Computer Networks: Definition, Purpose and Importance

Computer Networks: Definition

• A collection of interconnected devices that communicate and share resources

Computer Networks: Purpose

• Provide a communication medium
• Facilitate hardware and software sharing
• Centralize data management

Computer Networks: Importance

• Vital for personal, business, and governmental use
• From the backbone of the internet
• The basis for the internet

Computer Networks: Evolution

• 1960s: ARPANET (Advanced Research Project Agency Network) was created for military communication in the US.
• 1970s: Packet switching technology led to more applications.
• 1980s: Local Area Networks (LANs) grew with PCs like IBM PCs.
• 1990s: The internet expanded for public use.
• 2000s: Wireless networks were introduced.
• 2010s and beyond: High-speed broadband, fiber optics, and 5G networks emerged.

Computer Networks: Impact

• Enables global communication and e-commerce
• Led to the rise of social media and facilitated cloud computing

Personal Area Network (PAN)

• Definition: Small network connecting devices around a single person.
• Span: 1-10 meters
• Technology: Uses wireless media like Bluetooth and Infrared (IR).
• Applications: Connects a smartphone to a smartwatch or wireless earbuds, synchronizes data between a laptop and mobile devices and allows smart home devices to connect via Bluetooth.
• Advantages: Low cost, simple setup, low power consumption, secure.
• Disadvantages: Limited range (up to 10 meters).

Local Area Network (LAN)

• Definition: Network connecting computers within a limited geographical area, like a home, school, office, or lab
• Span: Up to 1.5 kilometers
• Characteristics: Smaller area coverage, high data transfer rates
• Uses Ethernet cables or Wi-Fi (Wireless Fidelity)
• Applications: Sharing files/printers/internet, connecting devices in a home network, offices, computer labs, universities, and hospitals.
• Advantages: Secure, manageable, high-speed communication and cost-effective due to shared resources
• Disadvantages: Limited to a small area

Campus Area Network (CAN)

• Definition: Network spanning multiple buildings within a campus, such as a university or corporate campus
• Span: Operates within a short range, typically 1 to 5 kilometers
• Characteristics: Expands across multiple buildings, employs advanced security measures such as firewalls and Intrusion Detection Systems (IDS), easily scalable, and provides fast and reliable connectivity
• Applications: University campus networks link libraries, laboratories, classrooms, and administrative offices, and corporate campuses link various departments
• Advantages: Allows centralized management of data and shared resources, efficient data communication, and centralized data management
• Disadvantages: Limited to campus only

Metropolitan Area Network (MAN)

• Definition: Network spanning a city or large area, connecting LANs.
• Span: Up to 50 kilometers
• Technology: Uses high-speed fiber optics or wireless connections and may use DQDB (Dual Queue Dual Bus) technology
• Management: Managed by an organization or ISP (Internet Service Provider).
• Applications: Cable TV, city-wide networks for government offices, and public Wi-Fi by municipalities
• Advantages: Wide coverage, cost-effective, supports high data rates and multiple users
• Disadvantages: More expensive than LAN to set up

Wide Area Network (WAN)

• Definition: Network over a broad area, connecting LANs, MANs, and CANs across cities, countries, and continents
• Span: Thousands of kilometers
• Technology: Leased telephone lines, satellite links, or the internet
• Management: Typically managed by multiple organizations
• Examples: The Internet (biggest WAN), multinational companies' private networks (can be private/public)
• Characteristics: Highly scalable
• Applications: Facilitates global communication, data sharing, and Connects ISPs.
• Advantages: Global connectivity
• Disadvantages: High latency, expensive infrastructure

Network Topologies

• The layout or organizational hierarchy of interconnected network devices.
• Determines network performance, reliability, scalability, and fault tolerance.

