Most recent satellite network research has focused on providing routing services without considering security. In this paper, for the sake of better global coverage, we introduce a novel triple-layered satellite netwo...Most recent satellite network research has focused on providing routing services without considering security. In this paper, for the sake of better global coverage, we introduce a novel triple-layered satellite network architecture including Geostationary Earth Orbit (GEO), Highly Elliptical Orbit (HEO), and Low Earth Orbit (LEO) satellite layers, which provides the near-global coverage with 24 hour uninterrupted over the areas varying from 75° S to 90° N. On the basis of the hierarchical architecture, we propose a QoS-guaranteed secure multicast routing protocol (QGSMRP) for satellite IP networks using the logical location concept to isolate the mobility of LEO and HEO satellites. In QGSMRP, we employ the asymmetric cryptography to secure the control messages via the pairwise key pre-distribution, and present a least cost tree (LCT) strategy to construct the multicast tree under the condition that the QoS constraints are guaranteed, aiming to minimize the tree cost. Simulation results show that the performance benefits of the proposed QGSMRP in terms of the end-to-end tree delay, the tree cost, and the failure ratio of multicasting connections by comparison with the conventional shortest path tree (SPT) strategy.展开更多
The intrinsic routing policy of NS2—a network simulation tool— based on flat or hierarchical address has the disadvantage such as small topology scale,high resource consumption,low efficiency and so on.This paper pr...The intrinsic routing policy of NS2—a network simulation tool— based on flat or hierarchical address has the disadvantage such as small topology scale,high resource consumption,low efficiency and so on.This paper proposes an IP based hierarchical routing strategy in network simulation to extend the topology scale and improve performance in simulating.Firstly,a stratification mechanism to identify IP address of nodes is described.Then,an algorithm of packet transmitting method(PTM) is presented for packet forwarding in the same subnet.Finally,algorithms of region partition(RP),routing computation based on region division(RCBRD) and routing distribution(RD) is proposed to implement regional segmentation,route calculation and route distribution for forwarding packets in different subnets respectively.The experiment results show that under the same condition,compared with plane address,the topology scale of the network simulation is extended two times and the consumption of time and memory during simulation is reduced by approximately 73%and 45.8% respectively.Compared with hierarchical address,the topology scale of the network simulation is expanded by more than 50%,and the consumption of time and memory is reduced by about 59.2% and 25% respectively.In addition,along with the growth of the node size,the proportion of reducing total simulation time and memory consumption would gradually increase.展开更多
We present an effective routing solution for the backbone of hierarchical MANETs. </span></span><span><span><span style="font-family:""><span style="font-family:Ver...We present an effective routing solution for the backbone of hierarchical MANETs. </span></span><span><span><span style="font-family:""><span style="font-family:Verdana;">Our solution leverages the storage and retrieval mechanisms of a Distributed Hash Table (DHT) common to many (structured) P2P overlays. Th</span><span style="font-family:Verdana;">e DHT provides routing information in a decentralized fash</span><span style="font-family:Verdana;">ion, while supporting different forms of node and network mobility. We split a flat network into clusters, each having a gateway who participates in a DHT overlay. These g</span><span style="font-family:Verdana;">ateways interconnect the clusters in a backbone network. Two routing </span><span style="font-family:Verdana;">approaches for the backbone are explore</span><span style="font-family:Verdana;">d: floodi</span><span style="font-family:Verdana;">ng and a new solution exploit</span><span style="font-family:Verdana;">ing the storage and retrieval capabilities of a P2P overlay based on a DHT.</span><span style="font-family:Verdana;"> We </span><span style="font-family:Verdana;">implement both approaches in a net</span><span style="font-family:Verdana;">work simulator and thoroughly evaluate th</span><span style="font-family:Verdana;">e performance of the proposed scheme using a range of stati</span><span style="font-family:Verdana;">c and mobile scenarios. We also compare our solution against flooding. The simulation results show that our solution, even in the presence of mobility, achieved well abo</span><span style="font-family:Verdana;">ve 90% success rates and maintained very low and constant round tr</span><span style="font-family:Verdana;">ip times, unlike the flooding approach. In fact, the performance of the proposed </span><span style="font-family:Verdana;">inter-cluster routing solution, in many cases, is comparable to the perfo</span><span style="font-family:Verdana;">rma</span><span style="font-family:Verdana;">nce of the intra-cluster routing case. The advantage of our proposed ap</span><span style="font-family:Verdana;">proach compared to flooding increases as the number of clusters increases, demonstrating the superior scalability of our proposed approach.展开更多
