Sunho Lim

Performance comparison of cache invalidation strategies for Internet-based mobile ad hoc networks

Internet-based mobile ad hoc network (IMANET) combines a mobile ad hoc network (MANET) and the Internet to provide universal information accessibility. Although caching frequently accessed data items in mobile terminals (MTs) improves the communication performance in an IMANET, it brings a critical design issue when data items are updated. We analyze several push and pull-based cache invalidation strategies for IMANETS. A global positioning system (GPS) based connectivity estimation (GPSCE) scheme is first proposed to assess the connectivity of an MT for supporting any cache invalidation mechanism. Then, we propose a pull-based approach, called aggregate cache based on demand (ACOD) scheme, to find the queried data items efficiently. In addition, we modify two push-based cache invalidation strategies, proposed for cellular networks, to work in IMANETs. These are a modified timestamp (MTS) scheme, and an MTS with updated invalidation report (MTS+UIR) scheme. Simulation results indicate that our proposed strategy provides high throughput, low query latency, and low communication overhead, and thus, is a viable approach for implementation in IMANETS.

RandomCast: An Energy-Efficient Communication Scheme for Mobile Ad Hoc Networks

In mobile ad hoc networks (MANETs), every node overhears every data transmission occurring in its vicinity and thus, consumes energy unnecessarily. However, since some MANET routing protocols such as dynamic source routing (DSR) collect route information via overhearing, they would suffer if they are used in combination with 802.11 PSM. Allowing no overhearing may critically deteriorate the performance of the underlying routing protocol, while unconditional overhearing may offset the advantage of using PSM. This paper proposes a new communication mechanism, called RandomCast, via which a sender can specify the desired level of overhearing, making a prudent balance between energy and routing performance. In addition, it reduces redundant rebroadcasts for a broadcast packet, and thus, saves more energy. Extensive simulation using NS-2 shows that RandomCast is highly energy-efficient compared to conventional 802.11 as well as 802.11 PSM-based schemes, in terms of total energy consumption, energy goodput, and energy balance.

Cache invalidation strategies for internet-based mobile ad hoc networks

Internet-based mobile ad hoc network (Imanet) is an emerging technique that combines a mobile ad hoc network (Manet) and the Internet to provide universal information accessibility. Although caching frequently accessed data items in mobile terminals (MTs) improves the communication performance in an Imanet, it brings a critical design issue when data updates. In this paper, we analyze several push and pull-based cache invalidation strategies for Imanets. A global positioning system (GPS) based connectivity estimation (GPSCE) scheme is first proposed to assess the connectivity of an MT for supporting cache invalidation mechanisms. Then, we propose a pull-based approach, called aggregate cache based on demand (ACOD) scheme that uses an efficient search algorithm for finding the queried data items. In addition, we modify two push-based cache invalidation strategies, proposed for cellular networks, to work in Imanets. They are called modified timestamp (MTS) scheme and MTS with updated invalidation report (MTS+UIR) scheme, respectively. We compare the performance of all these schemes as a function of query interval, cache update interval, and cache size through extensive simulation. Simulation results indicate that the ACOD scheme provides high throughput, low query latency, and low communication overhead, and thus, is a viable approach for implementation in Imanets.

Cache invalidation strategies for Internet-based vehicular ad hoc networks

Internet-based vehicular ad hoc network (Ivanet) is an emerging technique that combines a wired Internet and a vehicular ad hoc network (Vanet) for developing an ubiquitous communication infrastructure and improving universal information and service accessibility. A key design optimization technique in Ivanets is to cache the frequently accessed data items in a local storage of vehicles. Since vehicles are not critically limited by the storage/memory space and power consumption, selecting proper data items for caching is not very critical. Rather, an important design issue is how to keep the cached copies valid when the original data items are updated. This is essential to provide fast access to valid data for fast moving vehicles. In this paper, we propose a cooperative cache invalidation (CCI) scheme and its enhancement (ECCI) that take advantage of the underlying location management scheme to reduce the number of broadcast operations and the corresponding query delay. We develop an analytical model for CCI and ECCI techniques for fasthand estimate of performance trends and critical design parameters. Then, we modify two prior cache invalidation techniques to work in Ivanets: a poll-each-read (PER) scheme, and an extended asynchronous (EAS) scheme. We compare the performance of four cache invalidation schemes as a function of query interval, cache update interval, and data size through extensive simulation. Our simulation results indicate that the proposed schemes can reduce the query delay up to 69% and increase the cache hit rate up to 57%, and have the lowest communication overhead compared to the prior PER and EAS schemes.

Cooperative Cache Invalidation Strategies for Internet-Based Vehicular Ad Hoc Networks

Internet-based vehicular ad hoc network (IVANET) is an emerging technique that combines a wired Internet and a vehicular ad hoc network (VANET) for providing universal information and service accessibility. A key design optimization technique in IVANETs is to cache the frequently accessed data items in a local storage of vehicles. Since vehicles are not critically limited by the storage/memory space and power consumption, cache replacement scheme for accommodating new data items is not an issue. Rather, a more critical design question is how to keep the cached copies valid or to invalidate them when the original data items are updated. This is particularly important in IVANETs, where vehicles move very fast. This paper proposes state-aware cooperative cache invalidation (CCI) scheme and its enhancement (ECCI) that take advantage of the underlying location management mechanism. Extensive performance study shows that the proposed schemes can reduce the query delay as much as 69% and increase the cache hit rate up to 57% in comparison to two existing cache invalidation techniques, called poll-each-read (PER) and extended asynchronous (EAS). Note that PER and EAS have been modified to work in IVANETs.

