CREDITS
SCENE SELECT
NEW GAME
SCENE 1 A Strange Message (Odd Parity, Receiving)
SCENE 4 Calling for Help (Even Parity, Sending)
BACK
SCENE 2 Making Contact (Odd Parity, Sending)
SCENE 3 Disaster Strikes! (Odd Parity, Receiving)
SCENE 5 To the Rescue (Even Parity, Receiving)
INTRODUCTION
Signed,
are you doing?
Mr. Router
and Bob, how
Hello, Alice
Message:
INTRODUCTION
0011001
1110011
0010011
1101101
QUIT
1001100
Alice: Bob, Bob! It’s your sister, Alice!
Alice: I’m going overseas for a holiday!
Bob: But oh no, Alice...
Bob: How will we be able to keep in touch?
Alice: Don’t worry, Mr. Router can help!
Mr. Router: Hello, Alice! Hello, Bob!
Mr. Router: I’m Mr. Router, at your service!
Mr. Router: My job is to send and receive messages for you.
Mr. Router: To do this, I convert messages into packets...
Mr. Router: …that are made up of binary data!
5
1
6
2
3
Mr. Router: Unfortunately, I am not perfect.
4
Mr. Router: Sometimes, a packet may become corrupted.
Mr. Router: This means that a 0 in the packet may be turned into a 1...
Mr. Router: ...or a 1 may be turned into a 0.
Mr. Router: When the corrupted packet is converted back...
rur,!AlcB p
Mr. Router: ...the resulting message will have errors.
Bob: Oh dear, is there anything we can do to prevent this?
Mr. Router: Yes! We can add a parity bit to every packet of data.
Mr. Router: We set it so that the number of 1s in the packet is always odd.
Mr. Router: This is called odd parity.
Mr. Router: For example, the parity bit is 0 here...
Mr. Router: …so that the number of 1s in the packet is odd.
Mr. Router: For this other packet, the parity bit is 1 here...
Mr. Router: …so that the number of 1s in this packet is also odd!
Mr. Router: In this way, we can detect when a packet is corrupted...
Mr. Router: …because the number of 1s will no longer be odd!
Alice: Wow, that’s really smart!
Mr. Router: We could also use even parity instead of odd parity.
Mr. Router: With even parity, the parity bit is set...
Mr. Router: ...so the number of 1s in the packet is always even.
11011011
11011010
01101100
01101101
01111101
01111100
Message Received:
Bob: Hmm, what should I do?
01010110
Mr. Router: Okay, let me convert that packet to text!
Mr. Router: I’ve received the following packet...
Mr. Router: Oops, let me ask the sender to try again.
Mr. Router: Well, looks like that's the end of the message...
Bob: Oh no, what could this mean? The message doesn’t make sense.
Mr. Router: It could be corrupted... Should I ask the sender to try again?
Bob: Yes, please! I have to read this message!
0101011
Message to Send:
Mr. Router: Okay, let me send that packet for you!
Bob: Hmm, how should the next packet be sent?
or
Mr. Router: Oh dear, it looks like the message was not sent correctly.
Mr. Router: I am getting requests to send the message again.
Mr. Router: Would you like to try again?
Bob: Yes, please!
SCENE 1 A Strange Message
Bob: Alice has been gone for a while now…
Mr. Router: Bob, Bob! I’m receiving a message from overseas for you.
Bob: Oh, it must be from my sister!
Mr. Router: Yes, but I will need your help to read the message.
Bob: Really? Tell me what I need to do!
Mr. Router: Okay, I will show you each packet that I receive.
Mr. Router: The last bit is the parity bit.
Bob: Okay...
Mr. Router: You will tell me whether to accept or reject the packet.
Mr. Router: If the packet is valid, click “Accept”. I'll try to convert it into text!
Mr. Router: Otherwise, click “Reject”! I will ask the sender to try again.
Mr. Router: Are you ready to start?
Bob: Yes, I think so. Let's go!
NEXT >
Mr. Router: Now, for me to help, you two must first decide...
Mr. Router: …whether you want to use odd parity or even parity.
Alice: Hmm...
Alice: Alright, let’s use odd parity first!
Alice: This means that a good packet will always have an odd number of 1s!
Bob: Got it, sister. Let’s use Mr. Router to keep in touch!
Help, Bob!
PROCEED
has gone
Report Title
TRY AGAIN
wrong!
Something
Report Text
Bob: Oh no, what could this mean? Is my sister in trouble?
Mr. Router: I hope not. This is so strange...
Bob: Mr. Router, please help me send a message back to Alice...
Bob: I need to get to the bottom of this!
SCENE 2 Making Contact
Mr. Router: Bob, I'm ready to send your message!
