Time Packet Research Articles

Delay analysis for cognitive radio networks

In this article, we derive the waiting time and total delay of packets for cooperative cognitive radio networks. In the primary network, there are primary transmitter (PT) and receiver (PR). In the secondary network, there are a source, M relays and a destination. Our results are valid for any number of relays and different relaying protocols: opportunistic amplify and forward (AF), partial AF, reactive AF and reactive DF. The analysis is carried out for nodes with fixed and adaptive transmit power. For fixed transmit power (FTP), we cannot guarantee that interference to PR is less than threshold T. Therefore, some relays are inactive because they generate harmful interference to PR. For adaptive transmit power (ATP), the power of a relay node is fixed so that peak interference power (PIP) or average interference power (AIP) constraints are verified. We also take into account interference from the primary transmitter (PT) by analyzing the delays based on signal to interference plus noise ratio (SINR). © 2018 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.

Dynamic and adaptive multi-path routing algorithm based on software-defined network

Recently, there has been a surge of the video services over the Internet. However, service providers still have difficulties in providing high-quality video streaming due to the problem of scheduling efficiency and the wide fluctuations of end-to-end delays in the existing multi-path algorithms. To solve these two problems affecting video transmission quality, networks are expected to have the capability of dynamically managing the network nodes for satisfying quality-of-service requirements, which is a challenging issue for media streaming applications. Against this changing network landscape, this article proposes a dynamic and adaptive multi-path routing algorithm under three constraints (packet loss, time delay, and bandwidth) that are based on software-defined network for centralized routing computations and real-time network state updating in multimedia applications. Compared with related multi-path routing proposals, dynamic and adaptive multi-path routing makes efficient use of the latest global network state information achieved by the OpenFlow controller and calculates the optimal routes dynamically according to the real-time status information of the link. Moreover, our proposed algorithm can significantly reduce the computational overhead of the controller while completing a fine-grained flow balance. Experimental results show that dynamic and adaptive multi-path routing significantly outperforms other existing scheduling approaches in achieving a 35%–70% improvement in quality-of-service.

Steganographic Communication via Spread Optical Noise: A Link-Level Eavesdropping Resilient System

We are witnessing a rising concern over communication security and privacy. Conventional cryptography techniques encrypt data into unreadable codes, but still expose the existence of communications through metadata information (e.g., packet timing and size). In contrast, we propose a steganographic communication scheme adopting a novel combination of the intrinsic optical noise and a unique signal spreading technique to hide the existence of optical communications, i.e., optical steganography. We experimentally implement a prototype steganographic communication system, which requires zero cover-signal overhead to enable a stealth communication channel over the existing communication infrastructure. Both the frequency and time-domain characterizations of our prototype implementation verify the feasibility of our approach. We also demonstrate the first practical steganographic communication that provides reliable communication performances between real computers at the application layer (200–300 Mb/s file transfer rate and 25–30 Mb/s Internet data rate) over long-distance optic fibers (25–50 km). Additional bit-error-rate measurements illustrate negligible channel interference between the public and stealth communications (less than 1 dB power penalty). We further quantitatively demonstrate that the eavesdropper's chance of matching system parameters to effectively recover the stealth signal is ${2^{-10}}$ by random guessing, and that the eavesdropper's ability of detecting the stealth signal hidden in the transmission channel is strictly limited close to a random guess. Our steganographic communication scheme provides an attractive foundation for mitigating eavesdropping at the link level; thus, paving the way for future privacy-enhancing technologies using the physical layer characteristics of communication links.

High-order photoelectron holography in the midinfrared-wavelength regime

We study the dynamical photoelectron holography of an excited hydrogen atom with a strong midinfrared laser field using numerical solutions of the three-dimensional time-dependent Schrodinguer equation. A clear holographic interference pattern of first and high order (hologram) is recorded in the two-dimensional (2D) momentum distribution of the photoelectron. The patterns are well reproduced by additional quantitative calculations based on the Lippmann-Schwinger equation. Here, the high-order interference effect is linked to the multsicattering of low-momentum electrons driven by the midinfrared laser field prior to ejection. The phenomenon manifests by low-momentum structures in 2D momentum distributions and is found to be sensitive to the change of the optical carrier-envelope phase (CEP). By analyzing the temporal evolution of the buildup of the hologram, we show that this sensitivity results from the birth time of the continuum wave packet with an offset in time during the subcycle dynamics, thus encoding information about the ionization mechanism which is mapped into the CEP-resolved 2D momentum distributions and angle-resolved photoelectron spectra. It is indeed an indicator that the ejected electrons exhibit a memory of their birth-time. These findings suggest that the CEP-resolved photoelectron holography serves as a tool for a direct measurement of attosecond dynamics. Furthermore, the effects due to such multiple scattering electron paths can be used to design new atom interferometers to highlight mechanisms that require higher accuracy.