Instrumented is defined as a key characteristic in the upcoming smart cites, which demands a higher Wireless Sensor Networks (WSNs) performance. Tree-based Hierarchical Routing (THR) is a routing protocol for WSNs sta...Instrumented is defined as a key characteristic in the upcoming smart cites, which demands a higher Wireless Sensor Networks (WSNs) performance. Tree-based Hierarchical Routing (THR) is a routing protocol for WSNs static scenarios. THR hierarchically maps WSN area into a routing tree. However, fixed topology and hierarchical architecture leads to unbalanced energy overhead distribution and inflexible routes selection. To uniformly distribute routing energy overhead, reduce routing hops and extend network life cycle, we designed an enhanced THR routing protocol based on additional connections such as Neighbors, Brothers and Nephews. Based on these connections, three actions were introduced which are Shortcut, Overhead Balancing and Adoption. A simulation for different network loads on OMNet++4.1 is issued, and realized this THR routing in Chipcon SmartRF04?EB embedded boards based on Zigbee in a point-to-point topology. According to the simulation results and experiment data, this proposal obviously improved the latency performance, reduced energy overhead and extended the network’s life cycle.展开更多
In this paper, the concept of the Shortest-Route Traffic Matrix(SRTM) was first presented, and the generalized formula for computing ring capacity requirement in use of SRTM is given. Then, a new capacity design algor...In this paper, the concept of the Shortest-Route Traffic Matrix(SRTM) was first presented, and the generalized formula for computing ring capacity requirement in use of SRTM is given. Then, a new capacity design algorithm which is based on SRTM was presented for Synchronous Digital Hierarchical(SDH) Bi-directional Self-Healing Ring (BSHR). The algorithm simulation results demonstrate that this algorithm is very efficient for SDH BSHR capacity design and can make less project investment and make high utilization of lines and equipment. By means of the algorithm in this paper, capacity optimization assignment for SDH Hierarchical Self-Healing Ring (HSHR) and for ATM Virtual Path (VP)-based Self-Healing Ring (SHR) is also discussed.展开更多
The catalytic performance of Mo supported on hierarchical alumina–silica(Si/Al = 15) with Mo loadings of 3, 6 and 15 wt% was investigated for the oxidative desulfurization(ODS) of model and real oil samples. Hierarch...The catalytic performance of Mo supported on hierarchical alumina–silica(Si/Al = 15) with Mo loadings of 3, 6 and 15 wt% was investigated for the oxidative desulfurization(ODS) of model and real oil samples. Hierarchical alumina–silica(h Al–Si) was synthesized by economical and ecofriendly silicate-1 seed-induced route using cetyltrimethylammonium bromide(CTAB) as mesoporogen. The effect of CTAB on the structure of catalyst was studied by characterization techniques. The results revealed that 6%Mo/h Al–Si had the highest sulfur removal compared to the other catalyst loadings. The effect of operating parameters was evaluated using Box–Behnken experimental design. The optimal desulfurization conditions with the 6%Mo/h Al–Si catalyst were determined at oxidation temperature of 67 ℃, oxidation time of 42 min, H2O2/S molar ratio of 8 and catalyst dosage of 0.008 g·ml^-1 for achieving a conversion of 95%. Under optimal conditions, different sulfur-containing compounds with initial concentration of 1000 ppm, Dibenzothiophene(DBT), Benzothiophene(BT) and Thiophen(Th), showed the catalytic oxidation reactivity in the order of DBT > BT>Th. According to the regeneration experiments, the 6%Mo/h Al–Si catalyst was reused 4 times with a little reduction in the performance. Also, the total sulfur content of gasoline and diesel after ODS process reached 156.6 and 4592.2 ppm, respectively.展开更多
In deduplication, index-lookup disk bottleneck is a major obstacle which limits the throughput of backup processes. One way to minimize the effect of this issue and boost speed is to use very high course-grained chunk...In deduplication, index-lookup disk bottleneck is a major obstacle which limits the throughput of backup processes. One way to minimize the effect of this issue and boost speed is to use very high course-grained chunks for deduplication at a cost of low storage saving and limited scalability. Another way is to distribute the deduplication process among multiple nodes but this approach introduces storage node island effect and also incurs high communication cost. In this paper, we explore dCACH, a content-aware clustered and hierarchical deduplication system, which implements a hybrid of inline course grained and offline fine-grained distributed deduplication where routing decisions are made for a set of files instead of single files. It utilizes bloom filters for detecting similarity between a data stream and previous data streams and performs stateful routing which solves the storage node island problem. Moreover, it exploits the negligibly small amount of content shared among chunks from different file types to create groups of files and deduplicate each group in their own fingerprint index space. It implements hierarchical deduplication to reduce the size of fingerprint indexes at the global level, where only files and big sized segments are deduplicated. Locality is created and exploited first using the big sized segments deduplicated at the global level and second by routing a set of consecutive files together to one storage node. Furthermore, the use of bloom filter for similarity detection between streams has low communication and computation cost while it enables to achieve duplicate elimination performance comparable to single node deduplication. dCACH is evaluated using a prototype deployed on a server environment distributed over four separate machines. It is shown to have 10× the speed of Extreme_Binn with a minimal communication overhead, while its duplicate elimination effectiveness is on a par with a single node deduplication system.展开更多
