Lecture 1: Computer Networks

Computer Network Basics

• A computer network is a collection of connected devices (wired or wireless) designed to share resources and exchange information.
• Benefits of networking include reduced overall costs, hardware sharing (like network printers), file sharing, access to centralized services (ERP, Mail), and support for online gaming, E-learning, and IPTV.

Network Elements

• Client (Endpoint/Node): The device requesting services from the network.
• Server: The device providing services (e.g., Print server, Mail server, Internet router).
• Media: The physical or wireless medium (cables, Wi-Fi) connecting devices.
• Network Devices: Devices like switches, hubs, and routers that easily connect multiple clients to servers.
• NIC (Network Interface Card): Hardware on clients and servers where network media is plugged in to grant access to the network.

Network Types

• LAN (Local Area Network): Covers a small physical area (home, building) with very high speeds and distances up to hundreds of meters.
• CAN (Campus Area Network): Interconnects multiple LANs within a specific geographical area (educational or corporate campus) ranging from 5-50 km, typically without needing an ISP in between.
• WAN (Wide Area Network): A network of networks spanning large distances (the Internet is the largest WAN). Connects branch locations via ISPs, leased lines, or VPNs, and generally has limited speed compared to LANs.
• PAN (Personal Area Network): Very small range (about 10 meters) interconnecting devices like Bluetooth headsets and mice. Used primarily in SOHO (Small Office/Home Office) environments.

Network Topologies

• Bus Topology: Single cable connects all clients. Only one device can transmit at a time, causing high delay. Highly unreliable (if the main cable is cut, the network fails) and lacks security. It uses CSMA/CD (Collision Detection) to detect data collisions and a random backoff timer to re-transmit.
• Ring Topology: Devices are connected in a circular closed loop. Also suffers from high delay and low reliability.
• Star Topology: All devices connect to a central device (like a switch). Provides low delay, high reliability, and allows multiple devices to transmit simultaneously.
• Mesh Topology: Devices interconnect directly with one another. Provides very low delay and very high security/reliability, but is highly complex and very expensive.