Overview

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.

Vocabulary

Goals

Students will be able to:

Purpose

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.

Resources

Getting Started

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:

  1. which signal meant A and which meant B
  2. 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?

Activity

Use the Coordination and Binary Messages worksheet to complete the activity.

Rules for the Challenge


Wrap-up

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.

Content Corner

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.

Assessment

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?

2. Multiple Choice: When responding to a question with 4 choices, the most efficient method will require _____ number of bits.

3. Match the bit sending technology (numbers) with the underlying system (letters).


Extended Learning

Standards Alignment