H ELECTRICITY
H04 ELECTRIC COMMUNICATION TECHNIQUE
H04J MULTIPLEX COMMUNICATION
3/00 Time-division multiplex systems
H04J3/06 Synchronising arrangements
H04J3/0635 Clock or time synchronisation in a network
H04J3/0638 Clock or time synchronisation among nodes; Internode synchronisation
H04J3/0658 Clock or time synchronisation among packet nodes
H04J3/0661 using timestamps
H04J3/0667 Bidirectional timestamps, e.g. NTP or PTP for compensation of clock drift and for compensation of propagation delays