COMP 1030: Computer Networks Lecture 1

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Questions and Answers

What is the fundamental purpose of a communications system?

The fundamental purpose of a communications system is the exchange of data between two parties.

How does a Local Area Network (LAN) differ from a Wide Area Network (WAN)?

A LAN spans a single building or campus, while a WAN connects sites in multiple cities, countries, or continents.

What are the characteristics that differentiate local and wide area networks?

Characteristics include speed, management, security, reliability, and billing.

What is the role of TCP/IP in the development of the Internet?

<p>TCP/IP protocols standardized communication and enabled interoperability between different systems on the Internet.</p> Signup and view all the answers

Identify and explain the two main categories of transmission media.

<p>The two main categories are guided media, which direct electromagnetic waves along a physical path, and unguided media, which do not.</p> Signup and view all the answers

What technology does a Metropolitan Area Network (MAN) often rely on?

<p>A MAN often relies on cable TV infrastructure for connectivity.</p> Signup and view all the answers

Explain the significance of the ARPANET in relation to the Internet.

<p>ARPANET was the first operational packet network that laid the groundwork for the development of the Internet.</p> Signup and view all the answers

What does ‘heterogeneity’ refer to in the context of computer networks?

<p>Heterogeneity refers to the presence of various types of devices and technologies within a network alongside standardization.</p> Signup and view all the answers

What is a key difference between guided and unguided media?

<p>Guided media uses physical mediums like wires or fibers to transmit signals, while unguided media transmits signals through the air without a physical path.</p> Signup and view all the answers

Define simplex communication and provide an example.

<p>Simplex communication allows signals to be transmitted in only one direction. An example is a television broadcast.</p> Signup and view all the answers

What are analog signals and provide one characteristic?

<p>Analog signals are continuously varying electromagnetic waves. They exhibit no breaks or discontinuities in the signal.</p> Signup and view all the answers

Explain the relationship between bandwidth and data rate.

<p>The greater the bandwidth, the higher the information-carrying capacity, resulting in an increased data rate.</p> Signup and view all the answers

What is the primary concern regarding data in digital transmission?

<p>In digital transmission, ensuring the integrity of the data against attenuation is critical.</p> Signup and view all the answers

What does the term 'signal-to-noise ratio' (SNR) represent?

<p>The signal-to-noise ratio (SNR) represents the ratio of the power of a signal to the power of the noise present at a specific point in transmission.</p> Signup and view all the answers

Describe half duplex communication with an example.

<p>Half duplex communication allows both stations to transmit, but only one at a time. An example is a police radio system.</p> Signup and view all the answers

What is the formula for Nyquist Bandwidth for binary signals?

<p>For binary signals, the Nyquist Bandwidth formula is $C = 2B$, where $C$ is the channel capacity and $B$ is the bandwidth.</p> Signup and view all the answers

Explain the impact of noise on digital signals.

<p>Noise can cause errors in digital signals by distorting the received data, leading to a mismatch between transmitted and received values.</p> Signup and view all the answers

What does the formula for Shannon capacity indicate?

<p>The Shannon capacity formula $C = B log_2(1 + SNR)$ indicates the theoretical maximum data rate achievable over a communication channel.</p> Signup and view all the answers

What is the significance of using digital signals for digital data?

<p>Using digital signals for digital data is significant because equipment for encoding is generally less expensive than for analog signals.</p> Signup and view all the answers

How does attenuation affect analog and digital transmission differently?

<p>In analog transmission, attenuation limits the length of the transmission link, whereas in digital transmission, it endangers data integrity due to possible data loss.</p> Signup and view all the answers

What function do repeaters serve in digital transmission?

<p>Repeaters in digital transmission recover the signal and retransmit it to achieve greater distance without significant loss of data integrity.</p> Signup and view all the answers

What type of signals do optical fibers propagate?

<p>Optical fibers primarily propagate analog signals but are capable of transmitting both analog and digital data.</p> Signup and view all the answers

Flashcards

Computer Network

A collection of interconnected, autonomous computer systems that communicate with one another to share resources like hardware and software.

Data Communications

Focuses on how to transmit signals efficiently and reliably.

Networking

It deals with the structure and technology behind communication networks connecting devices.

