Institute for Systems Research Technical Reports
Permanent URI for this collectionhttp://hdl.handle.net/1903/4376
This archive contains a collection of reports generated by the faculty and students of the Institute for Systems Research (ISR), a permanent, interdisciplinary research unit in the A. James Clark School of Engineering at the University of Maryland. ISR-based projects are conducted through partnerships with industry and government, bringing together faculty and students from multiple academic departments and colleges across the university.
Browse
186 results
Search Results
Item Key Establishment in Heterogeneous Self-Organized Networks(2007) Taban, Gelareh; Safavi-Naini, Rei; ISRTraditional key pre-distribution schemes in sensor and ad hoc networks rely on the existence of a trusted third party to generate and distribute a key pool. The assumption of a single TTP however can be very strong in practice, especially when nodes belong to different domains and they come together in an ad hoc manner. Other important motivations to omit a TTP include preservation of privacy in a network as well as reducing the required knowledge base for the usage of sensor networks. In this work, we show the shortcomings of the previous approaches [3, 13] in terms of both efficiency and security. By incorporating a heterogeneous network, we show that we can dramatically reduce the load on resource constrained devices while also increasing their security. We also propose a new strengthened security model for self-organized ad hoc networks and evaluate the security of our protocol in this model. We evaluate the correctness of the protocol and show that we can achieve network connectivity with very high probability.Item Joint Scheduling and Routing for Ad-hoc Networks Under Channel State Uncertainty(2007) Pantelidou, Anna; Ephremides, Anthony; Tits, Andre L.; ISRWe determine a joint link activation and routing policy that maximizes the stable throughput region of time-varying wireless ad-hoc networks with multiple commodities. In practice, the state of the channel process from the time it is observed till the time a transmission actually takes place can be significantly different. With this in mind, we introduce a stationary policy that takes scheduling and routing decisions based on a possibly inaccurate estimate of the true channel state. We show optimality of this policy within a broad class of link activation processes. In particular, processes in this class may be induced by any policy, possibly non-stationary, even anticipative and aware of the entire sample paths, including the future, of the arrival, estimated and true channel state processes, as long as it has no knowledge on the current true channel state, besides that available through the estimated channel state.Item Broadcast Scheduling for Push Broadcast Systems with Arbitrary Cost Functions(2007) Raissi-Dehkordi, Majid; Baras, John S.; ISRIn this report the problem of broadcast scheduling in Push broadcast systems is studied. We introduce an optimization approach that leads to well justified policies for Push broadcast systems with generalized cost functions. In particular, we apply our results to a Push broadcast system with different deadlines associated to the files while allowing the files to have unequal demand rates and lengths. We will show that our proposed policy covers some of the previously investigated Push systems as special cases and is applicable to a wide range of cost functions assigned to the files. We also calculate the optimal average cost for our experimental settings and show, through extensive simulation studies, that our results closely match that value for each experiment.Item Distributional convergence of path durations in MANETs with dependent link excess lives(2006) La, Richard J.; La, Richard J.; ISR; CSHCNWe investigate the issue of path selection in multi-hop wireless networks with the goal of identifying a scheme that can select a path with the largest expected duration. To this end we first study the distribution of path duration. We show that, under a set of mild conditions, when the hop count along a path is large, the distribution of path duration can be well approximated by an exponential distribution even when the distributions of link durations are dependent and heterogeneous. Secondly, we investigate the statistical relation between a path duration and the durations of the links along the path. We prove that the parameter of the exponential distribution, which determines the expected duration of the path, is related to the link durations only through their means and is given by the sum of the inverses of the expected link durations. Based on our analytical results we propose a scheme that can be implemented with existing routing protocols and select the paths with the largest expected durations.Item Opportunistic packet scheduling in cellular networks with base station antenna arrays(2006) Ren, Tianmin; La, Richard J.; ISR; CSHCNWe study the issue of designing a downlink scheduling policy for a cellular network with base station antenna arrays. We derive an optimal scheduling policy that achieves the throughput region, which is a set of feasible arrival rate vectors that can be stabilized by some scheduling policy. Then, based on the structure of the derived optimal policy whose complexity increases exponentially with the number of users in the system, we propose two heuristic scheduling algorithms with much lower complexity. We demonstrate that our proposed algorithms perform much better than other heuristic algorithms that do not take into consideration the physical layer constraints and/or queue lengths in the sense that they have a larger throughput region than other heuristic algorithms.Item A Robust, Distributed TGDH-based Scheme for Secure Group Communications in MANETs(2005) Striki, Maria; Baras, John S.; ISR; CSHCNSecuring multicast communications in Mobile Ad Hoc Networks (MANETs) is now considered among the most challenging research directions in the areas of wireless networking and security. MANETs are emerging as the desired environment for an increasing number of commercial and military applications, addressing also a growing number of users. Security on the other hand, is now an indispensable requirement for these applications. However, the limitations of the dynamic, infrastructure-less nature of MANETs impose major difficulties in establishing a secure framework suitable for group communications.The design of efficient key management (KM) schemes for MANET is of paramount importance, since the performance of the KM functions (e.g. group key generation, entity authentication) imposes an upper limit on the efficiency and scalability of the whole secure group communication system. In this work, we contribute towards efficient, robust and scalable secure group communications for MANETs by extending the TGDH scheme to a novel distributed and topology aware protocol: DS-TGDH.
