Computer Networks Study Notes

Computer Networks Study Notes

Introduction

  • Instructor: Dr. Nihal Ahmed Mabrouk

Objectives

  • Introduce the fundamental types of computer networks.

  • Demonstrate the TCP/IP & OSI model merits & demerits.

  • Understand the role of various protocols in networking.

Course Outline

UNIT I: Introduction to Networking

  • Network Definition: A network is a set of devices, also referred to as nodes, connected by communication links. Nodes can be:

    • Computers

    • Printers

    • Any other devices capable of sending or receiving data.

  • Computer Network: A collection of autonomous computers interconnected by a singular technology.

  • Interconnection Definition: Two computers are interconnected if they can exchange information. Connections may use various media:

    • Copper wire

    • Fiber optics

    • Microwaves

    • Infrared

    • Communication satellites

  • Networks vary in size and form, often combined into larger networks; the Internet exemplifies a network of networks.

Uses of Computer Networks

  1. Business Applications:

    • Information distribution across companies (resource sharing).

    • Sharing physical resources (printers, backup systems).

    • Client-server model fundamental to network usage.

    • Communication medium among employees via email and IP telephony/VoIP.

    • Desktop sharing and virtual collaboration tools facilitate remote work.

    • E-commerce enhances business interactions with customers and suppliers.

  2. Home Applications:

    • Peer-to-peer communication.

    • Electronic commerce and entertainment (e.g., gaming).

    • Mobile user applications such as texting, GPS, and m-commerce (NFC).

  3. Social Issues:

    • Social networks and platforms enable widespread information sharing, but can lead to ethical issues.

    • Phishing Attack: Social engineering strategy to steal data, where attackers masquerade as trusted entities to exploit victims.

    • Botnet Attack: Networks of hijacked computers used for DDoS attacks and data theft.

Characteristics of Data Communications System

  1. Delivery: Data must reach the correct destination.

  2. Accuracy: Data must be delivered without alteration.

  3. Timeliness: Data must arrive promptly to be useful (real-time transmission).

  4. Jitter: Variation in packet arrival time; uneven delays affect audio/video quality (e.g., if video packets expected every (30\text{ms}) arrive with variations, quality deteriorates).

Components of a Data Communications System

  1. Message: Information to be communicated (text, numbers, images, etc.).

  2. Sender: Device sending the message (e.g., computers, phones).

  3. Receiver: Device receiving the message.

  4. Transmission Medium: Physical path from sender to receiver; includes twisted-pair wire, coaxial cable, fiber-optic cable.

  5. Protocol: Rules governing data communication; essential for devices to communicate.

Data Flow

  • Types of Communication:

    • Simplex: Unidirectional (one-way communication, e.g., keyboard to monitor).

    • Half-Duplex: Both devices can transmit and receive but not simultaneously (e.g., walkie-talkies).

    • Full-Duplex: Both devices can transmit and receive simultaneously (common in telephonic communication).

Performance Metrics

  • Performance can be assessed by:

    • Transit Time: Time for a message to travel from sender to receiver.

    • Response Time: Time interval between an inquiry and a response.

    • Throughput and Delay: More throughput can increase delay due to traffic (poor network efficiency).

Reliability and Security

  • Reliability: Measured by frequency of failures, recovery time from failures, and robustness.

  • Security: Protecting data from unauthorized access, damage, and recovery procedures following breaches.

Network Connection Types

Overview

  • Networks consist of connected devices through links.

  • Types of connections:

    • Point-to-Point: Dedicated link between two devices (e.g., direct cable connection).

    • Multipoint: More than two devices share a link; can be spatially or temporally shared.

Physical Topology

  • Definition: Physical topology is how a network is physically laid out, represented by the geometric relationship between links and nodes.

  • Basic Topologies:

    • Mesh: Every node interconnected.

    • Star: Each node connects to a central device.

    • Bus: All devices connected to a single backbone.

    • Ring: Nodes form a circular connection.

Mesh Topology

  • Definition: Every node connects to every other node.

  • Types:

    • Full Mesh: Each node connected to every other node (connections calculated by (\frac{n(n-1)}{2})).

    • Partial Mesh: At least two nodes linked to multiple other nodes.

  • Advantages: High traffic handling, no single point of failure.

  • Disadvantages: High cost and complexity due to redundant connections.

Star Topology

  • Definition: Nodes connect independently to a central hub.

  • Advantages: Centralized management, ease of adding nodes, individual node failure does not affect others.

  • Disadvantages: High costs if using switches; failure of the central node can bring down the whole network.

Bus Topology

  • Definition: All nodes share a single communication line.

  • Advantages: Suitable for small networks, lesser cabling than star topology.

  • Disadvantages: Difficulty in troubleshooting, performance decline with more devices, damage to the main cable can disrupt the network.

Ring Topology

  • Definition: Each device connects to two others forming a circle. Data travels in one or both directions.

  • Advantages: Reduced packet collision and high-speed data transfer.

  • Disadvantages: The failure of one node can affect the entire network, high-cost hardware for connections.

Hybrid Topology

  • Definition: Combination of multiple topologies, such as a star with bus connections.

Network Types Based on Size

  1. LAN (Local Area Network):

    • Covers small geographical areas (rooms, buildings).

    • Enables device sharing (files, printers).

    • Data transfer rates of 10 to 100 Mbps.

  2. MAN (Metropolitan Area Network):

    • Covers larger areas, connects multiple LANs.

    • Distances between 5 to 50 km.

    • Lower transfer rates compared to LAN.

  3. WAN (Wide Area Network):

    • Spans countries and regions.

    • Consists of multiple LANs and MANs; uses satellites and microwave relays.

    • Internet is the primary example.

Other Types of Networks

  • WLAN (Wireless LAN): High-frequency radio waves for communication; short-range high-speed connectivity.

  • PAN (Personal Area Network): User-organized networks for personal use.

  • SAN (Storage Area Network): Connects servers to data storage devices for data backup and mirroring.

Transmission Media

  • Definition: Any medium that can carry information from source to destination.

Classes of Transmission Media

  • Guided (Wired): Twisted-pair, coaxial, and fiber-optic cables.

  • Unguided (Wireless): Includes radio waves, microwaves, and infrared.

Guided Media

  1. Twisted Pair Cable:

    • Comprises two insulated copper conductors twisted together.

    • One wire carries signals and the other acts as a ground.

  2. Coaxial Cable:

    • Contains a central conductor, insulating sheath, and outer metallic shield; used for higher frequencies.

  3. Fiber-Optic Cable:

    • Made from glass or plastic; transmits data as light, offering high speeds and long-distance capabilities.

Unguided Media: Wireless

  • Types:

    • Radio Waves: Rely on the spectrum for transmission.

    • Microwaves: Used for point-to-point communication.

    • Infrared: Short-range and typically used for remote controls and short-distance data transfer.