Adjacent Packets Research Articles

PTA-Sync: Packet-Train-Aided Time Synchronization for Underwater Acoustic Applications

In underwater acoustic applications, time synchronization errors accumulate severely with time, owing to the unpredictable propagation delay change induced by mobility and low sound propagation speed. In previously reported schemes, error accumulation during underwater acoustic time synchronization occurred, decreasing their performance and affecting their applicability. To overcome this limitation, we propose packet-train-aided time synchronization (PTA-Sync) for underwater acoustic application. The proposed PTA-Sync adaptively tracks one-way travel time (OWTT) change using three-dimensional linear velocity vector, the transmit time difference and arrival time difference of two adjacent packets in a packet train, and the position information of a mobile reference node. Thus, this scheme enables us to reduce the synchronization error accumulation rate by estimating the propagation delay change more accurately. Simulation results show PTA-Sync achieves higher accuracy than existing OWTT-based synchronization schemes. Thus, PTA-Sync can be effectively used in underwater exploratory activities because it can successfully reduce time synchronization errors.

Nanoscale spin-wave wake-up receiver

We present the concept of a passive spin-wave device which is able to distinguish different radio frequency pulse trains and validate its functionality using micromagnetic simulations. The information is coded in the phase of the individual pulses which are transformed into spin-wave packets. The device splits every incoming packet into two arms, one of which is coupled to a magnonic ring which introduces a well-defined time delay and phase shift. Since the time delay is matched to the pulse repetition rate, adjacent packets interfere in a combiner, which makes it possible to distinguish simple pulse train patterns by the readout of the time-integrated spin-wave intensity in the output. Due to its passive construction, this device may serve as an energy-efficient wake-up receiver used to activate the main receiver circuit in power critical internet of things applications.

MIMO-UFMC Transceiver Schemes for Millimeter-Wave Wireless Communications

The universal filtered multicarrier (UFMC) modulation is among the most considered solutions for the realization of beyond orthogonal frequency division multiplexing (OFDM) air interfaces for future wireless networks. This paper focuses on the design and analysis of a UFMC transceiver equipped with multiple antennas and operating at millimeter-wave carrier frequencies. This paper provides the full mathematical model of an MIMO-UFMC transceiver, taking into account the presence of hybrid analog/digital beamformers at both ends of the communication links. Then, several detection structures are proposed, both for the case of single-packet isolated transmission and for the case of multiple-packet continuous transmission. In the latter situation, this paper also considers the case in which no guard time among adjacent packets is inserted, trading off an increased level of interference with higher values of spectral efficiency. At the analysis stage, several considered detection structures and transmission schemes are compared in terms of bit-error rate, root-mean-square error, and system throughput. The numerical results show that the proposed transceiver algorithms are effective and that the linear minimum mean-square error (MMSE) data detector is capable of well managing the increased interference brought by the removal of guard times among consecutive packets, thus yielding throughput gains of about 10%–13%. The effect of phase noise at the receiver is also numerically assessed, and it is shown that the recursive implementation of the linear MMSE exhibits some degree of robustness against this disturbance.

Impact toughness scattering of bainitic steel in the ductile-brittle transition temperature region

The impact toughness scattering in the ductile-brittle transition temperature (DBTT) region was experimentally examined on mixed and homogeneous grains of low alloy high strength bainitic steel under dynamic loading conditions. The results revealed that the mixed grain microstructure had larger impact toughness scattering than the homogeneous one, and the impact toughness scattering was mainly caused by the scattering in the cleavage fracture stress σf. The value of σf is related to the size of the microcrack formed in the bainitic packet. When a bainitic packet-sized microcrack propagates from one bainitic packet into the adjacent packet, cleavage fracture occurs. The cleavage fracture is controlled by the few coarse packets in the microstructures, and the σf scattering is influenced by the varied distances/relative locations between these coarse packets, and homogenizing the distribution of fine bainitic packet sizes is an effective way to reduce the impact toughness scattering in the DBTT region.

A Modular Self-Reconfigurable Robot with Enhanced Locomotion Performances: Design, Modeling, Simulations, and Experiments

This paper presents the design and implementation of a modular self-reconfigurable robot with enhanced locomotion capabilities. It is a small hexahedron robot which is 160 mm × 140 mm × 60 mm in size and 405 g in weight. The robot is driven by three omnidirectional wheels, with up and down symmetrical structure. The robot can perform rectilinear and rotational locomotion, and turn clockwise and counterclockwise without limitation. A new docking mechanism that combines the advantages of falcula and pin-hole has been designed for attaching and detaching different modules. The communication and image data transmission are based on a wireless network. The kinematics and dynamics of the single module has been analyzed, and the enhanced locomotion capabilities of the prototype robot are verified through experiments. The maximum linear velocity is 25.1cm/s, which is much faster than other modular self-reconfigurable robots. The mobility of two connected modules is analyzed in the ADAMS simulator. The locomotion of the docking modules is more flexible. Simulations on the wheel and crawling locomotion are conducted, the trajectories of the robot are shown, and the movement efficiency is analyzed. The docking mechanisms are tested through docking experiments, and the effectiveness has been verified. When the transmission time interval between the adjacent packets is more than 4 ms, the wireless network will not lose any packet at the maximum effective distance of 37 m in indoor environments.

