Understanding Computer Networks: LANs, WANs and IP Addresses

Networks

• A network: a group of connected computers for communication.
• Devices are networked to share data, peripherals, user accounts, printers, internet access, and files.
• Networks enable collaborative document and project work and feature change logging for rollback.
• Centralized software installation and automatic updates are benefits.

Network Types

• Local Area Network (LAN): confined to a smaller area like a school and devices connect to LANs directly.
• WAN (Wide Area Network): covers a larger area, such as the Internet, and connects existing LANs.
• LAN infrastructure is usually owned by the organization running it.
• WAN infrastructure is usually run by a third party.

IP Addresses and DNS

• IP addresses are unique identifiers for every device on a network.
• The addresses are 32-bit numbers in a 4-byte format (0.0.0.0-255.255.255.255).
• The Internet uses IP addresses.
• Routers calculate the quickest mesh network routes, which change based on router activity.
• Packets can take different routes.
• The Domain Name System (DNS) resolves domain names like www.bbc.co.uk to IP addresses.
• The process involves requesting a web page, sending the domain name to a DNS server, receiving the IP address, sending an HTTP GET request, and receiving the web page.

Routing

• Packet Switching: data divided into smaller packets for network transmission.
• Each packet has a source address (the sender's IP address), destination address (the recipient's IP address), sequence number, timestamp, data, and a checksum.
• Timestamp is the packet construction time, used for tracking and error detection.
• The checksum is a calculated value to detect data corruption.

Network Topologies

• Topology: The arrangement of computers and devices in a network.

Bus Topology

• All devices connect to the same wire.
• Unreliable, as wire breaks or faulty computer can disrupt the network.
• Difficult to add computers, increasing collision risk and slowing down the network.
• Bus networks are cheap to set up.

Star Topology

• All devices connect to a central hub or switch.
• Star networks have reduced collision risk, easy computer addition without network impact and are reliable, as one computer or wire failure doesn't disrupt the network.
• Central hub/switch dependence and expensive setup.

Mesh Topology

• Devices connect to multiple other devices, creating partial or full mesh configurations.
• It's a highly reliable setup, as messages take alternate routes if problems arise, and it is scalable for adding new computers.
• A mesh network requires routing.
• The Internet is a mesh network.

Network Speeds

• Transmission Speed: measured in bits per second (bps).
• Faster transmission speeds are measured in kilobits (1000 bits), megabits (1,000,000 bits), or gigabits (1,000,000,000 bits) per second.
• Transfer speed is calculated based on data transferred and time.
• Speed Equation: transmission rate (bps) = data transferred (bits) / time taken (seconds).
• Time Equation: time taken (seconds) = data transferred (bits) / transmission rate (bps).
• Data Equation: data transferred (bits) = transmission rate (bps) * time taken (seconds).
• Data transfer must be converted to bits, time must be converted to seconds and is usually done by converting data to bits per second.
• Data transfer speeds use base 10 prefixes (kilo - 103, mega - 106, giga - 109) whereas data sizes use base 2 prefixes (kibi – 210, mebi - 220, gibi - 230).

Network Protocols

• Protocol: set of rules for communication between devices.
• Protocols ensure communication between devices using different hardware/software.
• Some systems use proprietary protocols.
• Standard Protocols: implemented on a variety of devices and systems.

Protocol Families

• TCP/IP: covers sending and receiving data.
• Ethernet: Ethernet is a family of protocols that covers sending and receiving data over a wired network connection
• Wi-Fi: covers data transfer over a wireless network

Web Protocols

• HTTP (HyperText Transfer Protocol): requests webpages from servers.
• HTTPS (HTTP Secure): encrypts data for security.
• FTP (File Transfer Protocol): transfers files between devices.

Email Protocols

• POP3: delivers emails and deletes them from the server.
• IMAP: marks emails as read and stores them on the server.
• SMTP: sends mail and transfers emails.

Wired and Wireless Characteristics

• Wired/wireless connection performance is measured by speed, latency, range and bandwidth.
• Speed: real-world transmission speed.
• Latency: delay between sending and receiving, measured in milliseconds.
• Range: distance a signal travels before becoming unreadable.
• Bandwidth: maximum potential transfer speed.
• Wired connections use physical mediums.
• Electrical signals using copper wires use voltage to send bit patterns.
• Fiber Optics: transmits light through glass, with higher speed, lower latency, and greater range, but is more expensive than copper.
• Wireless communication uses radio waves and it has shorter range, slower speed, and higher latency than wired.
• Wireless range is be affected by solid structures and speed is affected by shared bandwidth.

Wireless Protocols

• Wireless Protocol: set of rules governing radio frequencies.
• Wi-Fi: connects computers to networks, with long-range capabilities, high power consumption, and high speed.
• Bluetooth: connects wireless peripherals, short-range, low power consumption, and slow speed.
• Zigbee: connects smart home devices using a low-power mesh network.
• RFID (Radio-Frequency Identification): wirelessly scans tags to identify products, using very low power and passive tags.
• NFC (Near-Field Communication): short-range communication between two devices, similar to RFID.

TCP/IP 4-Layer Model

• The TCP/IP 4-layer model breaks down network communication complexity.
• Each layer has a specific role and runs different protocols:

Application Layer

• The application layer contains user-facing applications.
• Example Protocols: HTTP, HTTPS, SMTP, POP3, IMAP, FTP.

Transport Layer

• Delivers data from one end of the network to the other.
• TCP Protocol: data split into numbered packets passed to the internet layer and packets are re-ordered and corrected.

Internet

• Routes packets to the destination.
• Uses IP protocol.

Link Layer

• Transfers data to another device, formatting it for Ethernet or Wi-Fi.
• Uses Ethernet, Wi-Fi protocols.

Network Security

• Network security is important to prevent data theft and system disruptions.
• Hacking: accessing data without authorization through social engineering or technical exploits.

Testing

• White box testing: internal testing to ensure authorized access only.
• Black box testing: external testing to find vulnerabilities.
• Ethical Hackers: White-hat hackers attempt to penetrate the network and report successful hacks.
• Black-hat hackers attack networks for financial gain, possibly selling the data they steal.

Data Security

• Businesses employ methods to secure data from theft and deletion:

Methods

• Access control: User accounts have limited access to the systems required for their job and accounts use usernames and passwords.
• File Permissions: Files have "read-only" or "read-write" access.
• Physical Security: servers are kept in locked rooms.
• Firewalls: Firewalls scan communication for unexpected activity and can block until approved.

This lesson explores the fundamentals of computer networks, including the definition of a network and its uses for data sharing and collaboration. It covers the differences between Local Area Networks (LANs) and Wide Area Networks (WANs), highlighting their infrastructure and scale. The lesson also explains IP addresses and their role in identifying devices on a network.