<DIV>IMHO, packet pair probing will not derive to real value of available bandwidth if it is not guaranteed that the two packets are scheduled specifically along the path.</DIV>
<DIV> </DIV>
<DIV>In other words, available BW is the speed with which we can satulate the e2e path when different queueing mechanism is adopted. So, what we want to find is : how the queue on the slowest link could be filled. This is really different from what PP based.</DIV>
<DIV> </DIV>
<DIV>Jing Shen<BR><BR><B><I>Jon Crowcroft <Jon.Crowcroft@cl.cam.ac.uk></I></B> wrote:</DIV>
<BLOCKQUOTE style="PADDING-LEFT: 5px; MARGIN-LEFT: 5px; BORDER-LEFT: #1010ff 2px solid">In missive <200305031752.h43HqiE18655@garden.whitehouse.gov>, Donald Rumsfeld typed:<BR><BR>>>I believe that Jon is essentially wrong. The packet-pair technique<BR>>>is definitely not one of the weapons of Mbps detection<BR><BR>I have to agree - but i must reveal a momentary prejudice against pp - i have never been<BR>sure about the gender identity of the 2 packets in question - typically, one packet is<BR>large and one small (to elicit different responses) but why? surely this is the usual<BR>"bigger is better" type engineering macho thing - i am sure people (typical male engineers)<BR>think of that MTUs-worth, thrusting its way thru those queues, while the slight,<BR>deferential-almost, acknowlegement sized frame wends its interesting path. of course, the<BR>alternative, use of similar type packets is in question in some states, where its probably illegal, <BR>and the ttl may therefore be exceeded sooner than expected. then there are the occasional uses by<BR>government agencies of xmas tree (aka bush) packets, accompanied by much smaller, shadow packets <BR>which are hard to detect (i have heard people say that there is almost a witch hunt for<BR>these so-called blur or blaring packets that are so dificult to pin down - i am sure caida have<BR>elegant tools and tweezers that will do the trick tho)<BR><BR>i guess there are those occasional people (some in scandinavia, i've heard)<BR>who prefer 3-somes or more, and claim that there<BR>is more fidelity in the reproduction of results - i await an IMW paper or two to supprt<BR>this<BR><BR>then there's the cloning method - why try a probe when you can imitate the patient to perfection?<BR>well, i for one am not a sheep, content merely to follow the flock. no, i think that if 0 or 1 <BR>are good enough, then the search should concentrate on figuring out what the capacity of a path is,<BR>using a lone wolf approach - the idea here is that we send 1 packet out, bu
t that it not<BR>only propogates, but it also removes another packet in flight - so as we extend the<BR>wolverine's ttl, it samples along hops with queues which either have the original, or 1 less,<BR>packet than previously encountered (think of this as a feynman interaction in reverse with<BR>packet and anti-packet starting at each point - kind of extreme, adversarial queueing)<BR><BR>now the trick with this latter idea is how to implement it! i guess it depends on whether<BR>one can affect already queued packets by modifying the ACL on the output queue (or perhaps<BR>changing priorities if custom queueing is enabled). a laudable part of this approach is<BR>that it incurs less load than packet-pair....<BR><BR>of course, i could just be joking...<BR><BR>cheers<BR>jon<BR></BLOCKQUOTE><BR><BR>Jing Shen<br><br>State Key Lab of CAD&CG<br>ZheJiang University(YuQuan)<br>HangZhou, ZheJiang Province 310027<br>P.R.China<p><br><hr size=1><b>Do You Yahoo!?</b><br>
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