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<TITLE>[e2e] A simple scenario. (Basically the reason for the sliding window thread ; -))</TITLE>
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<DIV id=idOWAReplyText14614 dir=ltr>
<DIV dir=ltr><FONT face="Courier New" color=#000000 size=2>Detlef
wrote:</FONT></DIV>
<DIV dir=ltr><FONT face="Courier New" size=2></FONT> </DIV></DIV>
<DIV dir=ltr><FONT face="Courier New" size=2>> The basic question is whether
the use of a splitter may shorten the RTT<BR>> seen by the sender to that
degree, that the appropriate rate cannot be<BR>> achieved by a sliding window
protocol even if CWND were set to 1 MSS,<BR>> the sender must hence be
stalled from time to time to have the rate slow<BR>> enough.</FONT></DIV>
<P><FONT size=2><FONT face="Courier New">Yes</FONT></P>
<DIV dir=ltr><FONT face="Courier New">Here is a more practical example
-<BR><BR>Sender<BR>-------------------------TCP-Splitter---------------------Receiver<BR> 100
Mbps, 10 us (LAN) 1 Mbps, 300 ms
(geo-satellite)<BR></FONT></DIV>
<DIV dir=ltr><FONT face="Courier New">A cwnd of 1 segment of 1500 bytes will
achieve roughly </FONT></DIV>
<DIV dir=ltr><FONT face="Courier New">1500 * 8 / (20 + 120) Mbps</FONT></DIV>
<DIV dir=ltr><FONT face="Courier New">i.e., 85 Mbps, on the LAN
segment,</FONT></DIV>
<DIV dir=ltr><FONT face="Courier New">which is much higher than the </FONT><FONT
face="Courier New">satellite link rate.</FONT><FONT face="Courier New"></DIV>
<DIV dir=ltr><BR>> So, what should the splitter do?<BR>> 1. stall the
sender periodically using zero windo packets?<BR>> 2. don´t care, doesn´t
matter?<BR>> 3. ??<BR><BR>Since, the network can support a maximum of 1 Mbps,
</DIV>
<DIV dir=ltr>on average, the sender should send 1 segment every </DIV>
<DIV dir=ltr>1500 * 8 / 1000000 seconds</DIV>
<DIV dir=ltr>i.e, every 12 ms.</DIV>
<DIV dir=ltr> </DIV>
<DIV dir=ltr>So, stalling the sender using zero window Ack packets is an </DIV>
<DIV dir=ltr>appropriate solution, which does not require any changes to the
</DIV>
<DIV dir=ltr>sender TCP stack. The cwnd value may be 1 segment or larger, </DIV>
<DIV dir=ltr>it does not matter.</DIV>
<DIV dir=ltr> </DIV>
<DIV dir=ltr>Anil</DIV>
<DIV dir=ltr>-----------</DIV>
<DIV dir=ltr>Anil Agarwal</DIV>
<DIV dir=ltr>ViaSat Inc.</DIV>
<DIV dir=ltr> </DIV></FONT></FONT>
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