Multi-protocol label switching（MPLS） has the advantage of high efficiency in the second layer, which improves the performance of data packets routing. In this paper, a new structure to implement optical MPLS is prop...Multi-protocol label switching（MPLS） has the advantage of high efficiency in the second layer, which improves the performance of data packets routing. In this paper, a new structure to implement optical MPLS is proposed. We construct a code family for spectral-amplitude coding（SAC） labels in the optical MPLS networks. SAC labels are suitable for optical packet switching because they can be constructed and recognized quickly at each router. We use the label stacking to provide hierarchical routing to avoid swapping labels at each forwarding node and reduce system complexity. However, the phase-induced intensity noise（PIIN） appears due to the incoherent property of the light source when the stacked labels set makes the correlation decoding with the local node label,which degrades system performance.展开更多
Subarea Tree Routing (STR), a new routing protocol for multi-hop wireless ad hoc networks, is proposed. The novelty of the STR protocol is to divide the whole network into many subareas constructed as a result of esta...Subarea Tree Routing (STR), a new routing protocol for multi-hop wireless ad hoc networks, is proposed. The novelty of the STR protocol is to divide the whole network into many subareas constructed as a result of establishing subarea trees. Its main idea is to identify root nodes by manual configuration or auto-discovery process firstly, then the root nodes originate the process of establishing subarea trees, and finally each node either joins in a subarea tree or become an interconnect node. STR belongs to hierarchical routing protocol and does not attempt to consistently maintain routing information in every node. Furthermore, through the use of tree’s intrinsic routing function, the STR protocol exhibits hybrid behavior of proactive and on-demand routing protocols. We prove the correctness of STR, and our simulation results show that the pro-posed scheme achieves lower route discovery delays, lower route discovery load and better performance of normalized routing load in large, mobile, ad hoc networks as compared with AODV.展开更多
A large variety of permutation routing protocols in a single-hop Network are known in the literature. Since they are single hop, there is always a wireless link connecting two nodes. One way to solve this problem in a...A large variety of permutation routing protocols in a single-hop Network are known in the literature. Since they are single hop, there is always a wireless link connecting two nodes. One way to solve this problem in a multiple hop environment is to partition nodes into clusters, where a node in each cluster called clusterhead is responsible for the routing service. In this paper, we propose a hybrid clustering mech?anism to perform permutation routing in multi-hop ad hoc Networks. We first propose to partition the network in single-hop clusters also named cliques. Secondly, we run a local permutation routing to broad?cast items to their local destinations in each clique. Next we partition the clusterheads of cliques with the hierarchical clustering technique. We show how the outgoing items can be routed to their destination cliques. We give an estimation of the number of broadcast rounds in the worse case. More precisely, we show that solving the permutation routing problem on a multi-hop sensor network need in the worse case. Where n is the number of the data items stored in the network, p is the number of sensors, |HUBmax| is the number of sensors in the clique of maximum size and k is the number of cliques after the first clustering. Finally, simulation results show that our algorithm performs better than the na?ve multiple gossiping. To the best of our knowledge, it is the first algorithm for permutation routing in multi-hop radio networks.展开更多
Optimizing the sensor energy is one of the most important concern in Three-Dimensional(3D)Wireless Sensor Networks(WSNs).An improved dynamic hierarchical clustering has been used in previous works that computes optimu...Optimizing the sensor energy is one of the most important concern in Three-Dimensional(3D)Wireless Sensor Networks(WSNs).An improved dynamic hierarchical clustering has been used in previous works that computes optimum clusters count and thus,the total consumption of energy is optimal.However,the computational complexity will be increased due to data dimension,and this leads to increase in delay in network data transmission and reception.For solving the above-mentioned issues,an efficient dimensionality reduction model based on Incremental Linear Discriminant Analysis(ILDA)is proposed for 3D hierarchical clustering WSNs.The major objective of the proposed work is to design an efficient dimensionality reduction and energy efficient clustering algorithm in 3D hierarchical clustering WSNs.This ILDA approach consists of four major steps such as data dimension reduction,distance similarity index introduction,double cluster head technique and node dormancy approach.This protocol differs from normal hierarchical routing protocols in formulating the Cluster Head(CH)selection technique.According to node’s position and residual energy,optimal cluster-head function is generated,and every CH is elected by this formulation.For a 3D spherical structure,under the same network condition,the performance of the proposed ILDA with Improved Dynamic Hierarchical Clustering(IDHC)is compared with Distributed Energy-Efficient Clustering(DEEC),Hybrid Energy Efficient Distributed(HEED)and Stable Election Protocol(SEP)techniques.It is observed that the proposed ILDA based IDHC approach provides better results with respect to Throughput,network residual energy,network lifetime and first node death round.展开更多