A differential bandwidth reservation policy for multimedia wireless networks

Provisioning of seamless communication for mobile terminal (MT) handoffs as well as guaranteeing a certain level of quality-of-service (QoS) to ongoing connections and new connections are critical issues in multimedia wireless networks. We present a differential bandwidth reservation(DBR) algorithm that can meet these requirements. For bandwidth reservation, the DBR scheme examines a sector of cells, which are located along the way to which the MT might move. The sector of cells are further divided into two regions depending on whether they have an immediate impact on the handoff or not. Two different bandwidth reservation policies are applied to cells in the two regions to optimize the connection dropping rate while maximizing the connection acceptance rate. Two possible MT movements are analyzed using the DBR mechanism. In the first case, no knowledge of the users moving path is assumed to be available, while in the second case, prior knowledge of a user profile is used in bandwidth reservation, and is called the user profile-based DBR (UPDBR) algorithm. Simulation results indicate that the DBR algorithm is more adaptable to optimize the system performance in terms of call dropping rate compared to prior schemes. The UPDBR scheme can exploit the MTs moving path history for better bandwidth utilization as well as reduction in the number of communication messages compared to the DBR scheme. The overall results show that the proposed schemes not only provide better performance, but also exploit the current state of the system in optimizing different performance parameters.

A realistic mobility model for wireless networks of scale-free node connectivity

Recent studies discovered that many of social, natural and biological networks are characterised by scale-free power-law connectivity distribution. We envision that wireless networks are directly deployed over such real-world networks to facilitate communication among participating entities. This paper proposes Clustered Mobility Model (CMM), in which nodes do not move randomly but are attracted more to more populated areas. Unlike most of prior mobility models, CMM is shown to exhibit scale-free connectivity distribution. Extensive simulation study has been conducted to highlight the difference between Random WayPoint (RWP) and CMM by measuring network capacities at the physical, link and network layers.

Analysis of attack models via Unified Modeling Language in Wireless Sensor Networks: A survey study

Wireless Sensor Networks (WSNs) are widely used in various environments in monitoring temperature, motion, sound, and vibration. These applications often include the detection of sensitive information from enemy movements in hostile areas or in locations of personnel in buildings. Due to characteristics of WSNs, nodes tend to be exposed to the enemy, and security is a major concern in WSNs. Many researchers have developed various security protocols. However, there is no research paper describing and analyzing security models in WSNs by using a standard notation such as The Unified Modeling Language (UML). Using the UML helps security developers to analyze security attacks and design secure WSNs. In this research, we provide standard models for security attacks by UML Sequence Diagrams to describe and analyze possible attacks in a network and transport layer.

A unified bandwidth reservation and admission control mechanism for QoS provisioning in cellular networks

Summary We propose a unified framework consisting of a differential bandwidth reservation (DBR) algorithm and a Quality of Service (QoS)-aware admission control scheme to provide QoS guarantees to on-going connections in cellular networks. The differential bandwidth reservation policy uses a sector of cells in making the bandwidth reservation for accepting a new call. Based on the distance of the target cells in the sectors, two different bandwidth reservation policies are applied to optimize the connection dropping rate (CDR), while maintaining a competitive connection blocking rate (CBR). In addition, two possible mobile terminal (MT) movements are analyzed using the DBR mechanism. In the first case, no knowledge of an MT’s moving path is assumed to be known, while in the second case, prior knowledge of an user profile is used in bandwidth reservation, and it is called user profile-based DBR (UPDBR) algorithm. Using the DBR scheme, we propose an admission control algorithm that uses varying number of cells in a sector to meet admission decisions. Extensive simulation is performed to evaluate our methodology. Comparison of the proposed scheme with two prior schemes shows that our approach is not only capable of providing better QoS guarantees, but is also flexible in terms of using varying number of cells in satisfying the high-level QoS requirements. Copyright # 2004 John Wiley & Sons, Ltd.

Hop-by-Hop cooperative detection of selective forwarding attacks in energy harvesting wireless sensor networks

Due to the lack of physical protections and security requirements of the network routing protocols, Wireless Sensor Networks (WSNs) are vulnerable to Denial-of-Service (DoS) attacks. Inherent resource constraints also hinder WSNs from deploying conventional encryption schemes and secure routing protocols. In this paper, we investigate a counter selective forwarding attack to efficiently detect the forwarding misbehaviors of malicious nodes and seamlessly deliver sensory data in energy harvesting WSNs. We first analyze a set of adversarial scenarios under an implicit acknowledgment overhearing and identify a vulnerable case. Then we propose a Hop-by-hop Cooperative Detection (HCD) scheme to efficiently detect the forwarding misbehaviors and mitigate the forwarding probabilities of malicious nodes. Extensive simulation results indicate that the proposed scheme can significantly reduce the number of forwarding misbehaviors by quickly decreasing the dropping probabilities of malicious nodes and achieve more than 95% packet delivery ratio in energy harvesting WSNs.