hardware was slower and less compatible than the specification promises. In some cases, problems with early-release 802.11g hardware can be solved through firmware upgrades. As with previous types of 802.11 wireless Ethernet network hardware, I recommend that you wait for 802.11g hardware that meets Wi-Fi Alliance or comparable certifications before you purchase it. You want the same mix-and-match assurance that different brands of network hardware work together in the wireless world that we've long enjoyed with wired Ethernet. Figure 20.26 demonstrates how the different 802.11-based wireless networks can interact with each other. Figure 20.26. Computers running 802.11b and 802.11g wireless Ethernet can connect with each other, and with computers with dual-band 802.11a/b hardware. 802.11a hardware can connect only with other 802.11a or with dual-band 802.11a/b hardware.
802.11 Network HardwareAll types of 802.11 wireless networks have two basic components:
An access point is a bookend-size device that uses an RJ-45 port to attach to a 10BASE-T or 10/100 Ethernet network (if desired) and contains a radio transceiver, encryption, and communications software. It translates conventional Ethernet signals into wireless Ethernet signals it broadcasts to wireless NICs on the network and performs the same role in reverse to transfer signals from wireless NICs to the conventional Ethernet network. For coverage of a large area, purchase two or more access points and connect them to an Ethernet switch or hub. This enables users to "roam" inside a building without losing contact with the network. Some access points can communicate directly with each other via radio waves, enabling you to create a wireless backbone that can cover a wide area, such as a warehouse, without the need to run any network cabling. Access points are not necessary for direct peer-to-peer networking (also called ad hoc mode), but they are required for a shared Internet connection or a connection with another network. When access points are used, the network is operating in the infrastructure mode. NICs equipped for wireless Ethernet communications have a fixed or detachable radio antenna in place of the usual coaxial or RJ-45 port or dongle. Because a major market for wireless Ethernet use is notebook computer users, a few vendors sell only PC Cards in their wireless Ethernet product lines, but most vendors support PCI cards for desktop computers. Most vendors also offer wireless USB adapters for use in both desktop and notebook computers. Because you can mix and match Wi-Fi-certified products that use the same frequency band, you can incorporate any mix of desktop and notebook computers into your wireless network. Figure 20.27 illustrates typical wireless network hardware. Figure 20.27. A typical family of Wi-Fi 2.4GHz band (802.11b) wireless products, including a wireless access point, USB, PC Card, and PCI wireless network adapters. The PC Card is used in notebook computers that lack Wi-Fi support and also acts as the transceiver for the PCI card used in desktop computers. Photos courtesy of Linksys.
Client systems lock onto the strongest signal from access points and automatically roam (switch) to another access point when the signal strength is stronger and the error level is lower than the current connection. Additional hardware you might want to add to your network include
Security and Other FeaturesWhen I was writing the original edition of Upgrading and Repairing PCs, the hackers' favorite way of trying to get into a network without authorization was discovering the telephone number of a modem on the network, dialing in with a computer, and guessing the password, as in the movie War Games. Today, war driving has largely replaced this pasttime as a popular hacker sport. War driving is the popular name for driving around neighborhoods with a notebook computer equipped with a wireless network card on the lookout for unsecured networks. They're all too easy to find, and after someone gets onto your network, all the secrets in your computer can be hers for the taking. Because wireless networks can be accessed by anyone with a compatible NIC, most models of NICs and access points provide for encryption options. Some devices with this feature enable you to set a security code known as an SSID on the wireless devices on your network. This seven-digit code prevents unauthorized users from sneaking onto your network and acts as an additional layer of security along with your normal network authentication methods, such as user passwords. Others use a list of authorized MAC numbers (each NIC has a unique MAC) to limit access to authorized devices only. All Wi-Fi products support at least 40-bit encryption through the wired equivalent privacy (WEP) specification, but the minimum standard on recent products is 64-bit WEP encryption. Many vendors offer 128-bit or 256-bit encryption on some of their products. However, the 128-bit and stronger encryption feature is more common among enterprise products than small-office/home-office–oriented products. Unfortunately, the WEP specification has been shown to be notoriously insecure against determined hacking. Enabling WEP will keep a casual snooper at bay, but someone who wants to get into your wireless network won't have much trouble breaking WEP. For that reason, many network products introduced in 2003 and beyond now incorporate a new security standard known as Wi-Fi Protected Access (WPA). WPA is derived from the developing IEEE 802.11i security standard, which will not be completed until mid-decade. WPA-enabled hardware works with existing WEP-compliant devices, and software upgrades might be available for existing devices. You should match the encryption level and encryption type used on both the access points and the NICs for best security. Remember: If some of your network supports WPA but other parts support only WEP, your network must use the lesser of the two security standards (WEP). Some products' access points can be managed via a Web browser and provide diagnostic and monitoring tools to help you optimize the positioning of access points. Many products feature support for Dynamic Host Configuration Protocol (DHCP), allowing a user to move from one subnet to another without difficulties. Figure 20.28 illustrates how a typical IEEE 802.11b wireless network uses multiple access points. Figure 20.28. A typical wireless network with multiple access points. As users with wireless NICs move from one office to another, the roaming feature of the NIC automatically switches from one access point to another, permitting seamless network connectivity without wires or logging off the network and reconnecting.
