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Wireless Networking Basics
D-1
Appendix D
Wireless Networking Basics
Wireless Networking Overview
The CG814WG v2 Gateway conforms to the Institute of Electrical and Electronics Engineers
(IEEE) 802.11g standard for wireless LANs (WLANs). On an 802.11 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 802.11g wireless link is 54
Mbps, but it will automatically back down from 54 Mbps when the radio signal is weak or when
interference is detected.
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 Wireless Cable Modem Gateway CG814WG v2
D-2
Wireless Networking Basics
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.
Wireless Channels
IEEE 802.11g/b wireless nodes communicate with each other using radio frequency signals in the
ISM (Industrial, Scientific, and Medical) band between 2.4 GHz and 2.5 GHz. Neighboring
channels are 5 MHz apart. However, due to spread spectrum effect of the signals, a node sending
signals using a particular channel will utilize frequency spectrum 12.5 MHz above and below the
center channel frequency. As a result, two separate wireless networks using neighboring channels
(for example, channel 1 and channel 2) in the same general vicinity will interfere with each other.
Applying two channels that allow the maximum channel separation will decrease the amount of
channel cross-talk, and provide a noticeable performance increase over networks with minimal
channel separation.
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Reference Manual for the Wireless Cable Modem Gateway CG814WG v2
Wireless Networking Basics
D-3
The radio frequency channels used are listed in
Table D-1
:
Note:
The available channels supported by the wireless products in various countries are different.
The preferred channel separation between the channels in neighboring wireless networks is 25
MHz (5 channels). This means that you can apply up to three different channels within your
wireless network. There are only 11 usable wireless channels in the United States. It is
recommended that you start using channel 1 and grow to use channel 6, and 11 when necessary, as
these three channels do not overlap.
Table D-1.
802.11g Radio Frequency Channels
Channel
Center Frequency
Frequency Spread
1
2412 MHz
2399.5 MHz - 2424.5 MHz
2
2417 MHz
2404.5 MHz - 2429.5 MHz
3
2422 MHz
2409.5 MHz - 2434.5 MHz
4
2427 MHz
2414.5 MHz - 2439.5 MHz
5
2432 MHz
2419.5 MHz - 2444.5 MHz
6
2437 MHz
2424.5 MHz - 2449.5 MHz
7
2442 MHz
2429.5 MHz - 2454.5 MHz
8
2447 MHz
2434.5 MHz - 2459.5 MHz
9
2452 MHz
2439.5 MHz - 2464.5 MHz
10
2457 MHz
2444.5 MHz - 2469.5 MHz
11
2462 MHz
2449.5 MHz - 2474.5 MHz
12
2467 MHz
2454.5 MHz - 2479.5 MHz
13
2472 MHz
2459.5 MHz - 2484.5 MHz
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Reference Manual for the Wireless Cable Modem Gateway CG814WG v2
D-4
Wireless Networking Basics
WEP Wireless Security
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 two types of authentication methods, Open System and Shared Key. With
Open System authentication, a wireless computer can join any network and receive any messages
that are not encrypted. With Shared Key authentication, only those computers that possess the
correct authentication key can join the network. By default, IEEE 802.11 wireless devices operate
in an Open System network. Recently, Wi-Fi, the Wireless Ethernet Compatibility Alliance
(
) developed the Wi-Fi Protected Access (WPA), a new strongly enhanced
Wi-Fi security. WPA will soon be incorporated into the IEEE 802.11 standard. WEP and WPA are
discussed below.
WEP 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 CG814WG v2:
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 WEP
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.
Page 105 / 122
Reference Manual for the Wireless Cable Modem Gateway CG814WG v2
Wireless Networking Basics
D-5
•
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.
WEP Open System Authentication
This process is illustrated below.
Figure D-1:
802.11 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.
2.
The access point authenticates the station.
3.
The station associates with the access point and joins the network.
FVM318
Access Point
1) Authentication request sent to AP
2) AP authenticates
3) Client connects to network
802.11b Authentication
Open System Steps
Cable or
DLS modem
Client
attempting
to connect

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