Lower Hop Count Research Articles

Exploring the effects of directional antennas on the secure connectivity and hop count of secure multi-hop ad-hoc wireless networks

Directional antennas can increase the received power in specific directions while reducing it in other directions. Utilizing this unique feature, we configure directional antennas at legitimate users to obtain twofold benefits for secure multi-hop ad-hoc wireless networks (AHWNs), i.e., enhancing the secure connectivity among legitimate users and lowering the hop count of the multi-hop paths. For the quantitative evaluation of these benefits, we first use a stochastic geometry graph to model the multi-hop AHWNs under the coexistence of eavesdroppers. Then, we introduce a simulation-based analysis method comprised of two algorithms: (a) the first algorithm provides the connectivity and the hop count of the shortest path between random source–destination pairs; (b) the second algorithm utilizes the results of the first one to return the average path connectivity, the probability mass function (pmf) of the hop count distribution, and the average hop count. This simulation-based analysis method helps to exhaustively study the behaviors of connectivity, hop count distribution, average hop count, and their mutual relationship in different scenarios. To the best of our knowledge, this paper is the first research work that studies the effects of directional antennas equipped at legitimate users on both secure connectivity and hop count of secure AHWNs in four combinations of two types of practical directional antennas, i.e., uniform circular array (UCA) antenna and uniform linear array (ULA) antennas, and two beamforming schemes, i.e., centralized and randomized beamforming. Moreover, comparisons with the case of using omnidirectional antennas are also provided. From the obtained simulation results, we demonstrate that using directional antennas does not always benefit the secure connectivity and hop count of secure AHWNs, i.e., only UCA-random gives higher secure connectivity and lower hop count than the omnidirectional antenna among four combinations of antenna type — beamforming scheme. Moreover, in the cases of high-density legitimate users and low-density eavesdroppers, lowering the average hop count is more remarkable than improving secure connectivity. The critical findings in this paper are valuable for deploying secure multi-hop AHWNs with directional antennas in practice.

A Cooperative Caching Scheme for VCCN With Mobility Prediction and Consistent Hashing

In order to mitigate the performance degradation of intermittent vehicular network caused by traffic mobility and sporadic connectivity issues, Vehicular Content Centric Network (VCCN) has been proposed to apply many technologies in Content Centric Network (CCN) into vehicular ad hoc networks. The open in-network caching strategy of CCN enables sharing and coordination of the cached data among multiple nodes as an efficient data access without relying on remote fetching. Nonetheless, few studies have considered the effective use of overall cache capacity with these cooperative nodes, especially the issues of cache duplication. Furthermore, most content replacement polices have ignored the needs of cooperative contents when making cache decisions. In this paper, we design a novel Cooperative Caching scheme by using Mobility Prediction and Consistent Hash for VCCN (called CCMPCH). Specifically, based on the observation that vehicles with the same trajectory are more likely to maintain stable communication links, we adopt Prediction by Partial Matching (PPM) to forecast each vehicle’s path and cluster the vehicles with similar future path, moving direction, and moving speed into one group. In each cluster, the consistent hash algorithm is used to allocate contents among cooperative nodes, thereby reducing unnecessary cache duplication while maintaining strong content availability. A popularity-based cache replacement policy is also developed to prioritize cooperative contents. We evaluate CCMPCH via extensive simulations, which demonstrates its higher cache hit ratio, shorter content access delay, and lower hop count compared to other state-of-the-art schemes.

Synthesizing Brain-network-inspired Interconnections for Large-scale Network-on-chips

Brain network is a large-scale complex network with scale-free, small-world, and modularity properties, which largely supports this high-efficiency massive system. In this article, we propose to synthesize brain-network-inspired interconnections for large-scale network-on-chips. First, we propose a method to generate brain-network-inspired topologies with limited scale-free and power-law small-world properties, which have a low total link length and extremely low average hop count approximately proportional to the logarithm of the network size. In addition, given the large-scale applications, considering the modularity of the brain-network-inspired topologies, we present an application mapping method, including task mapping and deterministic deadlock-free routing, to minimize the power consumption and hop count. Finally, a cycle-accurate simulator BookSim2 is used to validate the architecture performance with different synthetic traffic patterns and large-scale test cases, including real-world communication networks for the graph processing application. Experiments show that, compared with other topologies and methods, the brain-network-inspired network-on-chips (NoCs) generated by the proposed method present significantly lower average hop count and lower average latency. Especially in graph processing applications with a power-law and tightly coupled inter-core communication, the brain-network-inspired NoC has up to 70% lower average hop count and 75% lower average latency than mesh-based NoCs.

