PTP (Precision Time Protocol, IEEE 1588)

What it is

PTP (Precision Time Protocol), standardised as IEEE 1588, distributes a precise common clock across an Ethernet network. With hardware timestamping on the NIC and PTP-aware switches, PTP synchronises endpoints to sub-microsecond accuracy across an entire LAN. It is the timing backbone that allows SMPTE ST 2110 to send uncompressed video, audio, and ancillary data as separate IP flows and recombine them losslessly downstream.

How it works

One device on the network is elected Grandmaster Clock. It distributes sync messages at regular intervals; PTP-aware switches add timestamps as packets pass through, so each downstream endpoint knows both the master time and the residence-time of each packet through the network. Endpoints adjust their local clocks to match. IEEE 1588 itself defines the protocol and its default profiles; media networks use industry profiles built on it — SMPTE ST 2059-2 (the SMPTE profile used in broadcast plants for ST 2110 flows) and the AES67 media profile for networked audio.

Why it matters

Uncompressed AV-over-IP only works if every endpoint shares a common clock to sub-microsecond precision. Without PTP, an ST 2110-20 video flow and the ST 2110-30 audio flow that belongs to it will arrive with drift that accumulates into visible lipsync error. The cost is that the network has to be PTP-aware end-to-end — every switch on the path must support boundary or transparent clock function, and PTP becomes a line-item in the network spec rather than an afterthought.

PTP vs NTP

Common confusion. NTP (Network Time Protocol) is the standard internet time-sync protocol — it reaches millisecond accuracy on a typical LAN and tens of milliseconds across the public internet. That is fine for logging, file timestamps, and most application-level use. It is not fine for sub-frame video synchronisation, which is where PTP earns its complexity. Broadcast plants run PTP for media flows and NTP for everything else, on the same network or on separate ones.

PTP and IPMX

IPMX — the AIMS Alliance ProAV variant of ST 2110 — makes PTP optional rather than mandatory. The reason is operational: most control-room and ProAV deployments do not need sub-microsecond sync, and forcing PTP on every install raises the switch-spec barrier substantially. Optional PTP is one of the deliberate IPMX choices that makes the standard easier to deploy outside broadcast facilities.

Related terms

• SMPTE ST 2110
• IPMX
• NMOS
• AV over IP