Computer Networks and Web Technology Fundamentals
Introduction to Computer Networks
Definition of a Computer Network: A group of connected computers that exchange information and share equipment.
Shared Resources: Networking allows for the sharing of various hardware and digital resources, including:
Printers.
Fax machines.
Scanners.
Network connections.
Local drives (storage).
Copiers.
Advantages of Networking
Speed: Provides a very rapid method for sharing and transferring files. This replaces the need for copying files to disks and manually downloading them on other computers, or printing and retyping data.
Centralized Software Management: All necessary software can be loaded onto a single computer known as a server. This eliminates the effort of installing, updating, and tracking files on individual computers across the network.
Flexible Access: Files stored in public access areas can be accessed from any terminal or workstation on the network.
Security:
Files and programs can be marked as 'copy inhibit' to prevent illegal copying.
Password protection can be established for specific directories to restrict access to authorized users only.
Resource Sharing: Expensive peripherals (like laser printers) and data can be shared, optimizing equipment usage.
Cost Efficiency: Purchasing networkable versions of software is generally cheaper than buying individual licensed copies for every machine. Shared expensive peripherals further minimize hardware costs.
Disadvantages of Networking
Expensive Initial Installation: While cost-effective over time, the upfront cost of setup and hardware is high.
Administrative Requirements: Maintaining a network requires significant time and specialized expertise.
Cables May Break: Depending on the network topology, a single break in a cable can cause the entire network (or parts of it) to go down.
Lack of Access: If the network is down, users lose access to all shared hardware and software.
High Security Risks: Utmost importance must be placed on security to prevent the spread of viruses and other unauthorized breaches.
Critical Dependencies: In a Client-Server network, if the file server fails, the entire network comes to a halt.
Types of Networks Based on Geographic Span
Local Area Network (LAN):
Scope: Links computers in a small, limited geographical area, such as a building, a group of buildings, a computer lab, university campus, or hospital.
Distance: The maximum length for a typical LAN is approximately .
Connection: Uses direct physical connections, typically wire cables such as coaxial and fiber optic.
Speed: Typical data transmission speeds range from to .
Ownership: Generally serves a single organization.
Metropolitan Area Network (MAN):
Scope: Connects several LANs across a larger area, such as an entire city or a regional area.
Structure: More optimized than a LAN to handle the larger geography. It may span several blocks of a campus or a whole city.
Integration: Provides the means for inter-networking between different LANs.
Ownership: Might be owned by a single organization, though used by several individual organizations.
Wide Area Network (WAN):
Scope: Spread over a very large area, transcending national and international boundaries.
Connections: Uses satellite uplinks, microwaves, and dedicated transoceanic cabling rather than standard physical cables.
Gateways: Network gateways are used to connect multiple LANs together to form a WAN.
Example: The Internet is a prime example of a WAN.
Levels of Privacy: Intranet, Extranet, and Internet
Intranet:
Privacy: Private network.
Access: Only available to authorized employees or members within a large company or organization.
Function: Uses familiar web pages and browsers to shared internal data securely.
Ownership: Owned by a particular organization.
Extranet:
Privacy: Private network with limited external access.
Access: An intranet that is selectively opened to specific external individuals or organizations, such as customers, suppliers, or research associates.
Example: Online banking applications are common examples of extranets.
Ownership: May be owned by one or more collaborating organizations.
Internet:
Privacy: Public and globally accessible.
History: Formed in 1969 by the Advanced Research Projects Agency (ARPA), originally known as ArpaNet.
Original Purpose: To link computers across large areas for scientific and military communication and file sharing.
Ownership: Not owned by any single entity.
Network Communication Methods
Point-to-Point Transmission: One computer (node) connects directly to another. Data travels directly from the sender to the receiver.
Broadcast Transmission: One computer sends data to a group of computers on the network. All connected computers receive the same information.
Peer-to-Peer (P2P): Each computer on the network can communicate directly with every other computer, allowing users to view and open files on various nodes.
Broad-band Channel:
Provides bandwidth greater than ordinary telephone lines (> 64\,kbps).
Higher bandwidth equates to greater data-carrying capacity.
Supports high speeds and large volumes of data for text, voice, pictures, and video.
Utilizes coaxial cables, fiber optics, and microwaves.
Transmission Media: Wired and Wireless
Wired Media (Physical Lines):
Twisted Pair: Consists of eight copper wires twisted in pairs to reduce interference and encased in plastic. It is inexpensive, used for short distances, and handles small data volumes (common in telephone lines).
Coaxial Cable: Features a single copper core surrounded by a metal shield and plastic covering. It supports fast transmission over medium distances and handling medium data volumes. It is more expensive and used by TV cable companies, though rarely used in modern computer networks.
Fiber Optic Cable: Consists of flexible glass fibers (thin as human hair) that carry information using light. It is high-performance, very expensive, supports the fastest transmission speeds, the largest data volumes, and can span the furthest distances.
Wireless Media (Radio Signals):
Bluetooth: Uses radio signals for short-distance data transmission between devices.
Wi-Fi (Wireless Fidelity): Uses radio waves for high-speed internet and data exchange over a local network.
Hotspot: A site providing internet access via a wireless LAN and a router connected to an Internet Service Provider (ISP).
Satellite: Space-traveling devices used for global communication and data collection via radio/television signals.
Microwave: Electromagnetic waves with frequencies between and . Used in radar, radio transmission, and cooking.
Infra-red: Short-range electromagnetic radiation for wireless communication between computing devices.
Network Hardware Components
Hub: A central device that connects many cables and transfers network messages between them. Hubs are currently becoming obsolete, replaced by switches and routers.
File Server: A high-performance computer with large-capacity hard drives available to all network users.
Router: Acts as the 'traffic cop' of the network. It directs data from a modem to specific devices (Smart TVs, laptops). It connects a LAN to an internet connection. Routers come in wired and wireless types.
Switch: Expands the number of devices connected to a router. Similar to a hub but with advanced features. Includes multiple ports, power supply, and connection lights.
Modem (Modulator-Demodulator): Connects a computer to an internet connection over a telephone line.
Dial-up Modem: speed.
Cellular Modem: Used for mobile connectivity in laptops.
Cable Modem: Up to times faster than standard dial-up.
DSL Modem: Currently very popular.
Network Interface Card (NIC): Electrical circuitry that contains a port to connect a device to the network medium. Every device (node) on a LAN must have at least one.
Network Adapter: A device utilizing unique hardware addresses known as MAC addresses (Media Access Control) encoded on a chip to ensure data reaches the correct destination.
Wireless Access Point: A device attached to a LAN that contains a radio receiver to allow wireless signals to be processed.