You are hired as a consultant by the Faulty Networks Corporation to fix a proble

Question

You are hired as a consultant by the Faulty Networks Corporation to fix a problem that they are having with a proprietary transport layer protocol, FNC-TP. FNC-TP uses a Go-Back-4 ARQ scheme. The sequence number field and the acknowledgement field of the FNC-TP header are each two bits in length. Draw a diagram (similar to Figure 3.22 in Kurose and Ross) that demonstrates that FNC-TP may not always work properly.

Sender Receiver send pkt0 : , rcv pkt0 send ACKO send pktl: : rcv pktl send pkt2 send ACK1 (loss) send pkt3 (wait): :rcv pkt3, discard send ACK1 rCv ACKO send pkt4 rcv ACK1 send pkt5 : rcv pkt4, discard ; send ACK1 pkt2 timeout send pkt2: rcv pkt5, discard : send ACK1 send pkt3 send pkt4 send pkt5 . rcv pkt2, deliver send ACK2 : rcv pkt3, deliver : send ACK3 Figure 3.22 Go-Back-N in operation

Explanation / Answer

As in the diagram , it show how the data is transfar from one server to another using transport layer.while transfar data from one server to another then the data is divided in small packet and then the packet is transfar from connect route between them.

in this case ,when data is divided into small parts then it is necessary to check acknowledgement of each packet is properly recived at end users or reciver server.

while talk about the "GO BACK 4 ARQ". when the data packet 0 is send to reciver then the reciver send the acknowledgement regarding that packet with in certain time to sender for confirmation about the recived packet.

while the reciver send the acknowledgement in this period of time ,sender server send another packet in continuity.

and checked about the status of recived . If within certain time the acknowledgement is not recived and the all the next packet are held for acknowledgement of that particular contiuity of acknowledgement.

If the acknowledgement of next is reached before the previous one then the it discard the recvied packet.and send the previous again and then start for continuity as in diagram .

this is the concept of "go back 4arq".

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