PTP — IEEE 1588 Precision Time Protocol
Definition
The Precision Time Protocol (PTP), defined by IEEE 1588, synchronises the clocks of devices on a network, with sub-microsecond accuracy on suitable hardware. A best master clock algorithm (BMCA) elects one device as grandmaster, and the other devices lock to it. Dante uses IEEE 1588-2002 (PTPv1) natively, AES67 uses IEEE 1588-2008 (PTPv2), and AVB uses gPTP, a profile of PTPv2 defined by IEEE 802.1AS. Audio networks derive a common sample clock from this shared time. Audinate states that Dante does not require PTP-aware switches, and that in most cases Dante gains nothing from enabling the boundary clock or transparent clock functions of a switch.
In the field
Intermittent clicks on a Dante network that shows no packet loss often come from clock synchronisation, because a device that loses and regains lock on the grandmaster produces an audible glitch. Dante Controller shows which device is the current grandmaster and the clock status of every device. Common practice makes a stable, always-on device the preferred leader, rather than a computer that can sleep or enter a power-saving mode. Delay variation also degrades synchronisation, which is why Audinate places PTP traffic in the highest-priority QoS queue.
Related lessons
Sources
- Precision Time Protocol (Wikipedia, pointeur secondaire) : IEEE 1588, algorithme BMCA et élection du grandmaster, précision sous la microseconde · en.wikipedia.org
- Audinate, Dante Controller User Guide, Clock Synchronization : Dante en PTPv1 (IEEE 1588-2002), PTPv2 requis pour AES67 et ST 2110-30, choix du leader préféré · dev.audinate.com
- Audinate, Dante Information for Network Administrators : switches compatibles PTP non requis ; boundary clock sans bénéfice dans la plupart des cas · getdante.com
- AES67 (Wikipedia, pointeur secondaire) : synchronisation AES67 par IEEE 1588-2008 (PTPv2) · en.wikipedia.org
- Luminex, AVB terms and definitions : gPTP défini par IEEE 802.1AS, profil de l'IEEE 1588-2008 · support.luminex.be
- Audinate/Yamaha, Dante Network Design Guide, QoS : PTP en CS7, file de plus haute priorité · usa.yamaha.com