Link Propagation Delay Research Articles

Secrecy Analysis of Decode-and-Forward Relay Based Heterogeneous Terrestrial RF - Underwater Acoustic System

This study examines how well a heterogeneous dual-hop terrestrial radio frequency and underwater acoustic downlink system maintain confidentiality. It includes an RF source, an intermediate decode-and-forward relay, an underwater multi-hydrophone destination, and a nearby eavesdropper. Eavesdropper overhears underwater acoustic signal transmitted by the relay. RF and underwater acoustic links undergo Nakagami-m and Rayleigh fading, respectively. Due to the propagation delay of underwater scenario, both destination and eavesdropper links are associated with outdated channel state information which also employs maximal-ratio combining. The closed form expressions of secrecy outage probability, strictly positive secrecy capacity, and intercept probability are derived. Monte-Carlo simulations are obtained to certify the analytical expressions.

Cross-Layer Protocol Based on Directional Reception in Underwater Acoustic Wireless Sensor Networks

The long propagation delay of acoustic links leads to the complex randomness of packet collision, which reduces the network packet delivery rate (PDR) and aggravates network congestion. A single vector hydrophone with directional reception characteristics can concentrate the reception gain on a certain direction, which can increase spatial reuse, reduce packet collision, and help to improve the performance of the underwater acoustic wireless sensor networks (UASNs). Herein, this paper proposes a cross-layer protocol with low interference and low congestion (CLIC) based on directional reception. An integrated routing-medium access control (MAC) design is also devised in the CLIC scheme to use the directional beams to create the least-interfering, highest-capacity data transmission links, weighing key factors affecting network performance to obtain routes with low collisions and low congestion. Simulation results show that the CLIC has a higher packet delivery rate (PDR) and higher energy efficiency compared to the QELAR, CITP, and VBF protocols.

Delay Optimization for Cooperative Multi-Tier Computing in Integrated Satellite-Terrestrial Networks

The integrated satellite-terrestrial network is promising to provide global broadband communication service. However, the long propagation delay of satellite-terrestrial links will lead to high communication delay when users access the Internet via satellites. In this paper, we investigate the cooperative multi-tier computing in the integrated satellite-terrestrial network, in which the computation tasks of users are processed by leveraging the cooperation of devices, edge nodes, and cloud servers. Based on the proposed three-tier computing framework, we formulate the cooperative edge-cloud offloading problem to minimize the total delay of the network. Considering the computation task is dividable, we propose the optimal task splitting strategy based on the partial offloading model, in which the closed-form solution is derived for each computation task. With the optimal task splitting strategy obtained, the original optimization problem is reformulated as the problem of the time slot allocation strategy and the computation capacity allocation strategy. Then, we further propose the cooperative edge-cloud computing strategy to optimize the delay performance of the network. Finally, numerical results are presented to demonstrate the performance of the proposed three-tier computing architecture and the offloading strategies.

Optical fiber communication system links performance enhancement for high-speed data transmission through short-reach applications

Abstract This paper clarified the optical fiber communication system links the performance signature for short-indoor applications. The electrical propagation delay time is investigated for copper links. The polystyrene optical link propagation delay time is also analyzed. The optical pulse broadening and the data transmission bit rates in the optical links are analyzed. The electrical/optical links performance is discussed with the variations of electrical/optical link variations and ambient temperature variations. The optical link performance efficiency has presented better performance than the electrical links, especially for short-indoor applications.

Cooperative Multilayer Edge Caching in Integrated Satellite-Terrestrial Networks

The integrated satellite-terrestrial network is promising to provide global broadband communication service. However, the long propagation delay of satellite-terrestrial links will lead to high communication delay when users access the Internet via satellites. In this paper, we investigate the cooperative multilayer edge caching in the integrated satellite-terrestrial network to reduce the communication delay, in which the base station cache, the satellite cache, and the gateway cache cooperatively provide content service for ground users. We first propose the three-layer cooperative caching model of the network, based on which we analyze the content retrieving process and derive the cache hit probability for different caching locations. Considering limited cache sizes, we formulate the content placement problem to minimize the average content retrieving delay of users. Then, two caching strategies, the non-cooperative caching strategy and the cooperative caching strategy, are proposed with exhaustive theoretical analysis. By introducing the concept of delay reduction gains, the optimal caching strategies are obtained based on the proposed iterative algorithms. Finally, numerical results are presented to demonstrate the performance of the proposed cooperative caching architecture and the caching strategies.