A Wireless Sensors Network (WSN) is an ad-hoc network populated by small hand-held commodity devices, running on batteries called stations or sensors. Often used in hostiles and sometimes unreachable environments, sta...A Wireless Sensors Network (WSN) is an ad-hoc network populated by small hand-held commodity devices, running on batteries called stations or sensors. Often used in hostiles and sometimes unreachable environments, stations are subject to energetic constraints which can significantly decrease the network life time. Permutation routing problem is mainly found in the literature of WSN. This problem occurs when some stations have items that belong either or not to them. The goal is to send each item to its receiver. To solve this problem, several works are presented in the literature. In this paper, we present a new permutation routing protocol for multi-hop wireless sensors network that, compared to recent work in the field is more efficient in terms of conservation of sensors’ energy, which results in a longer life time of the network. Also, contrary to some other routing protocols which assume that the memory of the sensors is infinite, we show that the memory size of the sensors is limited, which in our opinion is more realistic.展开更多
A wireless MANET is a self-configurable network in which mobile, battery-powered devices dynamically create and change the network topology without relying on any intrastructure or administrative support. It offers un...A wireless MANET is a self-configurable network in which mobile, battery-powered devices dynamically create and change the network topology without relying on any intrastructure or administrative support. It offers unique benefits for certain environments, but there are still several open issues to be resolved before realizing these benefits, including QoS routing, multicasting, and mobility management. Specifically, an efficient QoS multicast routing protocol is needed, This paper presents a hierarchical QoS multicast routing protocol （QMRP） for mobile ad hoc networks. It can provide QoS-sensitive routes in a scalable and flexible way, in the network environment with mobility. In the proposed QMRP scheme, each local node only needs to maintain local multicast routing information and/or summary information of other clusters （or domains） but does not require any global ad hoc network states to be maintained. The QMRP also allows any ad hoc group member to join/leave the multicast group dynamically and supports multiple QoS constraints. This paper presents formal description and main procedures for realizing routing decision process of the QMRP and the proof of correctness and complexity analysis of the protocol. The performance measures of QMRP are evaluated using simulation. The simulation results verify the efficiency and availability of QMRP.展开更多
Hierarchical Mobile IPv6 (HMIPv6) can reduce the delay and the amount of signaling during handover compared with the basic mobile IPv6. However, the protocol still cannot meet the requirement for traffic that is delay...Hierarchical Mobile IPv6 (HMIPv6) can reduce the delay and the amount of signaling during handover compared with the basic mobile IPv6. However, the protocol still cannot meet the requirement for traffic that is delay sensitive, such as voice, especially in macro mobility handover. Duplicate address detection and the transmission time for the handover operation could cause high handover delay. This paper proposes a new mechanism to improve the fast handover algorithm's efficiency in HMIPv6 network. And we present and analyze the performance testing for our proposal by comparing it with the traditional HMIPv6 fast handover algorithm. The results of simulation show that our scheme can reduce the handover delay much more than the traditional fast handover method for HMIPv6 network.展开更多
In this article,the problem of load balance in hierarchical routing network is studied.Since conventional shortest path first（SPF） algorithm over aggregated topology in hierarchical routing network may result in wor...In this article,the problem of load balance in hierarchical routing network is studied.Since conventional shortest path first（SPF） algorithm over aggregated topology in hierarchical routing network may result in worse routing performance,a traffic sharing path selection algorithm and a variable weight scheme are put forward for hierarchical routing network,which can equilibrate the utilities of link resources and reduce the blocking probability of connections with the improvement on survivability.Simulations are conducted to evaluate proposed variable weight and traffics balance（VWTB） algorithm,which combines traffic sharing and variable weight.From the simulation results,it can be found that the proposed VWTB algorithm can balance the traffics and equilibrate the utilities of link resources significantly.展开更多
