Subrata Nandi

Designing delay constrained hybrid ad hoc network infrastructure for post-disaster communication

Following a disaster-strike, rapid and reliable communication between relief/rescue workers in the affected regions, and the control stations located at a distance, is essential. This is to facilitate seamless information exchange about the status of victims, requirement of relief personnel/commodities, supply chain of goods and services, and so on, thus rendering relief operations more timely and effective. However, the availability of Internet in a post-disaster scenario is ruled out more often than not; wireless communication and mobile phones may not be usable either except in only selected areas. Besides, geographical obstructions such as broken bridges or closed roads add to the worries of personnel trying to develop a temporary network infrastructure for effective communication. Furthermore, availability of resources - both technological and financial - may prove to be a bottleneck in case of disasters in under-developed regions. Under such circumstances, a post-disaster communication network need to be developed to meet the following: (i) close to 100% information packet delivery, (ii) minimum latency for information exchange, and (iii) compliance to the resource constraints. In this paper, we propose a latency-aware four-tier planned hybrid architecture to tackle the aforementioned challenges and focus on extensive modeling and analysis of the planned network architecture. For detailed evaluation with the help of case study scenarios, we make use of the ONE Simulator, customized to suit our requirements. Additionally, we measure the improvement in network resources utilization and performance achieved with modeling of the architecture over that without modeling.

Post Disaster Management Using Delay Tolerant Network

Delay-tolerant Networking (DTN) is an attempt to extend the reach of traditional networking methods where nodes are intermittently connected and an end-to-end path from source to destination does not exist all the time. Real networks like military, various sensors, post disaster management, deep space communication, Vehicular ad-hoc (VANETs) networks, are some examples of DTN. Our work mainly concentrates on the applicability of different flooding based routing scheme of DTN in post disaster scenarios. Cluster mobility model which maps human mobility more realistically rather than any other mobility in the context of disaster scenario has been considered. Further we have customized cluster mobility model according to the disaster like scenario and performed the simulation for delivery probability with respect to various constraints like buffer-size, transmission range, speed and density of nodes in ONE SIMULATOR. We also analyze the effect heterogeneous nodes in delivery probability.

Challenges in designing testbed for evaluating delay-tolerant hybrid networks

Challenged networking applications such as rural internet, battlefield communication, post-disaster communication etc. cannot rely on mere DTN for its unpredictable delay and unreliable delivery probability. To meet application specific QoS constraints, in addition to DTN-enabled mobile nodes (smart phones/tablets), an ad hoc backbone infrastructure is essential. Such backbone components include the use of laptops or custom-built storage units as Information Dropboxes and/or Data Mules and wireless mesh, long range Wi-Fi etc. as long range wireless communication units. Evaluation of such systems through simulation is not enough as there are problems related to compatibility and interoperability. Hence design of a testbed for evaluating a DTN-based hybrid system is a non-trivial problem. In this paper we attempt to reveal some of the system related challenges/issues for above and present DTHN-Test, a low-cost testbed prototype developed for evaluating challenged network scenarios, in general. As a case study we show some initial results on performance of a Delay-constrained Four-Tier Hybrid Ad hoc Network Architecture using DTHN-Test.

Mitigating route request flooding attack in MANET using node reputation

An ad hoc network is an infrastructure-less, decentralized network, consisting of a group of mobile wireless nodes, moving around freely and cooperating with each other in routing and forwarding of packets. Due to the lack of any clear line of defense, MANET is accessible to both legitimate users and malicious attackers. Among various types of attacks, it is particularly vulnerable to various denial of service (DoS) attacks. Route request flooding attack is one such distributed DoS attack, launched by compromised nodes or intruders. This triggers an acute need of flooding attack prevention mechanisms for this highly vulnerable type of network. In this paper, a reputation based scheme is proposed to resist the impact of flooding attack in MANET. This scheme observes the behavior of a node in the network periodically and limits its route request sending rate accordingly.

Community formation and search in P2P: A robust and self-adjusting algorithm

The existing literature deals with the problems dealing with decentralized content-based P2P community formation and community-based search separately. Contrary to this approach, in this paper we propose a novel search algorithm that has both the capability to form the community structure as well as search it with maximum efficiency. The key contribution is to design a self-organized and adaptive search algorithm where as the community topology evolves with time, the search process adapts automatically to the situation to provide best performance. It performs an automatic transition from the exploratory phase to search phase, by estimating the global state of communities using a local control parameter. Moreover, we show that the strategy is also robust enough to improve search performance even under node churn, though a graceful degradation in overall performance is seen. We consider realistic power-law distribution for node degrees and information profiles. The proposed search strategy shows more than twice efficiency than a pure random walk with proliferation on the same network.

