1.4 Digital Multiplexing Techniques
15
E1 Mux
to
2.048 Mb/s
Four
2.048 Mb/s
inputs
Thirty
64 kb/s
inputs
Four
34.368 Mb/s
inputs
139.264 Mb/s
Four
8.44 Mb/s
inputs
E3 Mux
to
34.368 Mb/s
E2 Mux
to
8.44 Mb/s
E4 Mux
to
139.264 Mb/s
(a)
(b)
Fig. 1.8 Digital transmission hierarchies used in the a North American and b European-based
telephone networks
information unit in a digital stream are called overhead bits. At any multiplexing
level a signal at the designated input rate is combined with other input signals at the
same rate.
In describing North American telephone network data rates, one sees terms such
as T 1, T 3, and so on. Often the terms Tx and DSx (e.g., T 1 and DS1 or T 3 and DS3)
are used interchangeably. However, there is a subtle difference in their meaning.
Designations such as DS1, DS2, and DS3 refer to a service type; for example, a
user who wants to send information at a 1.544 Mb/s rate would subscribe to a DS1
service. Abbreviations such as T 1, T 2, and T 3 refer to the data rate the transmission
line technology uses to deliver that service over a physical link. For example, the
DS1 service is transported over a physical wire or optical fiber using electrical or
optical pulses sent at a T 1 = 1.544 Mb/s rate.
Telephone networks in other countries use either European- or Japanese-based
multiplexing hierarchies. Similar to the North American hierarchies, basic 64 kb/s
channels are combined but at different multiplexed bit-rate levels as shown in
Table 1.5. Most countries outside of North America and Japan (such as in Europe,
South and Central America, Africa, Australia, and most of Asia) use the Europeanbased multiplexing hierarchy labeled by E1, E2, E3, and so on. Figure 1.8b shows
the number of channels multiplexed at each bit-rate level up to E4. For example,
multiplexing thirty 64 kb/s channels and adding required overhead bits results in a
2.048 Mb/s E1 rate.
15
E1 Mux
to
2.048 Mb/s
Four
2.048 Mb/s
inputs
Thirty
64 kb/s
inputs
Four
34.368 Mb/s
inputs
139.264 Mb/s
Four
8.44 Mb/s
inputs
E3 Mux
to
34.368 Mb/s
E2 Mux
to
8.44 Mb/s
E4 Mux
to
139.264 Mb/s
(a)
(b)
Fig. 1.8 Digital transmission hierarchies used in the a North American and b European-based
telephone networks
information unit in a digital stream are called overhead bits. At any multiplexing
level a signal at the designated input rate is combined with other input signals at the
same rate.
In describing North American telephone network data rates, one sees terms such
as T 1, T 3, and so on. Often the terms Tx and DSx (e.g., T 1 and DS1 or T 3 and DS3)
are used interchangeably. However, there is a subtle difference in their meaning.
Designations such as DS1, DS2, and DS3 refer to a service type; for example, a
user who wants to send information at a 1.544 Mb/s rate would subscribe to a DS1
service. Abbreviations such as T 1, T 2, and T 3 refer to the data rate the transmission
line technology uses to deliver that service over a physical link. For example, the
DS1 service is transported over a physical wire or optical fiber using electrical or
optical pulses sent at a T 1 = 1.544 Mb/s rate.
Telephone networks in other countries use either European- or Japanese-based
multiplexing hierarchies. Similar to the North American hierarchies, basic 64 kb/s
channels are combined but at different multiplexed bit-rate levels as shown in
Table 1.5. Most countries outside of North America and Japan (such as in Europe,
South and Central America, Africa, Australia, and most of Asia) use the Europeanbased multiplexing hierarchy labeled by E1, E2, E3, and so on. Figure 1.8b shows
the number of channels multiplexed at each bit-rate level up to E4. For example,
multiplexing thirty 64 kb/s channels and adding required overhead bits results in a
2.048 Mb/s E1 rate.