Effect of Bainitic Packet Size Distribution on Impact Toughness and its Scattering in the Ductile-Brittle Transition Temperature Region of Q&T Mn-Ni-Mo Bainitic Steels

The impact toughness of Q&T Mn-Ni-Mo bainitic steel in the ductile–brittle transition temperature (DBTT) region was measured. The fracture micromechanism associated with the microstructural features was studied, by statistically analyzing the grain sizes of various structures. The results reveal that the cleavage fracture behavior is controlled by bainitic packets. There exists a critical bainitic packet size. When a microcrack formed in the bainitic packet with a size exceeding the critical size propagates into adjacent packets, brittle cleavage fracture occurs. The probability of finding the bainitic packets larger than the critical size dominates the impact toughness and its scattering. It is suggested that refining the bainitic packets and homogenizing their sizes is an effective method of improving the impact toughness and reducing its scattering in the DBTT region.

Effective packet number for early stage internet traffic identification

Accurately identifying Internet traffic at the early stage is very important for the applications of traffic identification. Recent years, more and more research works have tried to build effective machine learning models to identify an Internet flow with the few packets at its early stage. However, a basic and important problem still needs to be studied in depth, that is how many packets are most effective in early stage Internet traffic identification. In this paper, we try to resolve this problem. Three Internet traffic data sets are applied. And the sizes of the first 10 packets are extracted for study. We firstly apply mutual information to analyze the information that the first n packets provide to the flow type. Then correlation analysis of each pair of adjacent packets is carried out to find out the feature redundancies. And then we execute a number of crossover identification experiments with different numbers of packets using 11 well-known supervised learning algorithms. Finally, statistical tests are applied for the experimental results to find out which number is the best performed one. Our experimental results show that 5–7 are the best packet numbers for early stage traffic identification.

A novel comprehensive steganalysis of transmission control protocol/Internet protocol covert channels based on protocol behaviors and support vector machine

AbstractCovert channels are malicious conversations disguised in legitimate network communications, allowing information leak to the unauthorized or unknown receiver. Various network steganographic schemes that modify the header fields of transmission control protocol/Internet protocol (TCP/IP) have been proposed in recent years. People before conducted detection research based on the surface content of the header field and did not take into account the differences between the behavior characters of covert channels and the inherent behavior regularities of the header fields. Up to date, there is little comprehensive research on the steganalysis against the storage covert channels. In this paper, we focus on the detection of storage covert channels and introduce a novel comprehensive detection method based on the protocol behaviors. The protocol behavior characters are utilized to evaluate the regularities or correlations of header fields between adjacent packets according to the conventional use. First, the behavior features of the header fields in TCP/IP are extracted; a support vector machine is then applied to the behavior feature sets for discovering the existence of covert channels. Some recognized covert channel tools are detected in our detection experiment. Experimental results and discussion show that our detection method is of effectiveness. Copyright © 2014 John Wiley & Sons, Ltd.

Demand-oriented Traffic Measuring Method for Network Security Situation Assessment

In the information of security situation, traffic is necessary data to describe the network performance. It is also an important indicator to measure attacks such as worms or DoS. During the process of situational awareness, the traffic measuring methods are often needed without the privilege of routers. Our work emphasizes on the measuring algorithms based on packet pair in end-to-end measuring technologies. The simulations have shown that the congestion status of network and the length of packet have greater effect on the measurement of path capacity. So on the basis of improved packet pair measuring algorithms, a novel traffic measuring method DTM for demand is put forward. DTM aims to acquire the optimum compromise between measuring overhead and accuracy through the utilization of detecting packets. The relation between sending rate and available bandwidth are decided by one-way delay and changes of packets. Simultaneously, DTM assigns corresponding weight to the transition bandwidth, according to the disturbed degree of packet which is set as transition point, and its adjacent packets. Then it can better reflect the influence caused by background traffic. DTM also provides the rules to judge whether two packets are transition points and it discusses the method to determine the measuring range dynamicly according to specific application bandwidth requirements. The experiments have studied the trend of relativity and the difference of packet pair, when the following factors are changing: size of detecting packet, network load, features of background traffic and bottleneck bandwidth. It is shown that DTM has characteristics in low overhead, high accuracy, good smoothness and sensitivity for network situation, compared to traditional algorithms.