A Qualitative Survey on Multicast Routing in Delay Tolerant Networks

Delay Tolerant Networks (DTNs) are a class of networks that make communication in stressed and challenging environments possible. DTN is characterized with a number of unique features by virtue of which a working environment is achieved in situations where traditional networking paradigms fail to deliver satisfactorily or entirely. The utility of multicasting in DTNs extends to numerous potential DTN applications i.e., crisis environments, battlefield situations, deep space communications, dynamic data size management, etc. In this paper, we propose taxonomy for the different multicast routing strategies and thereafter, we present a comprehensive up to date survey of these strategies. Further, we perform a qualitative comparison between the different multicast strategies with respect to important performance issues in DTN. We also highlight some unexplored areas in DTN multicasting that could inspire research in the near future.

Bio-inspired Search and Distributed Memory Formation on Power-Law Networks

In this paper, we report a novel and efficient algorithm for searching P2P networks having a power law topology. Inspired by the natural immune system, it is a completely decentralized algorithm where each peer searches by sending out random walkers to a limited number of neighbors. As it finds other peers having similar content, it restructures its own neighborhood with the objective of bringing them closer. This restructuring leads to clustering of nodes with similar content, thus forming P2P communities. Alongside, the search algorithm also adapts its walk strategy in order to take advantage of the community thus formed. This search strategy is more than twice as efficient as pure random walk on the same network.

C 3 -index: revisiting author's performance measure

Author ranking indices, like h-index and its variants, fail to resolve ties while ranking authors with low index values (major volume including the young ones). In this work we leverage the citations as well as collaboration profile of an author in a novel way using a weighted multi-layered network and propose a page-rank variant to obtain a new author performance measure, C3-index. Experiments on a massive publication dataset reveal several interesting characteristics of our metric: (i) we observe that C3-index is consistent over time, (ii) C3-index has high potential to break ties among low rank authors, (iii) C3-index can be used to predict future achievers at the early stage of their career.

UrbanEye: An outdoor localization system for public transport

Public transport in suburban cities (covers 80% of the urban landscape) of developing regions suffer from the lack of information in Google Transit, unpredictable travel times, chaotic schedules, absence of information board inside the vehicle. Consequently, passengers suffer from lack of information about the exact location where the bus is at present as well as the estimated time to be taken to reach the desired destination. We find that off-the-shelf deployment of existing (non-GPS) localization schemes exhibit high error due to sparsity of stable and structured outdoor landmarks (anchor points). Through rigorous experiments conducted over a month however, we realize that there are a certain class of volatile landmarks which may be useful in developing efficient localization scheme. Consequently, in this paper, we design a novel generalized energy-efficient outdoor localization scheme - UrbanEye, which efficiently combines the volatile and non-volatile landmarks using a specialized data structure, the probabilistic timed automata. UrbanEye uses speed-breakers, turns and stops as landmarks, estimates the travel time with a mean accuracy of ±2.5 mins and produces a mean localization accuracy of 50 m. Results from several runs taken in two cities, Durgapur and Kharagpur, reveal that UrbanEye provides more than 50% better localization accuracy compared to the existing system Dejavu [1], and consumes significantly less energy.

On design and implementation of a scalable and reliable Sync system for delay tolerant challenged networks

Seamless data synchronization among peer entities is a problem for any challenged network scenarios where infrastructural supports for synchronization are not available or insufficient. Such a network follows a delay/disruption tolerant approach, in which connection or contact time among devices are intermittent and short-lived, agents may use devices of heterogeneous nature with different communication and processing powers, and the communication channel may have high loss rate that impacts the application layer file synchronization protocols. The bundle protocol specifications for delay tolerant networks only describe the semantics for data transmission between two distant devices, and do not specify how a peer-to-peer (P2P) file synchronization protocol can cater seamless data exchange among multiple heterogeneous communication devices. We propose in this paper a new P2P sync, called pSync, on the top of the bundle protocol which precisely takes care of prioritized file Sync with role based transfer applicable for challenged networks. Our testbed experiments conducted with information dropbox, ground and aerial data mule suggest that pSync is scalable and clearly outperforms BitTorrent Sync in delivering even 30% more priority packets in certain test cases.