Our aim is to modify TGDH so that: a) it is feasible in the most general resource-constrained flat MANET where no nodes with special capabilities may exist, b) it produces considerably lower overhead for the network nodes involved, c) it handles disruptions with low cost. To meet our objectives we consider in our design the underlying routing protocol, and we apply a distributed version of TGDH over a robust schedule, optimizing parameters of interest. We assume that members have already been authenticated and we focus on the design and analysis of the einforcedDS-TGDH. We compare our scheme with the original, w.r.t. this cross-layer consideration.
Through our analysis and results we shed more insight on the actual feasibility of these protocols for MANETs and provide more realistic and aircomparison results that more accurately advocate the pros and cons of each protocol over the environment of interest.
Item Fault-Tolerant Extension of Hypercube Algorithm for Efficient, Robust Group Communications in MANETs(2005) Striki, Maria; Baras, John S.; ISR; CSHCNSecuring multicast communications in Mobile Ad Hoc Networks (MANETs) has become one of the most challenging research directions in the areas of wireless networking and security. MANETs are emerging as the desired environment for an increasing number of commercial and military applications, addressing also an increasing number of users. Security on the other hand, is becoming an indispensable requirement of our modern life for all these applications. However, the limitations of the dynamic, infrastructure-less nature of MANETs impose major difficulties in establishing a secure framework suitable for group communications. The design of efficient key management (KM) schemes for MANET is of paramount importance, since the performance of the KM functions (key generation, entity authentication, key distribution/agreement) imposes an upper limit on the efficiency and scalability of the whole secure group communication system. In this work, we contribute towards efficient, robust and scalable, secure group communications for MANETs, by extending an existing key agreement (KA) scheme (where all parties contribute equally to group key generation) ypercube - to tolerate multiple member failures with low cost, through its integration with a novel adaptively proactive algorithm. We assume that the participating users have already been authenticated via some underlying mechanism and we focus on the design and analysis of a fault-tolerant Hypercube, with the aim to contribute to the robustness and efficiency of Octopus-based schemes (an efficient group of KA protocols for MANETs using Hypercube as backbone). We compare our algorithm with the existing approach, and we evaluate the results of our analysis. Through our analysis and simulation results we demonstrate how the new Hypercube algorithm enhances the robustness of the Octopus schemes maintaining their feasibility in MANETs at the same time.Key terms: Key Management, Key Agreement, Hypercube Protocol, Fault-Tolerance, Octopus Schemes, Elliptic Curves Cryptography
Item Modeling locality of reference via notions of positive dependence -- Some mixed news!(2005) Vanichpun, Sarut; Makowski, Armand M.; ISR; CSHCNWe introduce the notion of Temporal Correlations (TC) ordering as a way to compare strength of temporal correlations in streams of requests. This notion is based on the supermodular ordering, a concept of positive dependence used for comparing dependence structures in sequences of rvs. We explore how the TC ordering captures the strength of temporal c correlations in several Web request models, namely, the higher-order Markov chain model (HOMM), the partial Markov chain model (PMM) and the Least-Recently-Used stack model (LRUSM). We also show how the comparison in the TC ordering is compatible with comparisons of some well-known locality of reference metrics, namely, the working set size and the inter-reference time. We establish a folk theorem to the effect that the stronger the temporal correlations, the smaller the miss rate for the PMM. Conjectures and simulations are offered regarding this folk theorem under the HOMM and under the LRUSM. The validity of this folk theorem is also discussed for general input streams under the Working Set algorithm.Item Resequencing delays under multipath routing -- Asymptotics in a simple queueing model(2005) Han, Yijie; Makowski, Armand M.; ISR; CSHCNWe study the resequencing delay caused by multipath routing. We use a queueing model which consists of parallel queues to model the network routing behavior. We define a new metric denoted by $gamma$, to study the impact of resequencing on the customer end-to-end delay. Our results characterize some properties of $gamma$ with respect to different service time distributions. In particular, the resequencing delay can be negligible when the delay along each path is light-tailed, but can be of major concern when it is heavy-tailed.Item HYBRID NETWORKS WITH A SPACE SEGMENT - TOPOLOGY DESIGN AND SECURITY ISSUES(2005) Roy-Chowdhury, Ayan; Baras, John S.; Hadjitheodosiou, Michael H.; Rentz, Nicolas; Baras, Dr. John S.; ISR; CSHCNIn this paper we investigate a hybrid network topology that is suitable for supporting interplanetary communications. We define an architecture comprised of a network of sensor nodes on a remote planetary surface, connected to a hybrid terrestrial network of wired and wireless LANs through a series of satellite relays. All the nodes in the network are IPaddressable and support public and symmetric key cryptography. The resulting network forms a hierarchical hybrid mesh that connects users on Earth to networks on or around a remote planetary surface. We describe the design of the network and present preliminary simulation results illustrating the network performance for various parameters. We also discuss how algorithms for user authentication, message integrity and data confidentiality can be incorporated in the network infrastructure for secure end-to-end communication.