Overview of the IEEE 802.11a Standard


Because IEEE 802.11b operates in the 2.4GHz bandwidth, it is subject to more interference because this bandwidth is basically a "free for all" (see the preceding chapter), meaning that many kinds of devices contend for the frequencies in the 2.4GHz spectrum. Spread spectrum techniques are used in 802.11a and 802.11b wireless radios to help minimize interference, and they are effective to some extent. For more information about spread spectrum techniques, see Chapter 19, "Introduction to Wireless Networking."

Interference from Consumer Devices

IEEE 802.11a uses frequencies in the 5GHz radio spectrum. This spectrum does not suffer from as much interference from consumer devices, such as microwave ovens, newer cordless telephones, and other devices that produce radio waves. Additionally, hardware using the 5GHz spectrum will not interfere with the previously mentioned consumer devices. Given the larger bandwidth provided by the 5GHz radio spectrum, there will be less interference, and the capability to support more channels than you can get from IEEE 802.11b. One thing to note, however, is that mobile phones that operate in the 5GHz bandwidth are becoming more popular, and this may become a problem for 802.11a in the near future.

Because 802.11a radio devices today suffer less interference by other devices, it might be a good choice if you are just starting to use wireless networking. One caveat is that the 802.11g standard, discussed in the next chapter, offers the same data rate but operates in the 2.4GHz spectrum and can easily interoperate with 802.11b.

If you choose a product based on the 5GHz spectrum (which is the subject of this chapter), you can forget that microwave oven in the break room or that cordless telephone that causes problems in an 802.11b network.

Note

There has recently been some discussion about U.S. military usage of this spectrum, but the outcome of that situation is unknown at this time. You should take this information into consideration when making a decision to use 802.11a.

Increased Bandwidth in the 5.4GHz Band

It may not seem like a lot ”going from the 2.4GHz range of radio frequencies to the 5GHz range. However, the larger bandwidth is capable of transmission of data at faster rates.

Note

The 802.11g standard provides the same data rate as 802.11a. With 802.11g using the 2.4GHz radio frequency spectrum, how is this possible? Just as twisted-pair cables in a wired network can be used to transfer data at 10Mbps or 100Mbps, new methods for modulating data on a particular network media make this possible. 802.11g technology can operate at the same data rate as 802.11a because it uses a different method for modulating data. However, that doesn't mean that the 5GHz spectrum has already been pushed to its maximum throughput. Just as newer technology has enabled faster data rates in the 2.4GHz spectrum (802.11g), it is inevitable that advances in technology will enable faster data rates in the 5GHz band sometime in the future.

The 5.4GHz range will give you about 54Mbps throughput using the 802.11a standard. And as with other wireless technologies, you will not always achieve the maximum speed defined by the standard. Which technology makes more sense for you when it comes to purchasing equipment should be determined based on budget and need. If you are still operating a network that uses 10BASE-T networking (10Mbps), then when adding 802.11b wireless components you won't notice much difference in response time when a wireless client exchanges data with a computer on the wired network. This assumes that the Access Points (APs) are placed close to the clients in order to maximize data throughput. If you were to use 802.11a devices that operate at a faster speed than 10Mbps then a 10BASE-T wired network is a bottleneck. A wireless client communicating with a client on the wired network would not utilize the throughput that it is capable of, because the wired network cannot operate at that higher speed. Keep in mind, however, that all the wireless technologies discussed in this section of the book will probably not operate at the upper limit that the standards specify, due to environmental factors and such.

Note

By adding additional Access Points at strategic points in your network, you can reduce congestion in the wireless portion of your network. And this might just also accomplish diminishing other bottlenecks in your network by moving some departmental clients to wireless, leaving the backbone of the wired network to handle the larger network traffic.

802.11a wireless clients, however, will still be able to transfer data at faster rates among themselves .

The opposite is true when using 802.11a clients with a 100Mbps wired network, because 100Mbps is faster than 54Mbps, and the wireless network then becomes a bottleneck.

