I'm copying Dave Mills on this, maybe he can say more and that's also the reason that I'm top-posting. . My feeling on this is that is a very restricted set of possible problems and is unlikely to be useful for NTP since most packets go through multiple hops and you are unlikely to get the outbound path and the return path follow the same paths.
URL: http://www.owlnet.rice.edu/~gurewitz/4.pdf Danny Yaakov Stein wrote: > Hi all, > > > > I have recently been working time distribution in the presence of strong > asymmetry, > > and have come across a method that helps in certain cases. > > > > I am sure that you all remember the CTP algorithm that I have brought up > before > > (and presented at IETF-74). > > > > The same academic group has an earlier article that I had previously > overlooked. > > I am talking about : > > > > Gurewitz O, Sidi M. > Estimating One-Way Delays from Cyclic Path Delay Measurements. > 16th IEEE INFOCOM 2001, Anchorage, Alaska. [PDF > <http://www.owlnet.rice.edu/~gurewitz/4.pdf>] > > > > > > This article gives a procedure for determining one-way delays > > based purely on round-trip delay measurements (i.e., what we would call > T4-T1), > > knowledge of topology, and the assumption of additivity of propagation > delays. > > > > The idea is that nodes measure round-trip times to various other nodes, > > knowing which nodes are traversed. > > For example, assume three nodes connected in a triangle > > 1 > > / \ > > / \ > > 2 -------- 3 > > and we measure the times for the following paths > > 1 2 3 > > 2 3 2 > > 3 1 3 > > 1 2 3 1 > > We thus have 4 equations for 6 variables > > (since the links are not assumed symmetric, the variables are D1-2, > D2-1, D2-3, D3-2, D1-3, D3-1 ). > > Using additivity and non-negativity it turns out that one can solve an > optimization problem > > which minimizes the error of these equations. > > > > The solution requires a centralized server to do the math PCE-style, > > but solves a problem that I don't know any other way to solve. > > > > Comments ? -- This message has been scanned for viruses and dangerous content by MailScanner, and is believed to be clean. _______________________________________________ TICTOC mailing list [email protected] https://www.ietf.org/mailman/listinfo/tictoc
