In the IEEE 802.11b wireless standard, how many non-overlapping channels are available for use in a typical 2.4 GHz wireless Local Area Network?

Introduction / Context:
Wireless Local Area Networks operating under IEEE 802.11b use the 2.4 gigahertz Industrial, Scientific, and Medical band. This band is divided into several channels, but due to the way frequencies overlap, only a limited number of channels can be used at the same time without interfering with each other. For proper design of wireless networks, especially in multi access point deployments, it is important to know the number of truly non overlapping channels that can be used for planning to reduce co channel and adjacent channel interference.

Given Data / Assumptions:

• Standard considered: IEEE 802.11b.
• Frequency band: 2.4 gigahertz.
• We are interested in non overlapping channels, not simply the total number of channels defined.
• We assume a typical North American or similar regulatory domain where channels are spaced at five megahertz intervals.

Concept / Approach:
Although the 2.4 gigahertz band defines many channels, each 802.11b channel occupies about 22 megahertz of bandwidth and channels are only five megahertz apart. This means that adjacent channels overlap significantly. In practice, only specific channel combinations can be used simultaneously in the same area without significant overlap. In many regions, channels 1, 6, and 11 are chosen as the three non overlapping channels. They are separated sufficiently in frequency space so that their signal spectra do not overlap significantly, allowing multiple access points to operate without causing major interference to one another.

Step-by-Step Solution:
1. Recognise that 802.11b operates in the 2.4 gigahertz band with channels that are 22 megahertz wide. 2. Channels are spaced five megahertz apart, so adjacent channel signals overlap heavily. 3. Through spectrum analysis and standard practice, it is known that channels 1, 6, and 11 are sufficiently separated so that their main lobes do not overlap. 4. These three channels are therefore considered non overlapping in typical deployments. 5. As a result, there are three non overlapping channels available for 802.11b network design in the 2.4 gigahertz band.

Verification / Alternative check:
Wireless design documentation from vendors and certification materials for entry level wireless certifications consistently highlight channels 1, 6, and 11 as the three non overlapping channels for 802.11b in North America. In other regulatory domains, alternative sets such as 1, 5, 9, and 13 may be considered with different overlap assumptions, but for the classic exam scenario, the widely accepted answer is three channels. Practical site surveys also confirm that reusing only channels 1, 6, and 11 in a staggered pattern greatly reduces interference and improves performance.

Why Other Options Are Wrong:
12: This number is closer to the total number of channels defined in some regions but does not reflect the count of non overlapping channels.
23: This value is far higher than any realistic channel count and does not match known allocations.
40: This is an unrealistic value and may cause confusion with other technologies that use wider channel bonding, but it is not applicable for basic 802.11b planning.
7: Although more than three channels exist, they are not all non overlapping. Using seven unique channels in a small area would result in significant interference due to overlapping spectra.

Common Pitfalls:
Learners often confuse the total number of channel numbers with the number of non overlapping channels. Others may recall that newer standards such as 802.11n and 802.11ac use bonding techniques and assume a higher count of effective channels. To avoid these mistakes, always focus on the specific standard and band described in the question. For classic 802.11b in the 2.4 gigahertz band, the safe answer to remember is three non overlapping channels, usually channels 1, 6, and 11.

Final Answer:
3