Network Time Protocol Research Articles

Precise relative clock synchronization for distributed control using TSC registers

Precise clock synchronization is essential in emerging time-critical distributed control systems operating over computer networks where the clock synchronization requirements are mostly focused on relative clock synchronization and high synchronization precision. Existing clock synchronization techniques such as the Network Time Protocol (NTP) and the IEEE 1588 standard can be difficult to apply to such systems because of the highly precise hardware clocks required, due to network congestion caused by a high frequency of synchronization message transmissions, and high overheads. In response, we present a Time Stamp Counter based precise Relative Clock Synchronization Protocol (TSC-RCSP) for distributed control applications operating over local-area networks (LANs). In our protocol a software clock based on the TSC register, counting CPU cycles, is adopted in the time clients and server. TSC-based clocks offer clients a precise, stable and low-cost clock synchronization solution. Experimental results show that clock precision in the order of 10 microseconds can be achieved in small-scale LAN systems. Such clock precision is much higher than that of a processor׳s Time-Of-Day clock and is easily sufficient for most distributed real-time control applications over LANs.

A Matter of Timing: Consumer Electronics and Network Time

Network time protocol (NTP) has become widely used across the Internet to synchronize clocks on computers and, more recently, on a wide variety of handheld devices. You are using NTP on a daily basis without even knowing it?when you set your mobile phone to get its time from the local network, you are linking into a global network of NTP servers that coordinate time across the entire Internet.

IEEE 1588 based time synchronization system for a seafloor observatory network

An IEEE 1588 based application scheme was proposed to achieve accurate time synchronization for a deep seafloor observatory network based on the communication topological structure of the Zhejiang University Experimental and Research Observatory. The principles of the network time protocol (NTP) and precision time protocol (PTP) were analyzed. The framework for time synchronization of the shore station, undersea junction box layer, and submarine science instrument layer was designed. NTP and PTP network signals were decoded by a PTP master clock on a shore station that receives signals from the Global Positioning System and the BeiDou Navigation Satellite System as reference time sources. These signals were remotely transmitted by a subsea optical-electrical composite cable through an Ethernet passive optical network. Accurate time was determined by time synchronization devices in each layer. Synchronization monitoring experiments performed within a laboratory environment indicated that the proposed system is valid and has the potential to realize microsecond accuracy to satisfy the time synchronization requirements of a high-precision seafloor observatory network.

Performance Analysis of DTSA in Distributed Network

a distributed system, synchronization of time is an important functionality for supporting real-time scenario like online banking applications, database queries and real time applications etc. A clock synchronization is necessary to measure the duration of activities that start on one node and terminate on another one. Although the some of the existing algorithms for time synchronization depend on sending and receiving messages from different system. Scheduling such task sets with time constraints requires timing information to be accurate. Synchronizing these clocks allows services in higher layers to assume a global time within certain bounds of accuracy. The system clocks of different nodes are not works on same clock time. Usually, there is an offset between the times, so accuracy is not achieved. The clock time collection interval, in which clock time of remote nodes are collected and corrected with global time, which determines the period of the correction of the local clocks. Such a decomposition can reduce delay and achieve accuracy in network. The paper presented in approach towards Delay Tolerant Synchronization Algorithm (DTSA) which is combination of Network Time Protocol (NTP) and Delay Tolerant Protocol (DTP) which synchronizes nodes in a network with Global Time Server (GTS) using NTP. Simulation results show that the DTSA reduces delay and achieve accuracy in scattered network.

Precise Clock Synchronization Algorithm for Distributed Control Systems

The distributed control systems are applied widely in communication, navigation and power fields. With growing in both systems complexity and speed of data exchange, the real time performance of systems is required. Existing clock synchronization techniques include those for wide-area network (WAN) applications with large propagation delays, e.g., the Network Time Protocol (NTP), and those for control systems over local-area networks (LANs), e.g., the IEEE 1588 Precise Time Protocol (PTP). However, NTP-like protocols have only millisecond-scale precision, which is too coarse for many LAN applications such as instrument monitoring systems, high-quality digital audio systems and sensor networks. The 1588 PTP like protocols, which are still under development, require support of a highly precise hardware clock. The key point of the existing Ethernet test and measurement is that the method needs to achieve precision clock synchronization between different terminals. In this paper, an improved method is proposed with consideration of the time drift and propagation delay, expressing master-slave synchronization as a linear relationship and inducting the line of least squares fitting algorithm that traded as linear matrix form. The precision time protocol (PTP) is also analyzed in this paper. The experiment results show that the synchronization accuracy reaches sub-microsecond grade, which is the same as the PTP. DOI: http://dx.doi.org/10.11591/telkomnika.v11i7.2832 Full Text: PDF

