rfc - What is the purpose of the Root Delay field in the NTP protocol? -


About it, is specified.

I understand that the area of ​​the root delay NTPV4 packet (or synchronizing distance field, as it has been named in previous versions NTPv3) The approximate roundtree indicates the delay in the primary / reference clock.

However, Why is the protocol need to know the delay in the primary clock ? As used in the specification, it uses Origin , get and transmit timestamp field to calculate the correct time (server / Peer), and too does not do any direct or indirect communication with the primary clock in the time calculation "travel".

That's because the server / coworker has been synchronized from the context clock in the past, and now wants to inform the client about the delay?

By the way, what does the related root spread mean? Farm? Unfortunately, I did not understand the dispersion dispersion, which has not really been explained in detail.

ntpd not only sets local clock but also acts as a time-server for other NTP customers Can also do To do this, it needs to know its accuracy. To calculate this, it (less than perfect) sees less and maximum round-trip delay than the root clock and its error in its system clock. It can then advertise how well its clock is for the customer.

Route Delay Delta Route clock delays (max - minimum) The error contributed by this part is considered DELTA / 2.

The dispersion is an error in the local system clock because it was synchronized with the last upstream clock. So it looks like an intimate function which drops for 0 when synchronized, then increases linearly to the next sync.

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