PA2: CSEE W4119 Computer Networks Programming Assignment 2 - Network Protocols Emulation

PART1: GBN

Ideas

• create a function that checks if a timer has already been set
  • use it in both the sender and receiver function
  • should have a function that turns off the timer whenever a packet is received.
  • starts again when realizes there are still packets waiting to be received
    • keep in mind of the scenario where the first "next"packet is sent but there are still packets awaiting a receive. the timer still restarts with these packets as well once the ACK is received.
      • can have the timer "restart" when the buffer is recognized as not empty. once the buffer is empty the clock is completely wiped.
  • once the timeout happens, the packets in the window are resent. buffer is cleared and the window packets are put back into the buffer

Notes

• sender/receiver in UDP protocol
• implementation of GBN on top of UDP on both sender and receiver
• guarantee packets be sent in correct order to higher layers****
• unreliable channel emulation:
  • sender/receiver drops incoming packet/ACK w/ prob
• [python3 gobackn.py self-port peer-port window-size [-d value-of-d | -p value-of-p]]
• argv[0] = file name
• argv[1] = sender port
• argv[2] = receiver port
• argv[3] = window size
• argv[4] = d/p
• argv[5] = value

Protocol

• packet
  • each char = one packet (packet max len = 1 byte)
  • data packet = seq # (no format requirement) + data
  • ACK = seq #
• buffer
  • sender/receiver have sending buffer
  • data packets put in buffer before send
  • data packets removed from buffer when corresp. ACK received
  • sending buff should be long enough to avoid conflict of packet #s
  • full buffer -> wait until more space is available
• window
  • moves along sending buff
  • window should wrap if implemented as array
  • packets in window = sent out immediately
  • window size = passed as argument****
• timer
  • starts after first packet sent out, stops when ACK received
  • timer restarts when window moves
  • timeout = 500ms

Emulation

• GBN nodes to send packets over UDP protocol
• receiver = deilberately discard data packets (probability)
• sender = deliberately discard ACKs before handling them (probability)
• probability = determinstic and probabilistic (passed as an arg)

Loss Rate Calculations (5pts/40pts)

• a summary at the end of transmission
• both sender and receiver print out ratioof packet failures/total packets received
• tests provided

PART2: DISTANCE-VECTOR ROUTING ALG

Notes

Protocol

PART3: COMBINATION

Notes

• Will be done later. Will see if have enough time

helpful links that sometimes slow my computer down like crazy so I save them all:

• https://www.tutorialspoint.com/a-protocol-using-go-back-n#:~:text=Go%2DBack%2DN%20protocol%2C,receiving%20window%20size%20of%201.
• https://www.baeldung.com/cs/networking-go-back-n-protocol
• https://docs.oracle.com/cd/E19620-01/805-4041/6j3r8iu2e/index.html