Wireless Network Installation
Now that you understand the basic components involved in a wireless network, it’s time to learn about their actual installation. Although we’ve stated earlier that wireless networks contain
fewer components and are less complex, there are several major factors that figure into a wireless network installation:
- Wireless LAN standards
- Installation type
- Signal degradation (Site Survey)
Wireless LAN Standards
Although wireless LANs have been around for only a relatively short time (in networking terms), there are many standards that have been ratified that deal with them. The majority of the technology in use today for wireless LANs is based on the IEEE 802.11 series of standards, although a slightly misaligned niche market exists for infrared and Bluetooth networking as
well. More suited to LAN networking than infrared, Bluetooth, and the original 802.11 standard, the three most commonly used 802.11 standards today are as follows:
IEEE 802.11a
IEEE 802.11b
IEEE 802.11g
NOTE:
All three of these wireless versions are technically subgroups of the 802.11 working group. Even though they are in the same group, they are fundamentally different, as you will see.Infrared Networking
One type of wireless networking that doesn’t receive much attention is infrared wireless. Infrared wireless uses the same basic transmission method as many television remote controls, infrared
technology. Infrared is used primarily for short distance, point-to-point communications, like those between a peripheral and a PC. The largest use of infrared wireless is for peripherals using
the IrDA standard.
NOTE:
A little-known fact about infrared is that the original IEEE 802.11 wireless standard specified a somewhat limited baseband infrared medium in addition to the more common Direct Sequence Spread Spectrum (DSSS) and Frequency Hopping Spread Spectrum (FHSS) modulation techniques.
IrDA stands for Infrared Data Association, which is the standards body that develops the IrDA standard for point-to-point, peer-to-peer communications over infrared radiation. Infrared
equipment that uses the IrDA standard can be found in many places, including cell phones, handheld PDAs and computers, keyboards, and so on. The standard specifies a data transmission rate of 16Mbps (that will soon be increased to over 100Mbps with updates to the standard) and a maximum range of about 1 meter (1m). As you can see, although it possesses significant throughput, the range is lacking for a wireless LAN standard for large LANs.
Bluetooth Networking
One of the newest wireless standards is the wireless networking standard known as Bluetooth. It was designed to replace the myriad cords on an average computer user’s desk. Cords for
things like keyboards, mice, and headphones can all be eliminated. The standard allows for these many different types of peripherals to all be able to communicate wirelessly with a host device, like a computer. For example, a popular Bluetooth accessory is the wireless headset for cellular phones. It’s battery powered and will communicate directly with the phone wirelessly. Bluetooth has a total maximum throughput of 1Mbps. It isn’t a speed demon as far as throughput is concerned, but it is still more than enough for peripheral communications like mice, keyboards, and headphones, and it is possible for two Bluetooth devices to network to
each other in a peer-to-peer fashion. But, as with infrared, it is impractical to build an entire multistation wireless LAN using the Bluetooth technology.
802.11
The original 802.11 standard specified a somewhat impractical recommendation, in terms of data rates, with regard to the bandwidth-hungry mentality of its contemporary LANs. In 1997, IEEE specified what is now referred to as 802.11-1997, a wireless LAN standard with a bandwidth of 2Mbps (with the ability to fall back to 1Mbps in noisy environments) when using DSSS modulation and a bandwidth of 1Mbps when using FHSS modulation. Even when using FHSS, the standard allows for possible 2Mbps operation in environments in which the noise level is below an acceptable threshold. Both the DSSS and FHSS methods operate in the unlicensed 2.4GHz frequency
range. 802.11-1997 has since been updated by 802.11-1999, the supplements to which have given rise to the newer, more common standards of 802.11a, 802.11b, and 802.11g.
802.11a
The IEEE 802.11a standard is an extension to the IEEE 802.11 standard that specifies a wirelessradio frequency LAN technology that provides for up to 54Mbps of available throughput.It
uses the 5GHz radio frequencies (regulated) and OFDM for data encoding. It has a maximum range of 250ft (76m) indoors and approximately 1000ft (305m) outdoors.
Wireless LAN Modulation Techniques
While a complete discussion of the technical workings of the wireless modulation techniques is beyond the scope of the objectives of the Network + exam and of this Study Guide, it is still important that you are aware of the mating of these techniques with their corresponding 802.11 standards.