Network time protocol performance evaluation in LAN environment

Network Time Protocol(NTP) is a simple,economic and efficient way to accomplish time and frequency synchronization of multiple nodes,while relevant study on the performance evaluation is hard to find in literature,which makes it a question whether to use NTP in application.Concerning this problem,the local network NTP performance and impact of system / network load were measured and analyzed on Windows platform.By comparing time value obtained from IRIG-B time code reader and GetLocalTime Windows API,frequency skew of computer clock signal was approximated.The skew value was close to the value calculated by NTP.

Evaluation of Time Gateways for Synchronization of Substation Automation Systems

The International Electrotechnical Commission (IEC) 61850 standard is widely used in substation automation system (SAS), even if some aspects related to the network-based time synchronization are still under investigation. The latest version of the IEC 61850 standard introduces IEEE 1588 Precision Time Protocol (PTP) for distributing time in the station and process buses, in addition to the previously used Simple Network Time Protocol (SNTP). Some time synchronization problems may arise when mixing old and new IEC 61850 devices in the same system; the IEEE 1588 PTP and SNTP technologies have somewhat different time representations and synchronization schemes, requiring time gateways for smooth integration. This paper introduces and compares the performance of some compact time gateways with different implementation architectures. All the examined gateways have the same external structure: They are transparent two-port devices which are inserted in the last network link between the switch and the end device, in order to perform the time conversion from IEEE 1588 PTP to SNTP. The time gateways are built using the same hardware platform based on a Field Programmable Gate Array that enables the creation of real embedded prototypes. The experimental results show that all the considered time gateways are applicable to SAS, but some of them have better performance than others in terms of synchronization accuracy. Moreover, the authors identify the bottleneck in the SNTP implementation of the time gateway architecture. A careful analysis of the behavior of SNTP is proposed, and useful suggestions for trading off between synchronization accuracy and time gateway complexity are given.

Clock synchronization in high‐end computing environments: a strategy for minimizing clock variance at runtime

SUMMARYWe present a new software‐based clock synchronization scheme that provides high precision time agreement among distributed memory nodes. The technique is designed to minimize variance from a reference chimer during runtime and with minimal time‐request latency. Our scheme permits initial unbounded variations in time and corrects both slow and fast chimers (clock skew). An implementation developed within the context of the message passing interface is described, and time coordination measurements are presented. Among our results, the mean time variance for a set of nodes improved from 20.0 ms under standard Network Time Protocol down to 2.29 μs under our scheme. Copyright © 2012 John Wiley & Sons, Ltd.

High accuracy sequence of event system based on GPS

In order to meet the resolution requirement of hundreds of microseconds,microsecond global clock synchronization must be achieved in Sequence of Event(SOE) system.By means of assessing the existing clock synchronization methods and analyzing the cause of the error in the clock synchronization process,a new method based on the combination of improved Network Time Protocol(NTP) server synchronization and 1PPS synchronization was proposed.That is: advanced NTP server was used to eliminate the clock error between the control stations,"cross-second" phenomenon was avoided in this situation;1 PPS was used to synchronize the millisecond counters in order to eliminate the crystal accumulated error of Field Programmable Gate Array(FPGA).This method is simple,precise and stable.The resolution of SOE system by using this technique can be up to 0.5 ms,and it has been applied to the turbine protection system in a power plant successfully.

