Gholamali C. Shoja

Solving the Multidimensional Multiple-choice Knapsack Problem by constructing convex hulls

This paper presents a heuristic to solve the Multidimensional Multiple-choice Knapsack Problem (MMKP), a variant of the classical 0-1 Knapsack Problem. We apply a transformation technique to map the multidimensional resource consumption to single dimension. Convex hulls are constructed to reduce the search space to find the near-optimal solution of the MMKP. We present the computational complexity of solving the MMKP using this approach. A comparative analysis of different heuristics for solving the MMKP has been presented based on the experimental results.

Heuristic Solutions for the Multiple-Choice Multi-dimension Knapsack Problem

The Multiple-Choice Multi-Dimension Knapsack Problem (MMKP) is a variant of the 0-1 Knapsack Problem, an NP-Hard problem. Hence algorithms for finding the exact solution of MMKP are not suitable for application in real time decision-making applications, like quality adaptation and admission control of an interactive multimedia system. This paper presents two new heuristic algorithms, M-HEU and I-HEU for solving MMKP. Experimental results suggest that M-HEU finds 96% optimal solutions on average with much reduced computational complexity and performs favorably relative to other heuristic algorithms for MMKP. The scalability property of I-HEU makes this heuristic a strong candidate for use in real time applications.

TTL based routing in opportunistic networks

One of the major problem in routing messages in an Opportunistic Network (OpNet) is the absence of a complete end-to-end path from the source to the destination. To deal with such adversity many routing protocols employ epidemic techniques to flood the network with multiple copies of a message. Although flooding many copies of a message in the network increases the chance of the message delivery, it can lead to a very high network overhead and can cause network congestion. On the other hand, the quota based routing protocols restrict the maximum number of copies of a message in the network by setting a replication factor. Such protocols maintain comparatively low overhead but suffer from low delivery ratio. In this paper, we introduce a novel quota based routing protocol, TTL Based Routing (TBR). TBR prioritizes both the schedule of messages to be forwarded to the neighbor and the schedule of messages to be dropped from the buffer. These priorities are based on massage time to live (TTL), message hop count, message replication count and message size. The TTL based message priority enhances the chance of message delivery by giving preference to the messages having the earliest deadline. Our simulation results show that, TBR achieves more than 10-15% higher delivery ratio than that of the available quota based routing protocols while incurring 10% to 15% less overhead. TBR not only matches the delivery ratio of flooding based routing protocols but also achieves better delivery ratio with 70% to 75% less overhead.

Social-Greedy: a socially-based greedy routing algorithm for delay tolerant networks

Efficient routing in mobile opportunistic networks and Delay Tolerant Networks (DTNs) in particular, is a challenging task because human mobility patterns are hard to predict. Several recent work have shown the importance of communities in efficient routing of messages in DTNs. However, real time community detection in DTNs is a complex and time consuming process. In this paper, we propose a simple and cost effective method for bootstrapping wireless devices by employing available social profiles. Moreover, we propose a simple greedy routing algorithm called Social-Greedy which uses a social distance derived from peoples social profiles to route messages in DTNs.

Optimal quality of service routing and admission control using the utility model

Real-time multimedia applications such as video and audio streaming, video conferencing and online collaboration are becoming increasingly popular. In order to guarantee effective support of many of these applications, the Internet must provide absolute Quality of Service(QoS) guarantees for such parameters as network bandwidth and end-to-end delay by incorporating session admission control, session routing, and resource reservation. In this article, we present the Utility Model for optimal routing and admission control (RAC) of a data network supporting sessions requiring QoS guarantees. This model maps the optimal RAC problem to a Multiple-choice Multi-dimension 0-1 Knapsack Problem (MMKP), a variation of the classical 0-1 Knapsack Problem. We also present a design for an optimal RAC system based on the Utility Model. This method uses the MMKP formulation of the optimal RAC problem to provide an integrated solution of the session routing, admission control and resource allocation problems. Our experiments show that optimal RAC using the MMKP formulation (OptRAC) would provide 7-16% more revenue than the revenue provided by a traditional RAC system (TradRAC).

