CEH

What Is a Wireless Network? 353

named wireless network. The SSID is embedded within the header of packets, thus making it
viewable. On open networks, the SSID is visible and can be viewed by any client searching for
it. On closed networks, the SSID is not visible and in some cases is said to be cloaked.

A client must have an SSID to access a wireless LAN (WLAN). However, the

reality is that the SSID does not provide any substantial security since sniffing

techniques can be used to easily obtain the SSID. In fact, the SSID is usually

freely given on open networks and is commonly called a shared secret.

Wireless Vocabulary

In addition to the term SSID, this chapter uses the terms shown in Table 15.2.

TABLE 15.2 Common wireless terms

Term Description

GSM (Global System for
Mobile Communications)

An international standard for mobile wireless

Association The process of connecting a client to an access point

BSSID (basic service set
identification)

The MAC address of an access point

Hot spot A location that provides wireless access to the public
such as a coffee shop or airport

Access point A hardware or software construct that provides wireless
access

ISM (industrial, scientific, and
medical) band

A unlicensed band of frequencies

Bandwidth How much speed is available for devices

Wireless Antennas

Something else you should be aware of when talking about wireless networks is the type of
antenna in use. If you are working with consumer-grade access points, this typically is not
a big concern as the antenna is built in or provided with these products. However, when
working with enterprise and commercial-grade access points you may very well need to
select an antenna to suit your environment or for a specific purpose. In this section we’ll
look at each of the available types and what makes them unique and why you would choose
one over another.
The first type of antenna we’ll discuss is the Yagi antenna (Figure 15.1), which is designed
to be a unidirectional (more commonly known as directional) antenna. As a unidirectional
antenna, it works well transmitting and receiving signals in some directions but not in others.
Typically this type of antenna is used in applications where the transmission of signals is