Chapter 1: Computing Systems
1.1 Introduction to Computer Networks
Definition:
A computer network allows different devices to connect and communicate with each other. It helps in sharing information quickly and easily, saving time and effort.
Uses:
Internet browsing
Mobile phones (calls, messages, and apps)
Online classes and learning systems
Online banking and ATMs
Social media platforms
Smart homes
Working:
Data is divided into small packets before transmission. These packets travel through cables or wireless signals, are guided by networking devices, and are finally reassembled by the receiving device.
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1.2 Network Architecture and Basic Concepts
Definition:
Network architecture is the overall design of a computer network. It shows how devices are arranged and how data is transmitted.
It includes:
Hardware
Software
Communication rules
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1.3 Types of Computer Networks
Local Area Network (LAN)
Connects devices within a small area such as a home, school, or office.
Provides high data transfer speed.
Usually owned by a single organization.
Uses Ethernet or Wi-Fi.
Wide Area Network (WAN)
Covers a large geographical area such as cities or countries.
Uses leased lines, satellites, or the Internet.
Generally slower than LAN.
Installation and maintenance can be expensive.
The Internet (Public WAN)
A global network connecting millions of devices worldwide.
Uses standard communication protocols.
Supports websites, email, cloud storage, and other online services.
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1.4 Networking Devices
Network Interface Card (NIC)
Allows a device to connect to a network.
Supports wired or wireless connections.
Each NIC has a unique MAC address.
Switch
Connects devices within a network.
Directs data to the specific target device.
Router
Connects different networks.
Uses IP addresses to route data packets.
Connects local networks to the Internet.
Modem
Connects a local network to an Internet Service Provider (ISP).
Converts digital data into transmission signals and vice versa.
Wireless Access Point (WAP)
Provides Wi-Fi connectivity.
Helps extend wireless network coverage.
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1.5 Network Topologies
Topology Advantages Disadvantages
Bus Simple, easy to install, cost-effective, uses less cable. Main cable failure can affect the whole network; difficult to troubleshoot.
Star Easy to install and manage; failure of one device does not affect others. Failure of the central switch/hub stops the network; requires more cable.
Ring Organized data flow, fewer collisions, equal access. Failure of one device can break the ring; difficult to add/remove devices.
Mesh Very reliable and fault-tolerant because of multiple paths. Expensive and complex to install.
Tree Hierarchical, scalable, easy to manage and expand. Backbone failure can stop communication; complex setup.
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1.6 Network Models & OSI Layer Functions
Application Layer
Provides services for end-user applications.
Handles user requests.
Examples: HTTP, FTP, Email
Presentation Layer
Translates data formats.
Handles encryption and compression.
Performs data conversion.
Session Layer
Establishes communication sessions.
Maintains and terminates sessions.
Provides checkpoints.
Transport Layer
Provides reliable and ordered data delivery.
Handles error recovery and flow control.
Network Layer
Manages logical addressing.
Uses IP addresses.
Routes data packets between networks.
Data Link Layer
Provides error-free communication between directly connected devices.
Uses framing and error detection.
Physical Layer
Transmits raw data bits.
Uses cables or wireless signals.
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1.7 Network Protocols & Services
TCP/IP
The standard protocol suite used on the Internet.
TCP: Ensures reliable and ordered delivery.
IP: Handles addressing and routing.
HTTP / HTTPS
Used to transfer web pages.
HTTPS provides security through SSL/TLS encryption.
FTP
Used to transfer files between computers.
Supports uploading and downloading.
DNS (Domain Name System)
Converts human-readable domain names into numerical IP addresses.
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1.8 IP Addressing and Subnetting
IPv4
Uses a 32-bit address.
Contains 4 octets separated by dots.
Each octet ranges from 0–255.
Provides approximately 4.29 billion addresses.
Has a Network Part and a Host Part.
IPv6
Uses a 128-bit address.
Contains 8 groups of hexadecimal values separated by colons.
Provides 2¹²⁸ possible addresses.
Subnetting
Subnetting divides a large network into smaller sub-networks (subnets).
Benefits:
Reduces network traffic
Improves performance
Enhances security
NAT (Network Address Translation)
Usually performed by routers.
Maps multiple private IP addresses to a single public IP address.
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1.9 Home Network Setup and Configuration
Main Components:
Modem
Router
ISP connection
Ethernet devices
Wi-Fi devices
Wired Connections
Advantages:
High speed
Stable connection
Better security
Disadvantage:
Limited mobility
Wireless Connections
Advantages:
Convenient
Provides mobility
Disadvantages:
May have speed or stability issues
Security & Configuration
Use WPA2 or WPA3 encryption.
Avoid WEP, as it is insecure.
Use a guest network to isolate visitor traffic.
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1.10 Diagnostic Tools & Commands
ipconfig / ifconfig
Displays network information such as:
IP address
Subnet mask
Default gateway
ipconfig: Mainly used in Windows
ifconfig: Commonly used in Linux/macOS systems
ping
Tests network connectivity.
Checks whether a destination device is reachable.
Measures response time.
Telnet
Provides remote device access.
Communication is unencrypted.
SSH (Secure Shell)
Provides secure remote access.
Uses encrypted communication.
PuTTY
A popular client application for SSH and Telnet remote logins.
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1.11 Network Performance & Load Balancing
Bandwidth
The maximum amount of data that can be transmitted over a network connection in a given time.
Unit: Mbps (Megabits per second)
Latency
The time taken for data to travel from the sender to the receiver.
Unit: Milliseconds (ms)
Load Balancing Methods
Round Robin
Distributes requests sequentially among servers.
Least Connection
Sends traffic to the server with the fewest active connections.
IP Hash
Uses the client's IP address to determine which server receives the request.
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1.12 Network Security & Data Protection
Firewalls
A firewall is a hardware or software security barrier that filters incoming and outgoing network traffic.
Purpose:
To block unauthorized or malicious traffic.
Encryption
Encryption converts data into a secure format that can only be read using the appropriate decryption key.
Common Network Threats
Viruses
Malware
Phishing emails
Denial of Service (DoS) attacks
Backup Types
Full Backup
Backs up all selected data.
Incremental Backup
Backs up data changed since the most recent backup of any type.
Differential Backup
Backs up data changed since the last full backup.
Usability vs. Security Tradeoff
Increasing security can sometimes reduce ease of use.
Example:
Complex passwords and multi-step verification provide better security but may make systems less convenient to use.
Build on these networking notes
Make an OSI layers memory aid
Create a one-page revision summary