Microstructural characterization of an as-quenched HSLA-100 plate steel via transmission electron microscopy

Abstract Detailed analysis of an HSLA-100 steel via transmission electron microscopy revealed a “fully” martensitic microstructure, despite a low carbon content of 0.06 mass%, a fine prior austenite grain size of about 10 μm, and a modest cooling rate of approximately 15 °C/s. Martensite laths typically contained a moderate-to-high dislocation content, and occasional regions of twinned martensite were observed. Laths were contained wholly within single grains of austenite, and about 5% austenite was present in the final as-cooled microstructure. Martensite crystals exhibited the Kurdjumov–Sachs orientation relationship with respect to the parent austenite phase, and multiple variants of this relationship were observed for adjacent packets. Autotempering of martensite resulted in a low volume fraction of cementite precipitates in the largest, first-formed laths.

Implementing a passive network covert timing channel

The paper concerns passive network covert timing channels, in which the channel senders reside in intermediate nodes (e.g. router, gateway) and forward the passing-by packets in a carefully planned manner to covertly transmit the information. In this study, we focus on constructing and testing a kind of passive network covert timing channel, in which the information is hidden in the transmission interval between two adjacent packets. We first introduce three channel states to cope with the fluctuation in the traffic used as carrier, and explore how to select suitable values for the channel parameters to obtain high communication performance. We then implement an actual channel using Video On Demand (VOD) traffic as carrier, and obtain the communication characteristics of the channel. Finally, we investigate an information transmission scheme over the channel, including frame design, frame synchronization and error correction.

Delay controlled wireless video playout system

Best-effort streamed video playout representing the most popular and cost-effective multimedia application today is unfortunately very sensitive to any fluctuations in packet loss and delay. There are always further problems for the provision of real-time playout applications over wireless links because of the complicated and highly variable nature of the channel and challenging quality issues for adopting the service in global scales, which necessitates adopting a new and effective buffer mechanism. As a solution to this problem, to smooth out the playout for quality viewing and improved overall systems' performance, in this study the authors propose a new adaptive media playout (AMP) system that makes the most effective use of a packet-delay prediction algorithm. Here, as the prediction method makes decisions based on the delay interdependency of the adjacent packets the differential auto-regression delay prediction model is used for working out the estimation. The proposed algorithm also adopts more refinement changing steps in the adjustment process and takes into accounts any packet losses with deadline constraint. The simulation results show that the proposed method outperforms the AMP-live method in reducing the average buffer delays as well as enhancing package loss rates for both overflow and underflow.

Nanosecond guard time packet-by-packet burst-mode optical 3R regeneration in an optical-label switching router

This letter discusses an experimental demonstration of 10-Gb/s packet-by-packet burst-mode optical 3R regeneration in an optical-label switching router. A monolithically integrated Mach-Zehnder interferometer with semiconductor optical amplifiers provides the all-optical 2R regeneration. Synchronous modulation with the use of Fabry-Pe/spl acute/rot filter-based clock recovery performs the burst-mode retiming function necessary for 3R regeneration. The clock recovery works successfully despite a clock phase discontinuity between adjacent packets. The optical 3R regenerator shows bit-error rates below 1/spl times/10/sup -10/ and sensitivity variations less than 1.5 dB over a wide range of guard times from 3 to 1000 ns.

Demonstration of high-speed optical packet routing using vertical coupler crosspoint space switch array

The routing of 10 Gbit/s optical data packets has been demonstrated using a compact InGaAsP/InP vertical coupler optical space switch array. The fast switching speed of the device allows an interpacket guard-band as short as 2 ns to be obtained with an adjacent packet suppression ratio of –50 dB.

An experimental study of wave packets in travelling ionospheric disturbances

The complex demodulation method was employed to analyse observations of TIDs carried out by means of multifrequency HF Doppler sounding at vertical incidence over Almaty (76°55′E, 43°15′N). Two types of behaviour of the amplitude and phase in the band-pass filtered Doppler shift oscillations were revealed. These were packet-like wave structures and quasi-stochastic TIDs. A study of the phase behaviour inside wave packets showed that most of them had a quasi-monochromatic structure, some of them had oscillations with a period which increased with time, and none had oscillations with a period which decreased with time. Phase jumps between nearby packets were explained as a result of interference between two adjacent packets having similar oscillation periods. A method of calculating the correlation coefficient for the wave packets propagating on a background of quasi-stochastic TIDs was developed. This showed that wave packets (having periods between 7 and 50 min) travelled in the vertical plane practically without any loss of coherence, while quasi-stochastic TIDs had a short coherence length; the velocity of the quasi-stochastic TIDs was noticeably larger than that of the wave packets.