A Risk-Sensitive Approach for Packet Inter-Delivery Time Optimization in Networked Cyber-Physical Systems

In networked cyber-physical systems, the inter-delivery time of data packets becomes an important quantity of interest. However, providing a guarantee that the inter-delivery times of the packets are “small enough” becomes a difficult task in such systems due to the unreliable communication medium and limited network resources. We design scheduling policies that meet the inter-delivery time requirements of multiple clients connected over wireless channels. We formulate the problem as an infinite-state risk-sensitive Markov decision process, where large exceedances of inter-delivery times for different clients over their design thresholds are severely penalized. We reduce the infinite-state problem to an equivalent finite-state problem and establish the existence of a stationary optimal policy and an algorithm for computing it in a finite number of steps. However, its computational complexity makes it intractable when the number of clients is of the order of 100 or so that is found in applications such as in-vehicle networks. To design computationally efficient optimal policies, we, therefore, develop a theory based on the high reliability asymptotic scenario, in which the channel reliability probabilities are close to one. We thereby obtain an algorithm of relatively low computational complexity for determining an asymptotically optimal policy. To address the remaining case when the channels are not relatively reliable, we design index-based policies for the risk sensitive case, which extends key ideas for index policies in risk-neutral multi-armed bandit problems. Simulation results are provided to show the effectiveness of our policies.

Survey on network flow watermarking: model, interferences, applications, technologies and security

Compared with passive flow correlation technologies based on flow characteristics, network flow watermarking, a kind of active flow correlation technology, is characterised by high accuracy, low false positive rate and short observation time. The basic framework and main elements of flow watermarking are formally described. The robustness and invisibility focused by flow watermarking as well as typical application scenarios (such as stepping-stone traceback, anonymous abuser correlation) of flow watermarking are expounded. The intra-flow and inter-flow interferences (such as repacketisation, packet reorder, delay normalisation, flow mixing, flow splitting and flow merging) faced by flow watermarking are briefly introduced. Analysis and comparison on different watermark carriers (packet payload, traffic rate, packet timing, packet number, packet length, packet order and hybrid carrier) based typical flow watermarking technologies, including flow fingerprinting technologies, are conducted, then, a review on security threats faced by flow watermarking, including multi-flow attack, mean-square autocorrelation attack, Kolmogorov–Smirnov test, BACKLIT detection and replication attack, and main countermeasures for increasing invisibility of flow watermarking is carried out. Current research hotspots and future development trends of flow watermarking are summarised and prospected from the aspects of architecture design, invisibility enhancement, adaptive capability improvement, performance evaluation, deployment and application.

Traffic-Adaptive Spectrum Leasing Between Primary and Secondary Networks

Spectrum leasing has been widely regarded as one of the most effective ways to improve the utilization of limited spectrum resources. In this paper, we propose a novel traffic-adaptive spectrum leasing (TASL) scheme by allowing secondary users (SUs) to lease part of licensed spectrum channels from primary users (PUs) temporarily for transmitting the dynamically generated secondary packets. As the time length of each leasing period is variable according to the dynamic generation of secondary packets, the proposed TASL can effectively satisfy the quality-of-service requirement of SUs and also benefit PUs with the financial payoff provided by SUs. By establishing a three-dimensional continuous Markov chain for the proposed TASL, we formulate the average utilities of PUs and SUs in terms of the expected buffering time of primary and secondary packets, as well as the expected transmission throughput of PUs and SUs. Moreover, to coordinate the interests of PUs and SUs in a noncooperative manner, we also propose a Stackelberg game model for PUs and SUs to negotiate various spectrum leasing parameters and further apply two specific rules to guarantee the existence of a unique equilibrium solution. Numerical simulation shows that, compared with those existing spectrum leasing schemes that preset a fixed-time length for leasing periods, the proposed TASL can effectively improve the utilization of the leased channels, increase the average utilities of both PUs and SUs, and be more suitable for newly emerging applications that are sensitive to packet transmission delay and buffering overhead.

