CMPG 315 Les 2 OUtcomes

What is Transmission media?

Transmission media are the physical or wireless paths used to carry data signals from one device to another.

What are the two main categories:

1. Guided transmission media

2. Wireless / unguided transmission media

What does Guided Transmission Media use to guide the signal?

Guided media use a physical path to guide the signal.

Examples of Guided Transmission Media.

Examples include:

• Twisted pair cable

• Coaxial cable

• Fibre optic cable

• Power lines

• Magnetic/persistent storage

What is Twisted Pair Cable?

Twisted pair cable consists of pairs of copper wires twisted around each other.

The twisting helps reduce electromagnetic interference and crosstalk between wires.

Name the advantages and disadvantages of Twisted Pair cable.

Advantages

• Cheap

• Easy to install

• Commonly used in LANs

• Flexible

Disadvantages

• Affected by electromagnetic interference

• Lower bandwidth than fibre

• Shorter transmission distance than fibre

Explain the structure of a coaxial cable and discuss why it provides better protection against electromagnetic interference compared to twisted pair cable.

Coaxial cable has a central copper conductor surrounded by insulation and shielding.

The shielding protects the signal from interference better than twisted pair.

Name the advantages and disadvantages of Coaxial Cable.

Advantages

• Better shielding than twisted pair

• Higher bandwidth than basic twisted pair

• Useful for cable TV and broadband

Disadvantages

• Bulkier than twisted pair

• Less flexible

• Less common in modern LANs

Example

Cable TV and cable Internet connections.

Describe how fibre optic cables transmit data and identify the two main types of fibre optic cable used in networking.

Fibre optic cable transmits data as light pulses through glass or plastic fibres.

There are two important types:

• Multi-mode fibre

• Single-mode fibre

Discuss the characteristics of multi-mode fibre optic cable and evaluate its advantages and disadvantages in network communication.

Multi-Mode Fibre

Multi-mode fibre allows light to travel along multiple paths.

Advantages

• Cheaper than single-mode fibre

• Good for shorter distances

• Easier to install

Disadvantages

• More distortion/dispersion

• Shorter range

Lower performance over long distances

Explain the operation of single-mode fibre optic cable and analyse its advantages and disadvantages for use in modern communication networks.

Single-Mode Fibre

Single-mode fibre allows light to travel along one main path.

Advantages

• Very high bandwidth

• Very long distance

• Low attenuation

• Excellent for backbone networks

Disadvantages

• More expensive

• More difficult to install

• Requires precise equipment

Discuss the use of power lines as a transmission medium for data communication and explain the advantages and disadvantages associated with this technology.

D. Power Lines

Power lines can be used to transmit data through existing electrical wiring.

Advantages

• Uses existing infrastructure

• Useful where new cables are difficult to install

Disadvantages

• Noisy medium

• Interference from electrical devices

• Performance can be unreliable

Explain the concept of magnetic or persistent storage as a data transmission method and discuss its advantages and disadvantages in comparison to real-time communication media.

E. Magnetic / Persistent Storage

Data can be stored on physical media and physically transported.

Advantages

• Very high bulk data transfer

• Cheap for massive data movement

Disadvantages

• Very high delay/latency

• Not useful for real-time communication

Define wireless transmission media and identify the different types of wireless technologies used for data communication.

Wireless media transmit data using electromagnetic waves through air or space.

Examples include:

• Radio waves

• Microwaves

• Infrared

• Light / laser transmission

• Satellites

Explain how radio transmission is used in wireless communication and evaluate its advantages and disadvantages in data networking.

Radio Transmission

Radio waves are used for long-distance wireless communication.

Advantages

• Can travel long distances

• Can pass through buildings

• Useful for broadcasting and mobile communication

Disadvantages

• Interference

• Less secure because signals spread widely

• Spectrum must be regulated

Explain the principle of microwave transmission in wireless communication and critically evaluate its advantages and limitations in modern networking systems.

Microwave Transmission

Microwaves are high-frequency waves that usually travel in straight lines.

Advantages

• High bandwidth

• Good for point-to-point links

• Used in cellular and satellite communication

Disadvantages

• Needs line of sight

• Affected by weather and obstacles

• Requires towers or antennas

Describe how infrared transmission is used in wireless communication and assess its advantages and limitations in short-range networking applications, using appropriate examples.

Infrared Transmission

Infrared is used for short-range communication.

Advantages

• Cheap

• Directional

• Does not pass through walls, so less interference between rooms

Disadvantages

• Short range

• Cannot pass through solid objects

• Limited use in networking

Example

TV remote controls.

Explain the principle of laser (light-based) transmission in wireless communication and critically evaluate its advantages and disadvantages in high-speed data networking environments.

