Andy Yates <[email protected]> writes: >Unruh wrote: >> Andy Yates <[email protected]> writes: >> >>> 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. >> >>> 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. >> >> I think you need some specifications. What accuracy do you really need? >> Without that you are simply wasting your, and everyones time and money. >> Direct GPS connection can give you >> 1 usec. Lan connection to those can give you 20usec average. Then each >> stratum will loose about 20-50 usec (my experience). Do you need better than >> msec
>Hi Unruh >Totally agree about specification - trouble is the customers include >third parties who don't issue specifications so we've been tasked to >make it v.accurate, industry leading etc. however I'm not going to >encourage blowing cash on diminishing returns. Thanks for the experience >figures, this is exactly what I need. Note also that it can depend on the network harware. When we ran 100Mb/s switches, the delay time was astonishingly regular and repeatable. Now that we have switched to Gb switches it is not. It much worse. There seems to be a one way "quantization" It used to be that the round trip time from the machines to the ntp stratum 1 source was consistantly 140-160usec. Now it varies, with one level still at the 140usec, but other round trip times of 280 or even longer (on the same machine). And they seem to be one way delays ( the worst kind). Ie, you really need to select the switches between your stratum 1 sources and your machines carefully to get the best behaviour. _______________________________________________ questions mailing list [email protected] https://lists.ntp.org/mailman/listinfo/questions
