Tech Note | Understanding PTP Transparent Clock on NS Series Gen 2 Switches
Learn how to effectively understand and optimize PTP transparent clocks on NS Series Gen 2 switches for improved network synchronization.
Information
This article explains what PTP‑TC is, how it works, and when it may be used in audio/video over IP (AVoIP) environments such as AES67 or Q‑SYS systems.
Overview
PTP Transparent Clock (PTP‑TC) is a feature supported on certain Netgear managed switches that improves time synchronization accuracy in networks using Precision Time Protocol (PTP, IEEE 1588).
Q‑SYS configurations no longer enable PTP‑TC by default on NS Series Gen 2 Switches (v09 and later). This change was made because enabling PTP‑TC has, in some cases introduced issues, and most deployments do not benefit from having it enabled. PTP‑TC can still be manually enabled if a specific deployment requires it.
What is …?
PTP
Precision Time Protocol (PTP) is used to synchronize clocks across devices on a network with very high accuracy. This is critical in applications such as:
- Audio over IP (AES67, Dante)
- Video over IP
- Real-time control systems
In a PTP network:
- A Grandmaster clock provides the reference time
- Other devices (endpoints) synchronize to that clock
PTP-TC
A Transparent Clock (TC) is a feature on a network switch that helps improve timing accuracy by accounting for network delay.
Unlike other PTP roles:
- A Transparent Clock does not act as a clock source
- It does not participate in clock selection or synchronization hierarchy
Instead, it enhances timing accuracy by correcting the delay introduced by the network.
How PTP‑TC Works
When PTP packets (such as Sync and Delay messages) pass through a switch with PTP‑TC enabled:
- The switch measures how long the packet takes to pass through it (residence time)
- The switch adds the delay information into the PTP packet
- The receiving device uses that information to calculate a more accurate clock
This process allows the network to compensate for variable delay introduced by switching and traffic conditions. [manualowl.com], [arubanetwo...ng.hpe.com]
Key Characteristics of PTP‑TC
- Does not generate or distribute time
- Does not replace a Grandmaster clock
- Does not act as a Boundary Clock
- Helps improve timing accuracy by tracking the delay
- Operates transparently between PTP devices
When is PTP-TC …?
Used
PTP‑TC may be beneficial in environments where:
- The network has multiple switch hops
- There is variable latency (jitter) affecting timing
- The application requires high timing precision
- There is no Boundary Clock available in the network
Typical use cases include:
- Large AES67 audio deployments
- Complex AVoIP infrastructures
- Systems requiring tighter synchronization accuracy
Not Required
In many deployments, PTP‑TC is not necessary, particularly when:
- The network is small or flat (few switches)
- Timing synchronization is already stable
- There is minimal delay variation across the network
- When using only PTPv1
Enabling PTP‑TC in environments where it is not required may add unnecessary complexity.
Best Practices
- Use PTP‑TC only when there is a demonstrated need for improved timing accuracy
- Avoid enabling it as a default configuration in standard deployments
- Validate the requirement through testing or system design
Reference
AV Line of Fully Managed Switches: Overview of preconfigured AV profile templates page 20.