Stable backbone-based geographic routing by using traffic lights as bridges in vehicular ad hoc networks

Routing is very challenging in vehicular ad hoc networks due to the highly dynamic nature of the vehicles. In this paper, a position-based routing protocol is proposed, which leverages the backbone structure. This protocol contains a bridge node selection algorithm and a route updating algorithm. The first algorithm considers traffic lights at intersections as the bridge nodes, which evaluate the routes by exchanging control packets, and select the best route regarding the path weights. In the second one, bridge nodes update the route. Destination informs the bridge nodes about its previous and new locations when passing an intersection, before the message is received. Bridge nodes forward the message to the new location of the destination through a more reliable path with lower hop counts. Simulation results demonstrate that the proposed protocol outperforms the similar existing method in terms of the end-to-end delay, packet delivery ratio, and network overhead.

Detection and Defense of Cache Pollution Attacks Using Clustering in Named Data Networks

Named Data Network (NDN), as a promising information-centric networking architecture, is expected to support next-generation of large-scale content distribution with open in-network cachings. However, such open in-network caches are vulnerable against Cache Pollution Attacks (CPAs) with the goal of filling cache storage with non-popular contents. The detection and defense against such attacks are especially difficult because of CPA's similarities with normal fluctuations of content requests. In this work, we use a clustering technique to detect and defend against CPAs. By clustering the content interests, our scheme is able to distinguish whether they have followed the Zipf-like distribution or not for accurate detections. Once any attack is detected, an attack table will be updated to record the abnormal requests. While such requests are still forwarded, the corresponding content chunks are not cached. Extensive simulations in ndnSIM demonstrate that our scheme can resist CPA effectively with higher cache hit, higher detecting ratio, lower hop count, and lower algorithm complexity compared to other state-of-the-art schemes.

Q-Learning-Based Fuzzy Logic for Multi-objective Routing Algorithm in Flying Ad Hoc Networks

Flying ad hoc networks (FANETs) that consist of multiple unmanned aerial vehicles (UAVs) have developed owing to the rapid technological evolution of electronics, sensors, and communication technologies. In this paper, we propose a multi-objective routing algorithm for FANETs. In addition to the basic transmission performance in the construction of the routing path, the network impact according to the mobility of the UAV nodes and the energy state of each node should be considered because of the characteristics of the FANET, and the overall efficiency and safety of the network should be satisfied. We therefore propose the use of Q-learning-based fuzzy logic for the FANET routing protocol. The proposed algorithm facilitates the selection of the routing paths to be processed in terms of link and overall path performances. The optimal routing path to the destination is determined by each UAV using a fuzzy system with link- and path-level parameters. The link-level parameters include the transmission rate, energy state, and flight status between neighbor UAVs, while the path-level parameters include the hop count and successful packet delivery time. The path-level parameters are dynamically updated by the reinforcement learning method. In the simulation results, we compared the proposal with the conventional fuzzy logic and Q-value-based ad hoc on-demand distance vector. The results show that the proposed method can maintain low hop count and energy consumption and prolong the network lifetime.

