This lesson will simulate a single shared wire, connecting two people. The wire can only be in one of two possible states (state A or state B) and either person can read the state of the wire at any time, but this is the only way you can communicate. You will invent a binary call-response protocol using the system. Coordination, speed and timing are problems that need to be solved.
- Bandwidth: Transmission capacity measured by bit rate
- Bit: A contraction of "Binary Digit"; the single unit of information in a computer, typically represented as a 0 or 1
- Bit rate: (sometimes written bitrate) the number of bits that are conveyed or processed per unit of time. e.g. 8 bits/sec.
- Latency: Time it takes for a bit to travel from its sender to its receiver
- Protocol: A set of rules governing the exchange or transmission of data between devices
Students will be able to:
- Explain how synchronization and coordination enable the transmission of binary messages
- Develop a protocol for exchanging binary messages in two directions
- Calculate the bit rate for a binary message exchange
- Provide a definition of "bit" and relate it to the binary messages they have seen so far
The major purpose of this lesson is to engage you in a challenging problem of engineering: a physical network for digital communications. If you must communicate in binary by setting the state of some object (such as a wire) to one of its two possible states, merely defining "State A" and "State B" is insufficient because there is no way to distinguish between a single bit "A" and a string of "AAA" for example. Some element of time must be incorporated into a communication protocol to make it functional for exchanging bits. This time-per-bit leads naturally to calculating a bitrate for a given device, or a measure of how quickly a system transmits digital data.
- Coordination and Binary Messages - Activity Guide, pdf
- Coordination and Binary Messages - Activity Guide, docx
- Coordination and Binary Messages - Activity Guide in Braille .brf
- Coordination and Binary Messages - Activity Guide in Braille .dxb
- Worksheet in Large Print - Video Guide for "Wires, Cables & WiFi"
- Worksheet in Braille .dxb - Video Guide for "Wires, Cables & WiFi"
- Worksheet in Braille .brf - Video Guide for "Wires, Cables & WiFi"
In the previous lesson you all made your made your own binary message devices. We learned that we could compose any number of messages by sending a sequence of states. In order to interpret the message we needed to know:
- which signal meant A and which meant B
- some kind of mapping between sequences of signals and a possible message.
What we were really doing was beginning to develop a communication protocol. Today you're going to develop a protocol to solve a problem.
Prompt: Imagine that you and your friend have made a binary signaling protocol using a flashlight. The light on is state A, off is state B. How could you effectively send a message back and forth using this protocol? Is this protocol specific enough to allow useful communication of a binary message? If not what information would need to be added to it?
Discuss: Would the two states of on and off enough to convey meaning? Would time and synchronization help add meaning? Should they be added to the protocol?
Use the Coordination and Binary Messages worksheet to complete the activity.
Rules for the Challenge
- Student pairs can decide who sends first
- Teacher or third student reveal sequence of bits to be sent
- Teacher will start a timer and say "go" signaling for partners to exchange messages
- During the challenge, students may not communicate with one another
- Students yell "stop" once they have finsihed and write down the amount of time it took to exchange messages
- Teacher will verify that each person received what the other sent
Watch the video "Wires, Cables, and Wifi" and (optionally) have students complete the Video Guide Worksheet which may be helpful for calling out vocabulary that shows up in the video.
What is the best bit rate you hit today? You would be hard-pressed to achieve a bit rate much faster than 1 bit/sec in this activity. You might think that, say, 1,000 bits/sec would be fast for a computer, but even typical household modems in the early 90s had bit rates higher than about 10,000 bits/sec. These days, transmission rates are well in excess of millions of bits/sec (or Mbps - Megabits per second). Typical mobile phone speeds range from 5-10 Megabits per second.
1. Multiple Choice: A binary message consisting of four bits was sent to you by a friend. The message was supposed to be ABAB. Unfortunately, your friend set the bit on the wire once every 2 seconds, but you read the wire once every second. Assuming that the first bit was sent and read at the same time, what message did you receive instead?
- A. ABAB
- B. AABB
- C. AAAA
- D. BBBB
- E. ABBB
2. Multiple Choice: When responding to a question with 4 choices, the most efficient method will require _____ number of bits.
- A. 5 bits
- B. 4 bits
- C. 3 bits
- D. 2 bits
- E. 1 bit
3. Match the bit sending technology (numbers) with the underlying system (letters).
- 1. Copper Wire
- 2. Radio Wave
- 3. Fiber Optic Cable
- A. Beam of Light
- B. Electric Voltage
- C. Alternating Frequencies
- Continue to increase the number of bits that students must be able to transmit in the Activity Guide's challenge.
- Require students to relay a message, but the response must be sent backwards. This ensures partner B must receive the entire message before responding. (e.g. if partner A sends: ABAB partner B should respond: BABA)
- CSTA K-12 Computer Science Standards: CL.L2:3, CL.L2:4
- CSTA K-12 Computer Science Standards: CT.L2:7, CT.L2:8, CT.L2:9
- Computer Science Principles: 2.1.1 (A, B, C, E)
- Computer Science Principles: 2.1.2 (D, E, F)
- Computer Science Principles: 2.3.1 (A, B, C, D)
- Computer Science Principles: 2.3.2 (A)
- Computer Science Principles: 3.1.3 (A)
- Computer Science Principles: 3.3.1 (A, B)
- Computer Science Principles: 6.1.1 (A, C)
- Computer Science Principles: 6.2.2 (D, J, K)