A Survey of Clock Synchronization Over Packet-Switched Networks

Clock synchronization is a prerequisite for the realization of emerging applications in various domains such as industrial automation and the intelligent power grid. This paper surveys the standardized protocols and technologies for providing synchronization of devices connected by packet-switched networks. A review of synchronization impairments and the state-of-the-art mechanisms to improve the synchronization accuracy is then presented. Providing microsecond to sub-microsecond synchronization accuracy under the presence of asymmetric delays in a cost-effective manner is a challenging problem, and still an open issue in many application scenarios. Further, security is of significant importance for systems where timing is critical. The security threats and solutions to protect exchanged synchronization messages are also discussed

Time Synchronization in Limited Resources Wireless Devices

This article deals with implementation of a time distribution protocol among limited resources wireless sensor devices. This type of protocol aims to distribute the same time reference among two or more devices within a network. Timestamps on measures help to relate them on causality studies. The PTP protocol defined at IEEE 1588-2008 is used, with little adaptations, to synchronize and tune software clocks inside the target boards of the Texas Instruments  ez430-RF2480ZigBee kit. Initially only synchronization was done, but it was verified the need to implement clock tuning. The devices clocks can be synchronized and tuned, even in heavily limited resources devices

TCP Performance Over Mobile IP Wired-cum-Wireless Networks

Reliable transport protocol like TCP has served well the wired Internet where the packet losses are mainly due to congestion but is not ready for Mobile IP wired-cum-wireless environments where the significant packet losses are due to bit errors and handoffs In this paper we have investigated the performance of TCP among the various TCP variants We have observed both TCP senders Newreno Vegas and TCP receivers Base Delayed-Ack Using ns-2 we have evaluated the TCP throughput and packet delay over a single TCP connection The simulation results suggest that a particular combination one TCP sender with one TCP receiver of TCP shows the best result in such Mobile IP network

The STACEE-32 Ground Based Gamma-ray Detector

We describe the design and performance of the Solar Tower Atmospheric Cherenkov Effect Experiment detector in its initial configuration (STACEE-32). STACEE is a new ground-based gamma ray detector using the atmospheric Cherenkov technique. In STACEE, the heliostats of a solar energy research array are used to collect and focus the Cherenkov photons produced in gamma-ray induced air showers. The large Cherenkov photon collection area of STACEE results in a gamma-ray energy threshold below that of previous detectors.Comment: 45 pages, 25 figures, Accepted for publication in Nuclear Instruments and Methods

Performance of charge-injection-device infrared detector arrays at low and moderate backgrounds

Three 2 x 64 element charge injection device infrared detector arrays were tested at low and moderate background to evaluate their usefulness for space based astronomical observations. Testing was conducted both in the laboratory and in ground based telescope observations. The devices showed an average readout noise level below 200 equivalent electrons, a peak responsivity of 4 A/W, and a noise equivalent power of 3x10 sq root of W/Hz. Array well capacity was measured to be significantly smaller than predicted. The measured sensitivity, which compares well with that of nonintegrating discrete extrinsic silicon photoconductors, shows these arrays to be useful for certain astronomical observations. However, the measured readout efficiency and frequency response represent serious limitations in low background applications