Detection and Defense of Cache Pollution Based on Popularity Prediction in Named Data Networking

Named Data Networking (NDN) is one of the most promising information-centric networking architectures that can improve the network performance by supporting the large scale content distribution. However, the use of in-network caching mechanism increases the opportunity of cache pollution attack, where the attackers intend to reduce the cache hit of legal users by releasing fake requests to fill the precious cache with non-popular contents. To prevent the degradation of network performance caused by such an attack, it is becoming particularly important to detect the attack and then throttle it. In this article, we propose a detection and defense scheme with the help of grey forecast, which can effectively exploit the regularity of past Interests and popularity by comprehensively considering three major factors to predict the future popularity of each cached content. If the predicted popularity of any content differs too much from the actually calculated one in several consecutive slices, the pollution attack will be determined. Once the attack is detected, the defense will be taken by suppressing the popularity increase of the suspicious content to mitigate the damage of the pollution attack. We also consider a special case, where there exists a sudden burst of traffic from legal users that cannot be simply dropped. The simulations in ndnSIM indicate that our proposed method is effective in detecting and defending the pollution attack with higher cache hit, higher detecting ratio, and lower hop count compared to other state-of-the-art schemes.

Increasing the Energy Efficiency of TICK by Selecting Adaptive Forwarding Nodes in Wireless Sensor Networks

Time-Based Dynamic Keying and En Route Filtering (TICK) reduces the communication costs for wireless sensor networks by eliminating the exchange of control keying messages. TICK is more energy-efficient and is good at securing events as they occur; it also selects predetermined forwarding nodes for re-encryption operation without considering their residual energy (RE) which causes more energy depletion. We propose an energy- efficient method that selects forwarding nodes for re-encryption with high energy levels and a low hop count (HC). Simulation results indicate that the proposed method achieves better energy conservation.

Geographic information and node selfish-based routing algorithm for delay tolerant networks

In Delay Tolerant Networks (DTNs), some routing algorithms ignore that most nodes are selfish, i.e., nodes are willing to use their own resources to forward messages to nodes with whom they have a relationship. In view of this phenomenon, we propose a routing algorithm based on Geographic Information and Node Selfishness (GINS). To choose a forwarding node, GINS combines nodes' willingness to forward and their geographic information to maximize the possibility of contacting the destination. GINS formulates the message forwarding process as a 0-1 Knapsack Problem with Assignment Restrictions to satisfy node demands for selfishness. Extensive simulations were conducted, and results show that GINS can achieve a high delivery ratio and a lower hop count compared with GRONE and LPHU. Furthermore, its overhead ratio is 25% and 30% less than that of GRONE and LPHU, respectively.

Effective Forwarding Scheme for Opportunistic Networks Based on Refined Contact Probability and Betweenness Centrality

When forwarding in opportunistic networks, the higher contact probability that the destination node has, the more likely it is to forward a message to the destination. Moreover, the higher the betweenness centrality that a node has, the more likely it is to act as a bridge node toward the destination in the network. Each of these two metrics is exploited in existing forwarding schemes. Nevertheless, these schemes suffer from high network traffic and fail to balance network traffic and transmission delay while maintaining a lower hop count. To resolve these problems, we propose a novel forwarding scheme that considers refined contact probability and betweenness centrality. In the proposed scheme, nodes with higher probabilities of contact with other nodes tend to gather together, while nodes with higher betweenness centralities compensate for intermittent connection disruptions among nodes in the network. Experimental results show that the proposed scheme outperforms most known forwarding schemes in balancing network traffic and transmission delay.

Performance analysis of structured peer-to-peer overlays for mobile networks

Distributed Hash Table (DHT) based Peer-to-Peer (P2P) overlays have been widely researched and deployed in many applications such as file sharing, IP telephony, content distribution and media streaming applications. However, their deployment has largely been restricted to fixed, wired networks. This is due to the fact that supporting P2P overlays on wireless networks such as the public mobile data network is more challenging due to constraints in terms of data transmissions on cellular networks, limited battery power of the handsets and increased levels of node churn. However, the proliferation of smartphones makes the use of P2P applications on mobile handsets very desirable. In this article, we have analysed and evaluated the performance and efficiency of five popular DHT based structured P2P overlays (Chord, Pastry, Kademlia, Broose and EpiChord) under conditions as commonly experienced in public mobile data networks. Our results show that the conditions in mobile networks, including a high churn rate and the relatively low bandwidth availability is best matched by Kademlia and EpiChord. These overlays exhibit a high lookup success ratio and low hop count while consuming a moderate amount of bandwidth. These characteristics make these two overlays suitable candidates for use in mobile networks.

