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COMPUTER SYSTEMS

Choosing and Buying Components
By: O'Reilly Media
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    2004-10-25

    Table of Contents:
  • Choosing and Buying Components
  • What You'll Need
  • Case
  • Power Supply
  • Processor
  • Heatsink/Fan Units (CPU Coolers)
  • Motherboard
  • Memory
  • Drives
  • Optical Drive
  • Video adapter
  • Display
  • FPD Monitors
  • Audio
  • Keyboards
  • Mice
  • Network adapters
  • Wireless Network Adapters
  • Modems
  • Buying Components
  • Recommended sources
  • Final Words

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    Choosing and Buying Components - Wireless Network Adapters


    (Page 18 of 22 )

    Wireless network adapters—also called WLAN (Wireless LAN) cards, 802.11 cards, or Wi-Fi (Wireless Fidelity) cards—use radio waves to communicate. WLAN adapters communicate with a central device called an access point (AP) or wireless access point (WAP). In a mixed wired/ wireless network, the AP connects to the wired network and provides an interface between the wired and wireless portions of the network. One AP can support many WLAN adapters, but all of the adapters must share the bandwidth available on the AP. In a large network, multiple APs may be used to extend the physical reach of the wireless network and to provide additional bandwidth to computers that connect to the network with WLAN adapters.

    WLAN adapters are commonly used in notebook computers, either in embedded form or as a PC card. WLAN adapters are also available as PCI expansion cards that can be installed in desktop systems to provide a network link when it is difficult or expensive to run a cable to a system. The original 1997-era WLAN adapters used the 802.11 standard, which supported a maximum data rate of only 2 Mb/s. Those adapters are long obsolete. Current WLAN adapters support one or more of the following standards.

    802.11b

    802.11b supports a maximum data rate of 11 Mb/s, comparable to 10BaseT Ethernet, and has typical real-world throughput of 5 Mb/s. 802.11b uses the unlicensed 2.4 GHz spectrum, which means it is subject to interference from microwave ovens, cordless phones, and other devices that share the 2.4 GHz spectrum. The popularity of 802.11b is waning because components that use the faster 802.11g standard, described below, are now available at low cost. Millions of 802.11b adapters remain in use, primarily as embedded or PC card adapters in notebook computers.

     
    Figure 2-1802.11g channels

    Wireless Interoperability

    802.11b and 802.11g components are standards-based, so devices from different manufacturers should interoperate. In practice, that is largely true, although minor differences in how standards are implemented can cause conflicts. In particular, some high-end 802.11b/802.11g components include proprietary extensions for security and similar purposes. Those components do generally interoperate with components from other vendors, but only on a “least common denominator” basis—that is, using only the standard 802.11 features. The best way to ensure that your wireless network operates with minimal problems is to use WLAN adapters and APs from the same vendor.

    802.11a

    802.11a supports a maximum data rate of 54 Mb/s and has typical real-world throughput of 25 Mb/s. It uses a portion of the 5 GHz spectrum that was licensed until late 2003, but is now unlicensed. 5 GHz signals have shorter range and are more easily obstructed than 2.4 GHz signals, but are also less likely to interfere with other nearby devices. 802.11a is incompatible with 802.11b because they use different frequencies. The higher cost for 802.11a devices means they are used almost exclusively in business environments. Most 802.11a components have business-oriented features, such as remote manageability, that add cost but are of little interest to home users.

    802.11g

    The most recent WLAN standard is 802.11g, which combines the best features of 802.11a and 802.11b. Like 802.11b, 802.11g works in the unlicensed 2.4 GHz spectrum, which means it has good range but is subject to interference from other 2.4 GHz devices. Because they use the same frequencies, 802.11b WLAN adapters can communicate with 802.11g APs, and vice versa. Like 802.11a, 802.11g supports a maximum data rate of 54 Mb/s and has typical real-world throughput of about 25 Mb/s. That is sufficient to support real-time streaming video, which 802.11b cannot. 802.11g devices now sell for little more than 802.11b devices, so 802.11g has effectively made 802.11b obsolete.

    “802.108g”

    Several manufacturers, including D-Link and NetGear, produce APs that claim to provide 108 Mb/s bandwidth. And in fact they do, but only by “cheating” on the 802.11g specification. Such APs, colloquially called “802.108g” devices, work as advertised, but using them may cause conflicts with 802.11g-compliant devices operating in the same vicinity.

