packetswitching.py

import random
import time

senderPackets = []
receiverPackets = []
r1 = []
r2 = []
message = ""
parity = 0

#input a message to send
message = input("Input a message: ")

#Go through each character of the message and turn it into a packet [header,payload,trailer]
#In each packet we will record the packet number which is the current list length, the character as payload, and the parity 'bit' which is the current length modulus 2 which alternates 0 or 1
for char in message:
    #[packet number, payload, parity check]
    senderPackets.append([len(senderPackets), char, len(senderPackets)%2])

print("Packets to be sent:", senderPackets)

#send each packet in the senderPackets list
for packet in senderPackets:
    #choose a random router to send to
    router = random.choice([r1,r2])
    #add packet to the router list
    print("Packet number", packet[0], "with payload", packet[1], "sent")
    router.append(packet)
    time.sleep(0.05)

#output the router lists for checking
print("Packets sent through router 1:", r1)
print("Packets sent through router 2:", r2)

#for each packet sent to a router, send it to the receiver
for packet in r1[:]:
    print("Packet number", packet[0], "with payload", packet[1], "sent to receiver")
    receiverPackets.append(packet)
    r1.remove(packet)

for packet in r2[:]:
    print("Packet number", packet[0], "with payload", packet[1], "sent to receiver")
    receiverPackets.append(packet)
    r2.remove(packet)

#output unsorted packets at receiver for checking
print("Unsorted packets received at receiver:")
for packet in receiverPackets:
    print(packet)

#this returns the packet number so we can sort
def packetNumber(e):
    return e[0]

#sort the packets by the packet number
receiverPackets.sort(key=packetNumber)

receiverMessage = ""
parity = 0

#reconstruct the message and also check for parity in message (should alternate between 1 and 0)
for packet in receiverPackets:
    if parity % 2 == packet[2]:
        print("Parity check for packet passed!")
    parity += 1
    receiverMessage += packet[1]
    time.sleep(0.05)

print("---------------")
print("Message received:", receiverMessage)