Light / Laser Transmission

Laser transmission uses light beams through open air.

Advantages

• Very high bandwidth

• Secure because the beam is narrow

• No radio licence needed

Disadvantages

• Must be aimed accurately

• Affected by fog, rain, heat, and obstacles

Usually needs line of sight

Comparison Table

Medium	Type	Main Advantage	Main Disadvantage	Best Use
Twisted pair	Guided	Cheap and common	EMI and shorter range	LANs
Coaxial cable	Guided	Better shielding	Bulky	Cable TV/Internet
Multi-mode fibre	Guided	Good speed, cheaper fibre	Shorter distance	Buildings/campuses
Single-mode fibre	Guided	Long distance, high bandwidth	Expensive	Backbones
Power lines	Guided	Existing wiring	Noisy	Home networking fallback
Radio	Wireless	Long range	Interference	Broadcasting/mobile
Microwave	Wireless	High bandwidth	Needs line of sight	Point-to-point/cellular
Infrared	Wireless	Cheap and secure in room	Cannot pass walls	Remote controls
Laser/light	Wireless	High bandwidth	Weather/aiming issues	Building-to-building links

When signals travel through a transmission medium, they do not remain perfect. Two major problems are:

1. Attenuation

2. Distortion

Define attenuation in data communication and explain how it affects signal transmission in networking systems, using a simple real-world analogy.

Attenuation means the loss of signal strength over distance or time.

As a signal travels, some of its energy is lost.

Simple Explanation

If you shout across a field, your voice becomes weaker the farther it travels. A data signal behaves similarly.

Explain the main causes of attenuation in data communication and analyse how each factor contributes to signal loss across different transmission media.

Causes of Attenuation

• Long transmission distance

• Resistance in copper cables

• Absorption or scattering in fibre

• Obstacles in wireless transmission

• Weather conditions

Poor-quality medium

Explain why attenuation is a critical issue in data communication systems and discuss its impact on signal integrity and accurate data interpretation at the receiver.

Why Attenuation Matters

If the signal becomes too weak, the receiver may not be able to correctly identify the bits.

For example:

• A strong signal may clearly represent a 1.

• After attenuation, it may become too weak and be confused with a 0.

Discuss the methods used to reduce attenuation in data communication systems and explain how each technique improves signal quality and transmission reliability.

How Attenuation Can Be Reduced

• Use repeaters or amplifiers

• Use better-quality media

• Use fibre instead of copper for long distances

• Reduce transmission distance

• Increase signal strength, within legal and technical limits

Define distortion in data communication and explain how it differs from attenuation, using a simple analogy to illustrate the concept.

Distortion means the change in the shape of a signal.

A signal may arrive looking different from how it was sent.

Simple Explanation

If attenuation is the signal getting quieter, distortion is the signal getting “bent out of shape.”

Explain the causes of signal distortion in data communication systems and analyse how each factor affects the integrity of transmitted signals across different media.

Causes of Distortion

• Different frequencies being weakened by different amounts

• Limited bandwidth

• Interference

• Noise

• Dispersion in fibre

• Multipath propagation in wireless transmission

Explain why signal distortion is a significant problem in digital communication systems and discuss its effect on data accuracy and bit interpretation at the receiver.

Why Distortion Matters

Digital signals depend on clear differences between 1s and 0s. If the signal shape changes too much, the receiver may decode the wrong bits

Compare attenuation, distortion, and noise/interference in data communication systems, clearly explaining how each affects signal transmission and reception.

Attenuation vs Distortion

Concept	Meaning	Main Problem
Attenuation	Signal becomes weaker	Receiver may not detect it
Distortion	Signal changes shape	Receiver may misread it
Noise/interference	Extra unwanted signal is added	Signal becomes corrupted

Define Modulation.

Modulation is the process of converting bits into signals and signals back into bits.

Computers use digital data, but transmission media carry physical signals such as voltage, current, light, or electromagnetic waves.

There are two main types:

1. Baseband modulation

2. Passband modulation

Explain baseband modulation in data communication systems and discuss how it is implemented using line coding in guided transmission media.

1. Baseband Modulation

Baseband transmission sends signals directly over the medium, starting from 0 up to a maximum frequency.

Baseband is mainly used in guided media such as cables.

Baseband modulation uses line coding.

Describe NRZ (Non-Return to Zero) line coding and evaluate its advantages and disadvantages in digital baseband transmission, particularly in relation to synchronization and signal reliability.

A. NRZ — Non-Return to Zero

NRZ represents bits using different signal levels.

