How to Effectively Enhance PTP Redundancy Using Dual Ports

In the recent past, media transport over IP networks has become a viable option for the broadcasting industry. The SMPTE ST-2110 family of standards has proven to be a key factor in guaranteeing the required level of performance as well as full interoperability between different vendors. A small but nevertheless crucial part of the All-IP-Studio is an accurate and reliable common notion of time throughout the whole network. The broadcasting industry chose the IEEE 1588 Precision Time Protocol (PTP) for time transfer because it is a well-established method and is used in many application domains. PTP offers a certain level of fault tolerance, coping with the loss of the reference (PTP Grandmaster) autonomously by electing an auxiliary device to assume this role. Mission-critical applications may require a higher level of resilience to detect and/or counteract more complex error conditions such as intermittent or permanent loss of time transfer as well as deterioration of its quality - both will remain undetected by PTP. Rather than keeping all auxiliary PTP Grandmasters in hot-standby mode, we propose to deploy more than one active time reference. This allows all PTP end devices (Followers) to select the best time source using extended selection criteria and thus cope with almost every error condition without transient or permanent deterioration of the synchronization accuracy. — We will describe in detail how to implement this extension without violating or extending the original PTP protocol, which is a mandatory requirement for any improvement of PTP time transfer. Within a multi-vendor testbed, we will demonstrate the performance and advantages of this approach by inducing the most common transient and permanent error conditions within a typical PTP network. The accuracy of the proposed solution will be evaluated by measuring the offset of the PTP hardware clocks of all Followers with respect to the PTP Grandmaster. The results will be compared with the performance of a commercial PTP implementation being subjected to the same error conditions. The paper will conclude by briefly describing how to implement this technology and commenting on the implementation overhead as well as the expected increase in resource usage.

Published

2023-10

Content type

Original Research

Keywords

ST2110, ST2059-2, Redundant Clock Synchronization, PTP, IEEE1588

DOI

10.5594/M002029

ISBN

978-1-61482-964-5