Large-Scale PTP: How Big Can It Get?

Abstract

Precision Time Protocol (PTP) is a standard to synchronize clocks across a network with submicrosecond accuracy. In the area of professional media networking, PTP is poised to replace traditional black burst sync methods, allowing both media and synchronization to be carried over the same network connection. To be useful, vendor PTP protocol implementations must scale to the size of the largest broadcast plants. This paper describes the results of PTP tests with more than 1,000 “slave” clocks, including an examination of scaling performance with both boundary and transparent modes of operation on the network devices. It also discusses the pros and cons of the end-to-end delay and peer delay mechanisms, and provides details on the performance seen using a range of sync message intervals and delay request intervals. These tests suggest several best practices for large-scale PTP installations using commercial-off-the-shelf (COTS) equipment, and provide real-world data to assist in planning and implementing a professional media Ethernet network leveraging PTP synchronization.