Murat Demirbas's research while affiliated with SUNY Ulster and other places

Publications (145)

Preprint
Full-text available
In this paper, we present BunchBFT Byzantine fault-tolerant state-machine replication for high performance and scalability. At the heart of BunchBFT is a novel design called the cluster-based approach that divides the replicas into clusters of replicas. By combining this cluster-based approach with hierarchical communications across clusters, piggy...
Article
Full-text available
Runtime verification focuses on analyzing the execution of a given program by a monitor to determine if it is likely to violate its specifications. There is often an impedance mismatch between the assumptions/model of the monitor and that of the underlying program. This constitutes problems especially for distributed systems, where the concept of c...
Preprint
Full-text available
This paper describes BigBFT, a multi-leader Byzantine fault tolerance protocol that achieves high throughput and scalable consensus in blockchain systems. BigBFT achieves this by (1) enabling every node to be a leader that can propose and order the blocks in parallel, (2) piggybacking votes within rounds, (3) pipelining blocks across rounds, and (4...
Conference Paper
Full-text available
Most of the Blockchain permissioned systems employ Byzantine fault-tolerance (BFT) consensus protocols to ensure that honest validators agree on the order for appending entries to their ledgers. In this paper, we study the performance and the scalability of prominent consensus protocols, namely PBFT, Tendermint, HotStuff, and Streamlet, both analyt...
Article
State machine replication protocols, like MultiPaxos and Raft, are a critical component of many distributed systems and databases. However, these protocols offer relatively low throughput due to several bottlenecked components. Numerous existing protocols fix different bottlenecks in isolation but fall short of a complete solution. When you fix one...
Preprint
Full-text available
Most of the Blockchain permissioned systems employ Byzantine fault-tolerance (BFT) consensus protocols to ensure that honest validators agree on the order for appending entries to their ledgers. In this paper, we study the performance and the scalability of prominent consensus protocols, namely PBFT, Tendermint, HotStuff, and Streamlet, both analyt...
Preprint
State machine replication protocols, like MultiPaxos and Raft, are a critical component of many distributed systems and databases. However, these protocols offer relatively low throughput due to several bottlenecked components. Numerous existing protocols fix different bottlenecks in isolation but fall short of a complete solution. When you fix one...
Preprint
Full-text available
Paxos family of protocols are employed by many cloud computing services and distributed databases due to their excellent fault-tolerance properties. Unfortunately, current Paxos deployments do not scale for more than a dozen nodes due to the communication bottleneck at the leader. PigPaxos addresses this problem by decoupling the communication from...
Article
Full-text available
Consistency properties provided by most key-value stores can be classified into sequential consistency and eventual consistency. The former is easier to program with but suffers from lower performance whereas the latter suffers from potential anomalies while providing higher performance. We focus on the problem of what a designer should do if he/sh...
Preprint
Full-text available
Deep learning has permeated through many aspects of computing/processing systems in recent years. While distributed training architectures/frameworks are adopted for training large deep learning models quickly, there has not been a systematic study of the communication bottlenecks of these architectures and their effects on the computation cycle ti...
Preprint
Full-text available
Consistency properties provided by most key-value stores can be classified into sequential consistency and eventual consistency. The former is easier to program with but suffers from lower performance whereas the latter suffers from potential anomalies while providing higher performance. We focus on the problem of what a designer should do if he/sh...
Conference Paper
Full-text available
Deep learning has permeated through many aspects of computing/processing systems in recent years. While distributed training architectures/frameworks are adopted for training large deep learning models quickly, there has not been a systematic study of the communication bottlenecks of these architectures and their effects on the computation cycle ti...
Article
WPaxos is a multileader Paxos protocol that provides low-latency and high-throughput consensus across wide-area network (WAN) deployments. WPaxos uses multileaders, and partitions the object-space among these multileaders. Unlike statically partitioned multiple Paxos deployments, WPaxos is able to adapt to the changing access locality through objec...
Conference Paper
Many distributed databases employ consensus protocols to ensure that data is replicated in a strongly-consistent manner on multiple machines despite failures and concurrency. Unfortunately, these protocols show widely varying performance under different network, workload, and deployment conditions, and no previous study offers a comprehensive disse...
Article
Retroscope is a comprehensive lightweight distributed monitoring tool that enables users to query and reconstruct past consistent global states of the system. Retroscope achieves this by augmenting the system with Hybrid Logical Clocks (HLC) and by streaming HLC-stamped event logs for storage and processing; these HLC timestamps are then used for c...
