On Sun, 2007-05-20 at 02:20 -0400, John Watlington wrote: > On May 20, 2007, at 2:01 AM, Hal Murray wrote: > > > > >> Yes, NTP is one of the services provided by the school servers. > >> Ideally, a laptop's NTP server would be determined by a protocol > >> similar to the one used for internet portal and DNS server --- > >> identifying the "closest" server in the mesh. In any case, network > >> propagation time is taken into account by the NTP (although I believe > >> Hal is far more knowledgable than I in such matters...) > > > > I'm pretty sure there us a slot allocated in DHCP to specify NTP > > servers. > > That requires some script to get the DHCP info and then rewrite > > ntp.conf. > > > > I don't know much about that area. It's not as common as it should > > be, > > mostly because ISPs have their head in the sand about providing NTP > > services > > for their customers which is partly a chicken/egg tangle. > > > > One obvious alternative for olpc is to have a magic DNS name that > > resolves to > > the local NTP server. > > Maigc DNS names at your service. And since the DNS server used by a > laptop in a school setting will also be the closest mesh portal, the > NTP server can be the closest on the mesh.
It's also fairly easy to do with NM if you push the info through DHCP. Dan > > How do the backup scripts find their local server? If they use a > > magic name, > > ntpd should be able to do something similar. > > > > ntpd assumes that the network delays between client and server are > > symmetric. > > It fudges the response by half the round trip delay and then > > filters that. > > That works pretty well except for several cases which may not be > > uncommon: > > > If you have an asymmetric link like ADSL, you will be off by the > > bandwidth > > differences multiplied by the packet size, even if the link is > > unloaded. > > That gives you a constant offset which is often OK. > > > > The filter gets confused by queuing delays if you have a link with > > asymmetric > > loads for extended periods of time, like when downloading a CD over > > SDSL. > > > > > >> Anybody on the XO side know if NTP is part of the build yet ? > > > > I think it is included in 406. The config file is setup to use > > several pool > > servers. That's typical. It's a lot better than nothing but > > generally picks > > servers at random from a set scattered around the world. What you > > really > > want is sane nearby servers where nearby means low network delays > > rather than > > few miles/kilometers. > > > > We'll know a lot more when somebody gets some ping data on a > > typical mesh. > > (I realize that "typical" probably doesn't exist, but we have to start > > somewhere.) > > > > [I've been using my own ntpd setup in order to collect some > > statistics. I > > noticed the default setup after updating to 406 before I smashed it > > with my > > stuff. I didn't investigate.] > > _______________________________________________ > Devel mailing list > [email protected] > http://mailman.laptop.org/mailman/listinfo/devel _______________________________________________ Devel mailing list [email protected] http://mailman.laptop.org/mailman/listinfo/devel
