1-8 Media and Topologies

1.8 Identify factors which affect the range and speed of wireless service (For example: interference, antenna type and environmental factors).

> 802.11g

Suffers from the same interference as 802.11b in the already crowded 2.4 GHz range. Devices operating in this range include microwave ovens, Bluetooth devices, and cordless telephones.

Since the 2.4 GHz band is heavily used, using the 5 GHz band gives 802.11a the advantage of less interference. However, this high carrier frequency also brings disadvantages. It restricts the use of 802.11a to almost line of sight, necessitating the use of more access points; it also means that 802.11a cannot penetrate as far as 802.11b since it is absorbed more readily, other things (such as power) being equal.

> 802.11a

Transmits radio signals in the frequency range above 5 GHz. This range is "regulated," meaning that 802.11a gear utilizes frequencies not used by other commercial wireless products like cordless phones. In contrast, 802.11b utilizes frequencies in the unregulated 2.4 GHz range and encounters much more radio interference from other devices.

> IEEE 802.11a / IEEE 802.11h

This is also a physical layer enhancement. IEEE 802.11a provides significantly higher performance than 802.11b, at 54 Mbps. Unlike 802.11b, the 802.11a standard operates within the frequency range of 5.47 to 5.725 GHz and is not subject to the same interference from other commercial electronic products. This higher frequency band allows significantly higher speeds of communication over the 2.4 GHz range.

802.11g APs are backward compatible with 802.11b APs. This backward compatibility with 802.11b is handled through the MAC layer, not the physical layer. On the negative side, because 802.11g operates at the same frequency as 802.11b, it is subject to the same interferences from electronic devices such as cordless phones. Since the standard’s approval in June 2003, 802.11g products are gaining momentum and will most likely become as widespread as 802.11b products. Table II-1 displays basic 802.11b/a/g characteristics.

The common range of operation for 802.11b is 150 feet for a floor divided into individual offices by concrete or sheet-rock, about 300 feet in semi-open indoor spaces such as offices partitioned into individual workspaces, and about 1000 feet in large open indoor areas. Disadvantages of 802.11b include interference from electronic products such as cordless phones and microwave ovens.

Range

The layout of your building can reduce the range.

• A lot of concrete walls can reduce your range.
• The size of the antenna and the placement greatly affect the range of their signals
• The weather and amount of water vapor in the air can affect your signals strength

Speed

• The layout of your building can reduce the speed
• The size of the antenna and its signal can affect your speed
• The weather and amount of water vapor can weaken the signal and affect your speed