I'm quite confused between time synchronization and clock synchronization.

Self-clocking signal is used to tell the receiver at which rate sender sending the bits so that it can read the bits at the same rate (to avoid data loss).

Precision Time Protocol is a protocol used to synchronize clocks throughout a computer network. On a local area network, it achieves clock accuracy in the sub-microsecond range, making it suitable for measurement and control systems.

are both doing the same job here? is Self-clocking signal still needed even if the network perfectly synced by PTP mechanism?

1 Answer 1


PTP runs on top of Ethernet (data link layer) or higher. Accordingly, it has no relation to the clocks used on the physical layer. The latter may require very tight relative synchronization of transmitter/receiver in the picosecond range (for 25 GBd PHYs) but no absolute synchronization (wall time) at all.

  • so physical layer always need some sort of line code mechanism (example: Manchester code) to embed clock to actual data so that receiver can decode at the same rate. is it right?
    – Vencat
    Nov 16, 2020 at 13:13
  • Yes - since physical-layer transmissions are generally self-clocking, they require an appropriate line code. The receiver must be able to sync to the transmitter's clock in order to recover the data. Note that 10 Mbit/s with Manchester is archaic, 8b/10b and 64b/66b are widely used today.
    – Zac67
    Nov 16, 2020 at 13:52

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