User's Manual

802.11b/g WiFi Module
Service Set Identification (SSID)
The Service Set Identification (SSID) is a thirty-two alphanumeric character (maximum) string identifying the wireless
local area network (WLAN). Some vendors refer to the SSID as network name. For stations to communicate with
each other, all stations must be configured with the same SSID.
Authentication and WEP Encryption
The absence of a physical connection between nodes makes the wireless links vulnerable to information theft. To
provide certain level of security, IEEE 802.11 standard has defined two types of authentication methods, Open System
and Shared Key. Open System authentication is a null algorithm. Shared Key authentication is an algorithm where
both the transmitting node and the receiving node share an authentication key to perform a checksum on the original
message. By default, IEEE 802.11 wireless devices operate in an open system network.
Wired Equivalent Privacy (WEP) data encryption is utilized when the wireless nodes or access points are configured to
operate in Shared Key authentication mode. There are two shared key methods implemented in most commercially
available products, 40-bit WEP data encryption and 104-bit WEP data encryption.
The 40-bit WEP data encryption method allows for a five-character (forty -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 may
refer to the 40-bit WEP data encryption as 64-bit WEP data encryption since the actual encryption key used in the
encryption process is 64 bits wide.
The 128-bit WEP data encryption method consists of 104 configurable bits. Similar to the 40-bit WEP data encryption
method, the remaining 24 bits are factory set and not user configurable. Some vendors allow pass phrases to be
entered instead of the cryptic hexadecimal characters to ease encryption key entry.
Wireless Channel Selection
IEEE 802.11g wireless nodes communicate with each other using radio frequency signals in the ISM (Industrial,
Scientific, and Medical) band between 2.4Ghz and 2.5Ghz. Neighboring channels are 5Mhz apart. However, due
to spread spectrum effect of the signals, a node sending signals using a particular channel will utilize frequency
spectrum12.5Mhz 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.
Channel Center Frequency Frequency Spread
1 2412Mhz 2399.5Mhz – 2424.5Mhz
2 2417Mhz 2404.5Mhz – 2429.5Mhz
3 2422Mhz 2409.5Mhz –2434.5Mhz
4 2427Mhz 2414.5Mhz –2439.5Mhz
5 2432Mhz 2419.5Mhz – 2444.5Mhz
6 2437Mhz 2424.5Mhz –2449.5Mhz
7 2442Mhz 2429.5Mhz –2454.5Mhz
8 2447Mhz 2434.5Mhz – 2459.5Mhz
9 2452Mhz 2439.5Mhz –2464.5Mhz
10 2457Mhz 2444.5Mhz –2469.5Mhz
11 2462Mhz 2449.5Mhz – 2474.5Mhz
12 2467Mhz 2454.5Mhz – 2479.5Mhz
13 2472Mhz 2459.5Mhz – 2484.5Mhz