| 1. |
- Corneo, Lorenzo
(författare)
-
Networked Latency Sensitive Applications - Performance Issues between Cloud and Edge
- 2021
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The increasing demand for industrial automation has motivated the development of applications with strict latency requirements, namely, latency-sensitive applications. Such latency requirements can be satisfied by offloading computationally intensive tasks to powerful computing devices over a network at the cost of additional communication latency. Two major computing paradigms are considered for this: (i) cloud computing and (ii) edge computing. Cloud computing provides computation at remote datacenters, at the cost of longer communication latency. Edge computing aims at reducing communication latency by bringing computation closer to the users. This doctoral dissertation mainly investigates relevant issues regarding communication latency trade-offs between the aforementioned paradigms in the context of latency-sensitive applications.This work advances the state of the art with three major contributions. First, we design a suite of scheduling algorithms which are performed on an edge device interposed between a co-located sensor network and remote applications running in cloud datacenters. These algorithms guarantee the fulfillment of latency-sensitive applications' requirements while maximizing the battery life of sensing devices. Second, we estimate under what conditions latency-sensitive applications can be executed in cloud environments. From a broader perspective, we quantify round-trip times needed to access cloud datacenters all around the world. From a narrower perspective, we collect latency measurements to cloud datacenters in metropolitan areas where over 70% of the world's population lives. This Internet-wide large-scale measurements campaign allows us to draw statistically relevant conclusions concerning the readiness of the cloud environments to host latency-sensitive applications. Finally, we devise a method to quantify latency improvements that hypothetical edge server deployments could bring to users within a network. This is achieved with a thorough analysis of round-trip times and paths characterization resulting in the design of novel edge server placement algorithms. We show trade-offs between number of edge servers deployed and latency improvements experienced by users.This dissertation contributes to the understanding of the communication latency in terms of temporal and spacial distributions, its sources and implications on latency-sensitive applications.
|
|
| 2. |
- Borgström, Gustaf
(författare)
-
Making Sampled Simulations Faster by Minimizing Warming Time
- 2022
-
Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- A computer system simulator is a fundamental tool for computer architects to try out brand new ideas or explore the system’s response to different configurations when executing different program codes. However, even simulating the CPU core in detail is time-consuming as the execution rate slows down by several orders of magnitude compared to native execution. To solve this problem, previous work, namely SMARTS, demonstrates a statistical sampling methodology that records measurements only from tiny samples throughout the simulation. It spends only a fraction of the full simulation time on these sample measurements. In-between detailed sample simulations, SMARTS fast-forwards in the simulation using a greatly simplified and much faster simulation model (compared to full detail), which maintains only necessary parts of the architecture, such as cache memory. This maintenance process is called warming. While warming is mandatory to keep the simulation accuracy high, caches may be sufficiently warm for an accurate simulation long before reaching the sample. In other words, much time may be wasted on warming in SMARTS.In this work, we show that caches can be kept in an accurate state with much less time spent on warming. The first paper presents Adaptive Cache Warming, a methodology for identifying the minimum amount of warming in an iterative process for every SMARTS sample. The rest of the simulation time, previously spent on warming, can be skipped by fast-forwarding between samples using native hardware execution of the code. Doing so will thus result in significantly faster statistically sampled simulation while maintaining accuracy. The second paper presents Cache Merging, which mitigates the redundant warmings introduced in Adaptive Cache Warming. We solve this issue by going back in time and merging the existing warming with a cache warming session that comes chronologically before the existing warming. By removing the redundant warming, we yield even more speedup. Together, Adaptive Cache Warming and Cache Merging is a powerful boost for statistically sampled simulations.
|
|
| 3. |
- Yan, Wenqing, Ph.D. Student, 1994-
(författare)
-
Design and Identification of Wireless Transmitters for a Low-power and Secure Internet of Things
- 2023
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Wireless communication is a key enabler for connecting billions of Internet of Things devices. For networked embedded devices operating on limited energy resources, wireless communication dominates the power consumption. Moreover, as networked devices increasingly handle sensitive data, security concerns in wireless communication are continuously expanding. This dissertation develops novel solutions for low-power and secure wireless communication. Wireless transmitters consist of a series of steps, involving both analog and digital components, each playing a distinct role in the transmit chain. Conventional transmitters employ power-hungry analog components, leading to power consumption on the order of milliwatt. Backscatter transmitters significantly reduce communication power consumption to levels well below one milliwatt. This remarkable power efficiency is achieved by offloading power-hungry components to an external carrier emitter. However, backscatter transmitters encounter challenges in applications that demand medium to long communication range, because they rely heavily on powerful emitters in their proximity for an effective communication range. Instead of removing power-hungry components, our solution integrates the functions of these components into a low-power design. While still requiring an emitter, our transmitter does not reflect the carrier signal. Instead, we utilize a weak carrier signal to stabilize the transmitter, allowing a communication range of over one hundred meters even when the emitter is far away. This contribution takes a step forward in moving low-power communication beyond backscatter.Passive radiometric fingerprinting leverages imperfections of hardware components to identify and authenticate transmitters. Its passive nature fits well to secure low-power transmitters operating within constrained resources. To enhance the viability of radiometric fingerprinting, we make three contributions in this dissertation to facilitate its widespread deployment. First, compared to conventional radios, low-power backscatter communication has a fundamentally different composition of hardware components in its transmit chain. In our work, we decompose fingerprints in a backscatter system for dual identification of tags and emitters. Beyond security purposes, recognizing the emitter embeds a notion of locality, enabling fingerprinting usage in backscatter network management tasks such as emitter coordination. Second, the dynamic nature of real-world wireless channels significantly impacts the robustness of fingerprinting. We decompose channel impacts and develop a hybrid system. This system employs pertinent strategies for different channel factors, ensuring reliable performance across complex wireless conditions. Lastly, based on the understanding of components' contributions to the transmit chain, we design a lightweight fingerprinting system. We demonstrate a complete implementation seamlessly integrated within the constraints of a single low-cost off-the-shelf chip. This contribution simplifies the conventionally bulky setup using sophisticated signal acquisition equipment and dedicated computer processing resources, which facilitates the practical deployment of fingerprinting on low-cost embedded devices.
