Papers by mostafa dehghan
In this paper, we consider the problem of allocating cache resources among multiple content provi... more In this paper, we consider the problem of allocating cache resources among multiple content providers. The cache can be partitioned into slices and each partition can be dedicated to a particular content provider, or shared among a number of them. It is assumed that each partition employs the LRU policy for managing content. We propose utility-driven partitioning, where we associate with each content provider a utility that is a function of the hit rate observed by the content provider. We consider two scenarios: i)~content providers serve disjoint sets of files, ii)~there is some overlap in the content served by multiple content providers. In the first case, we prove that cache partitioning outperforms cache sharing as cache size and numbers of contents served by providers go to infinity. In the second case, It can be beneficial to have separate partitions for overlapped content. In the case of two providers, it is usually always beneficial to allocate a cache partition to serve al...
The objective of the study is to reveal the seasonal variations in the groundwater quality with r... more The objective of the study is to reveal the seasonal variations in the groundwater quality with respect to heavy metal contamination. About 32 water well samples were analysed using Atomic Absorption Spectrophotometer for their mercury(Hg), cobalt (Co), cupper (Cu), zinc (Zn), nickel (Ni), chromium (Cr) and lead (Pb) content and their levels compared with international standards specified maximum contaminant level. Heavy metal contents of ground waters were below the permissible levels. Average total Hg, Co, Cu, Zn, Ni, Cr, Pb and As contents of ground waters were below the pollutant limits, but in some sampling sites for Hg and As concentrations were exceeded permissible limits. However, the average heavy metal evaluation index values for all metals in ground waters were below the critical value.
In this paper, we explore physical layer cooperative communication in order to design network lay... more In this paper, we explore physical layer cooperative communication in order to design network layer routing algorithms that are energy efficient. We assume each node in the network is equipped with a single omnidirectional antenna and that multiple nodes are able to coordinate their transmissions in order to take advantage of spatial diversity to save energy. Specifically, we consider cooperative MIMO at physical layer and multi-hop routing at network layer, and formulate minimum energy routing as a joint optimization of the transmission power at the physical layer and the link selection at the network layer. Using dynamic programming, we compute the energy consumption of the optimal cooperative routing in different network scenarios, which shows energy savings of up to 55%, compared with the optimal non-cooperative routing. As the network becomes larger, however, finding optimal routes becomes computationally intractable as the complexity of the dynamic programming approach increas...
Proceedings of the 1st Workshop on Content Caching and Delivery in Wireless Networks - CCDWN '16, 2016
The deployment of caches in the Internet has grown significantly in the last decade, thus enablin... more The deployment of caches in the Internet has grown significantly in the last decade, thus enabling the vision of Content-Centric Networks (CCNs). The caching policy employed at these routers has significant impact on the potential gains in network performance. Policies that adapt to changes in content popularities are of special interest. In this paper, we propose a novel caching policy called Data Stream Caching Algorithm (DSCA) with the goal of maximizing cache hit rate of CCN routers by incorporating content popularity in caching decisions. In contrast to existing popularitybased caching policies, DSCA copes with dynamics in content popularity while operating under the memory and high processing rate constraints of CCN network routers. DSCA achieves the above objectives using a data streaming algorithm that identifies the most popular contents adapted to work in a windowed manner. We analyze the performance and robustness of the proposed caching policy through simulations. Evaluations on synthetic data and real-world traces show that DSCA outperforms LRU and other caching policies evaluated in this work.
8th International Symposium on Modeling and Optimization in Mobile, Ad Hoc, and Wireless Networks, 2010
In this paper, we explore physical layer cooperative communication in order to design network lay... more In this paper, we explore physical layer cooperative communication in order to design network layer routing algorithms that are energy efficient. We assume each node in the network is equipped with a single omnidirectional antenna and that multiple nodes are able to coordinate their transmissions in order to take advantage of spatial diversity to save energy. Specifically, we consider cooperative diversity at physical layer and multi-hop routing at network layer, and formulate minimum energy routing as a joint optimization of the transmission power at the physical layer and the link selection at the network layer. We then show that as the network becomes larger, finding optimal cooperative routes becomes computationally intractable. As such, we develop a number of heuristic routing algorithms that have polynomial computational complexity, and yet achieve significant energy savings. Simulation results are also presented, which indicate that the proposed algorithms based on optimal po...
Optics and Photonics Society of Iran, 2015
Inserting a finite straight waveguide above the microring can causes dual resonance in it. Each r... more Inserting a finite straight waveguide above the microring can causes dual resonance in it. Each resonance is created by the waves with the same phase in the microring. The resonator have been modelized by using transform matrix method. In this paper the variations of the resonator characteristics such as FSR, FWHM, peak distance of dual resonance and quality factor versus their parameters have been investigated. In optimum condition a great quality factor is achieved. This system can be used whereever two high intensity close wavelength are needed.
