UNIT-2
Bandwidth utilization Multiplexing: FDM, TDM, spread spectrum. Transmission Media-
guided media and unguided media .Switching: message, Circuit and packet switched
networks, datagram networks, virtual- circuit networks.
Bandwidth utilization
Sometimes we need to combine several low-bandwidth channels to make use of one channel
with a larger bandwidth. Sometimes we need to expand the bandwidth of a channel to achieve
goals such as privacy and antijamming.
Two broad categories of bandwidth utilization:
• multiplexing
• spreading.
In multiplexing, our goal is efficiency;we combine several channels into one. In spreading,
our goals are privacy and antijamming; we expand the bandwidth of a channel to insert
redundancy, which is necessary to achieve these goals.
Bandwidth utilization is the use of available bandwidth to achieve specific goals.Efficiency
can be achieved by multiplexing;privacy and antijamming can be achieved by spreading.
MULTIPLEXING
Whenever the bandwidth of a medium linking two devices is greater than the bandwidth needs of
the devices, the link can be shared. Multiplexing is the set of techniques that allows the
simultaneous transmission of multiple signals across a single data link.
As data and telecommunications use increases, so does traffic. We can accommodate this increase
by continuing to add individual links each time a new channel is needed; or we can install higher-
bandwidth links and use each to carry multiple signals.
If the bandwidth of a link is greater than the bandwidth needs of the devices connected to it, the
bandwidth is wasted. An efficient system maximizes the utilization of all resources; bandwidth is
one of the most precious resources we have in data communications.
In a multiplexed system, n lines share the bandwidth of one link. Figure 6.1 shows the basic
format of a multiplexed system. The lines on the left direct their transmission streams to a
multiplexer (MUX), which combines them into a single stream (many-to-one).
At the receiving end, that stream is fed into a demultiplexer (DEMUX), which separates the
stream back into its component transmissions (one-to-many) and directs them to their
corresponding lines. In the figure, the word link refers to the physical path. The word channel
refers to the portion of a link that carries a transmission between a given pair of lines. One
link can have many (n) channels.
,There are three basic multiplexing techniques:
• Frequency-division multiplexing,
• Wavelength-division multiplexing
• Time-division multiplexing.
The first two are techniques designed for analog signals, the third, for digital signals.
Frequency-Division Multiplexing
Frequency-division multiplexing (FDM) is an analog technique that can be applied when the
bandwidth of a link (in hertz) is greater than the combined bandwidths of the signals to be
transmitted. In FDM, signals generated by each sending device modulate different carrier
frequencies. These modulated signals are then combined into a single composite signal that
can be transported by the link. Carrier frequencies are separated by sufficient bandwidth to
accommodate the modulated signal. These bandwidth ranges are the channels through which
the various signals travel. Channels can be separated by strips of unused bandwidth-guard
bands-to prevent signals from overlapping. In addition, carrier frequencies must not interfere
with the original data frequencies.
Figure 6.3 gives a conceptual view of FDM. In this illustration, the transmission path is
divided into three parts, each representing a channel that carries one transmission.
,FDM is an analog multiplexing technique that combines analog signals.If a source sends
digital signal it will be converted to analog signal before FDM is used to multiplex them.
Multiplexing Process
Figure 6.4 is a conceptual illustration of the multiplexing process. Each source generates a
signal of a similar frequency range. Inside the multiplexer, these similar signals modulates
different carrier frequencies (f1,f2, and f3). The resulting modulated signals are then
combined into a single composite signal that is sent out over a media link that has enough
bandwidth to accommodate it.
Demultiplexing Process
The demultiplexer uses a series of filters to decompose the multiplexed signal into its constituent
component signals. The individual signals are then passed to a demodulator that separates them
from their carriers and passes them to the output lines. Figure 6.5 is a conceptual illustration of
demultiplexing process.
, Time-Division Multiplexing
Time-division multiplexing (TDM) is a digital process that allows several connections to
share the high bandwidth of a line. Instead of sharing a portion of the bandwidth as in FDM,
time is shared. Each connection occupies a portion of time in the link. Figure 6.12 gives a
conceptual view of TDM. The same link is used as in FDM; here, however, the link is shown
sectioned by time rather than by frequency. In the figure, portions of signals 1,2,3, and 4
occupy the link sequentially.
Figure 6.12 TDM
Note that in Figure 6.12 we are concerned with only multiplexing, not switching. This means that all
the data in a message from source 1 always go to one specific destination, be it 1, 2, 3, or 4. The
delivery is fixed and unvarying, unlike switching.
TDM is a digital multiplexing technique. Digital data from different sources are combined into one
timeshared link. However, this does not mean that the sources cannot produce analog data; analog
data can be sampled, changed to digital data, and then multiplexed by using TDM.
