Introduction to Data Communications
10. Brief History of Networking

31a. FDM - Channel Groups

Telecommunications FDM is based on channel groups. The basic channel is called the Voice Channel and it has a bandwidth of 0-4 kHz. The channel groups are based on multiples of the voice channel:

Multiplex Level

Voice Circuits

Freq Band
(kHz)

BW
(kHz)

Voice Channel

1

0 - 4

4

Group

12

60 - 108

48

Supergroup

60

312 - 552

240

Mastergroup

600

564 - 3,084

2520

Jumbogroup

3600

564 - 17,548

16984

  • The Mastergroup and Jumbogroup have guard-bands added to the bandwidth.

  • A Group is made of 12 Voice Channels.

  • A Supergroup (60 Voice channels) is made of 5 Groups (12 Voice Channels).

  • A Mastergroup (600 Voice Channels) is made of 10 Supergroups (60 Voice Channels).

  • A Jumbogroup (3600 Voice Channels) is made of 6 Mastergroups (600 Voice Channels).

31b. TDM - T1 Carrier System

Telecommunications TDM is based on the T1 Carrier System. It is a digital system that digitizes the analog Voice Channel into 8 bit data. This means that there are 28 or 256 levels that the 8 bit data can represent.


 
 
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