4. OSI Model Open System Interconnection.py

# The OSI model is a conceptual model and does not have a specific implementation or programming interface. However, network protocols and applications can be designed and implemented using the OSI model as a reference.

#Here is an example of Python code that implements a simple client-server network communication using the TCP/IP protocols, which are based on the OSI model:

#Server code:

import socket

# Create a TCP/IP socket
server_socket = socket.socket(socket.AF_INET, socket.SOCK_STREAM)

# Bind the socket to a specific IP address and port number
server_address = ('localhost', 8000)
server_socket.bind(server_address)

# Listen for incoming connections
server_socket.listen(1)
print('Server is listening on', server_address)

while True:
    # Wait for a client to connect
    print('Waiting for a client to connect...')
    client_socket, client_address = server_socket.accept()
    print('Client', client_address, 'connected!')

    # Receive data from the client
    data = client_socket.recv(1024)
    print('Received data:', data.decode())

    # Send a response to the client
    message = 'Hello from the server!'
    client_socket.sendall(message.encode())

    # Close the client socket
    client_socket.close()

    # Client code:
    import socket

# Create a TCP/IP socket
client_socket = socket.socket(socket.AF_INET, socket.SOCK_STREAM)

# Connect to the server
server_address = ('localhost', 8000)
client_socket.connect(server_address)
print('Connected to', server_address)

# Send a message to the server
message = 'Hello from the client!'
client_socket.sendall(message.encode())

# Receive a response from the server
data = client_socket.recv(1024)
print('Received data:', data.decode())

# Close the socket
client_socket.close()

# This code demonstrates how the TCP/IP protocols, which are based on the OSI model, are used to establish a connection between a client and a server, transfer data between them, and then close the connection.