In data communication and computer networks, what does the term bandwidth of a link or channel refer to?

Introduction / Context:
Bandwidth is one of the most frequently used terms in data communication and computer networking. People casually say that a link has high bandwidth or low bandwidth, but in technical exams you must know the precise meaning. Understanding bandwidth is essential for topics such as link capacity, Quality of Service, congestion control and network performance analysis.

Given Data / Assumptions:

We are working in the context of digital data communication and computer networks.
Bandwidth is being used in the sense of capacity of a link or channel, not only in the pure analog frequency sense.
The question is asking for the correct conceptual definition, not for a numeric formula.
We assume that typical units such as bits per second (b/s, kb/s, Mb/s, Gb/s) are familiar.

Concept / Approach:
In networking, the term bandwidth commonly refers to the maximum rate at which data can be transmitted over a communication link under given conditions. For digital links this is often called channel capacity and is expressed in bits per second. While the original analog meaning of bandwidth is the width of a frequency band in hertz, for exam purposes bandwidth in computer networks usually means the link's data carrying capacity. This capacity depends on the physical medium, modulation scheme, signal to noise ratio and protocol overheads.

Step-by-Step Solution:
Step 1: Recognize that network performance is often summarized by two measures: bandwidth (capacity) and delay (latency). Step 2: Bandwidth answers the question: how many bits can be pushed through the link per unit time if the link is fully utilized. Step 3: Units such as 100 Mb/s Ethernet or 1 Gb/s optical links refer exactly to this maximum achievable data rate. Step 4: The physical width of a cable does not directly define bandwidth; two cables of similar thickness can have very different capacities depending on technology. Step 5: The number of users or size of IP address block are separate concepts and do not define the data rate over a physical or logical link.

Verification / Alternative check:
Standard textbooks define bandwidth in networking as the maximum amount of data that can pass through a network path per unit time. When an Internet Service Provider advertises a 50 Mb/s plan, it is offering a maximum downstream bandwidth of roughly 50 megabits per second. This directly matches option A and not the other interpretations.

Why Other Options Are Wrong:
The physical width of the cable is only loosely related to performance and is never used as the formal definition of bandwidth in networking.
The number of simultaneous users is a system capacity measure but not bandwidth of a single link.
An IP address range describes addressing capability, not data rate, so it is unrelated to bandwidth.

Common Pitfalls:
A common mistake is to confuse bandwidth with frequency bandwidth in analog signals or to mix it up with latency. Another pitfall is to assume that if bandwidth is high, performance is always good. In reality, delay, loss and protocol behavior also matter. However, as a definition, you should simply remember that in networking, bandwidth usually means maximum data rate.

Final Answer:
In computer networks, bandwidth of a link refers to the maximum data rate that can be transmitted over that link per second, typically measured in bits per second.