IEEE1588

The new IEEE Standard Precision Time Protocol (PTP) IEEE1588 is now a very comprehensive solution to do very precise time synchronization in an Ethernet network.

The protocol was originally developed by Agilent for distributed instrumentation and control tasks. The technique is based on the work of John Eidson, who, as chairman of the standardization committee, is largely responsible for the approval of the standard in November 2002.

Using IEEE1588, it is possible for the first time to synchronize, in the sub-microsecond range, the local clocks in sensors, actuators, and other terminal devices using the same Ethernet network that also transports the process data.

Without such a standardized synchronization protocol, which is defined to be used with any protocol, not just Ethernet, it would probably not be possible to synchronize local clocks in terminal devices from different manufacturers with this precision.

Existing time synchronization protocols such as NTP and SNTP do not achieve the required synchronization accuracy or the convergence speed. Others, such as SynUTC from the Technical University in Vienna, were not accepted on the market.

Like other protocols, PTP is based on the most precise matching of times when synchronization packets are transmitted and received possible. Unlike SNTP, the transmission time stamp does not need to be transmitted in the synchronization packet itself, as described in detail below, but is transmitted in a following packet. In this way measurement of transmission and reception, and transmission of measured time stamps can be decoupled.

The protocol was designed for small homogeneous and heterogeneous local networks. The designers paid particular attention to low resource usage so that the protocol can also be used in low end and low cost terminal devices. No special requirements are placed on memory or CPU performance, and only minimal network bandwidth is needed. The low administration effort for this protocol is also significant. As redundant masters are also supported, a PTP domain automatically configures itself using the best master clock algorithm and is also fault-tolerant.

The most important characteristic of the protocol is the synchronism in the microsecond and sub-microsecond range.