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Lectures notes for 2010 - KTH

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Measuring TCP Per<strong>for</strong>mance<br />

Measured per<strong>for</strong>mance:<br />

• Per<strong>for</strong>mance on Ethernets at ~90% of theoretical value (using<br />

workstations)<br />

• TCP over FDDI at 80-98% of theoretical value<br />

• TCP (between two Crays) at 781 Mbits/sec over a 800Mbit/sec HIPPI<br />

channel<br />

• TCP at 907Mbits/sec on a loopback interface of a Cray Y-MP.<br />

Practical limits:<br />

• can’t run faster than the slowest link<br />

• can’t go faster than the memory bandwidth of the slowest machine<br />

(since you have to touch the data at least once)<br />

• you can’t go faster than the window size offered by the receiver divided<br />

by the round trip time (comes from the calculation of the bandwidth<br />

delay product)<br />

• thus with the maximum window scale factor (14) ⇒ window size of 1.073 Gbits; just divide<br />

by RTT to find the maximum bandwidth<br />

Maguire TCP header continued 5: 36 of 77<br />

maguire@kth.se <strong>2010</strong>.03.21 Internetworking/Internetteknik

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