singha wrote: > I have read the description of NTP peers and I'm quoting one below....
There is a lot of mythology about peers, and I suspect the source you are quoting is mostly mythology (incidentally, for copyright reasons, you should always identify the source when quoting copyrighted material). There appear to be two web pages containing this text, one is <http://www.tavrosnetworks.com/timing.html>, which claims copyright, and one is <www.brillianttelecom.com/file.cfm?content=6&pageId=66>, which appears to give GPS World as a source. It's not clear where the real origin is. It is marketing white paper type material. > > Peer - An NTP peer is a member of a group of NTP servers that are > tightly coupled. In a group of two peers, at any given time, the most > accurate peer is acting as a server and the other peers are acting as In a group of two peers, there will be only one other peer, not "other peers"! Prior to orphan mode, and without it, both will collapse to stratum 16 and drift apart. Peers don't have to be in pairs. I'm not sure about orphan mode, but I think these articles describe the behaviour of the timed protocol, not of ntpd. In a normal peering configuration, some (in a proper configuration, all) the peers will have external time sources or reference clocks. A server with such a source and which is also peered, will set its time based on a weighted average of its external source and the peers to which it connects; it will not select one peer as its only source of time. Again, in such a configuration, at least one of the external time sources will have a lower stratum number than any of the peers and will be the official reference (but not the only source of time on that peer). Other peers will have successively higher stratum numbers as they get more and more hops away from the external clock. In a fully connected network, all except the peer with the external source will be at the same stratum, which will two greater than that of the external source. In a good configuration, many peers will have, independent external sources, and preferably many of them (in fact, I think it is desirable to have more external sources than peers). In that case, it is likely that all of the peers with external sources, will identify one of the external sources. The other peers will point outwards, to lower stratum numbers, and, if the system is stable there will be a chain out from every peer to one of the external sources. I'm not very familiar with orphan mode, but I think even orphan mode uses an average of the time from the adjacent nodes, and doesn't identify a single correct node. Even if it does, it will only select from its immediate neighbours. > clients. The result is that peer groups will have closely synchronized > times without requiring a single server to be specified. > > My question is how does NTP calculate which peer is more accurate? _______________________________________________ questions mailing list questions@lists.ntp.org https://lists.ntp.org/mailman/listinfo/questions
