EXERCISE 3.3 DESCRIBES THE STEPS FOR INSTALLING A PCI CARD IN A DESKTO...

2.4 GHz ISM Band Channel number Frequency in GHz USA Europe Israel* China Japan1 2.412 X X X X X2 2.417 X X X X X3 2.422 X X X X X4 2.427 X X X X X5 2.432 X X X X X6 2.437 X X X X X7 2.442 X X X X X8 2.447 X X X X X9 2.452 X X X X X10 2.457 X X X X X11 2.462 X X X X X12 2.467 X X X13 2.472 X X X14 2.484 X* Israel only allows 5–13 outdoors, but 1–13 indoors.The 5 GHz UNII band is also divided into channels. This band consists of three bands—lower, middle, and upper. These three bands consist of four different frequency ranges. Since there are fewer channels in the same amount of space, channels in the UNII bands do not overlap. In the 5 GHz UNII bands, channels are 20 MHz wide. Figure 4.9 shows the 5 GHz UNII bands for the FCC and ETSI locales.F i g u R e 4 . 9 Channels in the 5 GHz bandsLocale Frequency Number of Channels Americas/EMEA UNII-1 band 4(5.15–5.25) Americas/EMEA UNII-2 band 4(5.25–5.35) Americas/EMEA UNII-2e band 11(5.470–5.725) Americas/EMEA UNII-3 band 4(with restrictions) (5.725–5.825)Americas ISM 1(5.725–5.850)

Range

Range for wireless LANs is based on the wavelength or distance of a single cycle. The higher the frequency, the shorter the range of the signal. The lower the frequency, the longer the range of the signal. At the same output power level, a 2.4 GHz signal will travel almost twice as far as a 5 GHz signal. If a network design is planning to use dual-band access points, range will need to be considered to ensure proper coverage for both the 2.4 GHz ISM and 5 GHz UNII bands. A wireless site survey will help determine the useable range an access point will produce. A survey can involve physically walking around the proposed space and/or predictive modeling using one of many software programs. This process is discussed further in Chapter 9, “Performing a WLAN Site Survey.”

Coverage and Capacity

Coverage and capacity are two key factors to take into consideration when designing and implementing an IEEE 802.11 wireless LAN. During the design phase of an IEEE 802.3 wired network, the design engineer will take capacity into consideration, verifying and vali-dating that there are enough capacity switches, ports, etc., for the user base of the network. Coverage and Capacity 105The same is true for a wireless network. The number of users connected to an access point is something that needs to be carefully considered. The fact that wireless networks use a shared medium is an issue because the more users who are connected to an access point, the lower the performance may be, depending on what the users are doing. This capacity consideration will ensure satisfied end users and good network performance—proof of a successful network design and deployment.In wireless networks, coverage also needs to be considered. Coverage is determined by the RF cell size. In IEEE 802.11 wireless networks, a cell is the area of RF coverage of the transmitter, in most cases an access point. Depending on implementation, wide coverage or large cell size may not be the best solution. A large space covered by a single access point could result in less than adequate performance based on factors such as the users’ distance from the access point. The farther away from an access point, the less throughput a device or user will experience. If users will be scattered throughout a large space, it may be best to have several access points covering the space to allow for optimal performance.The term cell has several different meanings depending on the context. In the world of IEEE 802.11 wireless networks, a cell is the radio coverage area for a transmitter such as an access point.

Coverage

The term coverage has different meanings depending on the context in which it used. For example, if you buy a gallon of paint, the label will specify the approximate coverage area in square feet. If one gallon of paint covers 300 sq ft and the room you wish to paint is 900 sq ft, simple math shows at least three gallons of paint would be needed to effectively cover the room.The concept is similar in IEEE 802.11 wireless networks. However, unlike with paint, there is no simple rule that determines how much space an access point will cover with the RF energy it is transmitting. This coverage will depend on many factors, some of which include:Size of area

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Number of usersBandwidth-intensive applications in use or hardware applicationsObstacles and propagation (the way radio waves spread through an area)Radio frequency rangeWLAN hardware in use (this affects coverage because higher frequencies, e.g., 5 GHz, do not travel as far as lower ones, e.g., 2.4 GHz)Power output of transmitterYou might initially assume that you want the RF signal to propagate over the largest area possible. But this may not be the best solution. A very large cell may allow too many devices to connect to a single access point. For those clients connected at a greater distance, the per-formance will be lower than for stations closer to the access point. Figure 4.10 shows a large coverage area, approximately 11,250 sq ft (1,058 sq m) covered with a single access point. This is an example of too large an area for a single access point.F i g u R e 4 .10 Wide coverage with only a single access point is not recommended.150 ft/46 m75 ft/23 mStation at greater distance