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Reference Manual for the 108 Mbps Wireless Firewall Router WGT624 v3
C-22
Preparing Your Network
202-10090-01, April 2005
Page 117 / 148
Wireless Networking Basics
D-1
202-10090-01, April 2005
Appendix D
Wireless Networking Basics
This chapter provides an overview of Wireless networking.
Wireless Networking Overview
The WGT624 v3 wireless router conforms to the Institute of Electrical and Electronics Engineers
(IEEE) 802.11b and 802.11g standards for wireless LANs (WLANs). On an 802.11b or g wireless
link, data is encoded using direct-sequence spread-spectrum (DSSS) technology and is transmitted
in the unlicensed radio spectrum at 2.5GHz. The maximum data rate for the 802.11b wireless link
is 11 Mbps, but it will automatically back down from 11 Mbps to 5.5, 2, and 1 Mbps when the
radio signal is weak or when interference is detected. The 802.11g auto rate sensing rates are 1, 2,
5.5, 6, 9, 12, 18, 24, 36, 48, and 54 Mbps.
The 802.11 standard is also called Wireless Ethernet or Wi-Fi by the Wireless Ethernet
Compatibility Alliance (WECA, see
), an industry standard group promoting
interoperability among 802.11 devices. The 802.11 standard offers two methods for configuring a
wireless network - ad hoc and infrastructure.
Infrastructure Mode
With a wireless Access Point, you can operate the wireless LAN in the infrastructure mode. This
mode provides wireless connectivity to multiple wireless network devices within a fixed range or
area of coverage, interacting with wireless nodes via an antenna.
In the infrastructure mode, the wireless access point converts airwave data into wired Ethernet
data, acting as a bridge between the wired LAN and wireless clients. Connecting multiple Access
Points via a wired Ethernet backbone can further extend the wireless network coverage. As a
mobile computing device moves out of the range of one access point, it moves into the range of
another. As a result, wireless clients can freely roam from one Access Point domain to another and
still maintain seamless network connection.
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Reference Manual for the 108 Mbps Wireless Firewall Router WGT624 v3
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Wireless Networking Basics
202-10090-01, April 2005
Ad Hoc Mode (Peer-to-Peer Workgroup)
In an ad hoc network, computers are brought together as needed; thus, there is no structure or fixed
points to the network - each node can generally communicate with any other node. There is no
Access Point involved in this configuration. This mode enables you to quickly set up a small
wireless workgroup and allows workgroup members to exchange data or share printers as
supported by Microsoft networking in the various Windows operating systems. Some vendors also
refer to ad hoc networking as peer-to-peer group networking.
In this configuration, network packets are directly sent and received by the intended transmitting
and receiving stations. As long as the stations are within range of one another, this is the easiest
and least expensive way to set up a wireless network.
Network Name: Extended Service Set Identification (ESSID)
The Extended Service Set Identification (ESSID) is one of two types of Service Set Identification
(SSID). In an ad hoc wireless network with no access points, the Basic Service Set Identification
(BSSID) is used. In an infrastructure wireless network that includes an access point, the ESSID is
used, but may still be referred to as SSID.
An SSID is a thirty-two character (maximum) alphanumeric key identifying the name of the
wireless local area network. Some vendors refer to the SSID as network name. For the wireless
devices in a network to communicate with each other, all devices must be configured with the
same SSID.
The ESSID is usually broadcast in the air from an access point. The wireless station sometimes can
be configured with the ESSID
ANY.
This means the wireless station will try to associate with
whichever access point has the stronger radio frequency (RF) signal, providing that both the access
point and wireless station use Open System authentication.
Authentication and WEP Data Encryption
The absence of a physical connection between nodes makes the wireless links vulnerable to
eavesdropping and information theft. To provide a certain level of security, the IEEE 802.11
standard has defined these two types of authentication methods:
•
Open System
. With Open System authentication, a wireless computer can join any network
and receive any messages that are not encrypted.
Page 119 / 148
Reference Manual for the 108 Mbps Wireless Firewall Router WGT624 v3
Wireless Networking Basics
D-3
202-10090-01, April 2005
•
Shared Key
. With Shared Key authentication, only those PCs that possess the correct
authentication key can join the network. By default, IEEE 802.11 wireless devices operate in
an Open System network.
Wired Equivalent Privacy (WEP) data encryption is used when the wireless devices are configured
to operate in Shared Key authentication mode.
802.11 Authentication
The 802.11 standard defines several services that govern how two 802.11 devices communicate.
The following events must occur before an 802.11 Station can communicate with an Ethernet
network through an access point, such as the one built in to the WGT624 v3:
1.
Turn on the wireless station.
2.
The station listens for messages from any access points that are in range.
3.
The station finds a message from an access point that has a matching SSID.
4.
The station sends an authentication request to the access point.
5.
The access point authenticates the station.
6.
The station sends an association request to the access point.
7.
The access point associates with the station.
8.
The station can now communicate with the Ethernet network through the access point.
An access point must authenticate a station before the station can associate with the access point or
communicate with the network. The IEEE 802.11 standard defines two types of authentication:
Open System and Shared Key.
•
Open System Authentication
allows any device to join the network, assuming that the device
SSID matches the access point SSID. Alternatively, the device can use the “ANY” SSID
option to associate with any available Access Point within range, regardless of its SSID.
•
Shared Key Authentication
requires that the station and the access point have the same WEP
Key to authenticate. These two authentication procedures are described below.
Open System Authentication
The following steps occur when two devices use Open System Authentication:
1.
The station sends an authentication request to the access point.
Page 120 / 148
Reference Manual for the 108 Mbps Wireless Firewall Router WGT624 v3
D-4
Wireless Networking Basics
202-10090-01, April 2005
2.
The access point authenticates the station.
3.
The station associates with the access point and joins the network.
This process is illustrated below.
Figure 7-4:
Open system authentication
Shared Key Authentication
The following steps occur when two devices use Shared Key Authentication:
1.
The station sends an authentication request to the access point.
2.
The access point sends challenge text to the station.
3.
The station uses its configured 64-bit or 128-bit default key to encrypt the challenge text, and
sends the encrypted text to the access point.
4.
The access point decrypts the encrypted text using its configured WEP Key that corresponds
to the station’s default key. The access point compares the decrypted text with the original
challenge text. If the decrypted text matches the original challenge text, then the access point
and the station share the same WEP Key and the access point authenticates the station.
5.
The station connects to the network.
If the decrypted text does not match the original challenge text (the access point and station do not
share the same WEP Key), then the access point will refuse to authenticate the station and the
station will be unable to communicate with either the 802.11 network or Ethernet network.
FVM318
Access Point (AP)
1) Authentication request sent to AP
2) AP authenticates
3) Client connects to network
Open System
Authentication Steps
Cable or
DLS modem
Client
attempting
to connect

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