CSP Unit 2: The Internet – Study Sheet



Lesson 1: Welcome to the Internet

Key Ideas:

  • Network: A group of computers/devices connected to share information.

  • Server: A computer that provides resources or services.

  • Client: A computer that requests resources from a server.

  • Protocol: Rules that allow devices to communicate.

Tradeoffs in Networks:

  • Speed vs. cost vs. reliability.

  • Example: Wi-Fi (fast, flexible, can be unreliable) vs. wired (stable, more expensive).



Lesson 2: Building a Network

Network Types:

  • LAN (Local Area Network): Small area (home/school), fast, low cost.

  • WAN (Wide Area Network): Large area (cities/countries), slower, higher cost.

Tradeoffs:

  • More devices → slower speeds.

  • Longer distances → higher cost and complexity.



Lesson 3: The Need for Addressing

  • Every device needs a unique address to communicate.

  • IP Address: Unique numerical label for a device.

  • MAC Address: Hardware identifier for network interface.

  • Protocols ensure messages reach the correct device even if not directly connected.



Lesson 4: Routers and Redundancy

  • Router: Device that directs data packets between networks.

  • Redundancy: Multiple paths exist in case one fails.

  • Benefits: Reliability and faster recovery from failures.

Example: Data from A → B might take different routes if one path is down.



Lesson 5: Packets

  • Information is broken into packets before sending.

  • TCP/IP Protocol: Ensures packets are sent, received, and reassembled correctly.

  • Handles lost or delayed packets without losing data.

Example: Sending a photo → splits into packets → reassembled at destination.



Lesson 6: HTTP and DNS

  • DNS (Domain Name System): Converts domain names (e.g., code.org) into IP addresses.

  • HTTP (Hypertext Transfer Protocol): Rules for transferring web pages from server → browser.

  • Access Equality: Not everyone has equal Internet access (geography, cost, infrastructure).

Flow Example:

  1. Type website → Browser requests IP via DNS.

  2. Server responds → HTTP sends website content.



Lesson 7: Project – Internet Dilemmas

  • Think critically: Has the Internet improved or worsened the world?

  • Consider benefits (information access, communication) and drawbacks (misinformation, privacy issues).

  • Use personal experiences + articles for examples.



Quick Review Questions

  1. What is the difference between a LAN and WAN?

  2. Why are IP and MAC addresses necessary?

  3. How does a router know where to send packets?

  4. Why is redundancy important in networks?

  5. How do TCP/IP, HTTP, and DNS work together to load a website?

  6. List one positive and one negative impact of the Internet.



I can also make a one-page diagram summary showing:

  • Devices → packets → routers → servers → browser, with DNS + HTTP flow.
    This makes visual memorization super fast.