Enhanced Redundancy of ST 2059-2 Time Transfer Over ST 2022-7 Redundant Networks

Abstract

As the SMPTE ST 2059–2 standard for accurate time transfer enters real-world All-IP Studio deployments, it is important for broadcasters and system integrators to understand how the various parameters and options of the IEEE 1588 Precision Time Protocol (PTP) profile will impact both system performance and the network architecture for all media essence based on standardized IP transports, such as the recently adopted SMPTE ST 2110 series or AES67. Given the mission-critical nature of broadcast infrastructure, fully redundant networks are becoming a mandatory requirement. While ST 2022–7 defines a media essence redundancy model for switching between multiple identical flows on a per Realtime Transport Protocol (RTP) packet basis, such as it would apply to the SMPTE 2110 suite of standards, the IEEE 1588’s assumption of constant transmission delays would be violated by this approach, thus resulting in transient errors. The IEEE 1588 Precision Time Protocol (PTP) time transfer paradigm was not designed to be switched on a per PTP message basis. Although PTP has a certain level of redundancy built into the protocol to tolerate the loss of the time reference, it cannot utilize the advantages of redundant networks to their full extent. This paper addresses how the stability and availability of time and frequency transfer for SMPTE ST 2059–2 endpoints can be improved far beyond the basic redundancy mechanism provided by PTP if they are connected via separate paths toward the network as proposed in the SMPTE ST 2022–7 standard. For maximum utilization of multiple parallel channels for time transfer, PTP implementation requires additional enhancements. The solutions presented are complemented by comparative measurements demonstrating the improvements generated by such optimized designs, which includes the presence of common transient and permanent error conditions, thus showing the advantages of fully redundant time transfer over basic redundancy mechanisms provided by PTP.