Lithium-sulfur batteries have attracted wide research interest due to their high specific capacity(1675 mA h g^(-1))and high specific energy(2500 W h kg^(-1)).Herein,the two-dimensional nitrogen/sulfur synchronous-dop...Lithium-sulfur batteries have attracted wide research interest due to their high specific capacity(1675 mA h g^(-1))and high specific energy(2500 W h kg^(-1)).Herein,the two-dimensional nitrogen/sulfur synchronous-doped few-layer graphene(N,S-FLG)was prepared by a simple calcination route at 900℃under an argon atmosphere with g-C_(3)N_(4)as a structural template.The calcination temperature favorably adjusted the doping levels and surface texture of the as-obtained samples.Relying on the synergistic interaction of the structural traits,as the reservoir of sulfur,NS-FLG-900(calcination temperature 900℃)can maintain a reversible capacity of 602 mA h g^(-1)after 300 cycles at a current density of 0.8 A g^(-1)and 506.4 mA h g^(-1)after 500 cycles at a current density of 1.6 A g^(-1).The outstanding performance is obtained due to the synergistic effect of the introduction of N and S into the carbon lattice,the high pore volume(1.31 cm^(3)g^(-1))and large specific surface area(460.9 m^(2)g^(-1)).展开更多
文摘Most recent satellite network research has focused on providing routing services without considering security. In this paper, for the sake of better global coverage, we introduce a novel triple-layered satellite network architecture including Geostationary Earth Orbit (GEO), Highly Elliptical Orbit (HEO), and Low Earth Orbit (LEO) satellite layers, which provides the near-global coverage with 24 hour uninterrupted over the areas varying from 75° S to 90° N. On the basis of the hierarchical architecture, we propose a QoS-guaranteed secure multicast routing protocol (QGSMRP) for satellite IP networks using the logical location concept to isolate the mobility of LEO and HEO satellites. In QGSMRP, we employ the asymmetric cryptography to secure the control messages via the pairwise key pre-distribution, and present a least cost tree (LCT) strategy to construct the multicast tree under the condition that the QoS constraints are guaranteed, aiming to minimize the tree cost. Simulation results show that the performance benefits of the proposed QGSMRP in terms of the end-to-end tree delay, the tree cost, and the failure ratio of multicasting connections by comparison with the conventional shortest path tree (SPT) strategy.
基金Supported by the National Science and Technology Support Project(No.2012BAH45B01)the National Natural Science Foundation of China(No.61100189,61370215,61370211,61402137)the National Information Security 242 Project of China(No.2016A104)
文摘The intrinsic routing policy of NS2—a network simulation tool— based on flat or hierarchical address has the disadvantage such as small topology scale,high resource consumption,low efficiency and so on.This paper proposes an IP based hierarchical routing strategy in network simulation to extend the topology scale and improve performance in simulating.Firstly,a stratification mechanism to identify IP address of nodes is described.Then,an algorithm of packet transmitting method(PTM) is presented for packet forwarding in the same subnet.Finally,algorithms of region partition(RP),routing computation based on region division(RCBRD) and routing distribution(RD) is proposed to implement regional segmentation,route calculation and route distribution for forwarding packets in different subnets respectively.The experiment results show that under the same condition,compared with plane address,the topology scale of the network simulation is extended two times and the consumption of time and memory during simulation is reduced by approximately 73%and 45.8% respectively.Compared with hierarchical address,the topology scale of the network simulation is expanded by more than 50%,and the consumption of time and memory is reduced by about 59.2% and 25% respectively.In addition,along with the growth of the node size,the proportion of reducing total simulation time and memory consumption would gradually increase.
文摘We present an effective routing solution for the backbone of hierarchical MANETs. </span></span><span><span><span style="font-family:""><span style="font-family:Verdana;">Our solution leverages the storage and retrieval mechanisms of a Distributed Hash Table (DHT) common to many (structured) P2P overlays. Th</span><span style="font-family:Verdana;">e DHT provides routing information in a decentralized fash</span><span style="font-family:Verdana;">ion, while supporting different forms of node and network mobility. We split a flat network into clusters, each having a gateway who participates in a DHT overlay. These g</span><span style="font-family:Verdana;">ateways interconnect the clusters in a backbone network. Two routing </span><span style="font-family:Verdana;">approaches for the backbone are explore</span><span style="font-family:Verdana;">d: floodi</span><span style="font-family:Verdana;">ng and a new solution exploit</span><span style="font-family:Verdana;">ing the storage and retrieval capabilities of a P2P overlay based on a DHT.</span><span style="font-family:Verdana;"> We </span><span style="font-family:Verdana;">implement both approaches in a net</span><span style="font-family:Verdana;">work simulator and thoroughly evaluate th</span><span style="font-family:Verdana;">e performance of the proposed scheme using a range of stati</span><span style="font-family:Verdana;">c and mobile scenarios. We also compare our solution against flooding. The simulation results show that our solution, even in the presence of mobility, achieved well abo</span><span style="font-family:Verdana;">ve 90% success rates and maintained very low and constant round tr</span><span style="font-family:Verdana;">ip times, unlike the flooding approach. In fact, the performance of the proposed </span><span style="font-family:Verdana;">inter-cluster routing solution, in many cases, is comparable to the perfo</span><span style="font-family:Verdana;">rma</span><span style="font-family:Verdana;">nce of the intra-cluster routing case. The advantage of our proposed ap</span><span style="font-family:Verdana;">proach compared to flooding increases as the number of clusters increases, demonstrating the superior scalability of our proposed approach.