|
|
| 4. |
- Bjurefors, Fredrik, 1978-
(författare)
-
Opportunistic Networking : Congestion, Transfer Ordering and Resilience
- 2014
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Opportunistic networks are constructed by devices carried by people and vehicles. The devices use short range radio to communicate. Since the network is mobile and often sparse in terms of node contacts, nodes store messages in their buffers, carrying them, and forwarding them upon node encounters. This form of communication leads to a set of challenging issues that we investigate: congestion, transfer ordering, and resilience.Congestion occurs in opportunistic networks when a node's buffers becomes full. To be able to receive new messages, old messages have to be evicted. We show that buffer eviction strategies based on replication statistics perform better than strategies that evict messages based on the content of the message.We show that transfer ordering has a significant impact on the dissemination of messages during time limited contacts. We find that transfer strategies satisfying global requests yield a higher delivery ratio but a longer delay for the most requested data compared to satisfying the neighboring node's requests.Finally, we assess the resilience of opportunistic networks by simulating different types of attacks. Instead of enumerating all possible attack combinations, which would lead to exhaustive evaluations, we introduce a method that use heuristics to approximate the extreme outcomes an attack can have. The method yields a lower and upper bound for the evaluated metric over the different realizations of the attack. We show that some types of attacks are harder to predict the outcome of and other attacks may vary in the impact of the attack due to the properties of the attack, the forwarding protocol, and the mobility pattern.
|
|
| 5. |
- Borgström, Gustaf, PhD Student, 1984-, et al.
(författare)
-
Faster Functional Warming with Cache Merging
- 2022
-
Rapport (övrigt vetenskapligt/konstnärligt)abstract
- Smarts-like sampled hardware simulation techniques achieve good accuracy by simulating many small portions of an application in detail. However, while this reduces the detailed simulation time, it results in extensive cache warming times, as each of the many simulation points requires warming the whole memory hierarchy. Adaptive Cache Warming reduces this time by iteratively increasing warming until achieving sufficient accuracy. Unfortunately, each time the warming increases, the previous warming must be redone, nearly doubling the required warming. We address re-warming by developing a technique to merge the cache states from the previous and additional warming iterations.We address re-warming by developing a technique to merge the cache states from the previous and additional warming iterations. We demonstrate our merging approach on multi-level LRU cache hierarchy and evaluate and address the introduced errors. By removing warming redundancy, we expect an ideal 2× warming speedup when using our Cache Merging solution together with Adaptive Cache Warming. Experiments show that Cache Merging delivers an average speedup of 1.44×, 1.84×, and 1.87× for 128kB, 2MB, and 8MB L2 caches, respectively, with 95-percentile absolute IPC errors of only 0.029, 0.015, and 0.006, respectively. These results demonstrate that Cache Merging yields significantly higher simulation speed with minimal losses.
|
|
| 6. |
- Borgström, Gustaf, PhD Student, 1984-, et al.
(författare)
-
Faster FunctionalWarming with Cache Merging
- 2023
-
Ingår i: PROCEEDINGS OF SYSTEM ENGINEERING FOR CONSTRAINED EMBEDDED SYSTEMS, DRONESE AND RAPIDO 2023. - : Association for Computing Machinery (ACM). - 9798400700453 ; , s. 39-47
-
Konferensbidrag (refereegranskat)abstract
- Smarts-like sampled hardware simulation techniques achieve good accuracy by simulating many small portions of an application in detail. However, while this reduces the simulation time, it results in extensive cache warming times, as each of the many simulation points requires warming the whole memory hierarchy. Adaptive Cache Warming reduces this time by iteratively increasing warming to achieve sufficient accuracy. Unfortunately, each increases requires that the previous warming be redone, nearly doubling the total warming. We address re-warming by developing a technique to merge the cache states from the previous and additional warming iterations. We demonstrate our merging approach on multi-level LRU cache hierarchy and evaluate and address the introduced errors. Our experiments show that Cache Merging delivers an average speedup of 1.44x, 1.84x, and 1.87x for 128kB, 2MB, and 8MB L2 caches, respectively, (vs. a 2x theoretical maximum speedup) with 95-percentile absolute IPC errors of only 0.029, 0.015, and 0.006, respectively. These results demonstrate that Cache Merging yields significantly higher simulation speed with minimal losses.
