Richard B. Gilbert wrote: > Andy Yates wrote: >> Does anybody have any figures that shows the effect on accuracy of an >> NTP v3 client using a stratum 1 server rather than a stratum 2 or 3 >> server? It's all in a GE LAN based scenario, commercial stratum 1 >> servers connected to GPS and stratum 2 and 3 servers are typically >> dedicated Linux boxes. > > Stratum has very little to do with accuracy! It's simply a count of the > number of servers between you and the root of the tree; e.g. the atomic > clock.
Many thanks Richard - exactly my argument too. > > If you have low latency connections a stratum three server can give you > millisecond or maybe microsecond accuracy. Let those connections get > really busy and your accuracy goes down the toilet even at stratum two! >> >> The reasons is that I would rather scale by adding strata - its a very >> big data center with thousands of clients and has several "zones" that >> are isolated. However some opinion is suggesting we run IRIG-B between >> the GPS receiver and a bunch of stratum 1 servers and clients access >> these directly. Much more expensive and any increase in accuracy from a >> client experience may be negligible. >> >> However I'm been pressed to supply an SLA for accuracy. My argument is >> that although you can get your stratum one server to synchronize to >> microseconds of UTP, as soon as the client uses NTP v3 over the LAN, >> even a GE LAN, then the accuracy degrades and putting well designed well >> specified stratum between the boxes is not going to decrease accuracy >> sufficiently to warrant purchasing many stratum one appliances. >> >> Thoughts? > > NTP v4 over the LAN would be just as bad as V3. Think about broadcast or > multicast! That way you don't clutter up the net with queries and > response. Instead, every N seconds your server announces: "at the chime > the correct time. . . ." and your clients can adjust their clocks as > necessary. Your broadcast and/or multicast clients will exchange > packets initially in order to establish the round trip delay. After > that initial volley, the clients just sit and listen. > Agreed - we already use multicast clients by default however my point is that having your stratum 1 server synchronised to microseconds does not guarantee a microsecond NTP client experience and adding additional strata does not materially effect this. However I need evidence to back this up to support the SLA - I don't want to get into having to get testers in to prove the obvious however if anybody has already looked into this and has evidence then this would be useful. _______________________________________________ questions mailing list [email protected] https://lists.ntp.org/mailman/listinfo/questions