DSSS
DSSS is one of the modulation techniques specified by the original IEEE 802.11 standard and the one chosen for use in the widely accepted IEEE 802.11b standard. IEEE 802.11 uses Differential
Binary Phase Shift Keying (DBPSK) for 1Mbps DSSS and Differential Quadrature Phase Shift Keying (DQPSK) for 2Mbps DSSS. The DSSS defined in IEEE 802.11b uses the Complementary Code Keying (CCK) modulation technique, making 5.5Mbps and 11Mbps data rates. All three modulation schemes are compatible and can coexist by using 802.11-standardized rate-switching procedures. DSSS creates a redundant bit pattern for each bit that is transmitted, increasing DSSS’s resistance to interference. The benefit is that if one or more bits in the bit pattern are damaged
in transmission, the original data might be recoverable from the redundant bits.
FHSS
Although it’s the original modulation technique specified by the IEEE 802.11 standard, FHSS is not the modulation of choice for vendors or the 802.11 working group. As very few vendors
support FHSS in 802.11 products, it seems DSSS has become the preferred modulation standard. Continued developments within 802.11 favor DSSS. FHSS modulates the data signal with
a carrier signal that changes (hops) in a random yet predictable sequence of frequencies, over time These changes also occur over a wide frequency band. A spreading, or hopping, code determines the transmission frequencies. The receiver is set to the same code, allowing it to listen to the incoming signal at the right time and frequency to properly receive the signal. Manufacturers
use 75 or more frequencies per transmission channel. The maximum dwell time, or time spent during a hop at a particular frequency, has been established by the FCC at 400ms.
OFDM
802.11a uses Orthogonal Frequency Division Multiplexing (OFDM), with a system of 52 carriers (sometimes referred to as “subcarriers”)modulated by BPSK or QPSK. OFDM’s spread spectrum technique distributes the data over these 52 carriers, which are spaced apart at precise frequencies. This spacing helps prevent demodulators from seeing frequencies other than their
own. OFDM is resistant to RF interference, exhibiting lower multipath distortion. For more information on OFDM, check out the OFDM Forum’s website at www.ofdm-forum.com.
The IEEE 802.11a standard was released at approximately the same time as 802.11b. However, 802.11b received more attention because 802.11a equipment was released approximately
two years after the introduction of the 802.11b equipment and because of 802.11b’s lower equipment cost. Plus, 802.11a has shorter range due to its higher frequency (higher frequencies
attenuate sooner), and also due to the higher frequency, its signal is interfered with more easily. But, on the plus side, because it uses regulated frequencies, there is less chance of standard
devices like microwaves and such interfering with the wireless signal.
802.11b
The IEEE 802.11b standard has been given credit for the explosion of wireless networking. The equipment is cheap (and getting cheaper) and provides for decent network access speeds. It’s
easy to set up and use and is readily available. 802.11a and 802.11b were created at approximately the same time, but the 11b standard got the spotlight as the preferred LAN standard (primarily
because of cost and the late introduction of 11a equipment).
The IEEE 802.11b standard specifies a wireless radio frequency LAN technology that provides for up to 11Mbps of available throughput. It uses the 2.4GHz radio frequencies (unregulated)
and Direct Sequence Spread Spectrum (DSSS) for data encoding. It has a maximum range of 300ft (91m) indoors and about 1500ft (457m) outdoors.
NOTE:
Even though they are subsets of the same standard, IEEE 802.11a and 802.11b are incompatible.
So What Is Wi-Fi?
You may have seen products that are 802.11b compliant with a small sticker on them that says “Wi-Fi.” You might be able to guess that this rather odd phrase stands for Wireless Fidelity, but
you may not know what its implications are. Simply put, that sticker indicates that the product in question has passed certification testing for 802.11b interoperability by the Wi-Fi Alliance.
This nonprofit group was formed to ensure that all 802.11b wireless devices would communicate seamlessly. So, Wi-Fi is a good thing.
802.11g
The most recent player in the 802.11 standards game is the IEEE 802.11g standard. It is kind of a “best of both worlds” standard. It includes the high data rate (54Mbps) of 802.11a with
the stability and wide product base of 802.11b. Plus, it is backward compatible with 802.11b (alas, not so with 802.11a).
The IEEE 802.11g standard specifies a wireless radio frequency LAN technology that provides for up to 54Mbps of available throughput. It uses the 2.4GHz radio frequencies (unregulated)
and both DSSS and OFDM for data encoding. It has a maximum range of 300ft (91m) indoors and about 1500ft (457m) outdoors
NOTE:
It is important to note that most 802.11g devices are compatible with 802.11b devices. For example, a 802.11b NIC will work with an 802.11g access point (at the lower, 802.11b speed, of course) and vice versa.Table 6.2 summarizes these IEEE 802.11 wireless LAN standards in comparison to Bluetooth, a possible interferer.
TABLE 6 . 2 Bluetooth and Wireless LAN Standards