Usually:

• High signal = 1

• Low or zero signal = 0

Advantages

• Simple

• Easy to implement

Disadvantages

• Long strings of 1s or 0s cause synchronization problems

• Not very efficient for reliable communication

Explain NRZI (Non-Return to Zero Invert) line coding and critically evaluate how it improves synchronization compared to NRZ, including its limitations in long sequences of identical bits.

B. NRZI — Non-Return to Zero Invert

NRZI uses signal changes or transitions to represent bits.

Instead of only looking at high or low levels, the receiver looks for whether the signal changes.

Advantages

• Better synchronization than NRZ

• Used in real technologies such as USB

Disadvantages

• Long sequences without transitions can still cause problems

May require extra encoding such as 4B/5B

Explain Manchester encoding in data communication systems and evaluate how it achieves synchronization, including its advantages and disadvantages in terms of bandwidth efficiency.

Manchester Encoding

Manchester encoding combines data with a clock signal.

There is a transition in every bit period, which helps synchronization.

Advantages

• Excellent synchronization

• Receiver can keep track of timing

Disadvantages

• Uses more bandwidth

• Less efficient than some other methods

Exam Trap

Manchester is good for synchronization but bad for bandwidth efficiency.

Explain bipolar encoding in digital data transmission and evaluate how the use of alternating positive and negative voltage levels improves signal reliability, including its advantages and disadvantages.

Bipolar Encoding

Bipolar encoding uses positive and negative voltage levels.

This helps keep the average voltage balanced around zero.

Advantages

• Reduces problems caused by long periods of positive voltage

• Helps reduce certain types of attenuation problems

Disadvantages

• More complex

• Requires careful encoding

Explain passband modulation in data communication systems and describe how it differs from baseband transmission, including how carrier wave properties are modified to encode digital data.

Passband Modulation

Passband transmission shifts the signal into a higher frequency range.

It is used especially in wireless communication because wireless systems must transmit in assigned frequency bands.

Passband modulation changes one or more properties of a carrier wave:

• Amplitude

• Frequency

• Phase

Explain ASK (Amplitude Shift Keying) in passband modulation and critically evaluate how changes in amplitude are used to represent digital data, including its advantages and disadvantages in noisy communication environments.

ASK — Amplitude Shift Keying

ASK changes the amplitude of the carrier wave.

• Larger amplitude may represent 1.

• Smaller amplitude may represent 0.

Advantages

• Simple

• Easy to understand

Disadvantages

• Sensitive to noise

• Sensitive to attenuation

Explain FSK (Frequency Shift Keying) in passband modulation and critically discuss how it represents binary data using different frequencies, including an evaluation of its performance in noisy communication channels and its advantages and disadvantages compared to other modulation techniques.

FSK — Frequency Shift Keying

FSK changes the frequency of the carrier wave.

• One frequency represents 1.

• Another frequency represents 0.

Advantages

• More resistant to amplitude noise than ASK

• Useful in many communication systems

Disadvantages

• More complex than ASK

• Requires frequency space

Explain PSK (Phase Shift Keying) in passband modulation and analyse how changes in the phase of a carrier wave are used to encode binary data, including its advantages and disadvantages in modern communication systems.

PSK — Phase Shift Keying

PSK changes the phase of the carrier wave.

The wave shifts position in its cycle to represent different bits.

Advantages

• Efficient use of bandwidth

• Common in modern digital communication

Disadvantages

• More complex

• Requires accurate timing and electronics

Explain QAM (Quadrature Amplitude Modulation) in passband transmission and evaluate how combining amplitude and phase variations allows higher data rates, including its advantages and disadvantages in modern digital communication systems.

QAM — Quadrature Amplitude Modulation

QAM combines changes in:

• amplitude

• phase

This allows multiple bits to be sent per symbol.

Advantages

• Very efficient

• Sends more bits per signal change

• Used in modern networks

Disadvantages

• More sensitive to noise

• More complex

Exam Trap

More QAM levels means more bits per symbol, but also greater risk of errors because the signal points are closer together.

Modulation Comparison Table

Technique	What Changes?	Type	Main Strength	Main Weakness
NRZ	Signal level	Baseband	Simple	Synchronization problems
NRZI	Transitions	Baseband	Better synchronization	Long no-change runs
Manchester	Clock transitions	Baseband	Excellent synchronization	Uses more bandwidth
Bipolar	Positive/negative voltage	Baseband	Balanced signal	More complex
ASK	Amplitude	Passband	Simple	Noise-sensitive
FSK	Frequency	Passband	More robust than ASK	Uses frequency space
PSK	Phase	Passband	Bandwidth efficient	Complex
QAM	Amplitude + phase	Passband	High data rate	Noise-sensitive

The four line codes that you need to know are shown in the diagram below. They are all briefly discussed below the diagram.

