Digital switching

The ideal rectifier or diode is a two-terrninal device that allows current flow in only one direction. The transistor is a three-terminal device in which current flow through two terminals is controlled by the third. Transistors can be used as analogue amplifiers or digital switches. 

Fig. 20 The digital-switching multiplier is the simplest form of the phase-sensitive detector [36].

The signal and reference channels are mixed within the actual PSD unit. There are currently three common methods of implementing a PSD, i.e. using an analogue multiplier, a digital switch or a digital multiplier ... 

Clearly, the transistor could be used to replace the vacuum tubes used in amplifiers in the telephone network. Also, a rethinking of the switching function in the telephone central offices made possible a new device, the digital switch, and, in later years, the Internet and packet switching. 

Certainly the transistor, the integrated circuit, and the technology of digital switching were of immense value to the telecommunications industry. Of equal importance, however, was the change that took place in the use of the network itself. 

Access The portion of the network that connects end user terminals, such as telephones, to the service element, such as a digital switch. 

Trunk A trunk is a connection between service elements, such as digital switches. 

Only digital switches are now used for cellular service. This has been the case practically since the introduction of cellular service in the U.S. although there were a few switches initially that were based on an analog, electronic switch design. Digital switching, however, does not necessarily mean digital radio transmission in the cellular system. It simply refers to the manner in which calls are processed by the switch. 

In most digital switches, the number of ports are configured in multiples of 24 in order to accommodate aDSl -rate input or output channel Not aU of the channels maybe activated in any single DSL As shown in Fig. 16.65, some of the ports are connected to the cell sites by the MSC-ceU site Hnks, others are connected to the PSTN or other networks, whereas stiU others provide links between MSCs themselves. 

TADSS Tactical Automatic Digital Switching System... 

Digital switch line card. (Courtesy of AG Communication Systems. DuPont Application Note Reference H-84330.)... 

IR bolometers Mixers and receivers Digital switching Telecommunication... 

Analogue level sensors are preferred to digital (switched) sensors. 

See the detailed studies by Fransman (1992, 1995) on the Japanese telecommunications industry. For instance, Japanese telecom early adopted digital switching technology and Japan was the first country to introduce mobile cellular telephony, see chapter 4. Only the facsimile machine was an international success led by Japan. 

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