Frequency

Medium Access Control Sublayer

In any broadcast network, the key issue is how to determine who gets to use the channel when there is competition for it. To make this point clearer, consider a conference call in which six people, on six different telephones, are all connected so that each one can hear and talk to all the others. [...]

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Cunife Telephone Transmission Line

For decades prior to 1984, the Bell System provided both local and long distance service throughout most of the United States. In the 1970s, the U.S. Federal Government came to believe that this was an illegal monopoly and sued to break it up. The government won, and on January 1, 1984, AT&T was broken up [...]

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Geostationary Satellites

In 1945, the science fiction writer Arthur C. Clarke calculated that a satellite at an altitude of 35,800 km in a circular equatorial orbit would appear to remain motionless in the sky. so it would not need to be tracked (Clarke, 1945). He went on to describe a complete communication system that used these (manned) [...]

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Ethernet

Both the Internet and ATM were designed for wide area networking. However, many companies, universities, and other organizations have large numbers of computers that must be connected. This need gave rise to the local area network. In this section we will say a little bit about the most popular LAN, Ethernet.The story starts out in [...]

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A Message is a Communication between the Client and Server

A service primitives is formally specified by a set of primitives (operations) available to a user process to access the service. These primitives tell the service to perform some action or report on an action taken by a peer entity. If the protocol stack is located in the operating system, as it often is, the [...]

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Light Activated SCR

Like bipolar transistors, SCRs and TRIACs are also manufactured as light-sensitive devices, the action of impinging light replacing the function of triggering voltage. Optically-controlled SCRs are often known by the acronym LASCR, or Light Activated SCR. Its symbol, not surprisingly, looks like this: Optically-controlled TRIACs don’t receive the honor of having their own acronym, but [...]

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Shockley Diode

Our exploration of thyristors begins with a device called the four layer diode, also known as a PNPN diode, or a Shockley diode after its inventor, William Shockley. This is not to be confused with a Schottky diode, that two-layer metal-semiconductor device known for its high switching speed. A crude illustration of the Shockley diode, [...]

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Transistor Saturation

The term saturation is applied to any system where levels have reached their maximum values. A saturated sponge is one that cannot hold another drop of liquid. For a transistor operating in the saturation region, the current is a maximum value for the particular design. Change the design and the corresponding saturation level may rise [...]

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Organic Light Emitting Diodes

The increasing use of digital displays in calculators, watches, and all forms of instrumentation has contributed to the current extensive interest in structures that will emit light when properly biased. The two types in common use today to perform this function are the light-emitting diode (LED) and the liquid crystal display (LCD). Since the LED [...]

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