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we know that a rough estimation of TCP rate is: WINDOW/RTT, where WINDOW is the min(CWIN, RWIN), CWIN is the congestion window size of the sender, while RWIN is the receiving window.

nowadays, the encoding rate of videos may be 1000KB/s(8000kbit/s), if RTT is 500ms, it needs the window size to be 2000KB. But we know that usually the receiving window size is below 64KB, there is a big gap.

so if RTT is too large, TCP streaming is not possible?

Is my understanding right?


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up vote 0 down vote accepted

No, we just use very large windows. Per RFC1323, 1GB is the maximum TCP window size -- 2,000KB is not a problem.

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You meant the RWIN will be increased by the streaming client when it detects large RTT? But for the streaming server, its CWIN begins with 1 MSS in slow start phase, it takes a bit long time to reach 1GB – misteryes Jul 3 '13 at 1:01
@misteryes: The window can be enlarged very quickly. – David Schwartz Jul 3 '13 at 1:06
how about the RWIN on the client side? will the client TCP stack increase the RWIN quicklyl in reaction to high RTT ? – misteryes Jul 3 '13 at 1:14
Yes. It will as well. – David Schwartz Jul 3 '13 at 2:03

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