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Appendix B

Wireless Networking Basics

This chapter provides an overview of wireless networking and security.

Wireless Networking Overview

The Wireless USB Print Server 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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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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The radio frequency channels used are listed in

Table B-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 B-1.

802.11b 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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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 PC can join any network and receive any messages that are

not encrypted. 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. 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 WGPS606:

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.

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•

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 in below.

Figure B-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

Router with Integrated

Access Point

1) Authentication request sent to AP

2) AP authenticates

3) Client connects to network

802.11 Authentication

Open System Steps

Cable or

DLS modem

Client

attempting

to connect