Securing industrial communication with software-defined networking.

Industrial Cyber-Physical Systems (CPSs) require flexible and tolerant communication networks to overcome commonly occurring security problems and denial-of-service such as links failure and networks congestion that might be due to direct or indirect network attacks. In this work, we take advantage of Software-defined networking (SDN) as an important networking paradigm that provide real-time fault resilience since it is capable of global network visibility and programmability. We consider OpenFlow as an SDN protocol that enables interaction between the SDN controller and forwarding plane of network devices. We employ multiple machine learning algorithms to enhance the decision making in the SDN controller. Integrating machine learning with network resilience solutions can effectively address the challenge of predicting and classifying network traffic and thus, providing real-time network resilience and higher security level. The aim is to address network resilience by proposing an intelligent recommender system that recommends paths in real-time based on predicting link failures and network congestions. We use statistical data of the network such as link propagation delay, the number of packets/bytes received and transmitted by each OpenFlow switch on a specific port. Different state-of-art machine learning models has been implemented such as logistic regression, K-nearest neighbors, support vector machine, and decision tree to train these models in normal state, links failure and congestion conditions. The models are evaluated on the Mininet emulation testbed and provide accuracies ranging from around 91-99% on the test data. The machine learning model with the highest accuracy is utilized in the intelligent recommender system of the SDN controller which helps in selecting resilient paths to achieve a better security and quality-of-service in the network. This real-time recommender system helps the controller to take reactive measures to improve network resilience and security by avoiding faulty paths during path discovery and establishment.

CITP: Collision and Interruption Tolerant Protocol for Underwater Acoustic Sensor Networks

In underwater acoustic sensor networks (UASNs), the spatially and temporally varying acoustic channel causes random route interruptions and transmission void region. Further, the long propagation delay of acoustic links causes complicated randomness of packet collisions. Inspired by the unpredictability of both route interruptions and packet collisions in UASNs, a collision and interruption tolerant protocol (CITP) is proposed to jointly address the two challenges in a smart way. By exploiting the opportunistic transmission strategy, CITP forms the optimized route on the fly, which bypasses nodes that undergo collisions or interrupted links and void regions. Simulation results show that CITP achieves a high packet delivery ratio with reduced energy consumption.

Synchronisation of a distributed control and data acquisition system for modular multi‐level PHIL amplifiers

This research presents a novel technique to synchronise a modular control and data acquisition system for the testing of multi-level power hardware-in-the-loop (PHIL) amplifiers. The methodology is inspired by the precision timing protocol, used to compensate for communications latency between distributed control nodes. It uses a non-conventional digital pulse-width modulation (PWM) technique, phase accumulator carrier pulse-width modulation to achieve carrier synchronisation across the system. A prototype design has been demonstrated on a three-node test bench, showing single clock cycle (10 ns) precision when synchronising a 25 kHz PWM carrier wave, with minimal sensitivity to communications link propagation delays.

Active Delay Stabilization of a 440-km Fiber Link in a Wideband Microwave Delay System

In this paper, a wideband microwave delay system with an equivalent 440-km fiber link is presented. The fiber link propagation delay fluctuation, suffering from temperature variation, is detected incorporating with a reference RF signal. With the help of a variable optical delay line, the wideband microwave frequency output is phase-stabilized. A system figure of merit is investigated in detail. The results show that, with dispersion compensation, the fiber-optic delay system can operate for the frequencies up to 38 GHz. Moreover, the fiber-optic system can provide a noise figure of below 40 dB, a signal-to-noise ratio of above 51 dB and a spur level of less than -56 dB for the delayed wideband microwave frequency signal. An additive phase noise of -116 dBc/Hz at the 10 kHz offset frequency can be guaranteed for a 1 GHz frequency. With active delay stabilization, the 38 GHz frequency delayed achieves an Allan deviation of 5.8 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-13</sup> /s and 5.4 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-16</sup> /10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> s, respectively.

