Wireless Cable Modem Gateway Reference Manual

Reference Manual for the Model CG814M Wireless Cable Modem Gateway
B-14 Networks, Routing, and Firewall Basics
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.
Wireless Channel Selection
IEEE 802.11b 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 spectrum 12.5Mhz 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.
The radio frequency channels used are listed in Table B-1:
Table B-1. 802.11b Radio Frequency Channels
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