Computer Science - Unit 10: The Internet

Internet

A network of interconnected computer networks that allows users worldwide to communicate and share resources using an end-to-end communication protocol.

World Wide Web (WWW)

A collection of resources organized as websites and webpages, accessible via the Internet.

Internet Backbone

The main part of the Internet, made up of dedicated connections linking large networks globally. Each backbone point connects to several regional networks to provide access to users.

Internet Service Providers (ISPs)

Companies directly connected to the Internet backbone that provide Internet access to users through regional networks.

IP Address

A unique identifier for each resource on a network, used to send data to the correct destination.

IPv4

Internet Protocol version 4, consisting of 4 numbers (0-255) separated by dots (e.g., 14.35.146.50). Provides about 4.3 billion unique addresses.

IPv6

Internet Protocol version 6, consisting of 8 groups of 4 hexadecimal digits separated by colons. It provides vastly more unique addresses than IPv4.

Fully Qualified Domain Name (FQDN)

A combination of a resource's host name and domain name (e.g., www.google.com).

Uniform Resource Locator (URL)

Specifies how a resource is found on the Internet, including the protocol and FQDN (e.g., https://www.google.com).

Internet Registries

The five global organizations that manage the allocation of IP addresses, prioritizing reuse of unused addresses.

Domain Name System (DNS)

A hierarchy of domain types (.com, .uk, .edu, etc.) used to locate Internet resources.

DNS Lookup Process

The domain name search starts at a local DNS server and moves up the hierarchy until the address is found. The server then returns webpage data to the requester.

Packet

A chunk of data transmitted over networks, containing a header, payload, and trailer.

Packet Switching

Dividing data into packets that travel along shared lines, allowing simultaneous transfers.

Packet Components

Sender's and recipient's addresses, Packet sequence number, Payload (data), Time To Live (TTL)/Hop Limit, and Checksum/CRC (error checking).

Router

A device that connects different networks and directs packets via the fastest route (fewest hops or least congestion).

Hop

Each packet forwarding by a router.

Gateway

A device that reformats packet headers between networks using different protocols/media; often combined with routers.

Firewall

A security system that filters packets between a device and the Internet, blocking malicious or unauthorized access.

Packet Filtering

Blocking packets based on source IP, protocol, or port number.

Stateful Inspection

Filtering packets based on their contents and connection state, only allowing expected packets.

Proxy Server

A server that makes web requests on behalf of a computer, hiding its address.

Proxy Server Benefits

Enables anonymous surfing, filters undesirable content, logs user requests, and caches previously visited sites.

Encryption

Scrambling data before transmission to prevent unauthorized access.

Plaintext and Ciphertext

Plaintext = original data; Ciphertext = encrypted data.

Symmetric Encryption

Uses the same key for encryption and decryption; key must be privately shared.

Asymmetric Encryption

Uses public and private key pairs; sender encrypts with recipient's public key, and only recipient can decrypt with their private key.

Hybrid Encryption

Uses asymmetric encryption to share a symmetric key, then symmetric encryption for faster communication.

Digital Signature

Confirms a message's sender and ensures it hasn't been tampered with.

Digital Signature Creation Process

1. Digest (hash) calculated from message; 2. Digest encrypted with sender's private key; 3. Encrypted digest added to message; 4. Message encrypted with recipient's public key.

Digital Certificate

Verifies the identity of a public key owner and contains the key itself. Used by HTTPS sites.

Digital Certificate Contents

Serial number, Certificate Authority (CA) name, Expiry date, Subject (holder name), Subject's public key, and CA's digital signature.

Worms

Self-replicating malicious programs that spread between devices without user action.

Trojans

Malicious programs disguised as harmless software that rely on user installation.

Viruses

Malicious code embedded in executable files that activate when the file is run.

Buffer Overflow Attack

Occurs when excess data overwrites memory, allowing attackers to execute malicious code.

SQL Injection Attack

Injecting SQL commands into web forms to manipulate or delete database data.

Malware Prevention

Secure coding, strong passwords, two-factor authentication, file access rights, monitoring logs, and updated antivirus software.

TCP/IP

A stack of networking protocols enabling Internet communication.

TCP/IP Layers

Application Layer, Transport Layer, Network Layer, and Link Layer.

Application Layer

Interfaces with the user and app protocols.

Transport Layer

Uses TCP to split data into packets and label them with sequence and port numbers.

Network Layer

Adds source/destination IP addresses; routers operate here.

Link Layer

Handles hardware connections and MAC addressing.

Socket

A combination of IP address and port number (e.g., 42.205.11.140:80).

MAC Address

A unique 12-digit hexadecimal identifier for a device's Network Interface Card (NIC).

TCP/IP Receiving Process

Link Layer removes MAC addresses, Network Layer removes IPs, Transport Layer reorders packets and delivers to correct app, Application Layer presents data to user.

File Transfer Protocol (FTP)

Transfers files between client and server; operates on ports 20, 21.

Secure Shell (SSH)

Secure remote management using encryption; operates on port 22.

Simple Mail Transfer Protocol (SMTP)

Sends and forwards emails; ports 25, 465, 587.

Post Office Protocol 3 (POP3)

Downloads and deletes emails from server; ports 110, 995.

Internet Message Access Protocol (IMAP)

Manages emails on the server; ports 143, 993.

Hypertext Transfer Protocol (HTTP)

Sends website content (unencrypted); port 80.

Hypertext Transfer Protocol Secure (HTTPS)

Sends website content securely (encrypted); port 443.

Network Identifier

Determines the subnet a device belongs to.

Host Identifier

Uniquely identifies a device within a subnet.

Subnet

A smaller network within a larger one, each with a unique network identifier.

Subnet Mask

Distinguishes network and host parts of an IP address (e.g., 255.255.255.0).

Classful Addressing

Fixed divisions between network and host IDs.

Classless Addressing

Division can occur at any point in the address.

Public Address

Globally unique and routable IP address.

Private Address

Used only within local networks.

Dynamic Host Configuration Protocol (DHCP)

Dynamically assigns private IP addresses temporarily from a pool.

Network Address Translation (NAT)

Translates private IPs to a router's public IP for Internet communication.

Port Forwarding

Allows Internet clients to access servers on private networks by mapping ports to internal devices.

Client-Server Model

Clients send requests, servers process them, and return responses.

API (Application Programming Interface)

Defines rules for how software components interact.

WebSocket

An API protocol for full-duplex real-time communication between client and server, reducing packet size and load.

CRUD

Create, Retrieve, Update, Delete - basic database operations.

CRUD in HTTP

GET = Retrieve, POST = Create, PUT = Update, DELETE = Delete.

REST (Representational State Transfer)

Web design method using HTTP request methods to query databases.

REST Process

Client sends HTTP request via browser → JS loads API → server responds in JSON/XML → browser displays data.

JSON (JavaScript Object Notation)

Lightweight, readable data format compatible with JavaScript.

XML (Extensible Markup Language)

Tag-based data format similar to HTML.

JSON vs XML

JSON: Easier, compact, faster, JS compatible, limited data types. XML: Flexible, tag-heavy, slower, supports all data types.

Thick Clients

High-powered standalone computers connected via a network; powerful but costly and require individual maintenance.

Thin Clients

Low-powered terminals connected to a central server; cheaper, easier maintenance, but server-dependent.

Thick Client Pros

Robust, reliable, works offline, handles powerful apps.

Thick Client Cons

Expensive, software installed separately, data integrity issues.

Thin Client Pros

Easy setup, secure, automatic updates, simple OS.

Thin Client Cons

Server-reliant, needs powerful server, high bandwidth demand.