|
|
| 7. |
- Cambazoglu, Volkan
(författare)
-
Protocol, mobility and adversary models for the verification of security
- 2016
-
Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The increasing heterogeneity of communicating devices, ranging from resource constrained battery driven sensor nodes to multi-core processor computers, challenges protocol design. We examine security and privacy protocols with respect to exterior factors such as users, adversaries, and computing and communication resources; and also interior factors such as the operations, the interactions and the parameters of a protocol.Users and adversaries interact with security and privacy protocols, and even affect the outcome of the protocols. We propose user mobility and adversary models to examine how the location privacy of users is affected when they move relative to each other in specific patterns while adversaries with varying strengths try to identify the users based on their historical locations. The location privacy of the users are simulated with the support of the K-Anonymity protection mechanism, the Distortion-based metric, and our models of users' mobility patterns and adversaries' knowledge about users.Security and privacy protocols need to operate on various computing and communication resources. Some of these protocols can be adjusted for different situations by changing parameters. A common example is to use longer secret keys in encryption for stronger security. We experiment with the trade-off between the security and the performance of the Fiat–Shamir identification protocol. We pipeline the protocol to increase its utilisation as the communication delay outweighs the computation.A mathematical specification based on a formal method leads to a strong proof of security. We use three formal languages with their tool supports in order to model and verify the Secure Hierarchical In-Network Aggregation (SHIA) protocol for Wireless Sensor Networks (WSNs). The three formal languages specialise on cryptographic operations, distributed systems and mobile processes. Finding an appropriate level of abstraction to represent the essential features of the protocol in three formal languages was central.
|
|
| 8. |
|
|
| 9. |
- Rodhe, Ioana, 1981-
(författare)
-
Secure and Privacy-Aware Data Collection in Wireless Sensor Networks
- 2012
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- A wireless sensor network is a collection of numerous sensors distributed on an area of interest to collect and process data from the environment. One particular threat in wireless sensor networks is node compromise attacks, that is, attacks where the adversary gets physical access to a node and to the programs and keying material stored on it.Only authorized queries should be allowed in the network and the integrity and confidentiality of the data that is being collected should be protected. We propose a layered key distribution scheme together with two protocols for query authentication and confidential data aggregation. The layered key distribution is more robust to node and communication failures than a predefined tree structure. The protocols are secure under the assumption that less than n sensor nodes are compromised. n is a design parameter that allows us to trade off security for overhead. When more than n sensor nodes are compromised, our simulations show that the attacker can only introduce unauthorized queries into a limited part of the network and can only get access to a small part of the data that is aggregated in the network. Considering the data collection protocol we also contribute with strategies to reduce the energy consumption of an integrity preserving in-network aggregation scheme to a level below the energy consumption of a non-aggregation scheme. Our improvements reduce node congestion by a factor of three and the total communication load by 30%.Location privacy of the users carrying mobile devices is another aspect considered in this thesis. Considering a mobile sink that collects data from the network, we propose a strategy for data collection that requires no information about the location and movement pattern of the sink. We show that it is possible to provide data collection services, while protecting the location privacy of the sink. When mobile phones with built-in sensors are used as sensor nodes, location information about where the data has been sensed can be used to trace users and infer other personal information about them, like state of health or personal preferences. Therefore, location privacy preserving mechanisms have been proposed to provide location privacy to the users. We investigate how a location privacy preserving mechanism influences the quality of the collected data and consider strategies to reconstruct the data distribution without compromising location privacy.
|
|
| 10. |
- Bjurefors, Fredrik
(författare)
-
Measurements in opportunistic networks
- 2012
-
Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Opportunistic networks are a subset of delay tolerant networks where the contacts are unscheduled. Such networks can be formed ad hoc by wireless devices, such as mobile phones and laptops. In this work we use a data-centric architecture for opportunistic networks to evaluate data dissemination overhead, congestion in nodes' buffer, and the impact of transfer ordering. Dissemination brings an overhead since data is replicated to be spread in the network and overhead leads to congestion, i.e., overloaded buffers.We develop and implement an emulation testbed to experimentally evaluate properties of opportunistic networks. We evaluate the repeatability of experiments in the emulated testbed that is based on virtual computers. We show that the timing variations are on the order of milliseconds.The testbed was used to investigate overhead in data dissemination, congestion avoidance, and transfer ordering in opportunistic networks. We show that the overhead can be reduced by informing other nodes in the network about what data a node is carrying. Congestion avoidance was evaluated in terms of buffer management, since that is the available tool in an opportunistic network, to handle congestion. It was shown that replication information of data objects in the buffer yields the best results. We show that in a data-centric architecture were each data item is valued differently, transfer ordering is important to achieve delivery of the most valued data.
|
|
