Lecture-2 Data Transmission via Signals

Lecture-2: Data Transmission via Signals in Networking

Lecture Information

• Course: Systems Technology (ITEC10281)

• Office Hour: Mondays 1 pm to 2 pm in MAE-322

Lecture Outline

Part I: Fundamentals of Data Transmission

• Data transmission via signals

• Analogue signals and their properties

  • Amplitude

  • Frequency

  • Phase

• Digital signals and their properties

  • Bit interval

  • Bit rate

  • Baud rate

Part II: Key Concepts

• Analogue vs. Digital signals

• Modulation

• Multiplexing

• Common flaws in data transmission

Part I: Analogue and Digital Signals

Basic Terms in Data Transmission

1. Transmit

   • Issuing of signals along a network medium.

2. Transmission

   • Process of transmitting signals.

   • Signal is processed after transmitting from the signal tower.

3. Transceiver

   • A device with transmitting and receiving signals capability at the same time.

Transmission of Data via Signals

• Data is transmitted based on the representation of 0s and 1s as signals.

  • Properties of a signal (either electrical or radio) that can be varied include:

  • Amplitude

  • Frequency

  • Phase

Types of Signal in Networking

• Signalling is an important characteristic for data transmission (sending data via medium):

  • Analogue signal

  • Digital signal

Analogue Signals

• Defined as continuous wave form signals that change smoothly over time.

• Amplitude: Strength of analogue signal, measured in volts (V).

  • Example: Amplitude changes from 10V to 5V over time.

• Frequency: Measured in hertz (Hz), indicates the number of signal cycles within one second.

• Wavelength: Measured in meters, it is the distance travelled in one signal cycle.

Digital Signals

• Defined as discrete wave form signals with a limited number of amplitude values.

• Characteristics:

  • Digital signals provide easy representation of binary values.

  • Positive voltage typically represents 1.

  • Zero voltage typically represents 0.

• Properties of Digital Signals:

  • Amplitude: Strength of the signal with limited well-defined voltage states.

  • Example: A digital signal may range from 5V to -5V.

  • Period: Time taken by a signal in one complete cycle.

Properties of Digital Signals - Detailed Definitions

1. Bit Interval: Time taken to represent 1 bit.

2. Bit Rate: Total number of bits transmitted in 1 second.

3. Baud Rate: Number of signal units transmitted per second.

   • Formula: $Bit ext{ Rate} = Baud ext{ Rate} imes ext{ Number of bits per baud}$

Part II: Modulation and Multiplexing

Throughput and Bandwidth - Network Parameters

1. Throughput: The quantity of data successfully transmitted over a network in a certain time period.

2. Capacity or Bandwidth (for Digital Communication): Defined as the quantity of bits transmitted per second (bits/sec).

3. Bandwidth (for Analogue Communication):

   • Determined by the difference between the highest and lowest frequencies that a transmission medium can transmit.

   • Range measured in Hertz (Hz).

Analogue vs. Digital Signals

• Benefits of Analogue Signals:

  • Can represent more amplitude values.

  • Can carry more data with less energy.

• Drawbacks of Analogue Signals:

  • Susceptibility to transmission flaws such as noise and interference.

  • Difficulty or inability to regenerate erroneous signals.

Modulation of Analogue Signals

• Refers to modifying any characteristics (amplitude, frequency, phase) of an analogue (carrier) signal to represent digital signals (information).

  • Types of modulation include:

  • Amplitude Shift Keying (ASK)

  • Frequency Shift Keying (FSK)

  • Phase Shift Keying (PSK)

• Modem: Device that performs modulation and demodulation tasks.

Types of Modulation

1. ASK (Amplitude Shift Keying)

   • For digital representations of 0s and 1s through amplitude changes of a signal.
     ![ASK Example](data:image/png;base64,
     [Encoded image of ASK graph])

2. FSK (Frequency Shift Keying)

   • Utilizes frequency variations to encode binary data.
     ![FSK Example](data:image/png;base64,
     [Encoded image of FSK graph])

3. PSK (Phase Shift Keying)

   • Changes in the phase of the signal convey the digital data.
     ![PSK Example](data:image/png;base64,
     [Encoded image of PSK graph])

Multiplexing

• The practice of combining multiple signals for simultaneous transmission over a single channel.

  • Reasons for Multiplexing:

  • Efficient channel sharing through methods like TDM (Time Division Multiplexing) and FDM (Frequency Division Multiplexing).

  • Components:

  • Multiplexer: Combines multiple signals into one.

  • Demultiplexer: Separates combined signals back into their original states.

Types of Multiplexing

1. Time Division Multiplexing (TDM):

   • Divides channel into multiple time intervals.

   • Common usage in voice communication.
     ![TDM Example](data:image/png;base64,
     [Encoded image of TDM graph])

2. Frequency Division Multiplexing (FDM):

   • Divides the channel into multiple sub-channels using different frequency bands for each.

   • Common applications include cellular transmission and Internet access.
     ![FDM Example](data:image/png;base64,
     [Encoded image of FDM graph])

3. Wavelength Division Multiplexing (WDM):

   • Multiple colors of light are transmitted over a single fiber-optic connection.

   • Dense WDM (DWDM) provides extraordinary capacity in modern fiber-optic networks.

Modes of Transmission in Networking

1. Simplex: Uni-directional signal transmission with a fixed sender or receiver.

2. Half-Duplex: Signals can be transmitted in both directions but only one at a time over a single communication channel.

3. Full-Duplex: Signals are transmitted in both directions simultaneously.

Transmission Flaws in Networking

• Factors affecting network transmissions include:

  1. Noise: Electro-magnetic interference from the environment, such as heat.

  2. Attenuation: Loss of signal strength as it travels away from the source.

  • Mitigation strategies:

    • Amplification: Analogue signals processed through an amplifier.

    • Regeneration: Digital signals transmitted in original form.

  1. Latency: Delay between signal transmission and receipt, affected by cable length or intervening devices.

  • Depends on the propagation speed of the signal.

Summary

• The transmission of data relies on analogue or digital signals.

• Analogue and digital signals permit the representation of 0s and 1s, which are foundational for computing.

• Connections can be categorized into simplex, duplex, and full-duplex types, influencing data flow.

• Multiplexing enhances efficiency via channel sharing.

• Transmission media suffers from various flaws that need to be managed effectively with the right technology.