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Note:

Some 802.11b access points also support

Use WEP for Authentication Only

(Shared Key

Authentication without data encryption).

Key Size

The IEEE 802.11b standard supports two types of WEP encryption: 40-bit and 128-bit.

The 64-bit WEP data encryption method, allows for a five-character (40-bit) input. Additionally,

24 factory-set bits are added to the forty-bit input to generate a 64-bit encryption key. (The 24

factory-set bits are not user-configurable). This encryption key will be used to encrypt/decrypt all

data transmitted via the wireless interface. Some vendors refer to the 64-bit WEP data encryption

as 40-bit WEP data encryption since the user-configurable portion of the encryption key is 40 bits

wide.

The 128-bit WEP data encryption method consists of 104 user-configurable bits. Similar to the

forty-bit WEP data encryption method, the remaining 24 bits are factory set and not user

configurable. Some vendors allow passphrases to be entered instead of the cryptic hexadecimal

characters to ease encryption key entry.

128-bit encryption is stronger than 40-bit encryption, but 128-bit encryption may not be available

outside of the United States due to U.S. export regulations.

When configured for 40-bit encryption, 802.11b products typically support up to four WEP Keys.

Each 40-bit WEP Key is expressed as 5 sets of two hexadecimal digits (0-9 and A-F). For

example, “12 34 56 78 90” is a 40-bit WEP Key.

When configured for 128-bit encryption, 802.11b products typically support four WEP Keys but

some manufacturers support only one 128-bit key. The 128-bit WEP Key is expressed as 13 sets of

two hexadecimal digits (0-9 and A-F). For example, “12 34 56 78 90 AB CD EF 12 34 56 78 90”

is a 128-bit WEP Key.

Note:

Typically, 802.11b access points can store up to four 128-bit WEP Keys but some 802.11b

client adapters can only store one. Therefore, make sure that your 802.11b access and client

adapters configurations match.

WEP Configuration Options

The WEP settings must match on all 802.11b devices that are within the same wireless network as

identified by the SSID. In general, if your mobile clients will roam between access points, then all

of the 802.11b access points and all of the 802.11b client adapters on the network must have the

same WEP settings.

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Note:

Whatever keys you enter for an AP, you must also enter the same keys for the client adapter

in the same order. In other words, WEP key 1 on the AP must match WEP key 1 on the client

adapter, WEP key 2 on the AP must match WEP key 2 on the client adapter, etc.

Note:

The AP and the client adapters can have different default WEP Keys as long as the keys are

in the same order. In other words, the AP can use WEP key 2 as its default key to transmit while a

client adapter can use WEP key 3 as its default key to transmit. The two devices will communicate

as long as the AP’s WEP key 2 is the same as the client’s WEP key 2 and the AP’s WEP key 3 is

the same as the client’s WEP key 3.

Wireless Channels

IEEE 802.11 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.

The radio frequency channels used are listed in

Table 7-3

:

Table 7-3.

802.11 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

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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.

Ethernet Cabling

Although Ethernet networks originally used thick or thin coaxial cable, most installations currently

use unshielded twisted pair (UTP) cabling. The UTP cable contains eight conductors, arranged in

four twisted pairs, and terminated with an RJ45 type connector. A normal "straight-through" UTP

Ethernet cable follows the EIA568B standard wiring as described in

Table 7-4

.

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

Table 7-4.

UTP Ethernet cable wiring, straight-through

Pin

Wire color

Signal

1

Orange/White

Transmit (Tx) +

2

Orange

Transmit (Tx) -

3

Green/White

Receive (Rx) +

4

Blue

5

Blue/White

6

Green

Receive (Rx) -

7

Brown/White

8

Brown

Table 7-3.

802.11 Radio Frequency Channels

Channel

Center Frequency

Frequency Spread

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Uplink Switches and Crossover Cables

In the wiring table, the concept of transmit and receive are from the perspective of the PC. For

example, the PC transmits on pins 1 and 2. At the hub, the perspective is reversed, and the hub

receives on pins 1 and 2. When connecting a PC to a PC, or a hub port to another hub port, the

transmit pair must be exchanged with the receive pair. This exchange is done by one of two

mechanisms. Most hubs provide an Uplink switch which will exchange the pairs on one port,

allowing that port to be connected to another hub using a normal Ethernet cable. The second

method is to use a crossover cable, which is a special cable in which the transmit and receive pairs

are exchanged at one of the two cable connectors. Crossover cables are often unmarked as such,

and must be identified by comparing the two connectors. Since the cable connectors are clear

plastic, it is easy to place them side by side and view the order of the wire colors on each. On a

straight-through cable, the color order will be the same on both connectors. On a crossover cable,

the orange and blue pairs will be exchanged from one connector to the other.

Cable Quality

A twisted pair Ethernet network operating at 10 Mbits/second (10BASE-T) will often tolerate low

quality cables, but at 100 Mbits/second (10BASE-Tx) the cable must be rated as Category 5, or

"Cat 5", by the Electronic Industry Association (EIA). This rating will be printed on the cable

jacket. A Category 5 cable will meet specified requirements regarding loss and crosstalk. In

addition, there are restrictions on maximum cable length for both 10 and 100 Mbits/second

networks.

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