Live migration of virtual machines (VMs) has become an extremely powerful tool for cloud data center management and provides significant benefits of seamless VM mobility among physical hosts within a data center or across multiple data centers without interrupting the running service. However, with all the enhanced techniques that ensure a smooth and flexible migration, the down-time of any VM during a live migration could still be in a range of few milliseconds to seconds. But many time-sensitive applications and services cannot afford this extended down-time, and their clocks must be perfectly synchronized to ensure no loss of events or information. In such a virtualized environment, clock synchronization with minute precision and error boundedness are one of the most complex and tedious tasks for system performance. In this paper, we propose enhanced DTP and wireless PTP based clock synchronization algorithms to achieve high precision at intra and inter-cloud data center networks. We thoroughly analyze the performance of the proposed algorithms using different clock measurements. Through simulation and real-time experiments, we also show the effect of various performance parameters on the data center networking architectures.

虚拟机（VM）的实时迁移已成为用于云数据中心管理的极其强大的工具，并具有在不中断正在运行的服务的情况下，在数据中心内或跨多个数据中心的物理主机之间实现无缝VM移动的显着优势。但是，通过所有确保平滑，灵活迁移的增强技术，实时迁移期间任何VM的停机时间仍可能在几毫秒到几秒之间。但是许多对时间敏感的应用程序和服务无法承受如此长的停机时间，并且它们的时钟必须完全同步以确保事件或信息不会丢失。在这样的虚拟化环境中，具有微小精度和错误限制的时钟同步是系统性能最复杂和繁琐的任务之一。在本文中，我们提出了增强型DTP和基于无线PTP的时钟同步算法，以在云内部和云间数据中心网络中实现高精度。我们使用不同的时钟测量来彻底分析所提出算法的性能。通过仿真和实时实验，我们还展示了各种性能参数对数据中心网络体系结构的影响。