Comprehensive Study Guide to Computer Networks and Internet Infrastructure

Net: Short for network, defined as a system of interconnected computers, devices, and servers that share resources and data.
Computing Device: A machine capable of running a program.
- Examples include computers, tablets, servers, routers, and smart sensors.
Computing System: A group of computing devices and programs working together to accomplish a common purpose.
Computing Network: A group of interconnected computing devices capable of sending or receiving data.
Internet: A global network of interconnected computers and devices that communicate with each other using standardized protocols to exchange data, access websites, services, and applications.
World Wide Web (www): A system of linked pages, programs, and files accessible over the Internet.
Path: The series of connections between computing devices on a network, starting with a sender and ending with a receiver.
Bandwidth: The maximum amount of data that can be sent in a fixed amount of time, usually measured in bits per second.
Router: A specialized type of computer that forwards data across a network.

Protocol: An agreed-upon set of rules that specify the behavior of a system.
Internet Protocol (IP): A protocol for sending data across the Internet that assigns unique numbers to each connected device.
- Open Protocol Standard: IP is an open protocol used by all devices, ensuring that any device can connect to another simply by knowing its IP address.
- Public IP Address Assignment: Public IP addresses are assigned by an Internet Service Provider (ISP). Each device receives a unique IP address, functioning similarly to a telephone number.
- Binary Conversion: The IP addresses of both the sender and receiver are converted into binary so that devices know which incoming messages are intended for them and which device should receive a response.
IP Address: The unique number assigned to each individual device connected to the Internet.

Datastream: Information passed through the Internet in packets.
Packet: A chunk of data sent over a network.
- Larger original messages are divided into smaller packets prior to transmission.
- Packets travelling over a network may arrive at their destination in order, out-of-order, or not at all.
Packet Metadata: Data added to packets to assist in routing them through the network and reassembling the original message at the destination.
Transmission Control Protocol (TCP): A protocol responsible for sending and receiving packets of data over a network.
- Performs error-checking to ensure all packets are received and properly ordered.
User Datagram Protocol (UDP): A protocol for sending packets quickly with minimal error-checking and no resending of dropped packets.
Hypertext Transfer Protocol (HTTP): A protocol for computers to request and share the pages, files, and resources that make up the World Wide Web on the Internet.

Domain Name System (DNS): The system responsible for translating domain names (such as khanacademy.com or code.org) into IP addresses.
- Because IP addresses are not human-friendly, DNS provides humans an easy way to identify destinations on the Internet.
- Typing a domain name like www.wikipedia.org allows a computer to connect directly to the servers powering Wikipedia.
Domain Mapping and Scalability:
- Behind the scenes, each domain name maps directly to an IP address.
- When a URL is typed into a browser's address bar, the computer resolves its corresponding IP address.
- Domain names are structured in parts to ensure domain name management load is distributed across different levels, making the system globally scalable.
Hierarchical Structure Format:
- Formatted as [third-level-domain].[second-level-domain].[top-level-domain].
Top-Level Domain (TLD):
- A limited set of top-level domains exist.
- Common TLDs include .com, .org, and .edu.
Second-Level Domain:
- Unique to the company or organization that registers it, such as wikipedia, code, or khanacademy.
Third-Level Domain (Subdomain):
- Owned by the same entity holding the second-level domain.
- Directs users to a specific subset of the website, such as www.wikipedia.com or es.khanacademy.org (the Spanish-language Khan Academy site).

Redundancy: The inclusion of extra components (hardware, devices, or connections) so that a system can continue operating even if individual components fail.
Fault Tolerant: The ability of a computer system to continue functioning even in the event of individual component failures.
Benefits of Network Redundancy:
- Allows the network to be fault-tolerant.
- If part of the network fails or experiences a bottleneck, messages can still be routed and sent to their destination.
Issues and Trade-offs of Building Redundancy:
- Requires additional infrastructure and hardware devices on the network.
- Can be expensive or difficult to build and maintain.

Social Dilemma of the Internet: Numerous systemic issues arise from entities taking advantage of "open protocols".
Net Neutrality:
- A raging legal debate concerning the principle that Internet service providers (ISPs) should enable access to all content and applications regardless of the source.
- Prohibits favoring, prioritizing, throttling, or blocking particular products, services, or websites.
Internet Censorship:
- The attempt by authorities or groups to control or suppress what can be accessed, published, or viewed on the Internet by certain people.
- Protection: Can be used to protect populations (e.g., preventing access to child pornography).
- Restriction: Can also be used to limit free speech and restrict access to information.
Digital Divide:
- Differing levels of access to computing devices and the Internet based on socioeconomic, geographic, or demographic characteristics.

Internet Engineering Task Force (IETF):
- An open international community composed of network designers, engineers, researchers, and volunteers.
- Collaborates to develop and promote technical standards and protocols for the Internet.