Local Area Network (LAN)

A network that covers a small geographical area, typically within a building or campus.

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Metropolitan Area Network (MAN)

A network that spans a city, connecting different locations within that city.

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Wide Area Network (WAN)

A network spanning large geographical areas, connecting sites across cities, countries, or continents.

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Internet

A network that connects millions of computers globally, allowing communication and data sharing.

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Transmission Media

The physical medium through which data travels, categorized as either guided or unguided.

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Guided Media

Guided media, such as twisted pair, coaxial cable, and optical fiber, physically confine the signal, directing its propagation along a specific path.

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Unguided Media

Unguided media, also known as wireless, transmit signals through the air, vacuum, or water, without a physical conduit.

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Simplex Transmission

A communication mode where data flows in one direction only, from the transmitter to the receiver. Like a television broadcast, the signal only travels from the station to your TV.

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Half-Duplex Transmission

A communication mode where data can be transmitted in both directions, but only one device can transmit at a time. A classic example is a police radio; only one officer can speak at a time.

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Full-Duplex Transmission

A communication mode where data travels in both directions simultaneously. Think about a telephone conversation; you can talk and listen at the same time.

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Analog Signal

An analog signal is a continuous wave that smoothly fluctuates in amplitude over time. Think of a sound wave, which changes continuously to represent the different pitch and volume of music.

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Digital Signal

A digital signal represents information as a sequence of discrete voltage levels. Imagine a light switch, which is either on or off, representing 1 or 0.

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Data Rate

The rate at which data can be communicated over a channel, measured in bits per second (bps).

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Bandwidth

The range of frequencies within a signal, measured in Hertz (Hz). It's the bandwidth of the signal that allows it to carry data.

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Noise

Interfering signals that degrade the quality of data transmission. It's like static on a radio.

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Error Rate

The rate at which errors occur during transmission. For example, receiving a 1 instead of a 0, or vice versa.

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Frequency

The rate at which a signal repeats itself, measured in cycles per second or Hertz (Hz).

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Wavelength

The distance occupied by a single cycle of a wave, measured in meters or other units of distance.

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Peak Amplitude

The maximum value or strength of a signal over time, typically measured in volts.

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Relationship between Data Rate and Bandwidth

The greater the bandwidth, the higher the information-carrying capacity of the medium. Think of a wider road allowing for more cars to pass.

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Study Notes

Course Information

  • Course Title: Systems and Architecture (COMP 1030)
  • Topic: Computer Networks
  • Lecture: 1 (B)
  • Lecturer: KR. SELVARAJ

Computer Networks and Communications

  • Computer networks are an interconnection of autonomous computers.
  • Networks consist of independent computer systems that communicate to share hardware and software resources.
  • Data communications deals with reliable and efficient signal transmission.
  • Networking covers the technology and architecture of communication networks to connect devices.

A Communications Model

  • The fundamental purpose of a communication system is data exchange between two parties.
  • Components include Source, Transmitter, Transmission System, Receiver, and Destination.
  • Diagramatic representations illustrate the model and its components.

Data Communications Model

  • A data communications model outlines the process from input information to output information.
  • This model includes input information, input data (g(t)), transmitted signal (s(t)), received signal (r(t)), output data (g’(t)), and output information (m’).
  • The model illustrates the flow of data, including signal types (digital/analog).

Types of Networks

  • Local Area Network (LAN)

    • Spans a single building or campus.

  • Metropolitan Area Network (MAN)

    • Spans a single city.

  • Wide Area Network (WAN)

    • Spans multiple cities, countries, or continents.

  • Internet

    • Global network of networks.

Local Area Networks (LANs)

  • Can be wireless or wired.
  • Wireless LANs use standards like 802.11.
  • Wired LANs use network connections.

Metropolitan Area Networks (MANs)

  • A metropolitan area network based on cable TV is discussed.

Wide Area Networks (WANs)

  • A WAN connecting three branch offices in Australia is shown.

Internet Elements

  • Evolved from ARPANET.
  • The first operational packet network.
  • Applied to tactical radio and satellite networks.
  • Standardized TCP/IP protocols.