Types of Topologies: Star

• Concept: All devices connect to a central hub/switch. The hub acts as a repeater for data flow
• Advantage: Easy to install/manage. If one link fails, the rest of the network continues to operate
• Disadvantage: Failure of the central hub/switch can bring down the network, requires more cables

Types of Topologies: Bus

• Concept: All devices share a common backbone/central cable and data transmits in both directions
• Advantage: Simple, cost-effective for small networks, easy to add/remove devices.
• Disadvantage: Limited cable length/number of devices, a fault in the backbone cable can affect the entire network

Types of Topologies: Ring

• Concept: Devices are connected in a circular arrangement to form a closed ring, data travels in one direction or both, and each device has exactly two neighbors
• Advantage: Equal access to resources for all devices, predictable data flow, reduces collisions.
• Disadvantage: Failure of a single device can affect the entire network.

Types of Topologies: Mesh

• Concept: Each device is connected to every other device in the network via an exclusive line, and provides multiple paths for data transmission
• Advantage: High reliability and fault tolerance and efficient data transmission without traffic congestion
• Disadvantage: Complex setup/maintenance, high cost due to connections and cables.

Types of Topologies: Hybrid

• Concept: A combination of two or more different kinds of topologies.
• Advantage: Flexible, scalable, customizable, and integrates different topologies
• Disadvantage: Complex to design and maintain.

Networking Devices

• Physical devices that connect computers, servers, and other equipment in a network to communicate and share resources.
• Purpose: Facilitate communication, manage/monitor/secure data flow, and improve network performance and reliability

Key Devices: Switch

• Definition: Connects devices within the same network (LAN), forwards data to devices based on MAC addresses
• Types: Unmanaged (plug and play), Managed (advanced features), PoE (Power over Ethernet).
• Functions: MAC address learning, forwarding, and filtering.
• Applications: Used in offices, computer labs, data centers, and home networks.

Key Devices: Router

• Definition: Connects different networks and directs data traffic between them using IP addresses
• Types: Home routers, core routers, edge routers
• Functions: Determines the optimal path, uses a routing table, can apply NAT, can apply Quality of Service (QoS.)
• Applications: Internet connectivity, network segmentation, traffic management.

Key Devices: Gateway

• Definition: Serves as an entry/exit point between two networks with different protocols, and converts data into a suitable format.
• Functions: Protocol conversion, traffic management, and firewall capabilities.
• Types: Application Gateway, VoIP Gateway, Cloud Gateway.
• Applications: Interconnecting networks with different architectures/formats/communication protocols.

Other Network Devices

• Modem (Modulator-Demodulator): converts digital data to analog for transmission over phone lines.
• Firewall: Protects the network from unauthorized access/threats.
• Access Point (AP): Provides wireless connectivity to devices.
• Repeater/Extender: Amplifies/regenerates signal to extend network range
• Hub: Simple device connecting multiple Ethernet devices, sends incoming data packets to all ports, and has limitations of no data filtering, which results in network inefficiency/collisions.

Bridge

• Definition: Connects two or more Network segments of the same network (at the data link layer) to reduce traffic and extend network size.
• Functions: Traffic filtering, and collision domain segmentation.
• Types: Transparent Bridge, Source Route Bridge.
• Applications: Extends networks and connects different network segments with similar protocols.

Network Interface Card (NIC)

• Definition: A hardware component that allows a computer/device to connect to a network, has a unique MAC address
• Functions: Provides physical layer connectivity, handles encapsulation, addressing, and error detection
• Types: Ethernet NIC (for wired networks) and Wireless NIC (for Wi-Fi).
• Applications: Required for all network devices to connect to a network.

Network Cables

• Twisted Pair Cable (Cat 5, Cat 6): Used for Ethernet connections in LANs.
• Coaxial Cable: Used in cable TV, broadband internet, MANs, CANs, and as a backbone for LANs.
• Fiber Optic Cables: Used for high-speed data transmissions over long distances
• Proper cable selection ensures optimal network performance.

Network Connectors

• RJ45 Connector: Standard for Ethernet connections with twisted pair cables.
• BNC Connector: Used with coaxial cables.
• SC, ST, LC Connectors: Used with fiber optic cables.
• Proper connector selection ensures optimal network performance and reliability.