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ION Network Time Protocol (NTP) or Simple Network Time Protocol (SNTP) Implementation: Why does the ION NTP time implementation only have 1 second accuracy, when NTP time synchronizing has 10ms accuracy over a public network?

ION meters do not do NTP time synchronizing. The algorithm used is SNTP time synchronizing.

- NTP = network time protocol

- SNTP = simple network time protocol

- SNTP is only +/-1sec accuracy, The 1 second accuracy number is a result of the ntp max timeout parameter, which is set to 2 seconds. This means it'll accept time-synchs with up to 1 second network delay. (round-trip)

- No matter the amount of testing that is done, it is not possible to guarantee a time-sync accuracy of anything better than +-1 second. Even if it was possible to characterize the network, meter loading, and other factors, there is still no guarantee that it will always be that accuracy since the meter will accept 1 second old time-synchs. Therefore, the best that the meters can claim is that they will be accurate to at least 1 second. Typically, but not necessarily always, the delay will be less than 1 second.

- True NTP time synchronizing uses multiple time servers to verify the time and control the slew rate of the PC

- SNTP uses only one server to provide time, it then calculates the required jump to perform it, and can compensate for round trip network delay time

- Very similar in terms of TCP/IP protocols, except for the accuracy and that SNTP does not require storing previous communication data.



Date Created: November 27, 2009
Last Revised: December 23, 2009
Public
Original Author: TO
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