Vibrational coherence transfer in the ultrafast intersystem crossing of a diplatinum complex in solution

We investigate the ultrafast transient absorption response of tetrakis(μ-pyrophosphito)diplatinate(II), [Pt2(μ-P2O5H2)4]4- [hereafter abbreviated Pt(pop)], in acetonitrile upon excitation of its lowest singlet 1A2u state. Compared with previously reported solvents [van der Veen RM, Cannizzo A, van Mourik F, Vlček A, Jr, Chergui M (2011) J Am Chem Soc 133:305-315], a significant shortening of the intersystem crossing (ISC) time (<1 ps) from the lowest singlet to the lowest triplet state is found, allowing for a transfer of vibrational coherence, observed in the course of an ISC in a polyatomic molecule in solution. Density functional theory (DFT) quantum mechanical/molecular mechanical (QM/MM) simulations of Pt(pop) in acetonitrile and ethanol show that high-lying, mostly triplet, states are strongly mixed and shifted to lower energies due to interactions with the solvent, providing an intermediate state (or manifold of states) for the ISC. This suggests that the larger the solvation energies of the intermediate state(s), the shorter the ISC time. Because the latter is smaller than the pure dephasing time of the vibrational wave packet, coherence is conserved during the spin transition. These results underscore the crucial role of the solvent in directing pathways of intramolecular energy flow.

Energy Internet Oriented Services Awareness in Elastic Optical Networks

Aimed to improve the ability of EON (Elastic Optical Networks) to support multiple services brought by Energy Internet, this paper proposes a Echo-State-Network Based Services Awareness schem of EON system for Energy Internet. The proposed scheme is able to be aware of characteristics of multiple services and to match their requirements with better quality. Thus, resources allocation optimization is enabled by the proposed scheme in each edge node. Simulation results show that this proposed approach can greatly improve the supporting ability for multiple services of Energy Internet with better performance from aspects of both packet loss rate and time delay performances.

ESTIMATING THE SERVICE WAITING PROBABILITY IN A SINGLE-CHANNEL SYSTEM WITH SELF-SIMILAR TRAFFIC

Estimation of the service quality characteristics in a single-channel system with queue for the packet network is often reduced to the determination of the Hurst exponent for self-similar traffic, after which using the known Norros formula calculated average number of packets in the system. However, this method does not allow for the set value of the Hurst exponent to have calculated the yet very important characteristics of quality of service, such as the average delay time of packets in the storage buffer and the service waiting probability of packet. In this work we propose a method for approximating the distribution function of the states of the system and, on its basis, a formula for calculating the service waiting probability in a single-channel system with a self-similar traffic.

Health Monitoring of Bolted Spherical Joint Connection Based on Active Sensing Technique Using Piezoceramic Transducers.

Bolted spherical joints are widely used to form space steel structures. The stiffness and load capacity of the structures are affected by the looseness of bolted spherical joint connections in the structures. The looseness of the connections, which can be caused by fabrication error, low modeling accuracy, and “false twist” in the installation process, may negatively impact the load capacity of the structure and even lead to severe accidents. Furthermore, it is difficult to detect bolted spherical joint connection looseness from the outside since the bolts connect spheres with rods together from the inside. Active sensing methods are proposed in this paper to monitor the tightness status of the bolted spherical connection using piezoceramic transducers. A triangle-on-triangle offset grid composed of bolted spherical joints and steel tube bars was fabricated as the specimen and was used to validate the active sensing methods. Lead Zirconate Titanate (PZT) patches were used as sensors and actuators to monitor the bolted spherical joint tightness status. One PZT patch mounted on the central bolted sphere at the upper chord was used as an actuator to generate a stress wave. Another PZT patch mounted on the bar was used as a sensor to detect the propagated waves through the bolted spherical connection. The looseness of the connection can impact the energy of the stress wave propagated through the connection. The wavelet packet analysis and time reversal (TR) method were used to quantify the energy of the transmitted signal between the PZT patches by which the tightness status of the connection can be detected. In order to verify the effectiveness, repeatability, and consistency of the proposed methods, the experiments were repeated six times in different bolted spherical connection positions. The experimental results showed that the wavelet packet analysis and TR method are effective in detecting the tightness status of the connections. The proposed active monitoring method using PZT transducers can monitor the tightness levels of bolted spherical joint connections efficiently and shows its potential to guarantee the safety of space steel structures in construction and service.

