In the context of the IEEE 1588 Precision Time Protocol (PTP), estimating the delay's bias is a problem that appears in both one-way (using transparent devices) or two-way message exchange mechanisms. For estimating the offset via the two-way message exchange mechanism, it is usually assumed that the expected value of delays in forward and reverse directions are equal. However, this is not a realistic assumption for packet-based wide area networks, where delays in down-link and up-link directions may have a significant difference. In this work, we propose a solution to estimate the random delay's bias and improve the synchronization accuracy of IEEE 1588. Our method is easy to implement and is compatible with the current version of the protocol. We compared our results to no bias correction and the Boot-strap method. In addition to the improvement in synchronization accuracy, our method allows us to update the slave clock recursively. The proposed method works well even in the presence of large frequency offsets and can also be implemented by using different filters.

A two-way message exchange mechanism is at the core of many clock synchronization protocols. The basic concept of this method has been designed for symmetrical links, otherwise, depending on the level of asymmetric delays, large synchronization errors may occur. Many estimation based methods have been proposed so far for estimating the degree of asymmetry and reducing this error. However, many of them are solved for a specific distribution of link random delays. Moreover, imposing a high level of computational complexity upon network nodes is another problem of them. In this paper we introduce a recursive solution for improving the performance of the basic two-way message exchange mechanism. The advantage of this method is that it keeps the protocol simple and therefore easily implementable. The proposed method does not make any specific assumption about the distribution of the random delays. It also provides the network designer with some deployment flexibility, trading off convergence speed against stability.