Stop & Wait Protocol

Question

Assume a network that does not drop, duplicate, or corrupt any packets and that you are using a stop-and-wait protocol between two endpoints, A and B. The time it takes for a packet to get from A to B is uniformly distributed between 10 and 20ms. The time it takes for a packet to get from B to A is uniformly distributed between 20 and 30ms. The time it takes any packet to get from one endpoint to the other is independent of the time it takes any other packet.

You want to choose the timeout so that for each data packet that you send, 50% of the time you will not have to retransmit it due to a timeout. What is the largest possible timeout you can choose (in ms)?

Comments

20 ms?

Answer 1

40 ms

Comments

can u please explain how the value 40 came

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It's because the mean time from A to B is 15ms and the mean time from B to A is 25 ms. Therefore, the round trip time is a random variable that has a mean of 40ms. Half of the round trip times will be longer than 40ms and half will be shorter. 40 ms is the largest timeout that you can choose such that 50% of the time packets are not retransmitted due to timeout.

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SpeedLearner

What is will be the answer if 60 %, will it be 48ms ?