Experimental Characterization of Uncertainty Sources in a Software-Only Synchronization System

Over the past few decades, centralized computing systems have been replaced by decentralized systems, consisting of simple nodes interconnected by a communication network. The time reference of the distributed nodes must be synchronized in order to be able to coordinate the operation or compare the data collected by the different nodes. Several synchronization protocols have been developed to be used instead of global positioning system or dedicated synchronization systems. For example, the network time protocol (NTP) is a very popular synchronization protocol used to synchronize computers over wide area networks, like the Internet. In addition, IEEE 1588, a synchronization protocol dedicated to high-performance synchronization in local networks, was recently established. However, submicroseconds synchronization can be obtained only using dedicated hardware devices, thereby increasing the cost of each node. For these reasons, PTP software-only implementations are quite common in real systems, with a resulting synchronization uncertainty varying from a few to hundreds of microseconds and quite burdensome to estimate or measure. The work presented in this paper focuses on the analysis of the major uncertainty contributions in a software-only implementation. Particularly, a careful analysis of timestamp mechanism and time management in a PC platform is carried out. In addition, a method for the experimental evaluation of uncertainty contributions is proposed. A test case based on a software implementation of the IEEE 1588 (the so-called PTPd) is presented. The experimental tests presented in the paper highlight that the main uncertainty source of a software-only synchronization approach is the timestamp method. Timestamping accuracy can be affected by the computational load of the node itself: in normal conditions, the maximum uncertainty introduced by the timestamp mechanism is in the order of 10 , but in case of high computational load, it can raise up to 224 μs.

The realization of precision time protocol for distributed acoustic and vibration measurements

Distributed acoustic and vibration measurement based on Local Area Network (LAN) becomes a hot topic, recently. The performance of this measurement system is affected dramatically by the synchronization precision of different measurement nodes. Traditional synchronous methods, such as Network Time Protocol (NTP), Simple Network Time Protocol (SNTP) doesn't meet the precision needed for distributed acoustic and vibration measurements, because it can only achieves accuracy of microseconds. In addition, sync cable is not suitable for long distance distributed acoustic and vibration measurement due to the inconsistent delay. To sovle this problem, a method based on Precision Time Protocol (PTP, IEEE1588) is proposed in this paper for synchronization of distributed acoustic and vibration measurement device. A Field Programmable Gate Array (FPGA) is employed between Medium Independent Interface (MII) and PHY, which monitors all ingress and egress data packets. Only PTP packets are unpacked and proceeded. According to these packets, the time offsets are calculated. Then time offsets between master clock and slave clock are filtered, and the output of the filter is used to compensate the drift of crystal oscillator. Synchronization experiment show the proposed method can achieve synchronization accuracy of few hundred nanoseconds.

A distributed array processing using multi-channel signals over a network with an embedded time code by the network time protocol

A conventional microphone array system uses a conductor to wire from a microphone to an input via an amplifier. While, a wireless transmission for an array system makes the configuration flexible, and it is expected to provide novel applications widely, such as measuring of impulse response in wide area. One of the issues is a synchronization of time between channels. This paper proposes multiple signals transmission system over a network with a time code embedding to synchronize those signals. The system consists of clients and a server. Each client at a receiving point runs a network time protocol client daemon, and a packetized audio signal with a time code is sent to a server. The signal from a client is reconstructed at a server based on the time code. Since the time differences between clients affects to performance of the multichannel signal processing, small error in time at a client is preferred. This paper discusses how the error in time between channels affects to performance of the distributed microphone array system.

Highly Accurate Timestamping for Ethernet-Based Clock Synchronization

It is not only for test and measurement of great importance to synchronize clocks of networked devices to timely coordinate data acquisition. In this context the seek for high accuracy in Ethernet-based clock synchronization has been significantly supported by enhancements to the Network Time Protocol (NTP) and the introduction of the Precision Time Protocol (PTP). The latter was even applied to instrumentation and measurement applications through the introduction of LXI. These protocols are usually implemented in software; however, the synchronization accuracy can only substantially be improved by hardware which supports drawing of precise event timestamps. Especially, the quality of the timestamps for ingress and egress synchronization packets has a major influence on the achievable performance of a distributed measurement or control system. This paper analyzes the influence of jitter sources remaining despite hardware support and proposes enhanced methods for up to now unmatched timestamping accuracy in Ethernet-based synchronization protocols. The methods shown in this paper reach sub-nanosecond accuracy, which is proven in theory and practice.