Users per Access PointThe number of users per access point varies with the product; Wi-Fi access points are available in capacities supporting anywhere from 15 to as many as 254 users. You should contact the vendor of your preferred Wi-Fi access point device for details. Although wired Ethernet networks are still the least expensive network to build if you can do your own wiring, Wi-Fi networking is now cost-competitive with wired Ethernet networks when the cost of a professional wiring job is figured into the overall expense. Because Wi-Fi is a true standard, you can mix and match access point and wireless NIC hardware to meet your desired price, performance, and feature requirements for your wireless network, just as you can for conventional Ethernet networks provided you match up frequency bands or use dual-band hardware. Notebook Computers with Integrated Wi-Fi AdaptersMajor notebook computer makers, including Dell, IBM, and Toshiba, are now integrating built-in 802.11b or dual-band 802.11a/b wireless adapters and antennas into some of their notebook computers. Although computers with built-in Wi-Fi hardware are a little more expensive than comparable models lacking Wireless Ethernet support, building the adapter and antenna into notebook computers provides for a more durable and less cumbersome way to equip portable systems than the normal PC Card and external antenna arrangement that must be fitted to ordinary notebook computers. Most notebook computers with Wi-Fi hardware onboard use the mini-PCI interface for the wireless adapter and place the antenna inside the screen housing. This enables computers with built-in Wi-Fi hardware to have one more open PC Card slot than computers that must use an external PC Card adapter and antenna. BluetoothBluetooth is a low-speed (up to 700Kbps), low-power standard originally designed to interconnect notebook computers, PDAs, cell phones, and pagers for data synchronization and user authentication in public areas, such as airports, hotels, rental car pickups, and sporting events. Bluetooth is also used for a wide variety of wireless devices on PCs, including printer adapters, keyboards and mice (Microsoft's Bluetooth keyboard and mouse are available at many stores selling computer hardware), DV camcorders, data projectors, and many others. Bluetooth-compliant devices are becoming widely available, after first reaching the market in the second half of 2000. A list of Bluetooth products and announcements is available at the official Bluetooth wireless information Web site: www.bluetooth.com. Bluetooth devices also use the same 2.4GHz frequency range Wi-Fi/IEEE 802.11b devices use. However, in an attempt to avoid interference with Wi-Fi, Bluetooth uses a signaling method called frequency hopping spread spectrum, which switches the exact frequency used during a Bluetooth session 1,600 times per second over the 79 channels Bluetooth uses. Unlike Wi-Fi, which is designed to allow a device to be part of a network at all times, Bluetooth is designed for ad hoc temporary networks in which two devices connect only long enough to transfer data and then break the connection. Interference Issues Between Bluetooth and IEEE 802.11b/gDespite the frequency-hopping nature of Bluetooth, studies have shown that Bluetooth (up through version 1.1) and IEEE 802.11b devices can interfere with each other, particularly at close range (under 2 meters) or when users attempt to use both types of wireless networking at the same time (as with an 802.11b wireless Internet connection on a computer with Bluetooth wireless keyboard and mouse). Although 802.11g has not been specifically studied, it uses the same frequencies as 802.11b, and interference between 802.11g and Bluetooth can also take place under similar circumstances. Interference reduces throughput and in some circumstances can cause data loss. An improved version of the Bluetooth specification, version 1.2, due in mid- to late 2003, adds adaptive frequency hopping to solve interference problems when devices are more than 1 meter (3.3 feet) away from each other. However, close-range (under 1 meter) interference can still take place. IEEE has developed 802.15.2, a specification for enabling coexistence between 802.11b/g and Bluetooth. It can use various time-sharing or time-division methods to enable coexistence. However, these specifications are not yet part of typical 802.11b/g implementations. Chipset makers Silicon Wave (www.siliconwave.com) and Intersil (www.intersil.com) have developed Blue802 Technology, a combination of chipsets that enable coexistence between Bluetooth and 802.11b wireless networks at any distance. Until devices using Bluetooth specification 1.2 and 802.11b/g devices incorporating 802.15.2 or Blue802 technologies are common, interference is a real possibility. Wireless Network Logical TopologiesWireless networks have different topologies, just as wired networks do. However, wireless networks use only two logical topologies:
Figure 20.29 shows a comparison of wireless networks using these two topologies, and Table 20.10 compares the major wireless network standards in current use. Figure 20.29. A logical star topology (left) as used by IEEE 802.11–based wireless Ethernet in infrastructure mode compared to a point-to-point topology as used by Bluetooth and 802.11 in ad hoc mode (right).
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