QUESTION 1

a) Components of a Data Communication System

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  1. Source (Sender): The device that originates the data (e.g., a computer, smartphone).
  2. Transmitter: Converts the data into a transmittable signal (e.g., a modem, network interface card).
  3. Transmission Medium: The physical path through which the signal travels (e.g., cables, radio waves, fiber optic cables).
  4. Receiver: Accepts the signal and converts it back into a usable form.
  5. Destination (Receiver): The device that receives the data (e.g., a computer, server).
  6. Message/Data: The information being communicated.
  7. Signal: The electromagnetic or optical representation of the data

b) Importance of Data Modulation in Radio Networks

Importance of Data Modulation in Radio Networks 1. Efficient Transmission: Modulation shifts data to a higher frequency carrier wave suitable for radio transmission. 2. Multiplexing: Allows multiple signals to be transmitted simultaneously using different carrier frequencies. 3. Noise and Interference Reduction: Spread spectrum modulation enhances noise immunity. 4. Range and Coverage: Higher frequency signals can travel longer distances. 5. Channel Allocation: Ensures compliance with regulatory frequency bands. 6. Demodulation at the Receiver: Extracts original data from the received signal.

Data modulation allows efficient transmission, multiplexing, noise reduction, and extended range. It ensures proper channel allocation and facilitates demodulation at the receiver.

C) Impact of Transmission Media on Network Performance, reliability and scalability

  1. Performance Different transmission media offer varying bandwidth and data rate capabilities. o High Performance: Fiber optic cables provide the highest bandwidth and data rates, allowing for very fast data transmission. Coaxial cables also offer good bandwidth.
    o Lower Performance: Twisted-pair cables have lower bandwidth limitations compared to fiber and coaxial. Wireless media can be affected by factors like interference and distance, which can reduce the effective throughput.

  2. Reliability Different media exhibit varying levels of reliability due to their susceptibility to noise and interference. o High Reliability: Fiber optic cables are highly immune to electromagnetic interference (EMI) and radio frequency interference (RFI), resulting in very low error rates and consistent data delivery.
    o Lower Reliability: Twisted-pair cables are susceptible to EMI/RFI, which can introduce errors in data transmission. Wireless media is prone to interference from other wireless devices, physical obstacles (walls, etc.), and weather conditions, leading to potential data corruption and dropped connections.

  3. Scalability (Ease of Expansion and Cost) • The choice of media can affect how easily and cost-effectively a network can be expanded. o Good Scalability: Wireless media offers excellent flexibility in adding new devices without the need for physical cabling. Twisted-pair cables are relatively inexpensive and easy to install, making them suitable for scaling smaller networks.
    o Lower Scalability: Fiber optic installations can be more expensive and complex, particularly for adding new connections, which might limit scalability in certain situations. Coaxial cables are less flexible than twisted-pair for expansion.

Feature Twisted-Pair Cable Coaxial Cable Fiber Optic Cable Wireless Media
Performance Low to Medium Medium to High High Medium
Reliability Low Medium High Medium to Low
Scalability Good Medium Medium Good
Cost Low Medium High Variable
Interference Susceptible Less Immune Susceptible
Distance Short to Medium Medium Long Short to Medium

d) Concept of Token Ring in Networking

The Token Ring is a network protocol that uses a ring topology where a special packet called a token circulates, allowing only the device holding the token to transmit data, ensuring collision-free, reliable, and deterministic communication, but it has been largely replaced by Ethernet due to higher costs and lower speeds.

e) Data Movement using the OSI Reference Model

  1. Computer to Hub: Physical layer converts data into signals.
  2. Hub to Bridge: Data is forwarded without processing.
  3. Bridge Processing: Data Link layer examines MAC addresses.
  4. Bridge to Router: Router processes data at the Network layer.
  5. Router to Internet: Data is transmitted over the network. Computer → Sends data through NIC (Network Interface Card). Hub → Broadcasts data to all connected devices in a network. Bridge → Connects different network segments, filtering traffic. Router → Determines the best route to forward data to its destination. Internet → Data reaches external networks and final recipients.