文摘Instrumented is defined as a key characteristic in the upcoming smart cites, which demands a higher Wireless Sensor Networks (WSNs) performance. Tree-based Hierarchical Routing (THR) is a routing protocol for WSNs static scenarios. THR hierarchically maps WSN area into a routing tree. However, fixed topology and hierarchical architecture leads to unbalanced energy overhead distribution and inflexible routes selection. To uniformly distribute routing energy overhead, reduce routing hops and extend network life cycle, we designed an enhanced THR routing protocol based on additional connections such as Neighbors, Brothers and Nephews. Based on these connections, three actions were introduced which are Shortcut, Overhead Balancing and Adoption. A simulation for different network loads on OMNet++4.1 is issued, and realized this THR routing in Chipcon SmartRF04?EB embedded boards based on Zigbee in a point-to-point topology. According to the simulation results and experiment data, this proposal obviously improved the latency performance, reduced energy overhead and extended the network’s life cycle.
基金Supported by Key Project for the Ninth Five-Years Programming of Ministry of Posts and Telecommunications of China
文摘In this paper, the concept of the Shortest-Route Traffic Matrix(SRTM) was first presented, and the generalized formula for computing ring capacity requirement in use of SRTM is given. Then, a new capacity design algorithm which is based on SRTM was presented for Synchronous Digital Hierarchical(SDH) Bi-directional Self-Healing Ring (BSHR). The algorithm simulation results demonstrate that this algorithm is very efficient for SDH BSHR capacity design and can make less project investment and make high utilization of lines and equipment. By means of the algorithm in this paper, capacity optimization assignment for SDH Hierarchical Self-Healing Ring (HSHR) and for ATM Virtual Path (VP)-based Self-Healing Ring (SHR) is also discussed.
文摘The catalytic performance of Mo supported on hierarchical alumina–silica(Si/Al = 15) with Mo loadings of 3, 6 and 15 wt% was investigated for the oxidative desulfurization(ODS) of model and real oil samples. Hierarchical alumina–silica(h Al–Si) was synthesized by economical and ecofriendly silicate-1 seed-induced route using cetyltrimethylammonium bromide(CTAB) as mesoporogen. The effect of CTAB on the structure of catalyst was studied by characterization techniques. The results revealed that 6%Mo/h Al–Si had the highest sulfur removal compared to the other catalyst loadings. The effect of operating parameters was evaluated using Box–Behnken experimental design. The optimal desulfurization conditions with the 6%Mo/h Al–Si catalyst were determined at oxidation temperature of 67 ℃, oxidation time of 42 min, H2O2/S molar ratio of 8 and catalyst dosage of 0.008 g·ml^-1 for achieving a conversion of 95%. Under optimal conditions, different sulfur-containing compounds with initial concentration of 1000 ppm, Dibenzothiophene(DBT), Benzothiophene(BT) and Thiophen(Th), showed the catalytic oxidation reactivity in the order of DBT > BT>Th. According to the regeneration experiments, the 6%Mo/h Al–Si catalyst was reused 4 times with a little reduction in the performance. Also, the total sulfur content of gasoline and diesel after ODS process reached 156.6 and 4592.2 ppm, respectively.
文摘In deduplication, index-lookup disk bottleneck is a major obstacle which limits the throughput of backup processes. One way to minimize the effect of this issue and boost speed is to use very high course-grained chunks for deduplication at a cost of low storage saving and limited scalability. Another way is to distribute the deduplication process among multiple nodes but this approach introduces storage node island effect and also incurs high communication cost. In this paper, we explore dCACH, a content-aware clustered and hierarchical deduplication system, which implements a hybrid of inline course grained and offline fine-grained distributed deduplication where routing decisions are made for a set of files instead of single files. It utilizes bloom filters for detecting similarity between a data stream and previous data streams and performs stateful routing which solves the storage node island problem. Moreover, it exploits the negligibly small amount of content shared among chunks from different file types to create groups of files and deduplicate each group in their own fingerprint index space. It implements hierarchical deduplication to reduce the size of fingerprint indexes at the global level, where only files and big sized segments are deduplicated. Locality is created and exploited first using the big sized segments deduplicated at the global level and second by routing a set of consecutive files together to one storage node. Furthermore, the use of bloom filter for similarity detection between streams has low communication and computation cost while it enables to achieve duplicate elimination performance comparable to single node deduplication. dCACH is evaluated using a prototype deployed on a server environment distributed over four separate machines. It is shown to have 10× the speed of Extreme_Binn with a minimal communication overhead, while its duplicate elimination effectiveness is on a par with a single node deduplication system.
