Consider a TCP connection between hosts A and B. At some time the advertised win

Question

Consider a TCP connection between hosts A and B. At some time the advertised window size from B to A is 2 MSS. Every packet transmitted from A to B is successful with probability p and is dropped with probability 1 - p whereas the transmission from B to A is error-free. What is the total expected time for A to successfully transmit 2 packets? The time for successful transmission is measured from the moment of the transmission of the first packet until the reception of ACK for the second packet. Assume propagation delay between A and B is given by tau. Ignore transmission delay and processing time at each host. Assume the retransmission timeout value as 4tau. Also assume that the retransmission is triggered only by timeouts but not duplicate ACKs.

Explanation / Answer

Total expected time to with success transmit a packet/segment from host A to host B type the momemt of beginning transmission of packet until ACK is received is observed as trip Time (RTT) outlined as below:

RTT = 2*Time needed to deliver the packet + interval.

For the given drawback, interval are often neglected. Hence,

RTT = 2*Time needed to deliver the packet

where Time needed to deliver the packet is given as:

Time needed to deliver the packet = coordinated universal time + Propagation delay + Queueing time

For the given drawback, coordinated universal time and Queueing time are often neglected, whereas Propagation delay between A and B is T.

Hence,

Time needed to deliver the packet = T

Hence

RTT = 2T

As per the matter, two packets square measure to be sent between A and B. Since, window size is two MSS, therefore each the packets are often sent within the same transmission. Therefore, overall expected time are going to be

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