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rdt_layer.py
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rdt_layer.py
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from segment import Segment
import math
# #################################################################################################################### #
# RDTLayer #
# #
# Description: #
# The reliable data transfer (RDT) layer is used as a communication layer to resolve issues over an unreliable #
# channel. #
# #
# #
# Notes: #
# This file is meant to be changed. #
# #
# #
# #################################################################################################################### #
class RDTLayer(object):
# ################################################################################################################ #
# Class Scope Variables #
# #
# #
# #
# #
# #
# ################################################################################################################ #
DATA_LENGTH = 4 # in characters # The length of the string data that will be sent per packet...
FLOW_CONTROL_WIN_SIZE = 15 # in characters # Receive window size for flow-control
sendChannel = None
receiveChannel = None
dataToSend = ''
currentIteration = 0 # Use this for segment 'timeouts'
# Add items as needed
countSegmentTimeouts = 0
# ################################################################################################################ #
# __init__() #
# #
# #
# #
# #
# #
# ################################################################################################################ #
def __init__(self):
self.sendChannel = None
self.receiveChannel = None
self.dataToSend = ''
self.currentIteration = 0
# Add items as needed
self.seqnum = 0 # The next data segment to be sent.
self.recieved = {} # The list of data segments recieved.
self.prevAck = 0 # The last ACK recieved.
self.timoutCount = 0 # Timeout counter.
# ################################################################################################################ #
# setSendChannel() #
# #
# Description: #
# Called by main to set the unreliable sending lower-layer channel #
# #
# #
# ################################################################################################################ #
def setSendChannel(self, channel):
self.sendChannel = channel
# ################################################################################################################ #
# setReceiveChannel() #
# #
# Description: #
# Called by main to set the unreliable receiving lower-layer channel #
# #
# #
# ################################################################################################################ #
def setReceiveChannel(self, channel):
self.receiveChannel = channel
# ################################################################################################################ #
# setDataToSend() #
# #
# Description: #
# Called by main to set the string data to send #
# #
# #
# ################################################################################################################ #
def setDataToSend(self, data):
self.dataToSend = data
# ################################################################################################################ #
# getDataReceived() #
# #
# Description: #
# Called by main to get the currently received and buffered string data, in order #
# #
# #
# ################################################################################################################ #
def getDataReceived(self):
# ############################################################################################################ #
# Identify the data that has been received...
recieved = ""
i = 0
# Until a data segment is missing in the sequence...
while i in self.recieved:
# Put the data segment in-order
recieved += self.recieved[i]
# Incriment the iterator through the data list.
i += self.DATA_LENGTH
# ############################################################################################################ #
return recieved
# ################################################################################################################ #
# processData() #
# #
# Description: #
# "timeslice". Called by main once per iteration #
# #
# #
# ################################################################################################################ #
def processData(self):
self.currentIteration += 1
self.processSend()
self.processReceiveAndSendRespond()
# ################################################################################################################ #
# processSend() #
# #
# Description: #
# Manages Segment sending tasks #
# #
# #
# ################################################################################################################ #
def processSend(self):
# ############################################################################################################ #
# You should pipeline segments to fit the flow-control window
# The flow-control window is the constant RDTLayer.FLOW_CONTROL_WIN_SIZE
# The maximum data that you can send in a segment is RDTLayer.DATA_LENGTH
# These constants are given in # characters
# Somewhere in here you will be creating data segments to send.
# The data is just part of the entire string that you are trying to send.
# The seqnum is the sequence number for the segment (in character number, not bytes)
# Determine number of packets to be sent at once in pipeline
# End function if no data to send (this will happen on server calls).
# If there is no data to send, do nothing.
if self.dataToSend == '':
return
# If there's been a timeout, send the segment corresponding with the ACK.
# Or if all data has already been sent, bypass the timout and default to sending missing ACKs.
if self.timoutCount >= 5 or self.seqnum > len(self.dataToSend):
# Send the latest requested sequence.
segmentSend = Segment()
segmentSend.setData(self.prevAck, self.dataToSend[self.prevAck: (self.prevAck + self.DATA_LENGTH)])
print("Sending segment: ", segmentSend.to_string())
self.sendChannel.send(segmentSend)
# Reset the timeout counter.
self.timoutCount = 0
# If the resend flags have not been set...
else:
# For as many data segments that can fit in the window size...
for i in range(0, math.floor(self.FLOW_CONTROL_WIN_SIZE / self.DATA_LENGTH)):
# Send those new segments.
segmentSend = Segment()
segmentSend.setData(self.seqnum, self.dataToSend[self.seqnum: (self.seqnum + self.DATA_LENGTH)])
print("Sending segment: ", segmentSend.to_string())
self.sendChannel.send(segmentSend)
# Increment the data sent counter.
self.seqnum += self.DATA_LENGTH
# ################################################################################################################ #
# processReceive() #
# #
# Description: #
# Manages Segment receive tasks #
# #
# #
# ################################################################################################################ #
def processReceiveAndSendRespond(self):
# This call returns a list of incoming segments (see Segment class)...
listIncomingSegments = self.receiveChannel.receive()
# If the list is empty(aka there were no segments recieved), do nothing.
if listIncomingSegments == []:
return
# ############################################################################################################ #
# What segments have been received?
# How will you get them back in order?
# This is where a majority of your logic will be implemented
# If the segments have data...
if listIncomingSegments[0].acknum == -1:
# For each segment...
for segment in listIncomingSegments:
# If the segment data is valid...
if segment.checkChecksum() == True:
# Add it to the list of stored data.
self.recieved[segment.seqnum] = segment.payload
# Send an ACK with the value of the highest in-order segment catalogued.
segmentAck = Segment()
segmentAck.setAck(len(self.getDataReceived()))
print("Sending ack: ", segmentAck.to_string())
self.sendChannel.send(segmentAck)
# If the segment is an ACK...
else:
# If it's the same ACK as last time...
if self.prevAck == listIncomingSegments[0].acknum:
# Increment the timeout counter.
self.timoutCount += 1
# Note the new ACK value.
self.prevAck = listIncomingSegments[0].acknum
# If the same ACK has been seen too many times...
if self.timoutCount >= 5:
# Increment the total timeouts counter.
self.countSegmentTimeouts += 1
# ############################################################################################################ #
# How do you respond to what you have received?
# How can you tell data segments apart from ack segemnts?
# Data segments return with a -1 in the acknum.
# Somewhere in here you will be setting the contents of the ack segments to send.
# The goal is to employ cumulative ack, just like TCP does...