OBTAIN AN IP ADDRESS BY USING DHCPBEFORE YOU BEGIN THIS EXERCISE, YOU...

802.11g devices are compatible with 802.11b devices, but that compatibility comes

at a price. If a network uses only 802.11g devices, all wireless devices can operate

at up to 54 Mbps. If a network has even a single 802.11b device, 802.11g devices

must operate in mixed mode, which lowers the data transfer for 802.11g devices

by about 30 percent.

Note Some manufacturers make hybrid devices that support both 802.11a and 802.11g, and such devices can connect to networks using any of the three standards mentioned here.

Real World Rated Speeds

Although the standards covered in this lesson have rated speeds (up to 11 Mbps

for 802.11b and up to 54 Mbps for 802.11a and 802.11g), these are mostly theo-

retical values. In practice, you will never actually get that kind of data transfer rate.

Typical throughput for 802.11b products, for example, tops out around 4–5 Mbps.

The 802.11g products have an actual capacity of about 20 Mbps, and 802.11a

products have a capacity of 22 Mbps. In addition, even these more realistic trans-

fer rates are often further limited in the real world by interference from electrical

devices and materials in building structures.

Introduction to Wireless Networking Architecture

The 802.11 standard defines a number of main architectural components. These com-

ponents include the following:

■

Station (STA) A station (STA) is a client device on a wireless network—typically

a computer that has a wireless network adapter installed.

■

Access point (AP) An access point (AP) provides an interface with which stations

can communicate. APs are the bridge between the wireless stations and an existing

network backbone, allowing wireless clients to communicate with the network. APs

can be stand-alone devices, but are often combined with other network devices

such as routers.

■

Independent Basic Service Set (IBSS) An independent basic service set (IBSS)

represents a wireless network that consists of two or more stations, but does not

have an AP. This type of network, shown in Figure 15-16, is often referred to as an

ad-hoc wireless network. Ad-hoc networks offer the advantage of being able to

spontaneously create wireless network connections between stations with little

configuration required. However, ad-hoc networks are considerably less secure

and configurable than basic service set networks that include an AP.

Station Station

F15us16.bmp

Figure 15-16 An IBSS, or ad-hoc wireless network, has wireless stations but no AP. ■

Basic Service Set A basic service set (BSS) represents a network that allows stations

to communicate through an AP, as shown in Figure 15-17. This type of network is often

referred to as an infrastructure wireless network. In a BSS, all stations communi-

cate through the AP. The AP provides connectivity to the wired LAN and provides

bridging functionality when one station initiates communication to another station.

Basic Service SetAccess Point

F15us17.bmp

Figure 15-17 A BSS, or infrastructure wireless network, has wireless stations that communicate through an AP.