Bandwidth is an extremely important concept in communications systems. There
are two common ways of looking at bandwidth, which are referred to as analog
bandwidth and digital bandwidth. These related concepts are both important for
the study of WLANs. This section will explore these types of bandwidth in more
depth.
Analog bandwidth
Analog bandwidth typically refers to
the frequency range of an analog electronic system. For example, analog
bandwidth could be used to describe the range of frequencies radiated by an FM
radio station. Analog bandwidth could also refer to the range of frequencies
that can propagate down a copper cable. Analog bandwidth is described in units
of frequency, or cycles per second, which is measured in Hz. There is a direct
correlation between the analog bandwidth of any medium and the data rate in
bits per second that the medium can support.
Digital
bandwidth
Digital bandwidth is a measure of how much information can
flow from one place to another, in a given amount of time. Digital bandwidth is
measured in bits per second. When dealing with data communications, the term
bandwidth most often signifies digital bandwidth.
Throughput refers to
actual, measured bandwidth. In some cases, it is further restricted to only
include actual data, discarding any protocol overhead, such as headers,
trailers, and protocol messages, from the computed totals. Regardless of the
exact method of computation, the actual throughput is often far less than the
maximum possible digital bandwidth of the medium that is being used. Many
factors affect throughput, including the medium, the distance, noise, and the
protocols used.
When designing a network, it is important to consider
the theoretical bandwidth. The network will never be faster than the medium
will allow. A related consideration is the amount of bandwidth that the user
applications require. Figure
illustrates
different methods of connecting to the Internet and their corresponding
bandwidths, in Kbps. Also shown in Figure
are some typical
Internet applications and their corresponding bandwidth needs.