05 TCP Windowing Lab Manual

05 TCP Windowing Lab Manual - Lab 5: Predicting the Impact...

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OPNET IT Guru Lab 5, Page 1 Lab 5: Predicting the Impact of TCP Window Size on Application Performance Objective This lab teaches the use of a very important TCP parameter, the TCP window size value, which is contained in the window size field of the TCP segment. Suppose that Host A is transmitting a segment to Host B. The window size field value tells Host B how many more bytes of data the Host B may transmit before getting another TCP segment with a window size field value to extend the number of bytes that Host B may send. If the window size field value is made too small, Host B will often have to wait to transmit because it has reached its transmission limit. In the extreme case, Host A will have to wait after each transmitted TCP segment to get a response before sending the next segment. Having to wait will slow throughput considerably. On the other hand, if the window size field is made too large, the Host B may transmit so many segments that Host A will be overloaded. The window size field provides flow control, regulating the rate at which the transport processes on the two hosts may transmit. In this lab, we’ll investigate the performance of an account transfer application with different TCP window sizes. Overview Standard Chartered Bank has one of its branches located in Sydney, Australia from where it transfers daily account and transaction information of 25 MB to its backup center (data center) in Washington DC. The branch and the backup station are connected through a frame relay network with a latency of 5 ms. The time to transfer a 25 MB file over a T1 link is estimated by the IT team to be approximately 130 sec. We will first observe the actual transfer time for this transfer over a T1 link. After observing very high transfer times for the file transfer, the IT team decides to upgrade the link to the frame relay cloud to a T3 link, assuming that the delay is caused due to low bandwidth. Even the upgrade in bandwidth does not give the desired results. The
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05 TCP Windowing Lab Manual - Lab 5: Predicting the Impact...

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