Port 319: PTP Event — Where Microseconds Matter

Port 319 carries IEEE 1588 Precision Time Protocol (PTP) event messages—the critical timing packets that synchronize clocks across networks with sub-microsecond accuracy. Every industrial robot that needs coordinated motion, every power grid that balances load in real-time, every financial trading system where milliseconds cost millions—they all depend on precise time synchronization. Port 319 is how they achieve it.

What PTP Does

The Precision Time Protocol synchronizes clocks across a computer network with accuracy that NTP can't touch. NTP gives you milliseconds. PTP gives you microseconds, sometimes nanoseconds.¹ In a local network with proper hardware support, PTP can synchronize clocks to within a microsecond of each other.

Port 319 carries event messages—the time-critical packets where precise timestamps matter. These include sync messages, delay request messages, and other timing-critical communications. Port 320 carries general messages (non-time-critical PTP traffic). Together, they form the nervous system of precision timing.

How It Works

PTP uses a master-slave hierarchy. One clock is the master (usually the most accurate one on the network). All other clocks are slaves that synchronize to the master.

The key insight: hardware timestamping. Instead of letting the operating system handle timestamps (which introduces variable delays), PTP-capable network hardware timestamps packets the moment they hit the physical layer. This eliminates the jitter and latency that plague software-based timing protocols like NTP.²

The protocol works by exchanging messages between master and slave:

1. Master sends a sync message (timestamped at transmission)
2. Slave notes when it receives the message (timestamped at reception)
3. Slave sends a delay request back to master
4. Master responds with the reception timestamp

From these four timestamps, the slave can calculate both the network delay and the clock offset, then adjust its clock accordingly.

The History: Why PTP Exists

Before 2002, if you needed microsecond-accurate time synchronization across a network, you were out of luck. NTP gave you milliseconds. GPS gave you time but required antennas and clear sky. There was no good solution for local systems that needed precision timing—industrial automation, test and measurement equipment, power grid control systems.

John Eidson at Hewlett-Packard Laboratories saw the gap. In the 1990s, while looking for a replacement for test equipment trigger buses, he invented what would become IEEE 1588.³ The first version, IEEE 1588-2002, was published in 2002 and designed primarily for industrial automation environments.⁴

The protocol filled a niche not well served by either NTP or GPS: local networks requiring accuracies beyond NTP but without the complexity and cost of GPS receivers at every node.

In 2008, IEEE 1588-2008 (PTPv2) was released with significant improvements to accuracy, precision, and robustness—but it wasn't backward compatible with the 2002 version. The 2019 revision (PTPv2.1) added backwards-compatible improvements.⁵

Kang Lee, a researcher at the National Institute of Standards and Technology (NIST), was one of the key contributors to the standard and formally registered port 319 with IANA in 2010 for PTP event messages.⁶

Security Considerations

Like many industrial protocols, PTP was designed for controlled environments, not hostile networks. The protocol itself has minimal built-in security—it assumes the network is trusted.

Port 319 has been exploited in the past by malware for unauthorized communication.⁷ If PTP isn't needed on a system, the port should be closed. If it is needed, traffic should be restricted to trusted network segments, and PTP devices should be on isolated VLANs.

The IEEE 1588 working group has added security extensions in recent versions, but adoption varies. Many industrial systems still run PTP without authentication or encryption because adding security introduces timing uncertainty—the very thing PTP exists to eliminate.

Related Ports

• Port 320: PTP General Messages (non-time-critical PTP traffic)
• Port 123: Network Time Protocol (NTP)—the older, less precise but more widely deployed timing protocol

Why Port 319 Matters

Port 319 carries something invisible but essential: agreement about when "now" happens. In a distributed system, synchronized time isn't a convenience—it's the foundation that makes coordinated action possible.

Industrial robots moving in coordination. Power grids balancing load across substations. Financial markets establishing the order of trades. Telecommunications networks synchronizing base stations. Distributed measurement systems correlating data from multiple sensors. All of these depend on clocks that agree down to the microsecond.

Before PTP, achieving this level of precision required expensive, specialized timing hardware. After PTP, it became a protocol you could implement in network switches and industrial equipment. Port 319 democratized precision timing.