QUESTION TWO

a) Causes of Signal Impairment

  1. Attenuation – The loss of signal strength as it travels through a medium, requiring amplifiers or repeaters to maintain quality.
  2. Distortion – The alteration of a signal’s shape due to different propagation speeds of frequency components, affecting data integrity.
  3. Noise - Includes thermal noise, induced noise, crosstalk, and impulse noise.

b) NRZ-I Scheme Bitstreams

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c) Features of Fiber Optic Media Influencing Internet Connectivity Trend

  1. High Bandwidth: Supports high-speed data transmission.
  2. Long Distance Transmission: Reduces the need for repeaters.
  3. Immunity to EMI and RFI: Reduces interference and error rates.
  4. Security: Difficult to tap into, ensuring secure communication.
  5. Small Size and Lightweight: Easier to install and manage.
  6. Durability: Withstands harsh environmental conditions.

QUESTION THREE

a) Evolution of Multiplexing Techniques

Multiplexing has evolved from early Frequency Division Multiplexing (FDM) to Time Division Multiplexing (TDM), Wavelength Division Multiplexing (WDM), and modern techniques like Orthogonal Frequency Division Multiplexing (OFDM). These advancements enhance efficiency and data transmission capabilities.

b) Difference Between Analog and Digital Signals

  1. Analog Signals: Continuous waveforms, susceptible to noise.
  2. Digital Signals: Discrete values (0s and 1s), more reliable.
  3. Conversion Methods: o Analog to Digital: Sampling, Quantization, Encoding. o Digital to Analog: Modulation techniques like AM, FM, and PM.

c) Design a network topology for a small business with 50 employees. Include details about the types of devices, connections, and protocols you would use, and justify your choices.

For a small business with 50 employees, a star topology with some elements of a hierarchical (or extended star) topology would be suitable.

Devices:

Core Switch: A high-performance, managed Layer 3 switch would be the central point. Layer 3 capability allows for inter-VLAN routing, improving network segmentation and efficiency. Access Switches: Several managed Layer 2 switches (24 or 48 ports each, depending on office layout) would connect individual employee workstations, printers, and other devices. Managed switches allow for VLANs, QoS, and security configurations. Wireless Access Points (WAPs): Multiple 802.11ax (Wi-Fi 6) or 802.11ac (Wi-Fi 5) WAPs would provide wireless connectivity for laptops and mobile devices. Placement should ensure good coverage throughout the office. Firewall: A dedicated hardware firewall with advanced features (UTM - Unified Threat Management) is crucial for security, protecting the internal network from external threats. Router: If the firewall doesn’t handle routing to the external network (Internet), a separate router might be needed. Often, modern firewalls integrate routing functionality. Network Attached Storage (NAS): For centralized file storage and backup. Printers: Network-enabled printers. Connections:

Ethernet Cabling (Cat 6 or Cat 6a): For wired connections between workstations, printers, switches, and the firewall/router. Gigabit Ethernet (1 Gbps) should be the minimum standard, with 10 Gbps uplinks for inter-switch connections and to the core switch. Fiber Optic Cabling: For high-speed uplinks between switches (especially to the core switch) and potentially to the firewall/router, ensuring sufficient bandwidth for aggregated traffic. Wireless (Wi-Fi): 2.4 GHz and 5 GHz bands supported by the WAPs to accommodate various devices and minimize interference. Protocols:

TCP/IP: The fundamental protocol suite for network communication. Ethernet (802.3): For wired LAN connections. 802.11ax/ac: For wireless LAN connections. DHCP: For automatic IP address assignment. DNS: For name resolution. VLANs (802.1Q): To segment the network for security, performance, and management (e.g., separating departments, guest network). QoS (Quality of Service): To prioritize critical traffic like VoIP or video conferencing. SNMP: For network monitoring and management. HTTPS/TLS: For secure web browsing. VPN (Virtual Private Network): For secure remote access. Justification:

Star/Hierarchical Topology: Provides centralized management, easier troubleshooting, and good scalability. The core switch acts as a central point, and access switches branch out. Managed Switches: Enable VLANs for security and segmentation, QoS for prioritizing important traffic, and better control over the network. Gigabit Ethernet/Fiber: Ensures sufficient bandwidth for current and future needs. Dedicated Firewall: Essential for robust security. Wi-Fi 6/5: Provides fast and reliable wireless connectivity. # d) Assess the challenges and advantages of unbounded transmission media in modern communication networks.