The three baseband modulation techniques that you should know, which are shown in the diagram below, represent these three different methods.

Explain the concept of multiplexing in data communications. In your answer, discuss how multiplexing enables efficient use of a communication channel and why it is necessary in modern networking systems.

Multiplexing is the method of allowing multiple users or signals to share the same communication channel.

The three main methods for Multiplexing are:

The three main methods are:

1. Frequency Division Multiplexing

2. Time Division Multiplexing

3. Code Division Multiplexing

Discuss Frequency Division Multiplexing (FDM) as a channel sharing technique in communication systems. In your answer, explain how FDM allocates bandwidth to multiple users, and critically evaluate its advantages and disadvantages, including the role of guard bands and their impact on spectral efficiency. Provide a real-world example to support your explanation.

. Frequency Division Multiplexing — FDM

FDM divides the available bandwidth into separate frequency bands.

Each user gets a different frequency band and can transmit all the time.

Simple Explanation

FDM is like different radio stations. Each station broadcasts at a different frequency.

Advantages

• Users can transmit continuously

• Good for radio, TV, cellular, and satellite systems

• Simple idea

Disadvantages

• Requires guard bands

• Guard bands waste bandwidth

• Interference can happen if frequencies overlap

Example

AM/FM radio stations.

Critically discuss Time Division Multiplexing (TDM) as a method of channel sharing in digital communication systems. In your answer, explain how TDM allocates time slots to multiple users sharing a single communication channel, and evaluate its advantages and disadvantages, including the need for synchronization and the potential inefficiency caused by idle time slots. Provide relevant real-world applications to support your discussion.

Time Division Multiplexing — TDM

TDM divides the channel into time slots.

Each user gets the full bandwidth, but only during their assigned time slot.

Simple Explanation

TDM is like students taking turns to speak in class.

Advantages

• Each user gets full bandwidth during their turn

• Useful for digital communication

• Common in telephone and cellular systems

Disadvantages

• Requires synchronization

• Users must wait for their turn

• Slots may be wasted if a user has nothing to send

Explain Code Division Multiplexing (CDM) as a channel access technique in modern digital communication systems. In your answer, describe how CDM enables multiple users to transmit simultaneously over the same frequency band using unique spreading codes. Critically evaluate its advantages and disadvantages, including its resistance to interference, computational complexity, and requirements for signal processing. Provide relevant real-world applications such as cellular communication systems.Multiplexing Comparison Table

Code Division Multiplexing — CDM

CDM allows all users to transmit at the same time over the same frequency band, but each user has a unique code.

The receiver uses the code to extract the correct signal.

Simple Explanation

CDM is like many people speaking at once in different languages. If you understand only English, you focus on English and ignore the rest.

Advantages

• Users can transmit at the same time

• Uses the full frequency band

• More tolerant of interference

Disadvantages

• Complex

• Requires coding theory

Needs careful signal processing

Multiplexing Comparison Table

Method	Divides Channel By	User Gets	Analogy	Main Weakness
FDM	Frequency	Part of bandwidth all the time	Radio stations	Guard bands/interference
TDM	Time	Full bandwidth for a time slot	Taking turns	Synchronization needed
CDM	Code	Full bandwidth all the time	Different languages	Complex

What does Baseband Transmission do? What are the Characteristics? And give an example.

Baseband Transmission

Baseband transmission sends signals directly over the medium.

The signal starts at 0 and extends up to a maximum frequency.

Characteristics

• Used mainly in guided media

• Does not require shifting to a carrier frequency

• Uses line coding

• Examples include NRZ, NRZI, Manchester, and Bipolar

Example

Ethernet communication over copper cable.

What does Passband Transmission do? What are the Characteristics? And give an example.

Passband Transmission

Passband transmission shifts the signal to a higher frequency range.

It uses a carrier wave, and the data is placed onto that carrier wave.

Characteristics

• Used mainly in wireless communication

• Needed when only certain frequency bands are available

• Uses modulation techniques such as ASK, FSK, PSK, and QAM

• The lowest frequency is greater than 0

Example

WiFi transmitting in the 2.4 GHz or 5 GHz frequency bands

Baseband vs Passband Table

Feature	Baseband	Passband
Frequency range	Starts at 0	Shifted to higher frequency
Carrier wave	Not usually required	Required
Common use	Guided/wired media	Wireless media
Techniques	NRZ, NRZI, Manchester, Bipolar	ASK, FSK, PSK, QAM
Example	Ethernet cable	WiFi/radio
Main issue	Synchronization and attenuation	Noise, spectrum allocation, interference