    802.11g defines 11 channels (13 in Europe), each with 22 MHz of bandwidth. Each 22 MHz channel can support the full 54 Mb/s bandwidth of 802.11g. But these channels overlap, as shown in Figure 2-1. Three of the channels—1, 6, and 11— are completely non-overlapping, which means that three 802.11g-compliant APs in the same vicinity—one assigned to each of the three non-over-lapping channels—can share the 2.4 GHz spectrum without conflicts. Alternatively, two 802.11g-compliant APs can be assigned to two channels that do not overlap each other, for example, channels 2 and 8.

    An 802.108g device claims two of the three completely non-overlap-ping channels, typically either 1 and 6 or 6 and 11, although it could in theory use 1 and 11. That leaves only one channel available for other 802.11g devices. To make matters worse, although 802.11g APs detect other nearby 802.11g APs and adjust themselves to use nonconflicting channels, many 802.11g APs fail to detect 802.108g APs operating nearby. The 802.11g devices wrongly assume that the channels being used by the 802.108g devices are available, and so may choose to operate on those “available” channels. The upshot is that it’s possible, even likely, to end up with an 802.11g device and an 802.108g device attempting to use the same channel at the same time, which means that neither device works properly.


    RECOMMENDATIONS

    Network Adapters
    For a wired network adapter, try to choose a motherboard that includes an embedded 10/100, 100/1000, or 10/100/1000 network interface. 10/100 is acceptable for most people’s current needs, but Gigabit models provide “future-proofing” at small additional cost.

    Make sure you know what you’re getting when you order a motherboard. Many motherboards are available in several variants, only some of which may include embedded LAN. For example, the excellent Intel D865PERL motherboard is available in three models, one without embedded LAN (D865PERL), one with embedded 10/100 LAN (D865PERLL), and one with embedded Gigabit (1000) LAN (D865PERLK).

    If your motherboard does not provide an embedded LAN adapter or if you prefer to use a separate LAN adapter, choose a 10/100 PCI LAN adapter from Intel or D-Link.

    A PCI 1000 Mb/s LAN adapter can saturate the 133 MB/s PCI bus, or nearly so. Accordingly, we use PCI Gigabit LAN adapters only if there is no alternative. We prefer to use embedded Gigabit LAN that keeps LAN traffic off the PCI bus. For example, Intel motherboards with embedded Gigabit LAN route LAN traffic across the dedicated CSA (Communications Streaming Architecture) bus, leaving the PCI bus free for other purposes.

    If you are building a new wireless network, use a D-Link 802.11g or 802.108g WLAN adapter and AP. Choose 802.11g if channel conflicts are possible, e.g., if you live in an apartment or if your business is in close proximity to other businesses. Choose 802.108g if there are no 802.11b/g APs nearby, but note that you may have to replace 2.4 GHz cordless phones with models that use a different frequency band. If you are expanding a wireless network, use an 802.11g adapter from the same company that made the existing components.

    If you need to purchase an 802.11g or 802.108g AP, consider buying a model that also incorporates a hardware firewall/router. Using a hardware firewall/router on a home or SOHO network is the single most important thing you can do to improve security and reduce the likelihood that your systems will be infected by a worm.

    Avoid no-name network adapters and other components. If possible, avoid mixing components from different manufacturers, particularly in a wireless network. Avoid 802.11a unless you need SNMP remote manageability and other business-oriented features.



    WARNING

    If you use wireless networking, remember that you are broadcasting data omnidirectionally. The range of 802.11b/g is up to several hundred feet with a normal antenna, and can be extended to several miles using a simple antenna built from a soup or potato-chip can. In fact, rumor has it that U.S. surveillance satellites can easily receive 802.11b/g broadcasts from orbit.

    Unless you enable encryption, which is usually disabled by default, anyone nearby who has a WLAN adapter can intercept your data. Worse still, people can connect to your network and use it as though they were wired into it. Nor is this a merely theoretical danger. Wardriving—cruising around looking for unsecured access points—has been a popular pastime since 802.11b became popular. If you run an unsecured 802.11* network, it wil l be compromised.

    Various forms of wireless encryption and authentication are available, some standard and some proprietary to certain brands of gear. At a minimum, enable WEP (Wired-Equivalent Privacy). WEP is not secure in any real sense, but it is enough to discourage all but the most sophisticated intruders, and also ensures that others don’t innocently connect to your network—if you’re in a densely populated area and your AP is in range of a library, café, or other public space, it’s likely to be mistaken for a public hotspot. Read the manual for your WLAN gear and visit the maker’s web site to determine what security measures are right for you and how to implement them.


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