"David L. Mills" <[EMAIL PROTECTED]> writes: >Daivd,
>Well, I have done a market survey of sorts, if you can count my >consulting clients. There seems general agreement that 1 ms is a good >target, but there is a wide range of expecttions on how quickly that >must be achieved. Actually, if the TOY chip is within 1 PPM and the >downtime is less than 1000 s, convergence is essentially instantaneous. >My advice to the Aegis crew was to isolate the NTP puppies on the fire >control Ethernet and allow only a couple of other computers on the wire. >Crony would work just fine. >Here's another contribution to the market survey. There is a seismic >network on the sea floor off the Washington state coast. They need a >millisecond for experiments lasting months, not just 8-hour shifts, and >that when the experiment boxes get rather warm. Crony might work here as >well, but it would have to track large swings in temperature. >Here's another one. National Public Radio (NTP) distributes almost all >program media via IP and digital satellite. They don't need 1 ms, but >they do need good stability in the face of highly variable transmission >delays that could drive crony nuts. Your evidence that it would drive chrony nuts is what? >And another one. A transatlantic link used by Ford Motor was once a >statistical multilexor that interleaved terminal keystrokes on a >demand-assigned basis. Toss NTP packets in that mess and watch the huge >jitter. That not only drove NTP nuts, it drove the TCP retransmission >algorithm nuts, too. And you tested chrony on this? >Seems like the market is highly fragmented. Sure. >I hear you say "100 ms" which I interpret as 100 milliseconds. Even 25 >year old fuzzballs could to much better than that on the congested >ARPAnet. Did you mean 100 microseconds? >Dave >David Woolley wrote: >> David L. Mills wrote: >> >>> 5. This flap about the speed of convergence has become silly. Most of >>> us are less concerned about squeezing to the low microseconds in four >> >> >> Have you done the market surveys to confirm this? I don't have the >> resources or time to do that, but my impression from the sort of >> questions that appear on this newsgroup is that most IT managers and >> turnkey system developers who want better than 100ms clock accuracy want >> one or both of: >> >> - fast convergence (small compared with overall bootup time) - a >> a common case, these days, is that they are not allowed to process >> financial transactions until convergence is complete; >> >> - strict monotonicity. >> >> It may well be that most users don't need better than 100ms, but those >> users don't care about long term stability, and their long term may be >> an 8 hour shift. >> >> >> (My interest in NTP is more theoretical, as I work in an industry sector >> that, whilst it deals with timestamped data, those timestamps are often >> a minute or two out (and are added by equipment that is out of our >> control), but I do notice the sorts of questions that keep coming up >> time and time again.) _______________________________________________ questions mailing list questions@lists.ntp.org https://lists.ntp.org/mailman/listinfo/questions