Preprint
Full-text available
Causal consistency is an intermediate consistency model that can be achieved together with high availability and performance requirements even in presence of network partitions. In the context of partitioned data stores, it has been shown that implicit dependency tracking using timestamps is more efficient than explicit dependency tracking. Existin...
Conference Paper
The distributed consensus problem has been extensively studied in the last four decades as an important problem in distributed systems. Recent advances in decentralized consensus and blockchain technology, however, arose from a disparate model and gave rise to disjoint knowledge-base and techniques than those in the classical consensus research. In...
Preprint
Full-text available
The last decade has witnessed rapid proliferation of cloud computing. While even the smallest distributed programs (with 3-5 actions) produce many unanticipated error cases due to concurrency involved, it seems short of a miracle these web-services are able to operate at those vast scales. In this paper, we explore the factors that contribute most...
Preprint
Limitations of CAP theorem imply that if availability is desired in the presence of network partitions, one must sacrifice sequential consistency, a consistency model that is more natural for system design. We focus on the problem of what a designer should do if he/she has an algorithm that works correctly with sequential consistency but is faced w...
Article
Hybrid vector clock(s) (HVC) provide a mechanism to combine the theory and practice of distributed systems. Improving on traditional vector clock(s) (VC), HVC utilizes synchronized physical clocks to reduce the size by focusing only on causality where the physical time associated with two events is within a given uncertainty window ε and letting ph...
Article
Full-text available
Limitations of CAP theorem imply that if availability is desired in the presence of network partitions, one must sacrifice sequential consistency, a consistency model that is more natural for system design. We focus on the problem of what a designer should do if she has an algorithm that works correctly with sequential consistency but is faced with...
Conference Paper
In this paper, we discuss the feasibility of monitoring partially synchronous distributed systems to detect latent bugs, i.e., errors caused by concurrency and race conditions among concurrent processes. We present a monitoring framework where we model both system constraints and latent bugs as Satisfiability Modulo Theories (SMT) formulas, and we...
Article
Full-text available
In this paper, we discuss the feasibility of monitoring partially synchronous distributed systems to detect latent bugs, i.e., errors caused by concurrency and race conditions among concurrent processes. We present a monitoring framework where we model both system constraints and latent bugs as Satisfiability Modulo Theories (SMT) formulas, and we...
Poster
Full-text available
We investigate the architectural design of distributed machine learning platforms, such as Apache Spark, PMLS (Petuum), TensorFlow, and MXNet. The design decisions inevitably affect the performance, scalability, and availability of those platforms. We take a distributed systems perspective and analyze the communication and control bottlenecks for t...
Article
Question answering is a fundamental problem for artificial intelligence research. State-of-the-art question answering systems, such as search engines, can answer well-formed factual questions. However, they fail on nonfactual and natural language queries. On the other hand, crowdsourcing leverages human intelligence to present solutions for problem...
Article
We present WPaxos, a multileader wide area network (WAN) Paxos protocol, that achieves low-latency high-throughput consensus across WAN deployments. WPaxos dynamically partitions the global object-space across multiple concurrent leaders that are deployed strategically using flexible quorums. This partitioning and emphasis on local operations allow...
Conference Paper
Predicate detection is a critical aspect in debugging and monitoring of distributed systems. Runtime monitoring of distributed systems should satisfy two main requirements: wait-free execution and efficient computation. Monitoring is wait-free if it is non-intrusive (application being monitored is not stopped due to monitoring) and is efficient if...
Conference Paper
Runtime verification focuses on analyzing the execution of a given program by a monitor to determine if it is likely to violate its specifications. There is often an impedance mismatch between the assumptions/model of the monitor and that of the underlying program. This constitutes problems especially for distributed systems, where the concept of c...
Article
Full-text available
A Federated Sensor Network (FSN) is a network of geographically distributed Wireless Sensor Networks (WSNs) called islands. For querying on an FSN, we introduce the Layered Federated Sensor Network (L-FSN) Protocol. For layered management, L-FSN provides communication among islands by its inter-island querying protocol by which a query packet routi...
Article
This article describes LineKing, a crowdsensing system for monitoring and forecasting coffee shop line wait times. LineKing consists of a smartphone component that provides automatic and accurate wait-time detection, and a cloud backend that uses the collected data to provide accurate wait-time estimation. LineKing is used on a daily basis by hundr...