Proceedings of the 3rd ACM Conference on Information-Centric Networking, 2016
In-network cache deployment is recognized as an effective technique for reducing content access d... more In-network cache deployment is recognized as an effective technique for reducing content access delay. Caches serve content from multiple content providers, and wish to provide them differentiated services due to monetary incentives and legal obligations. Partitioning is a common approach in providing differentiated storage services. In this paper, we propose a utility-driven cache partitioning approach to cache resource allocation among multiple content providers, where we associate with each content provider a utility that is a function of the hit rate to its content. A cache is partitioned into slices with each partition being dedicated to a particular content provider. We formulate an optimization problem where the objective is to maximize the sum of weighted utilities over all content providers through proper cache partitioning, and mathematically show its convexity. We also give a formal proof that partitioning the cache yields better performance compared to sharing it. We validate the effectiveness of cache partitioning through numerical evaluations, and investigate the impact of various factors (e.g., content popularity, request rate) on the hit rates observed by contending content providers.
ACM Transactions on Modeling and Performance Evaluation of Computing Systems, 2021
Caching is a fundamental element of networking systems since the early days of the Internet. By f... more Caching is a fundamental element of networking systems since the early days of the Internet. By filtering requests toward custodians, caches reduce the bandwidth required by the latter and the delay experienced by clients. The requests that are not served by a cache, in turn, comprise its miss stream. We refer to the dependence of the cache state and miss stream on its history as hysteresis. Although hysteresis is at the core of caching systems, a dimension that has not been systematically studied in previous works relates to its impact on caching systems between misses, evictions, and insertions. In this article, we propose novel mechanisms and models to leverage hysteresis on cache evictions and insertions. The proposed solutions extend TTL-like mechanisms and rely on two knobs to tune the time between insertions and evictions given a target hit rate. We show the general benefits of hysteresis and the particular improvement of the two thresholds strategy in reducing download times...
IEEE/ACM Transactions on Networking, 2019
In any caching system, the admission and eviction policies determine which contents are added and... more In any caching system, the admission and eviction policies determine which contents are added and removed from a cache when a miss occurs. Usually, these policies are devised so as to mitigate staleness and increase the hit probability. Nonetheless, the utility of having a high hit probability can vary across contents. This occurs, for instance, when service level agreements must be met, or if certain contents are more difficult to obtain than others. In this paper, we propose utility-driven caching, where we associate with each content a utility, which is a function of the corresponding content hit probability. We formulate optimization problems where the objectives are to maximize the sum of utilities over all contents. These problems differ according to the stringency of the cache capacity constraint. Our framework enables us to reverse engineer classical replacement policies such as LRU and FIFO, by computing the utility functions that they maximize. We also develop online algorithms that can be used by service providers to implement various caching policies based on arbitrary utility functions.
Computer Networks, 2018
In-network caching is recognized as an effective solution to offload content servers and the netw... more In-network caching is recognized as an effective solution to offload content servers and the network. A cache service provider (SP) always has incentives to better utilize its cache resources by taking into account diverse roles that content providers (CPs) play, e.g., their business models, traffic characteristics, preferences. In this paper, we study the cache resource allocation problem in a Multi-Cache Multi-CP environment. We propose a cache partitioning approach, where each cache can be partitioned into slices with each slice dedicated to a content provider. We propose a content-oblivious request routing algorithm, to be used by individual caches, that optimizes the routing strategy for each CP. We associate with each content provider a utility that is a function of its content delivery performance, and formulate an optimization problem with the objective to maximize the sum of utilities over all content providers. We establish the biconvexity of the problem, and develop decentralized (online) algorithms based on convexity of the subproblem. The proposed model is further extended to bandwidth-constrained and minimum-delay scenarios, for which we prove fundamental properties, and develop efficient algorithms. Finally, we present numerical results to show the efficacy of our mechanism and the convergence of our algorithms.
IEEE/ACM Transactions on Networking, 2019
IEEE/ACM Transactions on Networking, 2017
2016 IFIP Networking Conference (IFIP Networking) and Workshops, 2016
The Named Data Networking (NDN) and Content-Centric Networking (CCN) architectures advocate Inter... more The Named Data Networking (NDN) and Content-Centric Networking (CCN) architectures advocate Interest aggregation as a means to reduce end-to-end latency and bandwidth consumption. To enable these benefits, Interest aggregation must be realized through Pending Interest Tables (PIT) that grow in size at the rate of incoming Interests to an extent that may eventually defeat their original purpose. A thorough analysis is provided of the Interest aggregation mechanism using mathematical arguments backed by extensive discrete-event simulation results. We present a simple yet accurate analytical framework for characterizing Interest aggregation in a CCN router, and use our model to develop an iterative algorithm to analyze the benefits of Interest aggregation in a network of interconnected routers. Our findings reveal that, under realistic assumptions, an insignificant fraction of Interests in the system benefit from aggregation, compromising the effectiveness of using PITs as an integral component of Content-Centric Networks.
