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. > 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