A Novel Optimal Mapping Algorithm With Less Computational Complexity for Virtual Network Embedding

Network virtualization (NV) is widely accepted as one enabling technology for future network, which enables multiple virtual networks (VNs) with different paradigms and protocols to coexist on the shared substrate network (SN). One key challenge in NV is VN embedding (VNE), which maps a VN onto the shared SN. Since VNE is NP-hard, existing efforts mainly focus on proposing heuristic algorithms that try to achieve feasible VNE in reasonable time, consequently the resulted embedding is not optimal. To tackle this difficulty, we propose a candidate assisted (CAN-A) optimal VNE algorithm with lower computational complexity. The key idea of the CAN-A algorithm lies in constructing the candidate substrate node subset and the candidate substrate path subset before embedding. This reduces the mapping execution time substantially without performance loss. In the following embedding, four types of node and link constraints are considered in the CAN-A algorithm, making it more applicable to realistic networks. Simulation results show that the execution time of CAN-A is hugely cut down compared with pure VNE-MIP algorithm. CAN-A also outperforms the typical heuristic algorithms in terms of other performance indices, such as the average VN request acceptance ratio and the average virtual link propagation delay.

Multimedia Content Delivery for Emerging 5G-Satellite Networks

Multimedia content delivery over satellite systems is considered as a promising service in emerging 5G networks. The aim of this paper is to design a novel radio resource management algorithm for efficiently managing multicast multimedia content transmission over satellite network. The proposed approach performs the spectrum management on a per-group basis, by splitting multicast terminals into different subgroups according to the experienced channel qualities. We demonstrate that subgrouping policy defined by the authors as multicast subgrouping-maximum satisfaction index (MS-MSI), based on a new metric (i.e., MSI), overcomes the weakness of the previous techniques proposed in the literature and provides the best tradeoff between user throughput and fairness. As a further result, we demonstrate that MS-MSI is robust to the long propagation delay of satellite links. An extensive simulation campaign has been conducted by considering several satellite environments.

Low-complexity time synchronization for energy-constrained wireless sensor networks: Dual-Clock delayed-message approach

Due to the ability of sensor nodes to collaborate, time synchronization is essential for many sensor network operations. With the aid of hardware capabilities, this work presents a novel time synchronization method, which employs a dual-clock delayed-message approach, for energy-constrained wireless sensor networks (WSNs). To conserve WSN energy, this study adopts the flooding time synchronization scheme based on one-way timing messages. Via the proposed approach, the maximum-likelihood (ML) estimation of time parameters, such as clock skew and clock offset, can be obtained for time synchronization. Additionally, with the proposed scheme, the clock skew and offset estimation problem will be transformed into a problem independent of random delay and propagation delay. The ML estimation of link propagation delay, which can be used for localization systems in the proposed scenario, is also obtained. In addition to good performance, the proposed method has low complexity.

Optimized performance data transmission in Mobile IP networks

In a Mobile IP network (MIPN), nodes move. When a node moves, it may go away from other nodes and this decreases available bandwidth and data rate and increases the propagation delay of links. Therefore, nodes' movement can decrease data delivery and handoff latency; these will reduce network efficiency. Suppose that an MIPN uses an optimal routing algorithm and transmits data from a source node to a destination node optimally. Nodes' movement can violate the optimality of the data transmission and this will waste bandwidth and network resources. In this paper we present a new parametric optimal unicast multichannel routing algorithm that computes a domain for a mobile node and this domain will hold the optimality of data transmission and prevent network efficiency failure. Our new method determines an optimal domain for each mobile node and does not allow nodes to exit from that optimal domain. Simulation results show that our new method increases data rate and network efficiency.

IEEE 1588 clock synchronization using dual slave clocks in a slave

IEEE 1588 is a standard used in the synchronization of independent clocks that run on separate nodes of a distributed measurement and control system. This work presents a method that employs dual slave clocks in a slave to measure the link propagation delay, clock skew and offset. By accurately deriving these parameters, the proposed approach can reduce the deviation from the master clock to several orders of magnitude better than the required specification. The proposed technique fully conforms to the IEEE 1588, and can be used in the environments of symmetric and asymmetric communication links, such as xDSL.

Routing and scheduling connections in networks that support advance reservations

A key problem in networks that support advance reservations is the routing and time scheduling of connections with flexible starting time and known data transfer size. In this paper we present a multicost routing and scheduling algorithm for selecting the path to be followed by such a connection and the time the data should start and end transmission at each link so as to minimize the reception time at the destination, or optimize some other performance criterion. The utilization profiles of the network links, the link propagation delays, and the parameters of the connection to be scheduled form the inputs to the algorithm. We initially present a scheme of non-polynomial complexity to compute a set of so-called non-dominated candidate paths, from which the optimal path can be found. We then propose two mechanisms to appropriately prune the set of candidate paths in order to find multicost routing and scheduling algorithms of polynomial complexity. We examine the performance of the algorithms in the special case of an Optical Burst Switched network. Our results indicate that the proposed polynomial-time algorithms have performance that is very close to that of the optimal algorithm. We also study the effects network propagation delays and link-state update policies have on performance.

