Networks: How Do Packets Get Routed?

Packet Switching

Packet switching is the process of breaking data down into packets, sending them across the Internet to another computer, and then re-assembling the data.

Sender's local area network

The sender will generate data in an application on their computer.
- This happens at the application layer.
The data is split into packets of data.
- This happens at the transport layer.
Internet Protocol adds IP addresses to each packet.
- This happens at the Internet layer.
Packets are grouped into frames and sent to the router on the LAN.
- This happens at the Network layer.

Over the Internet

The sender's router inspects the packet to determine if the destination IP is on the current LAN.
- If it is not then it will send the packet onto the Internet (or other wide area network).
- This happens at the Internet layer.
Each packet is sent from the sender's router to the destination router via connected routers.
- The path of each packet can be different, which maximises efficient use of the network by avoiding bottlenecks.

Recipient's local area network

Because they have taken different paths, the packets at the destination will be in the wrong order.
- These packets are unpackaged and reassembled into the correct order using the sequence number of each packet.

1Computer Systems

1.1Systems Architecture

1.1.1Architecture Introduction

1.1.2Von Neumann Architecture

1.1.3Fetch-Execute Cycle

1.1.4Factors Affecting CPU Performance

1.1.5Elements of Computer Systems

1.1.6Exam-Style Questions - Von Neumann Architecture

1.2Memory & Storage

1.3Computer Networks, Connections & Protocols

1.4Network Security

1.4.1Forms of Attack

1.4.2Malware

1.4.3Social Engineering

1.4.4Phishing

1.4.5Common Active Attacks

1.4.6Information Security

1.4.7SQL Injection

1.4.8Network Administration

1.4.9Protecting Against Malware

1.4.10Authentication & Passwords

1.4.11Encryption

1.4.12End of Topic Test - Networks

1.5Systems Software

1.5.1Types of System Software

1.5.2Operating Systems

1.5.3Operating System Managers

1.5.4File Management

1.5.5Device Management

1.5.6User Management

1.5.7Utility Software: Encryption & Defragmentation

1.5.8Utility Software: Data Compression & Backup

1.6Ethical, Legal, Cultural & Environmental Concern

1.6.1Open Source vs Proprietary Software

1.6.2Licensing Issues

1.6.3Ethical Issues

1.6.4Ethical Issues 2

1.6.5Exam-Style Questions - Ethical Issues

1.6.6Legal Issues

1.6.7Legal Issues 2

1.6.8Freedom of Information Act (2000)

1.6.9Cultural Issues

1.6.10Environmental Issues

1.6.11Positive Environmental Impact

1.6.12Privacy Issues

1.6.13Stakeholders

1.6.14End of Topic Test - Software & Issues

2Computational Thinking, Algorithms and Programming

2.1Algorithms

2.1.1Computational Thinking

2.1.2Algorithmic Thinking

2.1.3Pseudocode & Flow Diagrams

2.1.4Interpreting & Correcting Algorithm

2.1.5Completing Algorithms

2.1.6Search Algorithms

2.1.7Binary Search

2.1.8Overview of Sort Algorithms

2.1.9Bubble Sort & Insertion Sort

2.1.10Merge Sort

2.1.11Exam-Style Questions - Sorting Algorithms

2.2Programming Fundamentals

2.2.1Fundamentals

2.2.2Program Flow 1

2.2.3Program Flow 2

2.2.4Arithmetic & Relational Operators

2.2.5Boolean Operators

2.2.6Data Types

2.2.7Arrays

2.2.8Strings

2.2.9File Handling

2.2.10Structuring Data

2.2.11End of Topic Test - Programming

2.2.12Exam-Style Questions - Translation

2.3Producing Robust Programs

2.3.1Defensive Design Considerations

2.3.2Defensive Design Considerations 2

2.3.3Maintainability

2.3.4Testing

2.3.5Test Plans

2.3.6Error Types

2.3.7End of Topic Test - Programming

2.3.8Exam-Style Questions - Testing

2.4Boolean Logic

2.4.1Computational Logic

2.4.2Boolean Logic

2.4.3Boolean Operators

2.4.4Grade 9 - Logic

2.5Programming Languages & IDEs

2.5.1High-Level vs Low-Level Languages

2.5.2Translation - Compliers & Interpreter

2.5.3Translation - Assemblers

2.5.4Integrated Development Environments

2.5.5Exam-Style Questions - Translation

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