Bob: Oh, thank you so much!
Bob: What do I need to do?
Mr. Router: Well, your message for Alice is already converted into packets...
Mr. Router: …but I need you to set the parity bit correctly for each packet.
Mr. Router: There will be seven bits for each packet...
Mr. Router: …followed by a parity bit that is either 0 or 1.
Mr. Router: You will need to choose which parity bit to send.
Bob: Yes, I am. Let's go!
Mr. Router: Well, it looks like the message was sent correctly.
Bob: Now we wait for a reply. I hope Alice is safe…
SCENE 3 Disaster Strikes!
Mr. Router: Bob, looks like I’m receiving a response!
Mr. Router: Are you ready to help receive it?
Bob: Yes, I am. Let's go!
The Napper
Haha, Alice
strikes again!
hostage!
is now my
Bob: Alice is being held hostage? This is terrible!
Bob: And who is "The Napper"?
Mr Router: Let me search online...
Mr Router: Oh dear, it looks like the Napper is a nefarious criminal...
Mr Router: ...who kidnaps laptops and holds them for ransom!
Bob: That dastardly villain!
Bob: We must do something to help my sister!
SCENE 4 Calling for Help
Mr. Router: Aha, Bob!
Mr. Router: It looks like the Napper’s last message...
Mr. Router: ...was sent from a small town named Nomanisan.
Mr. Router: We should let the police know and get their help.
Bob: That’s a great idea! Let’s do it.
Mr. Router: However, be aware that the police use even parity.
Mr. Router: This means that they expect the number of 1s in each packet...
Mr. Router: ...to be even instead of odd!
Bob: Ah, I understand. Instead of keeping the number of 1s odd...
Bob: ...this time, I keep the number of 1s even.
Mr. Router: Are you ready to start sending the message?
Bob: Good. The Napper must be stopped!
SCENE 5 To the Rescue
Mr. Router: Bob, I’m getting a response from the police!
the tip-off!
We are on
Thanks for
our way.
Bob: Looks like our plan worked!
Bob: Oh, I hope they manage to rescue Alice...
Mr. Router: I’m sure it’ll be alright.
Mr. Router: The police might even catch the Napper too!
Bob: I certainly hope so!
EPILOGUE
Alice: Brother, brother! I’m so happy to see you!
Bob: Alice, I’m so happy to see you too! Are you hurt?
Alice: Don’t worry, just a few scratches here and there.
Alice: The police that you contacted were so efficient!
Alice: They launched a daring rescue and caught the Napper without a sweat.
Mr. Router: Alice! Alice! I’m so glad you’re alright.
Alice: Mr. Router! Thank you so much for keeping us in touch!
Mr. Router: No, your thanks should really go to parity bits.
Mr. Router: Without parity bits, I could not have done my job so effectively.
Bob: Yes, without parity bits, detecting corrupted packets would be hard!
Alice: Alright then, a big thank you to parity bits for saving the day!
All: HURRAY!
Acknowledgements “Anguish”Kevin MacLeod (incompetech.com) Licensed under Creative Commons: By Attribution 3.0 http://creativecommons.org/licenses/by/3.0 “Carpe Diem”Kevin MacLeod (incompetech.com) Licensed under Creative Commons: By Attribution 3.0 http://creativecommons.org/licenses/by/3.0 “Definitely a real trumpet fanfare”pfranzen (freesound.org) Licensed under Creative Commons: By Attribution 3.0 http://creativecommons.org/licenses/by/3.0 “Furious Freak”Kevin MacLeod (incompetech.com) Licensed under Creative Commons: By Attribution 3.0 http://creativecommons.org/licenses/by/3.0 “Inspired”Kevin MacLeod (incompetech.com) Licensed under Creative Commons: By Attribution 3.0 http://creativecommons.org/licenses/by/3.0 “jawharp_boing.wav”plingativator (freesound.org) Licensed under Creative Commons: By Attribution 3.0 http://creativecommons.org/licenses/by/3.0 “Rainbows”Kevin MacLeod (incompetech.com) Licensed under Creative Commons: By Attribution 3.0 http://creativecommons.org/licenses/by/3.0 “Shiny Tech”Kevin MacLeod (incompetech.com) Licensed under Creative Commons: By Attribution 3.0 http://creativecommons.org/licenses/by/3.0 “swosh.aif”man (freesound.org) Licensed under Creative Commons: By Attribution 3.0 http://creativecommons.org/licenses/by/3.0 “The Lift”Kevin MacLeod (incompetech.com) Licensed under Creative Commons: By Attribution 3.0 http://creativecommons.org/licenses/by/3.0