Hardware implemented network time protocol (HwNTP) based synchronization for digitized radio over fiber systems

Hardware implemented network time protocol (HwNTP) based synchronization for digitized radio over fiber systems

무선 센서 네트워크를 위한 인터넷 시각 동기 프로토콜 확장

스마트 센서 및 임베디드 시스템, 저전력/저가격의 무선 통신, 애드 혹 (ad hoc) 네트워크, MEMS (Micro-Electro-Mechanical System) 기술의 발달은 센서 네트워크의 개발을 가능하게 하였다. 센서 네트워크에서 이동체 트래킹, 상태 정보 관리 및 이벤트 순서화와 같은 기본적인 응용 서비스를 제공하기 위해서 시각 정보 제공 및 시각 동기는 기본적으로 요구되는 요소 중 하나이다. 제한된 자원과 에너지를 갖는 센서 네트워크의 특성을 고려하여 다양한 시각 동기 기법이 제시되어 왔으나, 시각 표현 방법에 대한 고려를 한 사례는 거의 없는 실정이다. UTC TOD와 같은 전역 시각 표현 방식은 센서 네트워크의 응용을 위해 매우 유용한 방식으로 볼 수 있다. 본 논문에서는 인터넷 시각 동기 프로토콜 확장을 통해 센서 네트워크에서 전역 시각 정보를 관리할 수 있는 기법을 제시하였다. Advances in smart sensors, embedded systems, low-power design, ad-hoc networks and MEMS have allowed the development of low-cost small sensor nodes with computation and wireless communication capabilities that can form distributed wireless sensor networks. Time information and time synchronization are fundamental building blocks in wireless sensor networks since many sensor network applications need time information for object tracking, consistent state updates, duplicate detection and temporal order delivery. Various time synchronization protocols have been proposed for sensor networks because of the characteristics of sensor networks which have limited computing power and resources. However, none of these protocols have been designed with time representation scheme in mind. Global time format such as UTC TOD (Universal Time Coordinated, Time Of Day) is very useful in sensor network applications. In this paper we propose network time protocol extension for global time presentation in wireless sensor networks.

펨토셀 기지국 동기 획득을 위한 AGNSS-Packet Timing 하이브리드 표준화

동기 획득은 펨토셀 기지국의 안정적인 동작을 위해 가져야 할 주요 기술적 과제 중 하나이다. 특히 펨토셀 기지국의 경우는 설치되는 환경적 특수성에 의해 제약을 받는다. 첫째 펨토셀 기지국이 위치하는 실내 환경에서의 전파 감쇄와 상호 간섭등의 제약 요인이다. 둘째, 펨토셀 기지국이 연결되는 백홀 네트워크에 따른 제약이 있다. 이 밖에도, 무선 연결성을 제공하는 다른 기술의 AP와 같이 기술 구성에 있어서 저 비용이 요구되는 기술이어야 한다. 본 논문에서는 실내에서 위치 측위와 타이밍 획득을 위한 기술들을 살펴보고 AGNSS-Packet Timing 하이브리드 기술의 필요성 및 진행 중인 관련 표준화와 연관된 내용을 다루도록 한다. The synchronization is one of the important issues for successful operation of femtocell. The synchronization of femtocell is distinctly different from that of larger wireless base stations in a number of important respects such as 1) The femtocell is located in indoor environment which may make it difficult to receive the adequate GNSS signals. 2) The backhaul of femtocell is connected to the public network which may have more PDV than private network. 3) The entire cost of femtocell needs to be very low. In our thesis, we investigate the candidate solutions including AGNSS (Assisted GNSS), NTP (Network Time Protocol), PTP (Precision Timing Protocol) and Cellular Network Listen for indoor timing solution. We propose the AGNSS-PTP Hybrid scheme which can improve time and frequency quality by selecting the better reference between AGNSS and PTP, and cover the standard status which are under discussion from IEEE, ITU-T, and IETF.

