> I searched the man page and google but can not find a definition for > mdev, which is a returned statistic when ping exits. Does anybody > know what it is measuring?
>>I found the answer. It is the standard deviation. mdev stands for mean >>deviation. mdev is the std dev? standard deviation is not the same thing as the mean deviation. http://mathworld.wolfram.com/StandardDeviation.html http://mathworld.wolfram.com/MeanDeviation.html i didn't look at the source, but what you've excerpted below looks like they are assigning 'mdev' the stnd deviation, which doesn't look right. quick, now is your chance to make a contribution to the open source movement!! submit a bug and patch: s/mdev/sdev/g on ping_common.c w00t! Josh Coates www.jcoates.org -----Original Message----- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] Behalf Of Derek Burdick Sent: Friday, June 17, 2005 12:28 AM To: Provo Linux Users Group Mailing List Subject: Re: Ping's definition of mdev I found the answer. It is the standard deviation. mdev stands for mean deviation. Derek Burdick wrote: > I searched the man page and google but can not find a definition for > mdev, which is a returned statistic when ping exits. Does anybody > know what it is measuring? I have looked through the code and > determined mathematically what the algorithm does, but I don't see any > relevance to networking. Does anybody have any insight? I have > attached my comments on what the code is doing in case somebody knows > of a generic use for this algorithm. > > Here is the sample output > 3460 packets transmitted, 3451 received, 0% packet loss, time 119983ms > rtt min/avg/max/mdev = 303.108/305.426/347.859/2.979 ms, pipe 11 > > Here is what I believe ping_common.c is doing to determine mdev: > > for each packet received and assuming tsum and tsum2 start at 0: > tsum += triptime > tsum2 += triptime * triptime > > Once ping finishes > tsum /= nreceived + nrepeats // Get the average of the triptimes. We > have 0 repeats so it has no effect here. > tsum2 /= nreceived + nrepeats // Get the average of the squared > triptimes. Once again we have 0 repeats > > tmdev = llsqrt(tsum2 - tsum * tsum); // Take the square root of the > difference of the average squared triptimes and the average triptime > squared. > > tmdev is then printed as printf("%ld.%03ld ms", tmdev /1000, > tmdev%1000); //This is giving us the results in milliseconds > > If anybody has any insight or comments i'd love to hear them. > > Thanks, > Derek > > p.s. This is not a class assignment. Our sales team wants to sell IP > phone service to a client in India using the Internet for the > bandwidth. I was looking for any numbers I could find to help me give > them a good idea of what to expect. > > I think I will add a Jitter calculation in to ping as that is usually > a great indication along with packet loss on what to expect with VOIP. > > Thanks again. > .===================================. > | This has been a P.L.U.G. mailing. | > | Don't Fear the Penguin. | > | IRC: #utah at irc.freenode.net | > `===================================' .===================================. | This has been a P.L.U.G. mailing. | | Don't Fear the Penguin. | | IRC: #utah at irc.freenode.net | `===================================' .===================================. | This has been a P.L.U.G. mailing. | | Don't Fear the Penguin. | | IRC: #utah at irc.freenode.net | `==================================='