Article
Full-text available
Using smartphones as mobile basestations and leveraging human mobility is a promising approach for urban data collection from Wireless Sensor Networks (WSNs). In this paper, we evaluate the feasibility of this approach applying analyses on a city-wide mobility dataset. Our spatial analysis shows that popular locations cluster close to each other an...
Article
This paper presents a survey on the timing performance of Google Cloud Messaging (GCM). We evaluate GCM in real world experiments, and at a reasonable scale involving thousands of real users. Our findings reveal that the GCM message delivery is unpredictable, namely having a reliable connection to Google's GCM servers on the client device does not...
Article
Research in system stabilization has traditionally relied on the availability of a complete system implementation. As such, it would appear that the scalability and reusability of stabilization is limited in practice. To redress this perception, in this paper, we show for the first time that system stabilization may be designed knowing only the sys...
Article
Abstract We present a new shared memory model, SF shared memory model. In this model, the actions of each node are partitioned into slow actions and fast actions. By contrast, the traditional shared memory model only includes fast actions. Intuitively, slow actions can utilize slightly stale state information to execute successfully. However, fast...
Conference Paper
There is a gap between the theory and practice of distributed systems in terms of the use of time. The theory of distributed systems shunned the notion of time, and introduced “causality tracking” as a clean abstraction to reason about concurrency. The practical systems employed physical time (NTP) information but in a best effort manner due to the...
Article
In many real world applications, the same item may be described by multiple sources. As a consequence, conflicts among these sources are inevitable, which leads to an important task: how to identify which piece of information is trustworthy, i.e., the truth discovery task. Intuitively, if the piece of information is from a reliable source, then it...
Article
Because of the spatiotemporal variability of people and air pollutants within cities, it is important to account for a person's movements over time when estimating personal air pollution exposure. This study aimed to examine the feasibility of using smartphones to collect personal-level time-activity data. Using Skyhook Wireless's hybrid geolocatio...
Article
We leverage crowd wisdom for multiple-choice question answering, and employ lightweight machine learning techniques to improve the aggregation accuracy of crowdsourced answers to these questions. In order to develop more effective aggregation methods and evaluate them empirically, we developed and deployed a crowdsourced system for playing the "Who...
Conference Paper
State-of-the-art question answering systems are pretty successful on well-formed factual questions, however they fail on the non-factual ones. In order to investigate effective algorithms for answering non-factual questions, we deployed a crowdsourced multiple choice question answering system for playing “Who wants to be a millionaire?” game. To bu...
Conference Paper
The proximity alert service on Android is important as an enabler of smart cities, however, it is also limited in this role due to its excessive energy expenditure. In this paper, we present the design and implementation of an energy-efficient proximity alert service for both high-precision and low-precision applications. Our methods utilize the di...
Conference Paper
As smartphones have emerged as the most widely deployed mobile computing platform, the scale of smartphone experimentation has lagged behind. New facilities enabling large-scale experiments are needed to ensure that research discoveries translate to the billions of smartphones in use today. To meet this challenge, we introduce PhoneLab, a 288-devic...
Conference Paper
Bulk Synchronous Parallelism (BSP) provides a good model for parallel processing of many large-scale graph applications, however it is unsuitable/inefficient for graph applications that require coordination, such as graph-coloring, subcoloring, and clustering. To address this problem, we present an efficient modification to the BSP model to impleme...
Conference Paper
The proximity alert service on Android is important as an enabler of ubiquitous location-based services, however, it is also limited in this role due to its excessive energy expenditure. In this paper, we present the design and implementation of an energy-efficient proximity alert service for Android. Our method utilizes the distance to the point o...
Conference Paper
Here we present our ubiquitous computing vision, Eywa. Eywa is an open publish-subscribe system that employs crowdsourcing for tasking and social networks & machine learning for identifying relevance. We argue that crowdsourcing (and the social networks and machine learning that enable it) should be a first class citizen in ubiquitous computing. We...
Article
Full-text available
In wireless sensor networks, querying services purpose to detect static events while tracking services continuously monitor mobile events. This paper surveys and discusses in-network querying and tracking services for static and mobile networks. Querying and tracking services are categorized by tree-based, hierarchical cluster-based, geometrical an...
Article
Due to its ever increasing popularity, Twitter has become a pervasive information outlet. In this paper, we present a passive sensing framework for identifying trends via Twitter. In our framework, we use a multi-dimensional corpus for fine-granularity sensing of trends, and employ both vector-space and set-space methods for achieving accuracy. We...