Advantages of Unbounded Transmission Media (Wireless):

Mobility: Allows users to connect to the network without being physically tethered, enhancing flexibility and productivity. Ease of Deployment: Can be deployed quickly and in areas where laying cables is difficult or costly (e.g., historical buildings, temporary setups). Scalability: Adding new devices is generally easier than with wired networks, as it primarily involves connecting to the wireless network. Cost-Effective in Certain Scenarios: For connecting remote locations or covering large areas with fewer infrastructure costs compared to extensive cabling. Flexibility: Supports various device types, including laptops, smartphones, and IoT devices. Challenges of Unbounded Transmission Media (Wireless):

Security: More susceptible to eavesdropping and unauthorized access compared to wired networks. Requires robust security protocols (e.g., WPA3). Interference: Signals can be affected by other wireless devices, electronic equipment, and physical obstacles, leading to reduced signal strength and data rates. Limited Bandwidth: Generally offers lower bandwidth compared to wired connections, and the available bandwidth is shared among all connected devices. Reliability: Signal strength and stability can fluctuate, leading to intermittent connectivity and dropped connections. Distance Limitations: The range of wireless signals is limited, requiring careful placement of access points. Spectrum Management: The radio frequency spectrum is a limited resource, requiring careful management to avoid interference. Power Consumption: Wireless devices often consume more power than wired devices. Health Concerns: Although generally considered low, some individuals have concerns about the health effects of electromagnetic radiation. # e) A network has a bandwidth of 10 Mbps and a signal-to-noise ratio (SNR) of 20 dB. Calculate the maximum channel capacity using Shannon’s capacity formula.

Shannon’s Capacity Formula is: C = B * log2(1 + SNR)

Where: C = Maximum channel capacity (bps) B = Bandwidth (Hz) SNR = Signal-to-Noise Ratio (linear)

First, we need to convert the SNR from dB to a linear ratio: SNR (dB) = 10 * log10(SNR (linear)) 20 dB = 10 * log10(SNR (linear)) 2 = log10(SNR (linear)) SNR (linear) = 10^2 = 100

Now, we can plug the values into Shannon’s formula: B = 10 Mbps = 10 * 10^6 bps. Since the formula uses bandwidth in Hz, and we assume the bandwidth given is the frequency bandwidth, we use this value directly. SNR = 100

C = (10 * 10^6) * log2(1 + 100) C = (10 * 10^6) * log2(101)

To calculate log2(101), we can use the change of base formula: log2(x) = log10(x) / log10(2) log2(101) = log10(101) / log10(2) log10(101) ≈ 2.0043 log10(2) ≈ 0.3010 log2(101) ≈ 2.0043 / 0.3010 ≈ 6.6588

Now, substitute this back into the capacity formula: C = (10 * 10^6) * 6.6588 C = 66.588 * 10^6 bps C = 66.588 Mbps

QUESTION FOUR

a) Analyze the stop-and-wait protocol and its role in feedback control mechanisms for reliable data transmission.

