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1 Perspectives on Lightwave Communications
1.4 Digital Multiplexing Techniques
To handle the continuously rising demand for high-bandwidth services from users
ranging from individuals to large businesses and research organizations, telecom
companies worldwide are implementing increasingly sophisticated digital multiplexing techniques that allow a larger number of independent information streams to
share the same physical transmission channel simultaneously. This section describes
some common electrical digital signal multiplexing techniques [29–32].
1.4.1 Basic Telecom Signal Multiplexing
Table 1.4 gives examples of information rates for some typical telecom services.
To send these services from one user to another, network providers combine the
signals from many different users and send the aggregate signal over a single transmission line. This scheme is known as time-division-multiplexing (TDM) wherein
N independent information streams, each running at a data rate of R b/s, are interleaved electrically into a single information stream operating at a higher rate of N
× R b/s. To get a detailed perspective of this methodology, this section looks at the
multiplexing schemes used in telecommunications.
Early applications of fiber optic transmission links were mainly for large capacity
telephone lines. These digital links consisted of time-division-multiplexed 64-kb/s
voice channels. The multiplexing was developed in the 1960s and is based on what
is known as the plesiochronous digital hierarchy (PDH). Figure 1.8 shows the
digital transmission hierarchies used in the North American and the European-based
telephone networks.
The fundamental building block in the North American network is a 1.544 Mb/s
transmission rate known as a DS1 rate, where DS stands for digital system. It is
formed by time-division-multiplexing twenty-four voice channels, each digitized at
a 64 kb/s rate (which is referred to as DS0). Framing bits, which indicate where an
information unit starts and ends, are added along with these voice channels to yield
the 1.544 Mb/s bit stream. Framing and other control bits that may get added to an
Table 1.4 Examples of
information rates for some
typical services
Type of service
Data rate
Video on demand/interactive video
1.5–6 Mb/s
Video games
1–2 Mb/s
Remote education
1.5–3 Mb/s
Electronic shopping
1.5–6 Mb/s
Data transfer or telecommuting
1–3 Mb/s
Video conferencing
0.384–2 Mb/s
Voice (single phone channel)
33.6–56 kb/s
1 Perspectives on Lightwave Communications
1.4 Digital Multiplexing Techniques
To handle the continuously rising demand for high-bandwidth services from users
ranging from individuals to large businesses and research organizations, telecom
companies worldwide are implementing increasingly sophisticated digital multiplexing techniques that allow a larger number of independent information streams to
share the same physical transmission channel simultaneously. This section describes
some common electrical digital signal multiplexing techniques [29–32].
1.4.1 Basic Telecom Signal Multiplexing
Table 1.4 gives examples of information rates for some typical telecom services.
To send these services from one user to another, network providers combine the
signals from many different users and send the aggregate signal over a single transmission line. This scheme is known as time-division-multiplexing (TDM) wherein
N independent information streams, each running at a data rate of R b/s, are interleaved electrically into a single information stream operating at a higher rate of N
× R b/s. To get a detailed perspective of this methodology, this section looks at the
multiplexing schemes used in telecommunications.
Early applications of fiber optic transmission links were mainly for large capacity
telephone lines. These digital links consisted of time-division-multiplexed 64-kb/s
voice channels. The multiplexing was developed in the 1960s and is based on what
is known as the plesiochronous digital hierarchy (PDH). Figure 1.8 shows the
digital transmission hierarchies used in the North American and the European-based
telephone networks.
The fundamental building block in the North American network is a 1.544 Mb/s
transmission rate known as a DS1 rate, where DS stands for digital system. It is
formed by time-division-multiplexing twenty-four voice channels, each digitized at
a 64 kb/s rate (which is referred to as DS0). Framing bits, which indicate where an
information unit starts and ends, are added along with these voice channels to yield
the 1.544 Mb/s bit stream. Framing and other control bits that may get added to an
Table 1.4 Examples of
information rates for some
typical services
Type of service
Data rate
Video on demand/interactive video
1.5–6 Mb/s
Video games
1–2 Mb/s
Remote education
1.5–3 Mb/s
Electronic shopping
1.5–6 Mb/s
Data transfer or telecommuting
1–3 Mb/s
Video conferencing
0.384–2 Mb/s
Voice (single phone channel)
33.6–56 kb/s