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182 Chapter 4 • Communication Security: Wireless

Figure 4.4 Infrastructure Network Configuration

Wireless Client

Basic Service Set (BSS)

Wireless Client
Wireless Client
Wireless Client

Basic Service Set (BSS)

Extended Service Set (ESS)

To distinguish different wireless networks from one another, the 802.11 stan-
dard defines the Service Set Identifier (SSID).The SSID is considered the identity
element that “glues” various components of a wireless local area network (LAN)
together.Traffic from wireless clients that use one SSID can be distinguished from
other wireless traffic using a different SSID. Using the SSID, an AP can determine
which traffic is meant for it and which is meant for other wireless networks.
802.11 traffic can be subdivided into three parts:

■ Control frames

■ Management frames
■ Data frames
Control frames include such information as Request to Send (RTS), Clear to
Send (CTS), and ACK messages. Management frames include beacon frames, probe
request/response, authentication frames, and association frames. Data frames are
802.11 frames that carry data, which is typically considered network traffic, such as
Internet Protocol (IP) encapsulated frames.

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