PGRP: Predictive geographic routing protocol for VANETs

Vehicular Ad hoc Networks (VANET) are a subclass of Mobile Ad hoc Networks (MANET). VANETs are used to build wireless networks between vehicles (V2V) and between vehicles and infrastructure (V2I). Unlike MANETs, VANETs introduce a variety of applications to enhance the safety of drivers and create a comfortable driving environment. These applications send messages through inter-vehicle communications. Routing in a VANET is a fundamental operation that allows a vehicle to construct a source-to-destination route. Routing in VANET is a challenging task due to rapidly changing topology and the high speed mobility of the vehicles involved. This paper presents a Predictive Geographic Routing Protocol (PGRP) that improves connectivity to deal with this challenge. In PGRP, every vehicle gives a weight to its neighbors according to the direction and the angle of the vehicle. PGRP can predict the location of every vehicle at the time of a hello packet based on a vehicle's acceleration. PGRP forwards packets according to the location of vehicle after a short interval. To simulate the PGRP, an integrated simulation model, a NS-2.35 based model and Simulator of Urban Mobility (SUMO) were used to generate a realistic traffic situation. The simulation results showed that PGRR outperformed PDGR, GPSR and GPCR in terms of packet delivery ratio, end-to-end delay, and average hops.

Performance Analysis of Network Coding with IEEE 802.11 DCF in Multi-Hop Wireless Networks

Network coding is an effective idea to boost the capacity of wireless networks, and a variety of studies have explored its advantages in different scenarios. However, there is not much analytical study on throughput and end-to-end delay of network coding in multi-hop wireless networks considering the specifications of IEEE 802.11 Distributed Coordination Function. In this paper, we utilize queuing theory to propose an analytical framework for bidirectional unicast flows in multi-hop wireless mesh networks. We study the throughput and end-to-end delay of inter-flow network coding under the IEEE 802.11 standard with CSMA/CA random access and exponential back-off time considering clock freezing and virtual carrier sensing, and formulate several parameters such as the probability of successful transmission in terms of bit error rate and collision probability, waiting time of packets at nodes, and retransmission mechanism. Our model uses a multi-class queuing network with stable queues, where coded packets have a non-preemptive higher priority over native packets, and forwarding of native packets is not delayed if no coding opportunities are available. Finally, we use computer simulations to verify the accuracy of our analytical model.

An Obstacle-Tolerant Path Planning Algorithm for Mobile-Anchor-Node-Assisted Localization

The location information obtained using a sensor is a critical requirement in wireless sensor networks. Numerous localization schemes have been proposed, among which mobile-anchor-node-assisted localization (MANAL) can reduce costs and overcome environmental constraints. A mobile anchor node (MAN) provides its own location information to assist the localization of sensor nodes. Numerous path planning schemes have been proposed for MANAL, but most scenarios assume the absence of obstacles in the environment. However, in a realistic environment, sensor nodes cannot be located because the obstacles block the path traversed by the MAN, thereby rendering the sensor incapable of receiving sufficient three location information from the MAN. This study proposes the obstacle-tolerant path planning (OTPP) approach to solve the sensor location problem owing to obstacle blockage. OTPP can approximate the optimum beacon point number and path planning, thereby ensuring that all the unknown nodes can receive the three location information from the MAN and reduce the number of MAN broadcast packet times. Experimental results demonstrate that OTPP performs better than Z-curves because it reduces the total number of beacon points utilized and is thus more suitable in an obstacle-present environment. Compared to the Z-curve, OTPP can reduce localization error and improve localization coverage.

Hierarchy Bayesian model based services awareness of high-speed optical access networks

As the speed of optical access networks soars with ever increasing multiple services, the service-supporting ability of optical access networks suffers greatly from the shortage of service awareness. Aiming to solve this problem, a hierarchy Bayesian model based services awareness mechanism is proposed for high-speed optical access networks. This approach builds a so-called hierarchy Bayesian model, according to the structure of typical optical access networks. Moreover, the proposed scheme is able to conduct simple services awareness operation in each optical network unit (ONU) and to perform complex services awareness from the whole view of system in optical line terminal (OLT). Simulation results show that the proposed scheme is able to achieve better quality of services (QoS), in terms of packet loss rate and time delay.

Exact Mean Packet Delay for Delayed Report Messages Multipoint Control Protocol in EPON

The infrastructure to develop the next generation optical access network is the Ethernet passive optical network (EPON). Interleaved polling with adaptive cycle time (IPACT) is a common polling method of an EPON. However, the mean waiting time of packets (= the mean packet delay) with IPACT is large depending on the arriving time of the packets. In this paper, a novel media access method for IPACT is proposed in order to minimize the mean packet delay. The mean packet delay with the proposed method is also derived as the exact solution. This solution is based on the non-trivial simplification of the previous work on the analytical solution for general IPACT. We confirm a close match between simulation and our theoretical results and show the effectiveness of our method.

