PTP Support on SONiC-based Open Network Switches
Why we need PTP?
Due to its openness, affordability, and ease of use, Ethernet technology is widely utilized in telecom-grade networks, with data transmission speeds increasing from 10 Mbps to 800 Gbps. Ethernet technology operates on a "plug-and-play" basis, allowing for seamless connectivity to an IP network and the provision of services at any given time. However, it is crucial to note that only a "synchronized" IP network truly meets the standards of a telecommunications-grade network, ensuring quality assurance for real-time and data services. Presently, telecommunication-level networks impose strict requirements for time synchronization, with the backbone network delay commonly enforced to be within 50ms. Unfortunately, the existing NTP (Network Time Protocol) and SNTP (Simple Network Time Protocol) protocols fail to attain the necessary precision or convergence speed. While NTP achieves millisecond-level time synchronization accuracy suitable for many applications, it falls short in meeting the high-precision demands of networks. GPS (Global Positioning System) can offer high-precision time synchronization, but its implementation and maintenance entail significant costs and pose security risks.
What is PTP (Precision Time Protocol)?
The Precision Time Protocol (PTP) is a protocol used to synchronize clocks in a network. It is defined in the IEEE 1588 standard. PTP is designed to provide highly precise time synchronization between devices on a network, typically in the sub-microsecond range. This is important for applications where accurate timekeeping is crucial, such as in financial trading, industrial automation, telecommunications, and multimedia streaming.
How does PTPv2 Work?
IEEE1588 PTPv2 uses a relative time synchronization mechanism. One participant is selected as the master time clock and it will send synchronization messages to the slaves. The master will send synchronization messages to the network and all the slaves calculate the time delay.
The principle of time synchronization is shown below
The time offset (Offset) and transmission delay (Delay) are calculated from the clock based on T1, T2, T3, T4, i.e.:
T2 – T1 = Offset + Delay
T4 – T3 = Delay – Offset
From this we can calculate:
Delay = (T4 – T3 + T2 – T1)/2
Offset = (T2 – T1 – T4 + T3)/2
Depending on the Offset, the slave can adjust its own clock for precise time synchronization.
The Precision Network Synchronization Protocol defined by the IEEE1588 PTPv2 standard achieves a high degree of synchronization in the network, eliminating the need for dedicated synchronization communications when assigning control jobs, thus achieving the effect of separating the communication time mode from the application execution time mode. Due to the highly accurate synchronization work, the data transmission time fluctuations inherent in Ethernet technology are reduced to an acceptable range that does not affect control accuracy.
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Asterfusion SONiC-based Open Network Switches with PTP Support
Currently, the Asterfusion CX series open network switch products offer support for the IEEE1588 PTPv2 standard through both hardware and software. When implemented using hardware, which means the time stamp function is carried out through hardware, we can achieve accuracy up to the nanosecond level. Similarly, when implemented using software, we can usually achieve nanosecond-level accuracy as well.
In terms of hardware, we have integrated a high-precision clock module into the machine to facilitate IEEE1588 and Synchronous Ethernet (SyncE) implementation. The hardware port offers full support for PTP and can be used as boundary clock（BC) or Ttransparent clock (TC). Furthermore, the module can be flexibly disassembled based on customer requirements.
On the software side, Asterfusion leads the community in implementing the PTP function in SONiC and optimizing its performance on our Enterprise SONiC Distribution –AsterNOS.
By utilizing hardware acceleration and software algorithm optimization, the PTP protocol achieves a synchronization deviation of only 10ns, significantly enhancing speed and stability in protocol interaction. Additionally, interoperability is greatly improved as it supports configurations such as restAPI, RestConf, Netconf, and CLI. This wider range of protocol compatibility enables seamless integration and application.
Currently, we have 4 model SONiC switches that provide PTP functionality, as the following:
Moreover, the CX102S-8GT-M-SWP, CX102S-16GT-DPU-M-SWP becomes the first open layer2/3 switch in the market to offer PTP support in both hardware and software at the access layer. For more: https://www.dhirubhai.net/feed/update/urn:li:activity:7177999988809981952
Additionally, we are excited to announce that next week, we will be presenting a detailed teardown analysis on the CX102S-16GT-DPU-M-SWP, which we invite you to explore.
Asterfusion PTP-optimized SONiC Open Network Switch Feature List — 2024.04
For more:contact [email protected]