<div>I would expect for non-real-time protocols such as FTP that if the packet at the head of the queue is dropped, there'd be several duplicate acks which could trigger congestion control. </div> <div>Regards<BR><BR><B><I>Craig Partridge <craig@aland.bbn.com></I></B> wrote:</div> <BLOCKQUOTE class=replbq style="PADDING-LEFT: 5px; MARGIN-LEFT: 5px; BORDER-LEFT: #1010ff 2px solid"><BR>For non-real time, the answer I believe is drop the new packet.<BR><BR>Dropping the earlier packet (assuming the earlier packet has a lower<BR>sequence number) is more likely to slow effective delivery of data<BR>to the recipient and require a more complex set of retransmissions to<BR>recover from.<BR><BR>Craig<BR><BR><BR>In message <463857A4.1020205@gmail.com>, Khaled Elsayed writes:<BR><BR>>Given a per-connection queue that could potentially become full (or in <BR>>case of RED, hits dropping threshold), an incoming packet arrives and <BR>>finds the queue full. What
would be the best policy:<BR>><BR>>1) admit the new packet and drop one at the queue front<BR>>2) drop the newly arriving packet.<BR>><BR>>For real-time connections, it is intuitive that dropping at queue front <BR>>would tend to result in better delay responses (this was already shown <BR>>in an early paper by Yin and Hluchyj in IEEE Trans. Comm, June 1993). <BR>>What about data/non-real time connections? Assume an FTP or HTTP session <BR>>subject to above situation, would TCP behave better if packet is dropped <BR>>from front or the new packet is dropped?<BR>><BR>>I have no evidence but I tend to feel that if the congestion is <BR>>persistent for some reasonable time, it would make more sense to deliver <BR>>whatever is in the queue right now and drop the new ones at the expense <BR>>of increasing overall avg. packet delay. If the congestion duration is <BR>>small, it would not make a lot of difference (I
guess).<BR>><BR>>Any thoughts?<BR>><BR>>Khaled<BR></BLOCKQUOTE><BR><BR><BR>Muhammad Saqib Ilyas<br>Assistant Professor<br>Department of Computer and Information Systems Engineering<br>NED University of Engineering and Technology, Karachi, Pakistan<br>http://www.saqibilyas.info<br>Graduate Student, LUMS<br>Country Leader, INETA Pakistan<br>Microsoft Most Valuable Professional - C++<p> 
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