NTP v4 (RFC 5905)

1. Implementation model and modes

   Client/server, symmetric and broadcast modes.

2. Data types and timestamps

   NTP date format, 64-bit timestamps and era numbers.

3. Packet header

   NTP packet fields: stratum, poll, root delay and dispersion.

4. On-wire protocol

   Offset and delay calculation from four timestamps.

5. Peer process

   Peer state variables and the clock filter.

6. System process

   Selection, clustering and combining algorithms.

7. Clock discipline

   Phase and frequency adjustment loops.

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