Analysis of fair rate calculations in resilient packet ring aggressive mode

Resilient packet ring (RPR) standardized as IEEE 802.17 is a new medium access control (MAC) protocol for metro-ring networks. RPR supports spatial reuse which increases the achieved throughput but it can also result in congestion and starvation of nodes on the ring. Therefore, it is necessary to employ mechanisms to enforce a fair allocation of the ring bandwidth in RPR. In order to maintain fairness among nodes, a fairness algorithm is deployed at each RPR node. When a node detects congestion, it calculates a fair rate which is advertised to all upstream nodes contributing to congestion. Upon receiving the fair rate, the upstream nodes limit the rate of their injected traffic to the advertised fair rate. Consequently, the congested node can utilize the unused capacity and add its local traffic to the ring. In this paper, we develop an analytical model for fair rate calculation in the RPR aggressive mode fairness algorithm in the parking-lot scenario. This model provides an insight on dynamics of the RPR fairness algorithm and can be used to evaluate its performance. We investigate this problem in two cases. First, we assume that the link propagation delay is zero and derive the fair rate equations for this ideal case. We then consider the link propagation delay and develop a more realistic model. We verify the accuracy of our model by simulation results. Furthermore, we use the developed model to study the impact of various parameters on convergence of the fair rate.

Path selection and bandwidth allocation in MPLS networks

Multi-protocol label switching extends the IP destination-based routing protocols to provide new and scalable routing capabilities in connectionless networks using relatively simple packet forwarding mechanisms. MPLS networks carry traffic on virtual connections called label switched paths. This paper considers path selection and bandwidth allocation in MPLS networks in order to optimize the network quality of service. The optimization is based upon the minimization of a non-linear objective function which under light load simplifies to OSPF routing with link metrics equal to the link propagation delays. The behavior under heavy load depends on the choice of certain parameters. It can essentially be made to minimize maximal expected utilization, or to maximize minimal expected weighted slacks (both over all links). Under certain circumstances it can be made to minimize the probability that a link has an instantaneous offered load larger than its transmission capacity. We present a model of an MPLS network and an algorithm which optimally distributes the traffic among a set of active paths and reserves a set of back-up paths for carrying the traffic of failed or congested paths. The algorithm is an improvement of the well-known flow deviation non-linear programming method. The algorithm is applied to compute optimal LSPs for a 100-node network carrying a single traffic class. A link carrying some 1400 routes fails. The back-up paths are activated and we compare the performance of the path sets before and after the back-up paths are deployed.

Routing stability in congested networks

Loss of the routing protocol messages due to network congestion can cause peering session failures in routers, leading to route flaps and routing instabilities. We study the effects of traffic overload on routing protocols by quantifying the stability and robustness properties of two common Internet routing protocols, OSPF and BGP, when the routing control traffic is not isolated from data traffic. We develop analytical models to quantify the effect of congestion on the robustness of OSPF and BGP as a function of the traffic overload factor, queueing delays, and packet sizes. We perform extensive measurements in an experimental network of routers to validate the analytical results. Subsequently we use the analytical framework to investigate the effect of factors that are difficult to incorporate into an experimental setup, such as a wide range of link propagation delays and packet dropping policies. Our results show that increased queueing and propagation delays adversely affect BGP's resilience to congestion, in spite of its use of a reliable transport protocol. Our findings demonstrate the importance of selective treatment of routing protocol messages from other traffic, by using scheduling and utilizing buffer management policies in the routers, to achieve stable and robust network operation.

A SAT-based network access scheme for fairness in high speed networks

This paper presents a fair network access scheme called MultiSAT which can be seen as a generalization of two access schemes proposed by Ofek and Yung (see IEEE/ACM Trans. Networking, vol.3, no.4, p.169-80, 1995) and Ngai and Seitz (1989). An upper bound on the delay before a node can inject a packet into the network is given which is valid when packet routes have no cyclic dependencies, backpressure flow control is used, and the processing and propagation delays are negligible. Upper bounds on packet injection delay are also given for ring networks employing shortest path routing for the case of negligible processing and propagation delays, and for the case of the MetaRing network when link propagation delays are significant.