1. THE NEED FOR ADDRESSING
UNIT 1 – CHAPTER 2 – LESSON 9
THE NEED FOR ADDRESSING

2. Explore more deeply how communication between multiple computers can work over the Internet. Time to play a simplified game of Battleship!

3. The first game is played unplugged, in groups
The first game is played unplugged, in groups. The second game is played using the Internet Simulator, so that multiple students can connect to each other and see each other’s messages. You must devise a messaging protocol that makes it clear who is sending the message and who the intended recipient is.

4. You devise a binary protocol for playing this game which will entail developing an addressing system for players, as a well as a formal packet structure for transmitting data about the state of the game.

5. “Internet Protocol” addressing system, commonly known as IP Addresses
“Internet Protocol” addressing system, commonly known as IP Addresses. Many computers are connected together by networks. So if a computer sends some bits out, those bits pass through many computers. How does a computer know who those bits are for? If a response is necessary, how does it send it back? This is a complicated question, but the first part of the answer is that you need an addressing system, and some kind of fixed structure for messages that everyone agrees on (a protocol) so messages can be interpreted properly. (We'll get to routing later).

6. The Internet Simulator for this lesson is setup to “broadcast” every message to every person in the group. Since everyone receives any bits that were sent by anyone else, a method for identifying the intended sender and receiver of the message is needed. Students will invent a protocol for addressing messages.

7. Many network systems, such as local Ethernet and WiFi, rely on addressing schemes to make sure bits are received by the correct computer based on address and for other computers to simply ignore messages not intended for them.

8. We will play a crazy game of Battleship where instead of playing against one other person you will play multiple games against multiple other people simultaneously -- We call this "Broadcast Battleship“ In our version today, you will play in groups of 3 or 4. To make it easier to track, we've also simplified the playing board to just a 3x3 grid (instead of the classic 10x10) And we'll just play with paper and pencil.

9. Look at the Rules of Play

10. Play the game, unplugged!

11. We are going to add a new challenge: Your team is going to have to play Battleship without talking. You will only be able to use the Internet Simulator to communicate

12. In Code Studio, find the Internet Simulation for Unit 1 – Lesson 9.

13. You connect to a “Room” with other people, instead of an individual partner. Every message that is sent gets broadcast to everyone in the "room", including you!

14. NO TALKING AT ALL!!! EVER!!
What do you need to do inside the simulator – without TALKING!

15. Discuss standardizing your protocol for sending messages
Discuss standardizing your protocol for sending messages. Consider: What protocol have you been using? Did your group have a protocol at all? How can you standardize your communication? How do you make your message as clear as possible? How do you make your message as efficient (short/easy to interpret) as possible?

16. New boards - Use your new protocol!
ROUND 2 – PLAY AGAIN
New boards - Use your new protocol!
NO TALKING!!

17. AG: INVENT A BINARY PROTOCOL FOR BATTLESHIP How will you standardize the recipient and sender addresses? Should you encode people's names or (hint) use a number? How would a recipient of your message know where address ends and the other begins? What other information do you need to include?

18. Security and Privacy: If the messaging scheme your group designed was really used on the Internet, what could go wrong in terms of security and privacy? Think about what a malicious person could do. What if the messages sent weren't about a game but about something more personal like a conversation with a friend, or communicating with a bank? There are two major security problems with the current version: Anyone can fake a return address. Bob could send you a message and claim it’s “from Alice,” and you’d have no way to confirm who sent it. Everyone can view everyone else’s messages! Because all messages are “broadcast” over Internet Simulator, messages have no expectation of privacy.

19. HOMEWORK: WATCH VIDEO: “IP ADDRESSES AND DNS” Know: IP Address IP Packets IPv4 versus IPv6 FILL OUT WORKSHEET AND TURN IN FOR CREDIT.

20. FILL OUT ASSESSMENTS, REFLECTIONS IN CODE STUDIO