Statistical multiplexing of random processes in packet switching networks

The authors present an analytical model for the closed form evaluation of relevant parameters characterising the process at the output of a statistical multiplexer. Compared with previous approaches, the proposed method is able to additionally describe transient conditions and, through the autocorrelation function and the mean length of adjacent packets sequences, to evaluate the extent of the correlation in the output process as a function of that in the input traffic, also taking into account the effect due to a finite buffer size. The reliability of the model is tested, under different operation conditions, by comparison with simulated results, showing everywhere an excellent agreement.

Dynamic interpretation of space shuttle photographs: Deepwater internal waves in the western equatorial Indian Ocean

Visible images of deep‐ocean internal waves in the western equatorial Indian Ocean taken by the space shuttle Atlantis during mission STS 44 in 1991 are interpreted and analyzed. The internal waves occurred in the form of a multisoliton packet in which there are about a dozen solitons. The average wavelength of the solitons is 1.8±0.5 km, ranging from 1.1 to 2.6 km. The crest lines are mostly straight and reach as long as 100 km. The distance between two adjacent packets is about 66 km. Using the deepwater soliton theory, we derived that the mean amplitude of the solitons is 25 m, the nonlinear phase speed is 1.7 m/s, and the average period is 18 min. The internal semidiurnal tides are the principal generating mechanism. The oblique collision of two multisoliton packets shown on photograph STS 44‐93‐103 is examined. The results show that the deep‐ocean internal waves obey the general properties of soliton collision. The leading solitons and a few followers exhibit some properties of inelastic collision characterized by a phase shift, and the rest of the solitons exhibit properties of elastic collision under resonance conditions.

The role of stationary cross-flow vortices in boundary-layer transition on swept wings

The spatial evolution of stationary cross-flow-vortex packets in a laminar boundary layer on a swept wing is computed by direct numerical simulation with the incompressible Navier–Stokes equations. Steady suction and blowing at the wing surface is used to generate disturbances that are periodic and equally spaced in the spanwise direction. The initiated disturbances become unstable and lead to distinct stages of instability evolution. Initially, each vortex packet undergoes a region of chordwise and spanwise linear independent growth; then the individual packets coalesce downstream and lead to spanwise wave adjustments and linear superposition of adjacent packets; finally, the vortex packets reach sufficiently large amplitudes in later stages of disturbance development to nonlinearly interact, which results in the rapid growth of the disturbances. In this later stage, the low-velocity fluid near the wing surface is lifted out into the boundary layer and rolled over the high-speed fluid in the direction of the positive spanwise velocity component. Highly inflectional chordwise and spanwise velocity profiles are recorded in this region. Previous studies have demonstrated that these inflectional profiles spawn the rapid growth of secondary instabilities, which lead to the catastrophic breakdown to turbulence.

Queueing analysis of an integrated services TDM system using a matrix-analytic method

A matrix-analytic method is used to analyze the queueing behavior of small time division multiplexing (TDM) integrated services systems. Such systems have priority services for time-critical traffics in which adjacent packets exhibit a strong interdependency. The TDM frame with a capacity of M packets is used to transmit the high-priority packets at every time step. Any unused capacity is utilized to transmit low-priority packets. The system can be modeled as a discrete-time system with a fluctuating number of servers for the low-priority packets. Because the number of servers is small and adjacent packets are dependent, the birth-and-death analysis is not appropriate. An algorithm, based on a modification of Neuts' method, is used to determine the boundary points required in the queuing analysis. Numerical results for two integrated services systems, each with different characteristics, are presented to demonstrate the feasibility of the analysis method and the computational algorithm. >

Performance analysis of integrated services on a single server system

The integration of time-critical (TC) and non-time-critical (NTC) services on a single resource, in which the TC traffic is given a higher service priority, can be modeled by a server that alternates between a work cycle and a vacation cycle. When a stream traffic is partitioned into packets, adjacent packets are correlated. With the TC traffic given a higher service priority than the NTC traffic, the correlation present in the TC traffic has the effect of increasing the queue size of the NTC traffic. Generating functions for the delay and queue length distributions of the NTC traffic, incorporating the signal dependency (packet-to-packet correlation) within the TC traffic, are derived. Exact expressions for the means and standard deviations as functions of the throughput are then obtained and computed. The incorporation of the packet-to-packet correlation in the analytical expressions offers a unified approach for analyzing the performance of integrated services systems. Numerical results indicate that the presence of correlation due to packetization of stream traffic introduces a significant effect on the queue length distribution of the low priority (NTC) traffic.