Precision Time Protocol

About: Precision Time Protocol is a research topic. Over the lifetime, 604 publications have been published within this topic receiving 6006 citations. The topic is also known as: PTP & IEEE 1588.

Towards high accuracy in IEEE 802.11 based clock synchronization using PTP

Abstract: The introduction of the precision time protocol has brought forth the possibility to have a standardised synchronization mechanism in networks, independent from the actual communication technology. However, it can be observed, for example in the annexes of the standard, that many implementations focus only on Ethernet based communication. The logical next step is to investigate how this protocol will fare when used for synchronizing clocks in a distributed manner over IEEE 802.11 based devices. The availability of features like roaming, the broadcast nature of the wireless medium and different hardware platform architectures require an investigation on how clock synchronization can be realized in wireless environments. This paper proposes an approach to import the precision time protocol to IEEE 802.11. Furthermore, standard nodes are enhanced with software timestamping, leading to a synchronization accuracy of a few microseconds.

Precise Clock Synchronization in High Performance Wireless Communication for Time Sensitive Networking

Abstract: In this paper, an enhanced precision time protocol (PTP) to enable precise clock synchronization between the nodes within an industrial wireless sensor network deployed for critical control and automation applications is proposed. As it will be shown, by incorporating clock drift factor, the accuracy of clock offset estimation of conventional PTP scheme can be significantly improved. Furthermore, in order to enhance the application of proposed clock synchronization scheme, typically in non-line-of-sight industrial communication environment, the problem of efficient symbol timing synchronization is also studied, and a simplified, yet efficient, start of the frame detector that enables robust timestamp message decoding during clock synchronization period is also proposed.

IEEE 1588 applied in the environment of high availability LANs

Abstract: High availability applications typically count on the network's ability to reconfigure in case of a failure. Since the precision time protocol (PTP) measures the delay of communication paths, it has to cope with network topology changes. The concept of peer-to-peer transparent clocks (TC), introduced with PTP version 2, facilitates the handling of path switchover by measuring the link delays from each node to its neighbors in advance. The parallel redundancy protocol (PRP) follows a different approach from the well-known reconfiguration protocols. It makes use of two independent Ethernet networks. Frames are replicated by the sending node and transmitted over both networks. Duplicates are discarded by the receiving node. There is no distinction between a working and a backup path. The combination of PTP and PRP is studied in this paper. Different models are presented and evaluated with respect to synchronization switchover and implementation issues. An experimental implementation is outlined. The results show that master clock failure as well as network failures can be handled with very low impact on synchronization quality.

IEEE 1588 syntonization and synchronization functions completely realized in hardware

Abstract: The Precision Time Protocol (PTP) is an application layer protocol and therefore destined to be implemented in software. Hardware functions, if present, include a high resolution clock that helps to generate precise timestamps for PTP messages. The presented paper describes an IEEE 1588 clock that realizes syntonization and synchronization functions completely in hardware. It combines a three-port bridge with peer-to-peer Transparent Clock (TC) functionality and an Ordinary Clock (OC), together with other protocol and application specific logic within an FPGA. The aim of such an implementation is to provide a high accuracy and robust system clock that can be driven by a simple crystal oscillator. It can cope with oscillator instabilities caused by environmental effects such as fast temperature changes or accelerations (shock/vibration). It may deliver synchronicity in deeply cascaded topologies.

Requirements for Secure Clock Synchronization

Abstract: This paper establishes a fundamental theory of secure clock synchronization. Accurate clock synchronization is the backbone of systems managing power distribution, financial transactions, telecommunication operations, database services, etc. Some clock synchronization (time transfer) systems, such as the global navigation satellite systems, are based on one-way communication from a master to a slave clock. Others, such as the network transport protocol, and the IEEE 1588 precision time protocol (PTP), involve two-way communication between the master and slave. This paper shows that all one-way time transfer protocols are vulnerable to replay attacks that can potentially compromise timing information. A set of conditions for secure two-way clock synchronization is proposed and proved to be necessary and sufficient. It is shown that IEEE 1588 PTP, although a two-way synchronization protocol, is not compliant with these conditions, and is therefore insecure. Requirements for secure IEEE 1588 PTP are proposed, and a second example protocol is offered to illustrate the range of compliant systems.