In this paper, we propose approximate models to assess the performance of a cache network with ar... more In this paper, we propose approximate models to assess the performance of a cache network with arbitrary topology where nodes run the Least Recently Used (LRU), First-In First-Out (FIFO), or Random (RND) replacement policies on arbitrary size caches. Our model takes advantage of the notions of cache characteristic time and Time-To-Live (TTL)-based cache to develop a unified framework for approximating metrics of interest of interconnected caches. Our approach is validated through event-driven simulations; and when possible, compared to the existing a-NET model [23].
Proceedings of the 8th International Conference on Performance Evaluation Methodologies and Tools, 2015
The performance evaluation of cache networks has gain a huge attention due to content-oriented de... more The performance evaluation of cache networks has gain a huge attention due to content-oriented delivery technologies. If general network topologies are more realistic than hierarchical networks widely studied in the literature, their analysis is significantly challenging. Existing models mainly focus on trees where content custodians are located at the root and the one-way child-to-parent request forwarding schema is common. In this paper, we consider complex and irregular networks where requests may flow possibly in opposite directions from/to several sources/destinations. Moreover, we assume that caches may run one of Time-To-Live (TTL)-based policies recently introduced for content-centric networks and modern Domain Name System [5]. We then derive an analytical framework and a polynomial-time algorithm that approximate accurately performance metrics of arbitrary graph-based and heterogeneous TTL-based cache networks. Simulations show that our simplified methodology may accurately predict metrics of interest on networks of caches running popular replacement algorithms (e.g. LRU, FIFO, or Random) without restricting its scope of application to this interesting use case. Unlike existing approaches, ours scales as network and content catalog sizes increase.
2015 IEEE Conference on Computer Communications (INFOCOM), 2015
We investigate the problem of optimal request routing and content caching in a heterogeneous netw... more We investigate the problem of optimal request routing and content caching in a heterogeneous network supporting in-network content caching with the goal of minimizing average content access delay. Here, content can either be accessed directly from a back-end server (where content resides permanently) or be obtained from one of multiple in-network caches. To access a piece of content, a user must decide whether to route its request to a cache or to the back-end server. Additionally, caches must decide which content to cache. We investigate the problem complexity of two problem formulations, where the direct path to the back-end server is modeled as i) a congestionsensitive or ii) a congestion-insensitive path, reflecting whether or not the delay of the uncached path to the back-end server depends on the user request load, respectively. We show that the problem is NP-complete in both cases. We prove that under the congestion-insensitive model the problem can be solved optimally in polynomial time if each piece of content is requested by only one user, or when there are at most two caches in the network. We also identify a structural property of the user-cache graph that potentially makes the problem NP-complete. For the congestionsensitive model, we prove that the problem remains NP-complete even if there is only one cache in the network and each content is requested by only one user. We show that approximate solutions can be found for both models within a (1 − 1/e) factor of the optimal solution, and demonstrate a greedy algorithm that is found to be within 1% of optimal for small problem sizes. Through trace-driven simulations we evaluate the performance of our greedy algorithms, which show up to a 50% reduction in average delay over solutions based on LRU content caching.
IEEE Transactions on Mobile Computing, 2015
There is a rich recent literature on informationtheoretically secure communication at the physica... more There is a rich recent literature on informationtheoretically secure communication at the physical layer of wireless networks, where secret communication between a single transmitter and receiver has been studied extensively. In this paper, we consider how single-hop physical layer security techniques can be extended to multi-hop wireless networks. We show that guaranteed security can be achieved in multihop networks by augmenting physical layer security techniques, such as cooperative jamming, with the higher layer network mechanisms, such as routing. Specifically, we consider the secure minimum energy routing problem, in which the objective is to compute a minimum energy path between two network nodes subject to constraints on the end-to-end communication secrecy and goodput over the path. This problem is formulated as a constrained optimization of transmission power and link selection, which is proved to be NP-hard. Nevertheless, we show that efficient algorithms exist to compute both exact and approximate solutions for the problem. In particular, we develop an exact solution of pseudo-polynomial complexity, as well as an ϵ-optimal approximation of polynomial complexity. Simulation results are also provided to show the utility of our algorithms and quantify their energy savings compared to a combination of (standard) security-agnostic minimum energy routing and physical layer security. In the simulated scenarios, we observe that, by jointly optimizing link selection at the network layer and cooperative jamming at the physical layer, our algorithms reduce the network energy consumption by half.
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Papers by mostafa dehghan