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March 16, 2020 02:01
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| #!/usr/bin/python | |
| # receiver.py | |
| # | |
| # Go-Back-N simulation based on the RDT 2.2 protocol described in | |
| # section 3.4.1 of Computer Networking: A Top-Down Approach, Kurose-Ross, 7th edition | |
| # | |
| import sys | |
| from sm import StateMachine | |
| import rdtlib | |
| from rdtlib import udt_send, rdt_rcv, deliver_data, make_pkt, extract, iscorrupt | |
| expectedSeqNum = 0 | |
| # Handle the receiver's 'Wait for call from below' states | |
| # | |
| # There are three cases to handle for each of these: | |
| # 1. Packet is corrupt | |
| # 2. Packet is out-of-sequence | |
| # 3. Packet is OK | |
| def receiver_wait_below(): | |
| global expectedSeqNum | |
| print 'Receiver in state WAIT_BELOW' | |
| packet = rdt_rcv() | |
| if iscorrupt(packet): | |
| packet = make_pkt(type=ACK, seq=expectedSeqNum-1) | |
| print 'Receiver: corrupt packet, sending ACK ', expectedSeqNum-1, " ", packet | |
| udt_send(packet) | |
| return 'WAIT_BELOW' | |
| else if not hasSeq(packet, expectedSeqNum): | |
| packet = make_pkt(type=ACK, seq=expectedSeqNum-1) | |
| print 'Receiver: wrong seq num, expected ', expectedSeqNum, ', sending ACK' | |
| udt_send(packet) | |
| return 'WAIT_BELOW' | |
| else: | |
| # OK, transition to waiting for packet with seq=1 | |
| data = extract(packet) | |
| deliver_data(data) | |
| packet = make_pkt(type=ACK, seq=expectedSeqNum) | |
| print 'Receiver: packet OK, sending ACK ',expectedSeqNum, packet | |
| expectedSeqNum +=1 | |
| udt_send(packet) | |
| return 'WAIT_BELOW' | |
| def ReceiverDone(): | |
| pass | |
| # | |
| # Set up the state machine | |
| # | |
| def start_receiver(): | |
| receiver = StateMachine('receiver') | |
| receiver.add_state('WAIT_BELOW', receiver_wait_below) | |
| receiver.add_state('R_END', ReceiverDone, end_state=1) | |
| receiver.set_initial_state('WAIT_BELOW') | |
| receiver.run() | |
| rdtlib.peer = ('10.0.0.1', 12002) | |
| start_receiver() |
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| #!/usr/bin/python | |
| # | |
| # Sender | |
| # | |
| # | |
| # Simulation of the RDT 2.2 protocol described in | |
| # section 3.4.1 of Computer Networking: A Top-Down Approach, Kurose-Ross, 7th edition | |
| # | |
| import sys | |
| from Queue import Queue | |
| from sm import StateMachine | |
| import rdtlib | |
| from rdtlib import rdt_send, udt_send, isACK, iscorrupt, rdt_rcv | |
| nextSeqNum = 0 | |
| base = 0 | |
| windowSize = 4 | |
| lastsndpkt = [None, None, None, None] # Holds last sent packet in case it needs to be retransmitted | |
| sent = 0 | |
| retrans = 0 | |
| # Set up a queue of packets to send | |
| sendbuf = Queue() | |
| for i in 'ABCDEFGHIJ': | |
| sendbuf.put(i) | |
| # Handle the sender's 'Wait for call from above' state | |
| def sender_wait_above(): | |
| global lastsndpkt, sent, nextSeqNum, retrans | |
| print 'Sender in state WAIT_ABOVE' | |
| # Determine whether to retransmit packet depending on RDT transmission window and wait | |
| # | |
| # If a packet in the transmission window is marked as having not been sent, retransmit | |
| # | |
| # If send buffer is not empty and the next sequence number of a packet to be sent is | |
| # within the transmission window, then resend | |
| # | |
| # Wait for a ACK response | |
| for i in range(windowSize): | |
| if lastsndpkt[i] != None: | |
| print 'Retransmitting', lastsndpkt[i] | |
| udt_send(lastsndpkt[i]) | |
| retrans += 1 | |
| elif not sendbuf.empty() and nextSeqNum < base+windowSize: | |
| lastsndpkt[i] = rdt_send(sendbuf.get(), nextSeqNum) | |
| sent += 1 | |
| nextSeqNum += 1 | |
| else: | |
| lastsndpkt[i] = None | |
| return 'WAIT_ACK' | |
| # Handle 'Wait for ACK' states | |
| def sender_wait_ack(): | |
| global lastsndpkt, retrans, nextSeqNum, base | |
| print 'Sender in state WAIT_ACK' | |
| prevBase = base | |
| # Receive and handle packet | |
| # | |
| # Indicate whether packet was either lost in transit or arrived corrupt and print | |
| # | |
| # If base < 10 and the packet was sent successfully (duplicate or not) then | |
| # reset the base to sent packets seq. number+1 | |
| # | |
| # If base = 10, then end sender | |
| for i in range(windowSize): | |
| if base == 10: | |
| return 'S_END' | |
| packet = rdt_rcv(timeout=2) | |
| if packet == None: | |
| print 'Sender: Timeout, for packet', nextSeqNum-windowSize+i | |
| elif iscorrupt(packet): | |
| print 'Sender: Corrupt ACK, for packet', nextSeqNum-windowSize+i | |
| elif not isACK(packet, prevBase+j): | |
| print 'Sender: Duplicate ACK, for packet', packet[0][1] | |
| base = packet[0][1]+1 | |
| break | |
| else: | |
| base = packet[0][1]+1 | |
| # Reset packet transmission history of RDT transmission window | |
| for i in range(windowSize): | |
| windowShift = base - prevBase + i | |
| if windowShift >= windowSize: | |
| lastsndpkt[i] = None | |
| else: | |
| lastsndpkt[i] = lastsndpkt[windowShift] | |
| return 'WAIT_ABOVE' | |
| def SenderDone(): | |
| print 'Send buffer empty, exiting' | |
| print 'Sent: ', sent | |
| print 'Retransmitted: ', retrans | |
| # | |
| # Set up the state machine | |
| # | |
| def start_sender(): | |
| sender = StateMachine('sender') | |
| sender.add_state('WAIT_ABOVE', sender_wait_above) | |
| sender.add_state('WAIT_ACK', sender_wait_ack) | |
| sender.add_state('S_END', SenderDone, end_state=1) | |
| sender.set_initial_state('WAIT_ABOVE') | |
| sender.run() | |
| rdtlib.peer = ('10.0.0.2', 12002) | |
| start_sender() |
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