文摘Multi-protocol label switching（MPLS） has the advantage of high efficiency in the second layer, which improves the performance of data packets routing. In this paper, a new structure to implement optical MPLS is proposed. We construct a code family for spectral-amplitude coding（SAC） labels in the optical MPLS networks. SAC labels are suitable for optical packet switching because they can be constructed and recognized quickly at each router. We use the label stacking to provide hierarchical routing to avoid swapping labels at each forwarding node and reduce system complexity. However, the phase-induced intensity noise（PIIN） appears due to the incoherent property of the light source when the stacked labels set makes the correlation decoding with the local node label,which degrades system performance.
文摘Subarea Tree Routing (STR), a new routing protocol for multi-hop wireless ad hoc networks, is proposed. The novelty of the STR protocol is to divide the whole network into many subareas constructed as a result of establishing subarea trees. Its main idea is to identify root nodes by manual configuration or auto-discovery process firstly, then the root nodes originate the process of establishing subarea trees, and finally each node either joins in a subarea tree or become an interconnect node. STR belongs to hierarchical routing protocol and does not attempt to consistently maintain routing information in every node. Furthermore, through the use of tree’s intrinsic routing function, the STR protocol exhibits hybrid behavior of proactive and on-demand routing protocols. We prove the correctness of STR, and our simulation results show that the pro-posed scheme achieves lower route discovery delays, lower route discovery load and better performance of normalized routing load in large, mobile, ad hoc networks as compared with AODV.
文摘A large variety of permutation routing protocols in a single-hop Network are known in the literature. Since they are single hop, there is always a wireless link connecting two nodes. One way to solve this problem in a multiple hop environment is to partition nodes into clusters, where a node in each cluster called clusterhead is responsible for the routing service. In this paper, we propose a hybrid clustering mech?anism to perform permutation routing in multi-hop ad hoc Networks. We first propose to partition the network in single-hop clusters also named cliques. Secondly, we run a local permutation routing to broad?cast items to their local destinations in each clique. Next we partition the clusterheads of cliques with the hierarchical clustering technique. We show how the outgoing items can be routed to their destination cliques. We give an estimation of the number of broadcast rounds in the worse case. More precisely, we show that solving the permutation routing problem on a multi-hop sensor network need in the worse case. Where n is the number of the data items stored in the network, p is the number of sensors, |HUBmax| is the number of sensors in the clique of maximum size and k is the number of cliques after the first clustering. Finally, simulation results show that our algorithm performs better than the na?ve multiple gossiping. To the best of our knowledge, it is the first algorithm for permutation routing in multi-hop radio networks.
文摘Optimizing the sensor energy is one of the most important concern in Three-Dimensional(3D)Wireless Sensor Networks(WSNs).An improved dynamic hierarchical clustering has been used in previous works that computes optimum clusters count and thus,the total consumption of energy is optimal.However,the computational complexity will be increased due to data dimension,and this leads to increase in delay in network data transmission and reception.For solving the above-mentioned issues,an efficient dimensionality reduction model based on Incremental Linear Discriminant Analysis(ILDA)is proposed for 3D hierarchical clustering WSNs.The major objective of the proposed work is to design an efficient dimensionality reduction and energy efficient clustering algorithm in 3D hierarchical clustering WSNs.This ILDA approach consists of four major steps such as data dimension reduction,distance similarity index introduction,double cluster head technique and node dormancy approach.This protocol differs from normal hierarchical routing protocols in formulating the Cluster Head(CH)selection technique.According to node’s position and residual energy,optimal cluster-head function is generated,and every CH is elected by this formulation.For a 3D spherical structure,under the same network condition,the performance of the proposed ILDA with Improved Dynamic Hierarchical Clustering(IDHC)is compared with Distributed Energy-Efficient Clustering(DEEC),Hybrid Energy Efficient Distributed(HEED)and Stable Election Protocol(SEP)techniques.It is observed that the proposed ILDA based IDHC approach provides better results with respect to Throughput,network residual energy,network lifetime and first node death round.
