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Questions and Answers
What is the simplest type of communications system composed of?
A transmitter that sends a signal along a channel to a receiver.
Which of the following are examples of communications channels?
Optical fibre is primarily used in access networks.
False
What form does the signal take in copper cables?
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Describe what happens to a signal as it is sent along a communications channel.
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Which type of signal is produced by the microphone in a telephone?
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Mobile communications systems require ____.
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Radio waves are confined to a defined route by cables.
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What is the term used to describe the form in which a message is sent along a communications channel?
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What is the simplest type of communications system?
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All communication channels are the same in terms of their properties and limitations.
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What does LAN stand for in networking?
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What is the public switched telephone network commonly referred to as?
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What is the primary function of the access network?
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What does the core network do?
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What were communication systems primarily built with before optical fibres?
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Optical fibre technology has advantages over copper cable, particularly over long distances.
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What type of radiation do mobile communications systems require?
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Radio waves are a confined medium.
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What happens to a signal when it is sent along a communications channel?
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What is an analogue signal?
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Study Notes
Communications Systems
- A basic communications system consists of a transmitter, a channel, and a receiver.
- The focus is on the physical channel, including optical fiber, copper cable, and radio waves.
- Each medium has unique strengths and limitations.
Access & Core Networks
- Access networks connect local exchanges to subscribers, covering smaller areas.
- Core networks handle long-distance communication between exchanges.
Copper Cables
- Copper cables transmit information as electrical signals.
- They were used extensively in early communication systems.
Optical Fiber
- Optical fiber uses light rays to transmit messages over long distances.
- It has significant advantages over copper cable, particularly for long distances.
- Optical fiber is dominant in the core network, while copper remains crucial in access networks.
Radio Waves
- Mobile communications rely on radio waves, a form of electromagnetic radiation.
- They can propagate through air or space.
- Unlike cables, radio waves spread over wide areas, making them a shared medium.
- This sharing leads to resource allocation issues and security concerns due to easily intercepted signals.
Analog and Digital Signals
- A signal represents the form of a message transmitted through a channel.
- In copper cables, signals are represented by varying electrical voltages.
- In optical fiber and radio, signals are represented by varying electromagnetic waves.
Analog Signals
- Analog signals continuously vary in proportion to the original message.
- Example: A speech signal from a telephone microphone.
Digital Signals
- Digital signals are represented by discrete values, often binary (0 or 1).
- Example: Data signal on a cable connecting a computer to a LAN.
Signal Degradation
- Signals deteriorate during transmission, experiencing attenuation (loss of strength) and distortion (shape changes).
- Digital signals are better at handling degradation because even with distortion, the receiver can easily identify the original signal.
- Digital signals are more robust than analog signals.
Introduction
- A typical communications system is comprised of a transmitter, a channel, and a receiver.
- This text will focus on the properties of optical fiber, copper cable, and radio waves, the main physical channels.
- One example of a communications system is Local Area Network (LAN), which covers a small area, such as a company site.
- The Public Switched Telephone Network (PSTN) is another example, commonly recognized as an ordinary telephone system.
- The physical channel is classified as either access network or core network.
- Access networks serve many users at different locations but only over short distances.
- Core networks primarily serve trunk lines, carrying calls over extended distances between locations.
Analogue and Digital Signals
- An electrical voltage or electromagnetic wave is used to signal the message in communications channels.
- An analogue signal is a continuously varying signal, analogous to the source, such as fluctuating air pressure in speech.
- A digital signal is a discrete, quantized representation of the signal, often used for computer data and communication.
Benefits of Transmitting Digital Signals
- Signals degrade in two ways during transmission: attenuation and distortion.
- Digital signals are better for transmission as they can be regenerated without losing information.
- Attenuation is the decrease of the signal's strength during transmission, which can be compensated for by amplification.
- Distortion occurs when the shape of the signal changes during transmission, introducing errors in the received data.
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Description
This quiz explores the fundamentals of communications systems, including the roles of transmitters, channels, and receivers. It also covers different communication mediums like copper cables, optical fiber, and radio waves, highlighting their strengths and limitations in various network types.