We can divide TDM into two different schemes:
Bandwidth utilization Multiplexing: FDM, TDM, spread spectrum. Transmission Media-
guided media and unguided media .Switching: message, Circuit and packet switched
networks, datagram networks, virtual- circuit networks.
Bandwidth utilization
Sometimes we need to combine several low-bandwidth channels to make use of one channel
with a larger bandwidth. Sometimes we need to expand the bandwidth of a channel to achieve
goals such as privacy and antijamming.
Two broad categories of bandwidth utilization:
• multiplexing
• spreading.
In multiplexing, our goal is efficiency;we combine several channels into one. In spreading,
our goals are privacy and antijamming; we expand the bandwidth of a channel to insert
redundancy, which is necessary to achieve these goals.
Bandwidth utilization is the use of available bandwidth to achieve specific goals.Efficiency
can be achieved by multiplexing;privacy and antijamming can be achieved by spreading.
MULTIPLEXING
Whenever the bandwidth of a medium linking two devices is greater than the bandwidth needs of
the devices, the link can be shared. Multiplexing is the set of techniques that allows the
simultaneous transmission of multiple signals across a single data link.
As data and telecommunications use increases, so does traffic. We can accommodate this increase
by continuing to add individual links each time a new channel is needed; or we can install higher-
bandwidth links and use each to carry multiple signals.
If the bandwidth of a link is greater than the bandwidth needs of the devices connected to it, the
bandwidth is wasted. An efficient system maximizes the utilization of all resources; bandwidth is
one of the most precious resources we have in data communications.
In a multiplexed system, n lines share the bandwidth of one link. Figure 6.1 shows the basic
format of a multiplexed system. The lines on the left direct their transmission streams to a
multiplexer (MUX), which combines them into a single stream (many-to-one).
At the receiving end, that stream is fed into a demultiplexer (DEMUX), which separates the
stream back into its component transmissions (one-to-many) and directs them to their
corresponding lines. In the figure, the word link refers to the physical path. The word channel
refers to the portion of a link that carries a transmission between a given pair of lines. One
link can have many (n) channels.
,There are three basic multiplexing techniques:
• Frequency-division multiplexing,
• Wavelength-division multiplexing
• Time-division multiplexing.
The first two are techniques designed for analog signals, the third, for digital signals.
Frequency-Division Multiplexing
Frequency-division multiplexing (FDM) is an analog technique that can be applied when the
bandwidth of a link (in hertz) is greater than the combined bandwidths of the signals to be
transmitted. In FDM, signals generated by each sending device modulate different carrier
frequencies. These modulated signals are then combined into a single composite signal that
can be transported by the link. Carrier frequencies are separated by sufficient bandwidth to
accommodate the modulated signal. These bandwidth ranges are the channels through which
the various signals travel. Channels can be separated by strips of unused bandwidth-guard
bands-to prevent signals from overlapping. In addition, carrier frequencies must not interfere
with the original data frequencies.
Figure 6.3 gives a conceptual view of FDM. In this illustration, the transmission path is
divided into three parts, each representing a channel that carries one transmission.
,FDM is an analog multiplexing technique that combines analog signals.If a source sends
digital signal it will be converted to analog signal before FDM is used to multiplex them.
Multiplexing Process
Figure 6.4 is a conceptual illustration of the multiplexing process. Each source generates a
signal of a similar frequency range. Inside the multiplexer, these similar signals modulates
different carrier frequencies (f1,f2, and f3). The resulting modulated signals are then
combined into a single composite signal that is sent out over a media link that has enough
bandwidth to accommodate it.
Demultiplexing Process
The demultiplexer uses a series of filters to decompose the multiplexed signal into its constituent
component signals. The individual signals are then passed to a demodulator that separates them
from their carriers and passes them to the output lines. Figure 6.5 is a conceptual illustration of
demultiplexing process.
, Time-Division Multiplexing
Time-division multiplexing (TDM) is a digital process that allows several connections to
share the high bandwidth of a line. Instead of sharing a portion of the bandwidth as in FDM,
time is shared. Each connection occupies a portion of time in the link. Figure 6.12 gives a
conceptual view of TDM. The same link is used as in FDM; here, however, the link is shown
sectioned by time rather than by frequency. In the figure, portions of signals 1,2,3, and 4
occupy the link sequentially.
Figure 6.12 TDM
Note that in Figure 6.12 we are concerned with only multiplexing, not switching. This means that all
the data in a message from source 1 always go to one specific destination, be it 1, 2, 3, or 4. The
delivery is fixed and unvarying, unlike switching.
TDM is a digital multiplexing technique. Digital data from different sources are combined into one
timeshared link. However, this does not mean that the sources cannot produce analog data; analog
data can be sampled, changed to digital data, and then multiplexed by using TDM.
We can divide TDM into two different schemes:
