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# Computer Networking : A Top-down Approach

 Authors: James F. Kurose, Keith W. Ross ISBN: 9780132856201 Edition: 6
 Chapter: Transport Layer Exercise: Problems Question: 15

### Question

Consider the cross-country example shown in Figure 3.17. How big would the window size have to be for the channel utilization to be greater than 98 percent? Suppose that the size of a packet is 1,500 bytes, including both header fields and data.

### Answer

Consider two systems A and B.

The round-trip propagation delay between A and B (RTT) = 30 ms.

Transmission rate of the link between A and B (R) = 1Gbps = 109bps.

The size of the data packet (L)= 1500 bytes (1500x8 bits)

The following is the formula to calculate the time required to transmit the packet over the 1 Gbps link: where Dtrans is the time required.

Calculate the window size such that the channel utilization is greater than 98%. Therefore, to utilize 98% of the channel, the window size should be 2451 packets approximately.

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