文摘A Wireless Sensors Network (WSN) is an ad-hoc network populated by small hand-held commodity devices, running on batteries called stations or sensors. Often used in hostiles and sometimes unreachable environments, stations are subject to energetic constraints which can significantly decrease the network life time. Permutation routing problem is mainly found in the literature of WSN. This problem occurs when some stations have items that belong either or not to them. The goal is to send each item to its receiver. To solve this problem, several works are presented in the literature. In this paper, we present a new permutation routing protocol for multi-hop wireless sensors network that, compared to recent work in the field is more efficient in terms of conservation of sensors’ energy, which results in a longer life time of the network. Also, contrary to some other routing protocols which assume that the memory of the sensors is infinite, we show that the memory size of the sensors is limited, which in our opinion is more realistic.
基金Supported by the National Natural Science Foundation of China(Grant Nos.60672137,60773211 and 60402028)the Specialized Research Fund for the Doctoral Program of Higher Education of China(Grant No.20060497015)the Key Project of Hubei Province(Grant No.2007AA101C63)
文摘A wireless MANET is a self-configurable network in which mobile, battery-powered devices dynamically create and change the network topology without relying on any intrastructure or administrative support. It offers unique benefits for certain environments, but there are still several open issues to be resolved before realizing these benefits, including QoS routing, multicasting, and mobility management. Specifically, an efficient QoS multicast routing protocol is needed, This paper presents a hierarchical QoS multicast routing protocol （QMRP） for mobile ad hoc networks. It can provide QoS-sensitive routes in a scalable and flexible way, in the network environment with mobility. In the proposed QMRP scheme, each local node only needs to maintain local multicast routing information and/or summary information of other clusters （or domains） but does not require any global ad hoc network states to be maintained. The QMRP also allows any ad hoc group member to join/leave the multicast group dynamically and supports multiple QoS constraints. This paper presents formal description and main procedures for realizing routing decision process of the QMRP and the proof of correctness and complexity analysis of the protocol. The performance measures of QMRP are evaluated using simulation. The simulation results verify the efficiency and availability of QMRP.
文摘Hierarchical Mobile IPv6 (HMIPv6) can reduce the delay and the amount of signaling during handover compared with the basic mobile IPv6. However, the protocol still cannot meet the requirement for traffic that is delay sensitive, such as voice, especially in macro mobility handover. Duplicate address detection and the transmission time for the handover operation could cause high handover delay. This paper proposes a new mechanism to improve the fast handover algorithm's efficiency in HMIPv6 network. And we present and analyze the performance testing for our proposal by comparing it with the traditional HMIPv6 fast handover algorithm. The results of simulation show that our scheme can reduce the handover delay much more than the traditional fast handover method for HMIPv6 network.
基金supported by the Hi-Tech Research and Development Program of China (2007AA01Z252)the National Basic Research Program of China (2007CB310705)+4 种基金the National Natural Science Foundation of China (60711140087, 60772024)the NCET (06-0090)the PCSIRT (IRT0609)the ISTCP (2006DFA11040)the 111 Project of China (B07005)
文摘In this article,the problem of load balance in hierarchical routing network is studied.Since conventional shortest path first（SPF） algorithm over aggregated topology in hierarchical routing network may result in worse routing performance,a traffic sharing path selection algorithm and a variable weight scheme are put forward for hierarchical routing network,which can equilibrate the utilities of link resources and reduce the blocking probability of connections with the improvement on survivability.Simulations are conducted to evaluate proposed variable weight and traffics balance（VWTB） algorithm,which combines traffic sharing and variable weight.From the simulation results,it can be found that the proposed VWTB algorithm can balance the traffics and equilibrate the utilities of link resources significantly.
基金financial supports provided by the National Natural Science Fund of China(No.21601108)Young Scholars Program of Shandong University(2017WLJH15)+1 种基金the Fundamental Research Funds of Shandong University(No.2016JC033,2016GN010)the Taishan Scholar Project of Shandong Province(No.ts201511004).
文摘Lithium-sulfur batteries have attracted wide research interest due to their high specific capacity(1675 mA h g^(-1))and high specific energy(2500 W h kg^(-1)).Herein,the two-dimensional nitrogen/sulfur synchronous-doped few-layer graphene(N,S-FLG)was prepared by a simple calcination route at 900℃under an argon atmosphere with g-C_(3)N_(4)as a structural template.The calcination temperature favorably adjusted the doping levels and surface texture of the as-obtained samples.Relying on the synergistic interaction of the structural traits,as the reservoir of sulfur,NS-FLG-900(calcination temperature 900℃)can maintain a reversible capacity of 602 mA h g^(-1)after 300 cycles at a current density of 0.8 A g^(-1)and 506.4 mA h g^(-1)after 500 cycles at a current density of 1.6 A g^(-1).The outstanding performance is obtained due to the synergistic effect of the introduction of N and S into the carbon lattice,the high pore volume(1.31 cm^(3)g^(-1))and large specific surface area(460.9 m^(2)g^(-1)).
