1.1 Basics of Computer Network
1.1.1 Definition
A Computer Network is a collection of interconnected devices (computers, servers, routers, switches) that communicate with each other to share resources and data. These networks can be local (within a building) or spread over long distances (across cities or countries).
1.1.2 Goals
The primary goals of computer networks are:
- Resource Sharing: Enable users to share hardware and software resources.
- Communication: Facilitate data transfer and communication through various protocols.
- Data Security: Ensure secure data exchange between networked devices.
- Scalability: Ability to add devices to the network as needed.
1.1.3 Applications
- File Sharing: Users can share and access files remotely.
- Communication: Email, video calls, VoIP (Voice over IP), etc.
- Internet Access: Networks enable devices to access the internet and the World Wide Web.
- Resource Sharing: Devices can share printers, storage, and processing power.
1.1.4 Network Hardware – Broadcast, Point to Point
- Broadcast Networks: A single communication channel is shared by multiple devices, and data is sent to all devices in the network (e.g., radio networks).
- Point-to-Point Networks: Involves direct communication between two devices, often using dedicated physical media like cables (e.g., telephone networks).
1.1.5 Components of Data Communication
- Sender: The device that initiates the communication.
- Receiver: The device that receives the data.
- Medium: The channel through which data is transmitted (e.g., copper wires, fiber optics).
- Protocol: Set of rules governing data communication.
- Message: The actual data being transmitted.
- Encoder/Decoder: Devices or software used to encode and decode messages.
1.2 Network Topologies
1.2.1 Mesh Topology
- In Mesh Topology, each device is connected to every other device, offering high redundancy and reliability but requiring more cabling.
1.2.2 Star Topology
- Star Topology has a central node (hub or switch) to which all devices are connected. It’s easy to manage and troubleshoot.
1.2.3 Bus Topology
- In Bus Topology, all devices are connected to a single communication line (bus), which is efficient but less fault-tolerant.
1.2.4 Ring Topology
- Ring Topology involves devices connected in a closed loop, where data circulates in one direction. Failure in one device can disrupt the entire network.
1.3 Types of Networks
1.3.1 LAN, MAN, WAN
- LAN (Local Area Network): A network confined to a small geographic area (e.g., office building, home).
- MAN (Metropolitan Area Network): Covers a city or large campus.
- WAN (Wide Area Network): Spans a large geographic area, connecting multiple LANs and MANs (e.g., the internet).
1.3.2 Internetwork
An Internetwork is a network of networks, which connects different types of networks (LANs, MANs, WANs) using routers and other devices.
1.3.3 Wireless Network
A Wireless Network uses radio waves or infrared signals to transmit data, allowing mobility for users (e.g., Wi-Fi, Bluetooth).
1.4 Modes of Communication
1.4.1 Simplex
In Simplex communication, data flows in only one direction, from sender to receiver (e.g., TV broadcasting).
1.4.2 Half Duplex
In Half Duplex communication, data can flow in both directions but not simultaneously (e.g., walkie-talkies).
1.4.3 Full Duplex
In Full Duplex communication, data can flow in both directions simultaneously (e.g., telephone calls).
1.5 Server-Based LANs & Peer-to-Peer LANs
Server-Based LANs
In a Server-Based LAN, a dedicated server manages resources and services like file storage, printing, and network security.
Peer-to-Peer LANs
In Peer-to-Peer LANs, each device can act as both a client and a server, sharing resources with other devices without a central server.
1.6 Protocols and Standards
- Protocols are a set of rules that determine how data is transmitted over a network. Some common network protocols include:
- TCP/IP (Transmission Control Protocol/Internet Protocol): The foundation of internet communication.
- HTTP/HTTPS (HyperText Transfer Protocol): Used for web page requests and data exchange.
- FTP (File Transfer Protocol): Used for transferring files across networks.
- Standards: The set guidelines established by organizations like IEEE (Institute of Electrical and Electronics Engineers) or IETF (Internet Engineering Task Force) to ensure interoperability.
1.7 Network Software
1.7.1 Protocol Hierarchies, Layers, Peers, Interfaces
- Protocol Hierarchy: Networks use layers to simplify design and troubleshooting (e.g., OSI model, TCP/IP stack).
- Layers: Each layer performs specific tasks, such as data transmission, routing, and application management.
- Peers: Devices at the same layer communicate with each other using the appropriate protocol.
- Interfaces: The point where two layers interact or exchange data.
1.7.2 Design Issues of the Layers
Each layer must balance various factors:
- Efficiency: Ensuring data is transferred without delays.
- Reliability: Ensuring error-free transmission.
- Scalability: Supporting more devices and users as the network grows.
1.7.3 Connection-Oriented and Connectionless Service
- Connection-Oriented Service: Involves establishing a connection before data transfer (e.g., TCP).
- Connectionless Service: Data is sent without establishing a connection (e.g., UDP).