Computer Networks: A Comprehensive Overview

Posted on Nov 1, 2024 in Computers

Computer Networks

Introduction

A computer network is a set of interconnected computers that communicate with each other via various mediums like cable, satellite, microwave, telephone lines, and fiber optics to share information. Each active device connected to the network is called a node.

Uses of Networks

Networks are primarily used for:

  • Resource Sharing: Sharing resources, especially information, is a primary function of networks. This includes sharing programs, files, and peripherals like printers and hard drives.
  • Reliability: Networks provide reliability by offering multiple sources for resources, ensuring that if one source fails, others are available.
  • Scalability: Networks offer scalability of computational resources. If more computing power is needed, a customer can simply add more resources to the network instead of purchasing a larger mainframe.
  • Communication: Networks facilitate communication between users and devices through various applications like email and collaborative platforms.

Importance of Installing a Network

Installing a network offers several benefits:

  • Cost Savings: Sharing programs and files across a network can lead to significant cost savings compared to purchasing individual licenses for each computer.
  • Resource Sharing: Networks enable the sharing of peripherals like printers and hard drives, reducing the need for individual devices for each user.
  • Data Sharing: Networks provide a basis for data sharing, allowing users to access and search databases concurrently.
  • Group Work: Networks facilitate group work by enabling users to share resources like email and collaborate on projects regardless of their physical location.
  • Centralized Control: Networks allow for centralized control of information and resources, making it easier to maintain, repair, upgrade computers, and perform backups. The network administrator has control over the server and can provide professional supervision.
  • Security: Networks incorporate security mechanisms to control access and ensure that only authorized individuals can enter the network.
  • Compatibility: Networks can connect any type of computer, regardless of brand.

Network Models

OSI Model (Open System Interconnection)

The OSI model represents the seven layers of the process by which data is packaged and transmitted from a sending application through physical cables to the receiving application.

Responsibilities of the Emitter

  • Recognize the data
  • Divide the data into manageable chunks
  • Add timing information and error checking
  • Place the data on the network and send them on their route

Layers of the OSI Model

  • Physical Layer: Sends bits in a physical environment and ensures they are error-free. It also describes the associated electrical and mechanical means, connectors, and specifies whether the communication medium allows duplex, half-duplex, or simplex communication.
  • Data Link Layer: Groups the bits provided by the physical layer into hundreds or thousands of bits to form frames. It detects errors that may occur if frames are lost or damaged in the physical environment.
  • Network Layer: Handles the operation of the subnet. Its task is to decide how to make the packages reach their destination. It also handles bottleneck resolution by choosing optimal paths based on available routes and parameters.
  • Transport Layer: Takes data from the session layer and ensures it reaches its destination. It splits data into smaller sizes if it exceeds the network interface’s allowed size and sends it in smaller segments. It also multiplexes connections with different speeds and provides a mechanism to identify and distinguish multiple existing connections.
  • Session Layer: Responsible for controlling communication between application processes in their home, including establishing and terminating connections.
  • Presentation Layer: Interprets the data for the application layer and performs syntactic transformations so that the data can be recognized by the implementation processes.
  • Application Layer: Specifies the nature of communication to meet the user’s needs, such as file transfer, remote access, remote jobs, and terminal access.

TCP/IP Model

The TCP/IP model is a set of protocols used for communication over the Internet. It has only four layers:

  • Network Access
  • Internet
  • Transport
  • Application

Network Topology

Network topology refers to the physical or logical arrangement of nodes and connections in a network. Common topologies include:

  • Bus
  • Star
  • Tree
  • Ring

Network Classification

Networks can be classified based on various criteria:

  • According to Size: LAN (Local Area Network), MAN (Metropolitan Area Network), WAN (Wide Area Network)
  • According to Logical Distribution: Server, Client
  • According to the Predominant Role: Client/Server Networks, Peer-to-Peer Networks

IP Addresses

Matching IP Addresses

  • Accessibility: Public and Private IP addresses
  • Durability: Static and Dynamic IP addresses

IP Address Classes

  • Class A: Uses the first octet for the network address and the remaining three octets for host addresses (0 to 127). Valid range: 1-126.
  • Class B: Uses the first two octets for the network address and the remaining two for host addresses (128.1 to 192.254).
  • Class C: Uses the first three octets for the network address and the last octet for host addresses.
  • Class D: Used for multicast or multicasting.
  • Class E: Reserved for future use.

Network Devices

Hubs

Hubs are repeaters that amplify and retransmit signals. A thin coaxial cable can have a length of 185 meters and connect up to 30 nodes. A thick coaxial cable can have a length of 500 meters and connect up to 100 nodes.

Bridges

Bridges connect two networks. They listen to network traffic and learn the location of devices on each network, generating a table with MAC addresses.

Switches

Switches analyze Ethernet frames and send them to the correct port based on the destination address, reducing collisions produced by broadcasts.

  • Store and Forward: Receives a frame from a port, analyzes it, and then retransmits it.
  • Cut-Through: Scans the first bytes of the frame for the destination address and immediately starts forwarding the frame.

Spanning Tree

Spanning Tree is an algorithm used to avoid frame looping in a network. It blocks links that close a loop, preventing frames from circulating endlessly.

Routers

Routers review each packet, examine the IP address, and determine the best path to send the packet to its destination. They allow interconnection of multiple systems, improving transmission performance between networks. They also enable linking networks with different protocols.

VLANs (Virtual LANs)

VLANs create separate broadcast domains. Routers are necessary to transmit information between different VLANs. The difference between a subnet and a VLAN is that a VLAN provides broadcast control at Layer 2.

Cable Types

  • Crossover Cable: Used for connecting devices of the same type, such as router to router, hub to hub, switch to switch, PC to PC, PC to router, and hub to switch.
  • Direct Cable: Used for connecting devices of different types, such as router to switch, router to hub, hub to PC, and switch to PC.