Fast track article: Predicting missing contacts in mobile social networks

Experimentally measured contact traces, such as those obtained in a conference setting by using short range wireless sensors, are usually limited with respect to the practical number of sensors that can be deployed as well as available human volunteers. Moreover, most previous experiments in this field are partial since not everyone participating in the experiment is expected to carry a sensor device. Previously collected contact traces have significantly contributed to development of more realistic human mobility models. This in turn has influenced proposed routing algorithms for Delay Tolerant Networks where human contacts play a vital role in message delivery. By exploiting time-spatial properties of contact graphs as well as popularity and social information of mobile nodes, we propose a novel method to reconstruct the missing parts of contact graphs where only a subset of nodes are able to sense human contacts.

A framework for live software upgrade

The demand for continuous service in mission- and safety-critical software applications is increasing. For these applications, it is unacceptable to shutdown and restart the system during software upgrade. This paper examines issues relating to on-line upgrades for mission- and safety-critical software applications. We believe that a dynamic architecture and communication model provides an excellent foundation for runtime software evolution. To solve the problems mentioned above, we designed and implemented a framework, which addresses four main areas: dynamic architecture and communication model, reconfiguration management, the upgrade protocol, and the upgrade technique. The framework can be used for online upgrading of multi-task software applications, which provide multiple mission-critical services. In the framework discussed in the paper, the ability to make runtime modifications is considered at the software architecture-level. The dynamic architecture and communication model makes it possible for software applications to add, remove, and hot swap modules on the fly. The transition scenario is specified by the upgrade protocol. The framework also provides the mechanism for maintaining state consistency. In order to ensure a reliable upgrade, a two-phase commit protocol is utilized to implement the atomic upgrade transactions. In addition, a command line interface facilitates the reconfiguration management. A simulation study of the proposed framework was carried out for live software upgrade of several practical applications. The results of the simulation are also presented.

Geographic grid routing for wireless sensor networks

High resolution data collection using low-cost wireless sensor networks has recently become feasible due to advances in electronics and wireless networking technologies. The geographic grid routing (GGR) protocol described in this paper aims to provide robust task dissemination and data collection from large sensor networks such that the useful lifetime of the network is prolonged. The work builds on a previously developed routing protocol called two-tier data dissemination (TTDD). Our work is differentiated by the use of multiple paths, a more efficient and useful data collection model, and more authentic environmental assumptions, including the presence of asymmetric links. Extensive and realistic experiments were used to evaluate the performance of GGR. The results show GGR to be a highly efficient, scalable, versatile and robust solution.

A distributed trust model for e-commerce applications

The access control mechanisms used in traditional security infrastructures have been proven inadequate, inflexible, and difficult to apply to the Internet of today. In this work, we have proposed a general-purpose, application-independent dynamic distributed trust model (DDTM). In DDTM, access rights are directly associated with a trust value. The trust values are further classified into direct trust values, indirect trust values and trust authorization levels. We have calculated and expressed each type of the trust values into explicit numerical numbers. The core of this model is the recommendation-based trust model, organized as a trust delegation tree (TDT), and the authorization delegation realized by delegation certificate chains.

Routing reliability analysis of partially disjoint paths

Alternative paths may significantly improve routing reliability in an IP network, One application of this technique is to enhance the reliability of the popular open shortest path first (OSPF) routing protocol. In our proposed reliable OSPF (ROSPF) routing protocol, one primary path and two alternate backup paths are deployed for data transmission. As expected, the number of shared links and routers among the three paths dominates the reliability of the routing connection between two routers. The calculation of routing reliability of multiple paths is very important in alternate path-finding algorithms. To solve this problem, we use the Venn diagram model to analyze the overall failure probability of three partially disjoint paths and to understand how the double- and triple-shared links affect the routing reliability. General mathematical formulas to calculate the failure probability are also obtained.