<div>Ok so how I see this is in 2 scenarios:</div>
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<div>Say the no of packets ur sending i.e 10 in ur case could be either a set of 10 packets in the middle of a connection or the last set of packets in a connection. If its in the middle of a connection and if the last 4 packets have been lost as u say, the previous 6 packets would have triggered the sender to send few more packets (depending on whether its in slow start or congestion avoidance), thus the flight size would not be 4 as u claim - but would be more than that. If its the latter case where the set of packets were last in the connection, then if these 4 packets were lost - then they would be recovered only by a retransmission timeout.
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<div>-Arjuna</div>
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<blockquote class="gmail_quote" style="PADDING-LEFT: 1ex; MARGIN: 0px 0px 0px 0.8ex; BORDER-LEFT: #ccc 1px solid"><br>Message: 2<br>Date: Thu, 11 May 2006 17:03:12 +0200<br>From: "Daniel Minder" <<a href="mailto:daniel.minder@informatik.uni-stuttgart.de">
daniel.minder@informatik.uni-stuttgart.de</a>><br>Subject: [e2e] Question on ssthresh setting in RFC 2581<br>To: <<a href="mailto:end2end-interest@postel.org">end2end-interest@postel.org</a>><br>Message-ID: <001701c6750c$08c16ff0$10d24581@pcvs7
><br>Content-Type: text/plain; charset="us-ascii"<br><br>Hi,<br><br>can anybody explain why equation (3) in RFC 2581 is<br>ssthresh = max (FlightSize / 2, 2*SMSS)<br>and why this has changed from RFC 2001 where min(rwnd, cwnd)/2 was used.
<br><br>In some postings, I found that FlightSize is usually equal to min(rwnd,<br>cwnd) - but not always. According to the RFC, flightsize is "the amount of<br>data that has been sent but not yet acknowledged".
<br><br>Let's assume that 10 packets have been sent. If all 10 get lost, flightsize<br>is 10 and ssthresh will be set to 5. But if only the last 4 get lost (and no<br>more packets are to be sent), flightsize is 4 and ssthresh will be set to 2.
<br>This seems counterproductive to me since the network is propably more<br>congested in the first case than in the second. Therefore, ssthresh should<br>be set to a lower value if more packets get lost, i.e. when flightsize is
<br>larger. For example:<br>ssthresh = max( (min(rwnd, cwnd) - FlightSize) / 2, 2 * SMSS)<br><br>Or did I miss the point?<br><br>TIA,<br>Daniel<br><br><br clear="all"><br>-- <br>Regards,<br>Arjuna<br><br>Postdoctoral Researcher
<br>Engineering Research Lab,<br>Department of Engineering,<br>University of Aberdeen </blockquote></div>