Precision Time Protocol (PTP)

What is Precison Time Protocol (PTP)?

PTP (Precision Time Protocol) is a time transfer protocol defined in IEEE1588v2(2008) for the precise synchronisation of clocks across a packet network, typically Ethernet. It offers a cost-effective and accessible way of synchronising data over a packet-based network at very high accuracy levels.

History of IEEE1588

IEEE1588 version 1 was published in 2002 and defines a Precision Time Protocol (PTP) designed to synchronize real-time clocks in a distributed system. It was intended for Local Area Networks using multicast communications only.

IEEE1588 version 2 was published in 2008, as an upgrade to version 1:

  • Resolution of known errors
  • Conformance enhancements
  • Enhancements to address new applications (including telecoms)

PTP vs. NTP

PTP is basically a faster version of NTP. IEEE 1588 is designed for local systems requiring very high accuracies beyond those attainable using NTP, which is sufficient to transfer data across networks at speeds of up to 10mbps. As data rates have increased, the need for synchronised tranmission and reception have increased with it. At speeds of 1 gbps and above, PTP is necessary.

PTP Practical Industry Applications

Telecoms – As the whole telecoms industry changes from bitstream (telephony) networks to packet switched networks, PTP will be used more and more. PTP is suitable for a range of packet network types such as metro area networks, base-station backhaul networks and access aggregation networks.

Industrial automation – Modern robotics are increasingly being controlled over a netowrk (Ethernet), both wirelessly, and using fibre optics. Using a time-based control method can effectively eliminate jitter delays experienced through traditional scan-based or event-triggered control methods.

Power – In electricity sub-stations, Ethernet is used for monitoring power going out, to control power surges, etc, and as such micro-second time accuracy is an essential requirement for control purposes.

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