Enabling multiparty karaoke over Internet based on low-level computers: practice and experiment

Karaoke is a system for amateur singing. The traditional online karaoke system does not allow multi-singers to sing a song in one session. This study designs and implements multiparty karaoke over Internet (MKI) based on low-level computers. The MKI is an online karaoke system of distributed architecture that allows multi-singers to sing a song in one session. The MKI must deal with the problems of feedback, asynchronous audio latency at singers’ nodes, round-trip latency at an inviter's node, and multi-singers singing a song in one session. The acoustic isolation between microphone and speakers avoids feedback. Network Time Protocol avoids asynchronous audio latency. The third method's round-trip latency in this study is within 86 ms, and all participants experience the simultaneous singing of the inviter and the invitees. MKI can be used for increasing leisure time, singing skills, and interpersonal relationships. Copyright © 2011 John Wiley & Sons, Ltd.

Time Synchronism of Dynamic Password Status Authentication

The e-commerce transaction process customers are most worried about is the security issues. Targeted e-commerce transaction authentication security that prevail in question time synchronization based on a dynamic password authentication technology, and gives a concrete realization of identity authentication process. The main advantage of this technology is a dynamic one-time passwords, and simple operation, transmission using RSA encryption algorithm. Network Time Protocol NTP for time synchronization of standard internet protocols, to solve the difficult problem of time synchronization.

Measurement Scheme for One-Way Delay Variation with Detection and Removal of Clock Skew

One-way delay variation (OWDV) has become increasingly of interest to researchers as a way to evaluate network state and service quality, especially for real-time and streaming services such as voice-over-Internet-protocol (VoIP) and video. Many schemes for OWDV measurement require clock synchronization through the global-positioning system (GPS) or network time protocol. In clock-synchronized approaches, the accuracy of OWDV measurement depends on the accuracy of the clock synchronization. GPS provides highly accurate clock synchronization. However, the deployment of GPS on legacy network equipment might be slow and costly. This paper proposes a method for measuring OWDV that dispenses with clock synchronization. The clock synchronization problem is mainly caused by clock skew. The proposed approach is based on the measurement of inter-packet delay and accumulated OWDV. This paper shows the performance of the proposed scheme via simulations and through experiments in a VoIP network. The presented simulation and measurement results indicate that clock skew can be efficiently measured and removed and that OWDV can be measured without requiring clock synchronization.

터치 인터페이스를 이용한 사물놀이 협주 시스템 구현

최근 문화콘텐츠 시장의 규모가 커짐에 따라 한국의 소리문화의 경쟁력을 갖추고 세계에 알릴 수 있는 독창적인 콘텐츠 개발이 요구되고 있다. 이러한 흐름에 따라 본 논문에서는 한국 전통음악인 사물놀이를 터치 인터페이스를 이용하여 연주하는 '사물놀이 협주 시스템'을 제안한다. 본 시스템은 터치기능을 지원하는 '콘트롤 디바이스'와 콘트롤 디바이스에서 입력한 터치 신호를 감지하여 연주음을 재생하는 '연주관리자', 다른 디바이스와 협주를 가능하게 하는 '통신 관리자', 협주시 시간 동기화 프로토콜을 활용하여 속도의 차이가 있는 통신환경에서도 연주의 순서를 유지할 수 있도록 하는 '동기화 관리자'로 구성 하여 설계하였다. 또한 사물놀이의 재미를 느낄 수 있도록 멀티터치를 활용한 조작방법을 고려했고, 여러 사람이 함께 연주할 수 있는 협주 기능을 구현하여, 사물놀이의 관심이 부족한 사람들에게 흥미를 끌어낼 수 있도록 하였다. Recently, as the scale of the cultural content business market is being growed, it required that we should introduce the Korean music culture which is unique and competitive cultural contents to the worldwide. This paper proposes a Samulnori Ensemble System (SES), using a touch interface which plays the Korean traditional musical instruments. A SES consists of the Control Device which supports touch functions, the Performance Manager that detects signals from the Control Device and plays a melody, and the Communication Manager making a ensemble among the possible devices. Also, using the Network Time Protocol which is part of Synchronization Manager can be paly different speed communication environments. We utilized multi-touch functions to operate the system. We also implemented multi-touch interface and multi-play with other player for fun and interesting who are not interested Samulnori.