To put it another way, if you choose 802.11a hardware, you will benefit from this increased bandwidth only if your other network components can work at this speed (or faster). Because most enterprise networks, as well as SOHO networks, now operate using Fast Ethernet (100Mbps), IEEE 802.11a is a good fit. Though not as fast as Fast Ethernet, 802.11a does offer (depending on the manufacturer) over a five-fold increase in bandwidth over 802.11b, just over one-half of the bandwidth that Fast Ethernet will give you. In comparison, 802.11b, the current widespread wireless standard, will give you only about 11Mbps, which is almost a tenth of what Fast Ethernet can attain. These are performance statistics under perfect conditions, however. Have you ever been driving late at night and that great radio station just fades away, and then you have to look for another one? With wireless, including 802.11a, other factors, such as distance, buildings , and electrical devices, can also limit the actual bandwidth you will achieve.

Using Wireless Networking in Public Places

Wireless can be used for so many situations in which wired-network components would not be a good fit. As mentioned in previous chapters, just being able to sit in an airport or a shopping mall (waiting on that other shopper), and connect directly to the Internet while you are waiting, is going to be where wireless networking succeeds with the ordinary consumer as well as computer enthusiasts . Today several large telecommunications companies are beginning to lay the groundwork for this capability by creating a large network of 802.11b APs in public places where computers are likely to be used.

For example, in many airports there are rooms set aside for business travelers who need access to computer services, the Internet, faxing, and so on. These services aren't necessarily cheap. Yet if an Internet provider can offer its services over a network that spans most of the country, the price for an Internet connection will continue to drop, and you will be able to use your laptop computer pretty much anywhere in a public place. The main drawback to this for the next few years is that it will take time to create a large network, and builders will concentrate on the larger metropolitan areas first because that's where revenues from the service will be larger. Such a network will have to be built-out over the long run, just as the telephone network was when that technology was first introduced over a hundred years ago.

This type of network will not be entirely wireless. Instead, the wireless APs will be connected to backbone cabling in a similar way that wireless APs are used in a corporate LAN. For the long haul, this backbone cabling will be joined to the WAN using existing high-speed technologies such as ATM and Frame Relay. This is also the way that the Internet operates. Your connection to the local ISP can be accomplished using a telephone line (DSL service) or a cable modem. Whichever method is used, your line terminates back at the ISP's central office, and from there it is connected to the Internet using high-speed connections.

The only problem with this technology is that because it has already been adopted by so many current users, this type of network will initially consist of 802.11b technology. The reason it is mentioned here is that competition will eventually drive this type of network to use faster technology, such as 802.11a. Internet communications are becoming more bandwidth- intensive , and a mere 11Mbps (if you can get that maximum speed) won't suffice for many users in the near future. Uploading a large spreadsheet or graphics file using 802.11b probably won't suffice as applications begin to generate more data, and larger files. For email and other applications that don't need a lot of bandwidth, 802.11b will work well. The transition from 802.11b to 802.11a will probably be accomplished by using dual-mode APs, which were discussed in Chapter 20, "IEEE 802.11b: It's Here and It's Inexpensive."

If you can afford it, 802.11a is a good start for an enterprise network, again because applications that transfer larger amounts of data are typical in this type of network. For those who do not require the larger bandwidth, 802.11b is ideal ”for example, in a SOHO or home network.

Security Concerns

The 802.11b standard suffers from a weak security link: the Wireless Equivalent Privacy (WEP). The first version of WEP used a key size that made it easy to penetrate a network. IEEE 802.11a also uses WEP, with much larger keys, ranging from 64 to 152 bits. Service Set Identification (SSID) is another method that offers additional security for wireless networks. Administrators can manage their wireless clients more efficiently today than a few years ago. You can read more about wireless security mechanisms, such as WAP (Wireless Application Protocol) in Chapter 24, "Other Wireless Technologies."



Upgrading and Repairing Networks
Upgrading and Repairing Networks (5th Edition)
ISBN: 078973530X
EAN: 2147483647
Year: 2003
Pages: 434

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