A Routing Metric to Improve Route Stability in Mobile Wireless Sensor Networks

The hop count routing metric is widely used in routing protocols of Wireless Sensor Networks (WSNs) due to its simplicity and effectiveness. With a lower hop count route, fewer transmissions are required to send a packet from the source to the destination. This can improve the throughput of a network because fewer transmissions results in less channel contention and interference. Despite this, the hop count routing metric may not be ideal for mobile scenarios where the topology of a network changes constantly and rapidly. In this paper, we propose to increase route stability in mobile WSNs by discovering paths that are more stable during route discoveries using routing metrics. Two routing metrics were proposed, the true beauty of these routing metrics lies in the fact that they can even be used even without specialized hardware such as GPS and other sensors. We implemented the proposed routing metrics in the AODV routing protocol and found that they are highly effective and outperform other stability-based routing metrics and the hop count routing metric.

Sensor-free route stability metric for mobile ad hoc networks

The hop count routing metric is widely used in conventional ad hoc routing protocols due to its simplicity and effectiveness. With a lower hop count route, fewer transmissions are required to send a packet from the source to the destination. This can improve the network throughput because fewer transmissions results in less channel contention and interference. In spite of this, the hop count routing metric may not be ideal for mobile scenarios, where the network topology changes constantly and rapidly. Many routing metrics have been proposed to improve route stability. However, they are usually only marginally effective or incur additional cost by requiring the use of information from additional hardware such as GPS sensor and compass. In this paper we propose a routing metric to guide nodes discover/select stable paths to improve route stability. We implemented the proposed routing metric in the AODV routing protocol and proved through simulation studies that it outperforms other routing metrics.

Low Latency Optical Switch for High Performance Computing With Minimized Processor Energy Load [Invited

Power density and cooling issues are limiting the performance of high performance chip multiprocessors (CMPs), and off-chip communications currently consume more than 20% of power for memory, coherence, PCI, and Ethernet links. Photonic transceivers integrated with CMPs are being developed to overcome these issues, potentially allowing low hop count switched connections between chips or data center servers. However, latency in setting up optical connections is critically important in all computing applications, and having transceivers integrated on the processor chip also pushes other network functions and their associated power consumption onto the chip. In this paper, we propose a low latency optical switch architecture that minimizes the power consumed on the processor chip for two scenarios: multiple-socket shared memory coherence networks and optical top-of-rack switches for data centers. The switch architecture reduces power consumed on the CMP using a control plane with a simplified send and forget server interface and the use of a hybrid Mach-Zehnder interferometer and semiconductor optical amplifier integrated optical switch with electronic buffering. Results show that the proposed architecture offers a 42% reduction in head latency at low loads compared with a conventional scheduled optical switch as well as offering increased performance for streaming and incast traffic patterns. Power dissipated on the server chip is shown to be reduced by more than 60% compared with a scheduled optical switch architecture with ring resonator switching.

POST: a scalable optical data center network

We propose a WDM based power efficient data center interconnect called as POST (Passive Optical Scalable Tree data center network). POST interconnects thousands of servers and provides low hop count transmission paths among all the servers connected. Furthermore, we propose architectures for two switching components required for the operation of POST network.

A Novel Link Stability and Energy Aware Routing with Tradeoff Strategy in Mobile Ad Hoc Networks

Mobile ad hoc networks (MANETs) are self- organizing, rapidly deployable networks without any fixed infrastructure. In MANETs, mobile terminals can move freely, which cause frequent link breakage. Due to the dynamic nature of the network, finding a stable route for transmitting data is a challenging task. In order to adapt to the topological changes and provide some quality of service (QoS), this paper propose a novel link stability and energy aware routing algorithm with tradeoff strategy, and implement it on Ad Hoc On-demand Distance Vector Routing Protocol (AODV), namely NLSEA- AODV. The new protocol sets up routes with high stability in route discovery based on link stability and node energy information, and predict the breaking link in route maintenance. Besides, the routing takes a route stability-hop count tradeoff strategy to select routes with high stability and low hop count. Simulation results show that the new protocol has a better overall performance than original AODV protocol, which improved the network utilization greatly.