Differences between LANs and WANs

  • Speed (bit rate/baud rate)
  • Management
  • Security
  • Reliability
  • Billing
  • Heterogeneity (and standards)

Transmission Media

  • Transmission media can be guided or unguided.
    • Guided media guides waves along a path (e.g., twisted pair, coaxial cable, optical fiber).
    • Unguided media (wireless) do not guide waves (e.g., air, vacuum, seawater).

Guided and Unguided Media Characteristics

  • Media and signal characteristics determine quality.
  • Unguided media prioritize bandwidth produced by antennas.
  • Guided media prioritize medium properties.
  • Key concerns are data rate and distance.

Transmission Terminology

  • Simplex: One-way signal transmission (e.g., television).
  • Half-duplex: Two-way transmission, but only one direction at a time (e.g., police radio).
  • Full-duplex: Two-way transmission simultaneously (e.g., telephone).

Signals

  • Analog signals, have continuously varying intensity over time.
  • Digital signals have constant intensity levels changing between levels.

Analog and Digital Data Transmission

  • Analog signals are waves with continuously varying amplitude.
  • Digital signals are represented by voltage pulses.
  • Data rate: Speed of data communication (bps).
  • Bandwidth: Frequency range of transmitted signal (Hertz).
  • Noise: Average noise level.
  • Error rate: Rate of errors in transmission.
  • Frequency (f): Cycles per second (Hertz).
  • Wavelength (λ): Distance of a single signal cycle.

Time-Domain Concepts

  • Peak amplitude (A)
  • Frequency (f)
  • Period (T)
  • Phase (Φ)
  • Wavelength (λ)

Analog and Digital Data Transmission Diagrams

  • Illustrates sine waves and square waves.

Relationship between Data Rate and Bandwidth

  • Higher bandwidth equates to higher information carrying capacity.
  • Digital waveforms have theoretically infinite bandwidth, but transmission systems have limits.
  • Higher transmitted bandwidth increases cost.

Attenuation of Digital Signals

  • Digital signals lose strength over distance, a concept known as attenuation.
  • Attenuation is graphically represented.

Examples of Analog and Digital Data

  • Analog examples include video and audio.
  • Digital examples include text and integers.

Analog Signals

  • Continuous electromagnetic wave propagating over different media (frequency dependent).
  • Media Examples: Copper wire (twisted pair and coaxial cable), fiber optic cables, atmosphere/space propagation.

Digital Signals

  • Sequence of voltage pulses.
  • Generally cheaper than analog signaling.
  • Less susceptible to noise interference.
  • Suffers more from attenuation than analog signals.
  • Can propagate analog and digital data.

Reasons for Choosing Data and Signal Combinations

  • Digital data with digital signals - less expensive equipment.
  • Analog data with digital signals - permits use of modern equipment.
  • Digital data with analog signals - some mediums only support analog signals (e.g., optical fiber, satellite).
  • Analog data with analog signals - analog data is easily converted.

Analog and Digital Signaling

  • Diagramatic examples demonstrating analog-to-analog, analog-to-digital, digital-to-analog, and digital-to-digital conversions.

Analog Transmission

  • Transmits analog signals without regard to content.
  • Attenuation limits transmission distances.
  • Cascadable amplifiers increase signal strength but can cause distortion.
  • Analog signals can tolerate distortion, while digital signals cannot.

Digital Transmission

  • Concerns signal content.
  • Attenuation affects signal integrity.
  • Repeaters extend signal distance.
  • Devices recover digital data from analog signals and generate new, clear signals.

Effect of Noise on Digital Signal

  • Noise interferes with signals in transmission.
  • Noise can cause errors in received data.

Nyquist Bandwidth

  • For binary signals with two voltage levels, bandwidth (B) is half the data rate (C).
  • With multilevel signaling, bandwidth is dependent on the number of discrete signal levels (M).

Signal-to-Noise Ratio (SNR)

  • Ratio of signal power to noise power.
  • High SNR means low noise and higher data transmission quality, and vice-versa.
  • SNR limits achievable data rates in transmission.

Shannon Capacity Formula

  • Represents the theoretical maximum data rate achievable.
  • Formula assumes white noise, not factors like attenuation distortion or delay distortion.

References

  • "Computer Networks and Internets" by Douglas E. Comer, Prentice Hall, 3rd edition.

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