Speed under sail during the early industrial revolution (c. 1750–1830)

AbstractThis article measures technological progress in oceanic shipping directly by using a large database of daily log entries from British, Dutch, and Spanish ships to estimate daily sailing speed in different wind conditions from 1750 to 1850. Against the consensus among economic (but not maritime) historians that the technology of sailing ships was fairly static during this time, we find that average sailing speeds of British East India Company and Navy ships in moderate to strong winds rose considerably after the 1770s. Driving this progress was the introduction of coppering in the 1780s, but subsequent rises are probably due to a continuous evolution of sails and rigging, and improved hulls that allowed a greater area of sail to be set safely in a given wind. By contrast, the speeds of Dutch and Spanish vessels were stagnant. Using separate data on the crossing times of Atlantic mail packets, we find gradual progress from the 1750s, followed by marked improvements when American packets appeared in the 1820s.

Enhanced class based dynamic priority scheduling to support uplink IoT traffic in LTE-A networks

Internet of Things (IoT) has now become a common term in technological communities. Machine-to-machine communications (M2M) is one of the components of IoT which deals with communication of devices to device and device to the network aspects. LTE-A networks have emerged as one of the preferred underlying communication networks to support IoT or M2M traffic. However, the uplink packet scheduling to optimize the QoS (quality of service) of M2M traffic without affecting or least affecting the QoS of Human-to-human (H2H) traffic (traffic generated by regular users (also called as H2H users) such as smartphone traffic, Internet traffic, voice traffic, etc.) is one of the main challenges in LTE-A networks. As a solution, we propose an uplink packet scheduling algorithm, called as enhanced class based dynamic priority (E-CBDP) algorithm, which ensures the QoS of H2H traffic by giving it priority over M2M traffic but, optimizes the QoS of M2M traffic by pushing the scheduling of H2H traffic to their delay boundaries. Further, a dynamic M2M traffic control threshold is defined to enable the operator for proactive regulation of the huge M2M traffic to avoid network congestion as well as to minimise the impact on H2H traffic. We characterize the proposed scheduling algorithm via a mathematical analysis for the metrics such as average length of the H2H queue, average length of the M2M queue, average waiting time of H2H packets, and average waiting time of M2M packets. We compare the performance of E-CBDP algorithm with some recent solutions in terms of average delay, percentage of packets dropped, aggregate throughput, fairness, and energy consumption. Simulation results show that E-CBDP algorithm demonstrates excellent performance in terms of packet drop rate and fairness while provides satisfactory performance in terms of delay, throughput, and energy consumption.

Performance Evaluation of Blackhole Attack on AODV in VANET

Black hole is one of the ongoing network threats that impact the physical components of Vehicular Ad hoc Networks (VANETs) when more layers deal with routing mechanism of vehicular ad hoc network. An algorithm for Ad hoc On-Demand Distance Vector (AODV) protocol in VANET was developed in order to identify collaborative group of nodes that behave as black hole. The simulation was configured to perform three scenarios with number of nodes set to 10, 20 and 40 nodes respectively. The result showed that the proposed algorithm provides a better throughput performance, less end to end delay, high packet delivery ration, less packet drops and less time for processing the incoming and outgoing nodes. Future works may consider testing the proposed solution on other types of attacks such as Wormhole, Jellyfish and Sybil attacks.

DPSAF: Forward Prediction Based Dynamic Packet Scheduling and Adjusting With Feedback for Multipath TCP in Lossy Heterogeneous Networks

As multihomed terminals are equipped with multiple interfaces and allowed to access heterogeneous networks, transferring data simultaneously through all the available paths becomes possible and also brings many benefits. Multipath TCP (MPTCP) has been proposed to distribute an application stream over different TCP connections. However, due to the disparate latencies of different paths, the problem of existing out-of-order packets usually occurs at the receiver. Large number of these packets exhaust the limited receiving buffer and make the receive window be stalled, which greatly degrade the throughput. Thus, an efficient scheduling mechanism will play an important role to keep in-order delivery. However, almost all of the previous intelligent scheduling mechanisms ignored packet losses, and didn't consider window changes of the congestion control algorithm and utilize the feedback information, which cannot perform well in the lossy heterogeneous networks. In this paper we propose a new scheduling algorithm: Forward Prediction based Dynamic Packet Scheduling and Adjusting with Feedback (DPSAF). DPSAF first utilizes maximum likelihood estimation in TCP modeling to estimate the data amount sent on other paths simultaneously, which takes packet loss rate and time offset into consideration, then gets feedback information from SACK options and fixes the scheduling value. From the simulation, we can see that our mechanism obviously improves throughput and reduces cache occupancy at receiver in lossy heterogeneous networks.