PTP4SDN: A Low-Jitter PTP Clock Provisioning Service via Software Cross-Timestamping

Highly accurate timing services are critical to ensure data integrity over wireless networks where data from multiple sensors needs to be processed with precise synchronization. The IEEE 1588 standard Precision Time Protocol (PTP) is typically used to meet the timing accuracy requirements of modern wireless networks; however, implementing PTP is becoming a challenge as telecommunication equipment companies replace fixed function designs with cost-effective General-Purpose Processor (GPP) based designs. One example is the Virtual Radio Access Networks (vRAN) design, where fixed-function appliances are replaced with Commercial-Off-The-Shelf (COTS) servers. To maintain consistent clock service management while implementing PTP on a GPP system, the Operating System (OS) manages the respective clock operations. Kernel-based PTP clock provisioning presents a unified interface for all the network services running in the same computer node. Still, it does not adequately address network services inside a Virtual Machine (VM) where the guest OS resides in a different clock domain. In addition, a software-based PTP clock provisioning service is subject to system jitters, which results in non-deterministic clock accuracy. To address these VM provisioning requirements, we devised a CPU clock-based cross-timestamping technique, ptp4sdn. In this design, we developed a new analytical equation to correlate TimeStamp Counts (TSC) between the PTP clock (available from an IO device) and the CPU clock. In addition, a new algorithm was also developed to remove inherent system jitters introduced with software-based cross-timestamping implementations. Finally, we empirically demonstrate that ptp4sdn can achieve sub-100 ns clock synchronization accuracy, previously only achievable with HW-based implementations.