Conference Paper
This paper describes the design, implementation and deployment of LineKing (LK), a crowdsourced line wait-time monitoring service. LK consists of a smartphone component (that provides automatic, energy-efficient, and accurate wait-time detection), and a cloud backend (that uses the collected data to provide accurate wait-time estimation). LK is use...
Conference Paper
Full-text available
Concurrent execution is a big challenge for distributed systems programming and cloud computing. Using locks is the most common technique for developing distributed applications that require tight synchronization. Unfortunately, locking is manual, error-prone, and unscalable. To address this issue, we propose a scalable automated locking framework...
Article
In this paper, we propose a novel page view based session model and session construction method to address the Web Usage Mining (WUM) problem. Unlike the simple session models, where sessions are sequences of web pages requested from the server (or served from a browser/proxy cache) and viewed in the browser (which may not guarantee a direct relati...
Article
Stationary wireless sensor networks (WSNs) fail to scale when the area to be monitored is unbounded and the physical phenomenon to be monitored may migrate through a large region. Deploying mobile sensor networks (MSNs) alleviates this problem, as the self-configuring MSN can relocate to follow the phenomenon of interest. However, a major challenge...
Article
We consider the problem of tracking of a mobile target node in a mobile ad hoc network (MANET) set-up. We propose a lightweight probabilisticmodel-based tracking protocol (PMBT) that achieves a short catching path with a high success rate. PMBT is a probabilistic online tracking algorithm that computes information utilities at each step, and then c...
Conference Paper
Full-text available
Idle-listening is the biggest challenge for energy-efficiency and longevity of multihop wireless sensor network (WSN) deployments. While existing coordinated sleep/wakeup scheduling protocols eliminate idle-listening for simple traffic patterns, they are unsuitable to handle the complex traffic patterns of the random routing protocols. We present a...
Conference Paper
Full-text available
Federated sensor networks (FSNs) connect and combine several partitioned wireless sensor networks (WSNs) to extend the scope of WSNs to larger scale geographical areas. The federated and sparsely/intermittently connected nature of FSNs introduce several challenges for deploying middleware services such as routing, querying, tracking, time synchroni...
Article
Improving throughput and delay is an important challenge in multi-hop wireless sensor networks. In this work, we propose ABC-MC, a simple multi-channel geographic forwarding scheme. ABC-MC is based on ABC which is a lightweight and reliable routing protocol where nodes do not need to set up or maintain routing/neighbor tables. A unique feature of A...
Conference Paper
In this study, we provide a lightweight singlehop primitive, Read-All-Write-Self (RAWS), that achieves optimistic concurrency control. RAWS guarantees serializability, which simplifies implementation and verification of distributed algorithms, compared to the low level message passing model. We also present a self-stabilizing multihop extension of...
Conference Paper
In wireless sensor network (WSN) deployments, Receiver-side Collision Detection (RCD) has been proposed for speeding up collaborative feedback collection from a single hop neighborhood. Using RCD, an initiator node can query the existence of a predicate P in its neighborhood in constant time by making all P-positive nodes answer simultaneously. Des...
Article
Full-text available
Nowadays, most of the basic web services use instant location information for providing suitable content to smartphone users. However, more intelligent smartphone applications such as context-based search and advertising, early warning systems and city-wide sensing applications may require additional information about smartphone users such as their...
Conference Paper
Location-based queries are quickly becoming ubiq- uitous. However, traditional search engines perform poorly for a significant fraction of location-based queries, which are non- factual (i.e., subjective, relative, or multi-dimensional). As an alternative, we investigate the feasibility of answering location- based queries by crowdsourcing over Twi...
Conference Paper
Full-text available
In this paper, we propose a novel routing protocol, PRO, for profile-based routing in pocket switched networks. Differing from previous routing protocols, PRO treats node encounters as periodic patterns and uses them to predict the times of future encounters. Exploiting the regularity of human mobility profiles, PRO achieves fast (low-delivery-late...
Conference Paper
Consider a wireless sensor network in which each sensor has a bit of information. Suppose all sensors with the bit 1 broadcast this fact to a basestation. If zero or one sensors broadcast, the basestation can detect this fact. If two or more sensors broadcast, the basestation can only detect that there is a ”collision.” Although collisions may seem...
Conference Paper
Transformations from shared memory model to wireless sen- sor networks (WSNs) quickly become inefficient in the presence of preva- lent message losses in WSNs, and this prohibits their wider adoption. To address this problem, we propose a variation of the shared memory model, the SF shared memory model, where the actions of each node are partitione...