How is PTP supported on Omada Switches

Contents

Introduction

Key Definitions

How is PTP supported on Omada Switch?

Which models support PTP?

Introduction

PTP is short for Precise Time Protocol; it is a protocol proposed by the IEEE to address high-precision synchronization requirements.

For the quality of communication, the accuracy of time synchronization plays a crucial role. Given the significant impact of synchronization on communication quality and user experience, ISPs or communication operators often impose demands on vendors to achieve high-precision synchronization. In current communication implementations, clocks are a commonly used component, with nearly all digital circuits relying on clocks for driving and operation. Moreover, if synchronization issues are not adequately ensured, they could have a substantial adverse effect on the communication system.

PTP enables time synchronization accuracy at a sub-microsecond level, which is highly ideal for communication equipment. Such stringent high-precision synchronization demands cannot be met by earlier protocols like the Network Time Protocol (NTP), and in these contexts, PTP demonstrates its unique advantages. Its key features include the introduction of a master-slave clock mechanism and the adoption of high-precision hardware timestamps for transmitting time information, followed by network delay measurements to achieve master-slave clock synchronization ultimately.

Key Definitions

• PTP Domain: The network with PTP operating is a PTP domain. There can be only one clock acting as a source within this domain; all other clocks in the domain will synchronize with the source clock.
• Clock Node: The nodes within a PTP domain are called clock nodes. Usually, a switch with PTP enabled will act as a clock node.
• Master Clock: The clock elected as the master within the PTP domain serves as the clock source for this domain. Other clocks must synchronize their time with the master clock.
• Slave Clock: A clock that is not the master clock within the PTP domain synchronizes its time with the master clock.
• PTP Interface: The interfaces running PTP on a clock node are called PTP interfaces.
• OC: Ordinary Clock. This type of clock node has only one PTP interface for time synchronization within the same PTP domain, using which it synchronizes time from the upstream clock node. When this clock node is acting as the clock source, it will only distribute time to downstream clock nodes through this interface.
• BC: Boundary Clock, this kind of clock node will have multiple PTP interfaces participating in time synchronization within the same PTP domain. It will synchronize time from the upstream clock node through one of the PTP interfaces and distribute the time to other downstream clock nodes through other PTP interfaces. When this clock node is acting as the clock source, it could distribute time information through multiple PTP interfaces.
• TC: Transparent Clock, this kind of clock node will have multiple PTP interfaces, but it will not participate in time synchronization itself; it only forwards PTP packets between its PTP interfaces and helps correct the forwarding delay. It will not synchronize time through any of the PTP interfaces. There are two kinds of TCs in IEEE 1588v2 PTP networks: E2ETC and P2PTC.
• E2E (End-to-End) is a method for calculating the time difference between a master clock and a slave clock. It calculates based on the total link delay between the two clocks, regardless of the number of other clock nodes or devices that do not support PTP connected in between.
• P2P: Peer to Peer, a kind of method to calculate the time difference between the master clock and the slave clock, it calculates based on the delay of each link segment between the master clock and the slave clock, which means the delay between each node connected in between needs to be calculated, the devices connected in between must support PTP.

How is PTP supported on Omada Switch?

Currently, on Omada switches supporting PTP, we offer two PTP profiles: IEEE 1588v2 and IEEE 802.1AS. Users can then assign clock roles, such as OC and BC, based on the rules of these profiles and definitions. Both P2P and E2E methods of calculating the time difference between clock nodes are provided. When using the IEEE 1588v2 profile, the clock role could be set as BC, OC, E2ETC, or P2PTC. When using the IEEE 802.1AS profile, the clock role could be set as BC, OC, or P2PTC.

By default, PTP packets are transmitted through multicast. Users can manually change this to unicast by defining the destination MAC address. An alternative method for securing PTP information within UDP and enabling IP forwarding is also supported on Omada switches.

Which models support PTP?

• Omada S6500 & S7500 series switches

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