Boundaries of Ethernet layer 2 hardware timestamping

Synchronizing clocks in a distributed system is an indeed challenging task. Although there exists a various class of applications, like synchronizing the clock of a PC with the network time protocol, where an accuracy of several milliseconds is sufficient, many applications, such as synchronized test and measurement or localization services in wireless LANs require a higher confidentiality in the time domain. This paper enlights some of the key restrictions and possibilities in the case of IEEE 802.3 Ethernet. As this case not only challenges the state of the art oscillator models, but also timestamping techniques, a novel, highly accurate approach for that is proposed. Moreover, a highly accurate deterministic approach also concerns the behavior of the physical layer devices and their influence on the asymmetry, as well as the underlying control loops an analysis of the behavior of both is given together with some preliminary results for Ethernet based clock synchronization in the nanosecond range.