Stop-and-Wait Protocol Analysis:

The stop-and-wait protocol is a simple automatic repeat request (ARQ) protocol used for reliable data transmission over unreliable channels. Here’s how it works:

Sender sends a frame: The sender transmits a single data frame to the receiver. Sender waits for acknowledgment: The sender then stops and waits for an acknowledgment (ACK) from the receiver indicating that the frame was received correctly. Receiver receives the frame: If the frame is received correctly, the receiver sends an ACK back to the sender. If the frame is lost or corrupted, the receiver does not send an ACK. Sender receives the ACK: Upon receiving the ACK, the sender can transmit the next frame. Timeout: If the sender does not receive an ACK within a predetermined timeout period, it assumes the frame was lost or corrupted and retransmits the same frame. Duplicate ACKs/Frames: To handle lost ACKs, sequence numbers (0 and 1) are often used for both data frames and ACKs. This helps the receiver identify and discard duplicate frames and the sender identify if an ACK is for the correct frame. Role in Feedback Control Mechanisms for Reliable Data Transmission:

The stop-and-wait protocol fundamentally relies on a positive acknowledgment (ACK) as the primary feedback control mechanism to ensure reliability. Here’s how:

Error Detection and Recovery: The absence of an ACK within the timeout period serves as implicit feedback to the sender that an error (loss or corruption) occurred. This triggers the retransmission mechanism, which is the core of error recovery. Flow Control (Basic): While not its primary purpose, stop-and-wait provides a very basic form of flow control. The sender can only send one frame at a time and must wait for the receiver to be ready (indicated by the ACK) before sending the next. This prevents the sender from overwhelming a slow receiver. Reliability Guarantee: By requiring explicit confirmation for each frame, stop-and-wait ensures that no data is lost in transit (assuming the retransmission mechanism eventually succeeds). Limitations:

Inefficiency: Stop-and-wait is very inefficient, especially for channels with high latency (long delay). The sender spends a significant amount of time waiting for ACKs, leading to low throughput. Only one frame can be in transit at any given time. Susceptibility to ACK Loss: If ACKs are lost, the sender will retransmit the frame, leading to duplicate frames being received. Sequence numbers help mitigate this but add complexity. Despite its simplicity and inefficiency, the stop-and-wait protocol illustrates the fundamental principles of using feedback (ACKs and timeouts) to achieve reliable data transmission over unreliable channels. It laid the groundwork for more efficient ARQ protocols like Go-Back-N and Selective Repeat.

b) Compare frequency division multiplexing, time division multiplexing, and statistical multiplexing in terms of efficiency, complexity, and applications.

Here’s a comparison of FDM, TDM, and Statistical Multiplexing:

Feature Frequency Division Multiplexing (FDM) Time Division Multiplexing (TDM) Statistical Multiplexing (StatMux) Efficiency Low, fixed bandwidth allocation even if a channel is idle. Medium, fixed time slots, idle slots if a channel has no data. High, bandwidth/time slots allocated dynamically based on demand. Complexity Moderate, requires filters and modulators/demodulators for each frequency band. Low to Moderate, requires synchronization and time slot allocation/deallocation. High, requires buffering, addressing, and dynamic allocation algorithms. Applications Analog systems (radio, television), early telephone systems. Digital systems with constant bit rate (CBR) traffic (circuit-switched networks, ISDN). Data networks with bursty traffic (packet-switched networks, internet, ATM). Bandwidth Usage Inefficient, fixed allocation. Less inefficient than FDM, but still fixed allocation. Most efficient, dynamic allocation. Synchronization Not critical. Critical for proper time slot assignment and retrieval. Less critical than TDM, but still needs some level of coordination. Overhead Guard bands between frequencies. Guard times between time slots. Addressing information in each packet, buffering.

Export to Sheets # c) Discuss how multiplexing and demultiplexing techniques have evolved to address the increasing demands of modern communication networks.

