Communication Protocols

How do two computers communicate?

Communication Protocol

We can make a parallel with human communication.

A protocol is a set of rules that ensure information is well understood. We can highlight two extremes:

structured human conversation
incoherent messages, hubbub

We will here realize the construction of a basic communication protocol, as well as a program that will allow us to use it to create a chat system:

sending global messages
sending personal messages
creating a discussion group

Using micro:bit cards

We will use micro:bit cards to practice a communication network simulation. They allow us to approach the question with useful simplifications:

no network to configure
radio communication, so wireless
using Python

micro:bit editor v3

After Capytale notebooks, Thonny, Mu, a new editor!

Editor source code

The editor is open-source.

The radio module

The radio module of micro:bit cards is very simple to use. A code example:

from microbit import *
import radio

radio.on()  # Activate radio
radio.config(channel=10)  # Set a channel (10 here)

while True:
    if button_a.was_pressed():
        radio.send("Hello!")  # Send a message
    message = radio.receive() # Check regularly for message reception
    if message:
        print(message)  # Display received message in console

Explanations:

the radio module contains functions to interact with the micro:bit card's radio
the radio.config() function allows configuring the radio
the radio.on() function allows activating the radio
the radio.send() function allows sending data by radio

Communications without protocol

In this first exercise, we will get familiar with the editor interface, ensure proper functioning of sending a program to a card, and set up our first chat discussion system.

Instructions

The objective is simple:

create a program to join channel 10
the microbit card detects button A press - if button A is pressed, it asks the user for the message to send (input() function) - once the result of input() has been stored in a variable, we send the content of this variable with radio.send() - to avoid multiple sends, we can use immediately after radio.send() the sleep(100) function which will delay the program - with radio.receive(), we detect message reception, which we'll display with print() in the console

This system quickly shows its limits: a set of messages whose sender and recipient we don't know succeed each other, it's impossible to follow a conversation. The whole thing corresponds to a sort of unintelligible background noise.

Setting up a protocol

A communication protocol will easily allow us to improve our messages to reach our objective: a large forum where you can communicate with whoever you want, knowing precisely who is speaking to you and to whom you are addressing.

We therefore need to find a way to add information to the simple message content, notably the sender and recipient. We must therefore, together, agree on a format that will be common to all our messages, and that our programs will be able to process: a protocol.

We remind some useful functions:

the split() function allows dividing a string into a list of strings. The argument is the separator.

message = "Hello! How are you?"
message.split('.') # Will give a list: ["Hello ", " How are you?"]

the + operator allows concatenating strings:

author = "Mathieu"
message = "Hello"
frame = author+message
# frame will equal "MathieuHello"

Improving our program

Continue on page 2