Professional Broadcast

1588 PTP Networks: Tutorial

Network synchronization is crucial for professional broadcast, both for traditional aspects such as audio alignment and lip-sync, and especially as tasks such as high quality live event broadcasting, becomes more prevalent.

Ethernet + PTP for network synchronisation
Ethernet + Precision Time Protocol (PTP) is fast becoming the most popular method of delivering network synchronization in a broad range of environments. Ethernet-based networks have the benefits of high bandwidth, joint infrastructure for file-based and A/V signals, and access to advanced network management functions.

PTP, as a message-based time transfer protocol, ensures different points in the network are precisely synchronised to the reference (master) clock, allowing the network as a whole to meet specific performance limits. As an integral part of the ITU-T standards for packet transport networks, it allows for different profiles in order to meet the needs of various applications, for example, industrial and financial networks, and automotive systems.

ST 2059-2 is commonly referred to as the Broadcast profile. Defined by the Society of Motion Picture and Television Engineers (SMPTE), this profile proposes a timing requirement of 1 µs (±500ns) across the network. Most of the available options from the PTP “default profile” can be used: IPv4/IPv6 encapsulations, multicast or unicast transmission, using ordinary, boundary or transparent clock devices.

PTP Broadcast diagram

How do you prove PTP performance of the network equipment?

There are four main aspects to consider:

  • Ensuring all devices apply the same PTP profile correctly and consistently is key to deploying a robust PTP network. Testing can reduce interoperability risks by highlighting device and network misconfigurations and protocol-related issues.

  • The Broadcast profile provisions for a Synchronisation Metadata Type Length Value (SM-TLV) which is carried in the PTP management message. It is critical to generate and interpret the SM-TLV correctly to prove system performance.

  • Measure the “Steady State” timing accuracy to ensure standard compliance and prove the PTP performance of network equipment. Test equipment should have a measurement accuracy of at least an order of magnitude greater than the specified requirements.

  • Monitoring the responses of network equipment under negative conditions allows designers to evaluate how each device within the network might respond under such conditions. Test equipment must be able to simulate negative network conditions such as protocol errors and timing offsets.

How can Calnex help?

Whether you need to validate PTP message fields for interoperability, measure the steady state timing accuracy, test devices in negative conditions, or generate/interpret SM TLV, Calnex can help ensure your broadcast service complies with the latest standards.

The Paragon family of testers is designed to help address the challenges of reducing the complexity of test, enhance test effectiveness, and validate standards compliance of devices and networks to the highest levels of accuracy.