Multiplexing and demultiplexing techniques have evolved significantly to address the ever-increasing demands of modern communication networks, driven by factors like higher data rates, more users, diverse traffic types, and the need for efficient resource utilization. Here’s a look at the evolution:

Early Days (Analog Focus):

Frequency Division Multiplexing (FDM): Dominated early analog systems like radio and telephony. It was simple to implement but inefficient for bursty digital data. Time Division Multiplexing (TDM): Emerged with digital communication, dividing time into fixed slots. Better for constant bit rate digital traffic but still inefficient for variable rate data. Transition to Digital and Increased Capacity Needs:

Wavelength Division Multiplexing (WDM): Revolutionized optical fiber communication by transmitting multiple data streams simultaneously using different wavelengths of light. This dramatically increased the capacity of fiber optic cables. Dense WDM (DWDM) further increased capacity by packing wavelengths closer together. Statistical Multiplexing: Gained prominence with the rise of packet-switched networks. It dynamically allocates bandwidth based on demand, leading to significantly higher efficiency for bursty data traffic common in computer networks. Techniques like Asynchronous Transfer Mode (ATM) and early internet protocols utilized statistical multiplexing. Modern Era (Wireless and High-Speed Data):

Code Division Multiplexing (CDM): Essential for early cellular networks, allowing multiple users to share the same frequency band by assigning unique codes to each user. Orthogonal Frequency Division Multiplexing (OFDM): Became the cornerstone of modern wireless systems (Wi-Fi, LTE, 5G). It divides the bandwidth into numerous closely spaced orthogonal subcarriers, improving spectral efficiency and resilience to multipath fading. Space Division Multiplexing (SDM): Increasingly used in both wired (multi-core fibers) and wireless (MIMO) systems to increase capacity by utilizing different spatial paths. Network Function Virtualization (NFV) and Software-Defined Networking (SDN): While not strictly multiplexing techniques, these technologies enable more flexible and dynamic allocation of network resources, effectively achieving multiplexing gains in virtualized environments. Key Trends in Evolution:

Increased Efficiency: Moving from fixed allocation (FDM, TDM) to dynamic allocation (Statistical Multiplexing, OFDM) to better utilize available bandwidth. Higher Capacity: Leveraging physical properties like wavelength (WDM) and space (SDM) to transmit more data over the same medium. Adaptability to Traffic Patterns: Developing techniques like statistical multiplexing and OFDM that are well-suited for the bursty nature of modern data traffic. Integration and Hybrid Approaches: Combining different multiplexing techniques to optimize performance for specific scenarios. Software Control and Virtualization: Using software to manage and allocate resources, providing greater flexibility and efficiency. In conclusion, the evolution of multiplexing and demultiplexing techniques has been crucial in keeping pace with the exponential growth in demand for communication bandwidth and the diverse nature of modern network traffic. The trend has been towards more efficient, higher-capacity, and adaptable techniques that can be dynamically managed and controlled.

d) With an aid of a diagram explain how Server-Based network is different from peer-to-peer network

              Server-Based Network

      Centralized Resource Management

    [Server]
      |
  ----------------------
  |                     |

[Client A] [Client B] (Requests (Requests Services) Services) | | [Printer] [Shared Files]

Peer-to-Peer Network

  Decentralized Resource Sharing

[Peer A] <—–> [Peer B] <—–> [Peer C] (Shares (Shares & (Shares Resources) Requests) Resources) | [Printer] Server-Based Network:

Centralized Control: Relies on a dedicated server to manage network resources, security, and user access. Client-Server Relationship: Clients request services from the server, and the server provides those services (e.g., file sharing, printing, authentication). Dedicated Hardware: Servers are typically powerful computers dedicated to serving network functions. Enhanced Security: Easier to implement and enforce security policies centrally. Centralized Backup and Management: Data backup and network administration are simplified. Cost: Can be more expensive due to the need for a dedicated server. Single Point of Failure: If the server fails, the entire network or significant parts of it can be affected. Peer-to-Peer Network:

Decentralized Control: No dedicated server. Each computer (peer) acts as both a client and a server. Resource Sharing: Peers share their own resources (files, printers, internet connection) directly with other peers. No Dedicated Hardware: Uses existing workstations as servers. Security Challenges: Security is managed individually on each peer, making it less robust and harder to enforce consistent policies. Difficult Backup and Management: Backup and administration are distributed and can be complex. Cost-Effective: Lower initial cost as no dedicated server is required. No Single Point of Failure: If one peer fails, the rest of the network is generally unaffected.