Terrain dependant hop count selection for transparent relay transmissions

In this Letter, the selection of the best hop count for a particular topography, in the context of enhanced connectivity using multi-hop transparent relay communication is addressed. Based on the coefficient of variation and the terrain specific fading severity factor of the distribution, it is possible to estimate the optimal hop count that can provide the required performance at detector. Two distribution models, which can adequately characterise the terrain fading effects on empirical data are considered for performance comparison. The results are useful in selecting branches, with low variability and optimal hop count for connectivity, in multi-stream switched diversity combining systems.

An ICN In-Network Caching Policy for Butterfly Network in DCN

In-network caching is a key component of information-centric networking (ICN) for reducing content download time, network traffic, and server workload. Data center network (DCN) is an ideal candidate for applying the ICN design principles. In this paper, we have evaluated the effectiveness of caching placement and replacement in DCN with butterfly-topology. We also suggest a new cache placement policy based on the number of routing nodes (i.e., hop counts) through which travels the content. With a probability inversely proportional to the hop counts, the caching placement policy makes each routing node to cache content chunks. Simulation results lead us to conclude (ⅰ) cache placement policy is more effective for cache performance than cache replacement, (ⅱ) the suggested cache placement policy has better caching performance for butterfly-type DCNs than the traditional caching placement policies such as ALWASYS and FIX(P), and (ⅲ) high cache hit ratio does not always imply low average hop counts.

Chemical-Mechanical Polishing-Aware Application-Specific 3D NoC Design

Three-dimensional (3D) integration with through-silicon vias (TSVs) is promising in the integration of many cores into a single chip. Network-on-chip (NoC) can efficiently manage the complicated 3D interconnections. However, irregular and dense TSV arrays used as vertical links in 3D NoC cause severe TSV height variation during silicon-thinning and chemical-mechanical polishing (CMP) processes. It may lead to TSV bonding failure between silicon layers. In this paper, we propose the first CMP-aware application-specific 3D NoC design that minimizes such TSV height variation and thus reduces the bonding failure, and meanwhile optimizes conventional NoC design objectives such as hop count, wirelength, power consumption, and area. Our 3D NoC design assigns cores to proper silicon layers, determines the 3D NoC topology, allocates routing paths, and then floorplans all cores, routers, and TSV arrays in a CMP-aware manner. The key idea behind this 3D NoC design flow is to determine the CMP-aware 3D NoC topology where TSV arrays with low and uniform metal density are inserted between adjacent layers. Experimental results show that our CMP-aware 3D NoC design achieves, on average, 17.9% lower TSV height variation, 15% lower hop count, 2.3% shorter total wirelength, and 7.8% lower power consumption than the previous state-of-the-art 3D NoC designs.

Functional performance deficits associated with ligamentous instability at the ankle

ObjectivesTo examine whether ankle anterior drawer ligament laxity is associated with deficits in performance testing among otherwise healthy sportspeople. DesignCross-sectional cohort study. MethodsEighty-six volunteers from among sports participants at a military academy consented to the use of their pre-participation musculoskeletal screening information for the lower limb, and to an additional test of ankle proprioception. The lower limb screening included tests of ankle ligament laxity, dorsiflexion range of movement, single leg hop-for-distance, hexagon agility hopping test, and hop-and-hold landing stability test. ResultsThere was a significant difference between lax and stable ankles on the 4 screening tests when they were examined together with MANOVA (F=3.52, df=4, 167, p=0.009, Wilks’ Lambda=0.92). Independent t-tests showed worse performance on the hop-for-distance (p=0.001), hexagon hop (p=0.039) and the proprioception tests (p=0.033) associated with laxity. Comparing stable and unstable ankles in the same individual, paired t-tests showed significantly lower hop counts for lax ankles on the hexagon hop test (p=<0.001). ConclusionsAnkle ligament laxity is associated with persisting deficits in explosive power, agility and proprioception, as demonstrated by less hopping distance, fewer hops in hexagon hop testing, and reduced proprioceptive acuity, despite ongoing participation in sport. Attention to maximising sport-related performance in the late stages of rehabilitation is suggested as an essential addition to clinical management of these injuries.