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| 2. |
- Enström, Emma, et al.
(författare)
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Five Years with Kattis – Using an Automated Assessment System in Teaching
- 2011
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Ingår i: 2011 Frontiers in Education Conference (FIE). - New York : IEEE. - 9781612844695
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Konferensbidrag (refereegranskat)abstract
- Automated assessment systems have been employed in computer science (CS) courses at a number of different universities. Such systems are especially applicable in teaching algorithmic problem solving since they can automatically test if an algorithm has been correctly implemented, i.e., that it performs its specified function on a set of inputs. Being able to implement algorithms that work correctly is a crucial skill for CS students in their professional role, but it can be difficult to convey the importance of this in a classroom situation. Programming and problem solving education supported by automated grading has been used since 2002 at our department. We study, using action research methodology, different strategies for deploying automated assessment systems in CS courses. Towards this end, we have developed an automated assessment system and both introduced it into existing courses and constructed new courses structured around it. Our primary data sources for evaluation consists of course evaluations, statistics on students' submitted solutions, and experience teaching the courses. Authors of this paper have been participating in teaching all of the courses mentioned here.
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| 3. |
- Szegedi, Peter, et al.
(författare)
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Enabling future internet research : the FEDERICA case
- 2011
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Ingår i: IEEE Communications Magazine. - : IEEE. - 0163-6804 .- 1558-1896. ; 49:7, s. 54-61
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Tidskriftsartikel (refereegranskat)abstract
- The Internet, undoubtedly, is the most influential technical invention of the 20th century that affects and constantly changes all aspects of our day-to-day lives nowadays. Although it is hard to predict its long-term consequences, the potential future of the Internet definitely relies on future Internet research. Prior to every development and deployment project, an extensive and comprehensive research study must be performed in order to design, model, analyze, and evaluate all impacts of the new initiative on the existing environment. Taking the ever-growing size of the Internet and the increasing complexity of novel Internet-based applications and services into account, the evaluation and validation of new ideas cannot be effectively carried out over local test beds and small experimental networks. The gap which exists between the small-scale pilots in academic and research test beds and the realize validations and actual deployments in production networks can be bridged by using virtual infrastructures. FEDERICA is one of the facilities, based on virtualization capabilities in both network and computing resources, which creates custom-made virtual environments and makes them available for Future Internet Researchers. This article provides a comprehensive overview of the state-of-the-art research projects that have been using the virtual infrastructure slices of FEDERICA in order to validate their research concepts, even when they are disruptive to the test bed’s infrastructure, to obtain results in realistic network environments.
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| 4. |
- Söderman, Pehr, 1982-, et al.
(författare)
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A Comparative Analysis of Buffer Management Algorithms for Delay Tolerant Wireless Sensor Networks
- 2021
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Ingår i: IEEE Sensors Journal. - : Institute of Electrical and Electronics Engineers (IEEE). - 1530-437X .- 1558-1748. ; 21:7, s. 9612-9619
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Tidskriftsartikel (refereegranskat)abstract
- One of the challenges in Delay Tolerant Wireless Sensor Networks (DT-WSN), is to handle situations where the available buffer space is insufficient- the buffer management problem. Although several buffer management algorithms have been proposed for DT-WSNs, to the best of our knowledge, there is no comprehensive study on the effects different factors have on their performance, and which evaluates the relative performance of these algorithms in different contexts. This paper evaluates in a fixed-factor factorial experiment the performance in terms of latency and Quality of Information (QoI) of four representative buffer management algorithms for DT-WSNs; two traditional, FiFO and Random, and two QoI-based algorithms- one proposed by Humber and Ngai and the SmartGap algorithm. The evaluation suggests that the buffer management algorithm in combination with employed routing protocol and the sensor node buffer sizes have a significant impact on latency, while the obtained QoI rather depends on the characteristics of the transported data and the routing protocol, provided a single-copy routing protocol is used. Moreover, the evaluation suggests that QoI-based buffer management algorithms do offer improved QoI, with an 31% improvement in MAE for SmartGap compared to FIFO. However, they do so at the expense of higher latency, with SmartGap giving a 60% higher latency than FIFO on average.
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| 5. |
- Söderman, Pehr, et al.
(författare)
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An SCTP-based mobility management framework for smartphones and tablets
- 2012
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Ingår i: Proceedings - 26th IEEE International Conference on Advanced Information Networking and Applications Workshops, WAINA 2012. - : IEEE Computer Society. - 9780769546520 ; , s. 1107-1112
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Konferensbidrag (refereegranskat)abstract
- The current wireless network landscape comprises a plethora of technologies including WLAN, WiMAX and 3G, and not much speaks for a radical change of the state of affairs in the near future. In light of this, it becomes pivotal to facilitate vertical handover between different types of wireless networks. Although, a large number of vertical handover schemes have been proposed in the past several years, the majority of the proposed solutions reside in the network and/or link layer - e.g., Mobile IP and various IEEE 802.21 schemes - and relatively few are transport-layer solutions. However, we think transport-layer solutions many times are attractive, particularly in cases where there are no economic incentives to upgrade the existing network infrastructure. To this end, we have designed a lightweight, transport-level mobility framework based on the Stream Control Transmission Protocol (SCTP) and its extension for dynamic address reconfiguration. The framework API has been kept very small and closely aligned with the SCTP sockets extensions, which makes porting of existing applications fairly straightforward. To demonstrate its usefulness for low-power tablets and smart phones, we have implemented our framework on a Motorola Xoom tablet running the Android OS. Our initial proof-of-concept experiment gave satisfactory results with a handover performance on par with that of other vertical handover solutions.
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| 6. |
- Söderman, Pehr, 1982-
(författare)
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Aspects of Quality : Using Quality Measurements to Improve Computer Network Performance
- 2016
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- As computer networks grow in complexity, measuring the performance becomes a challenge. Intrinsic properties of the networks capability to transport data, such as bandwidth, latency, loss, and error rate are not always enough to provide a clear picture of how well the network can satisfy the users' expectations. In these situations, the relationship between the users' expectations and the quality provided by the network is of interest. Today multiple approaches to quantifying quality exists, such as Quality of Service (QoS), Quality of Experience (QoE) and Quality of Information (QoI). In this thesis, we explore how such quality measurements can be used as means to improve network performance. In the first part, we examine the Quality of Service in shared experiment networks, with a focus on the FEDERICA network. We present a method for statistical analysis of metadata, based on clustering. We show that, using this method, it is possible to improve the reliability of experiments in shared experiment networks. In the second part, we take a Quality of Experience viewpoint, while doing experimental development. The goal is to improve the mobility performance of an implementation of the Stream Control Transfer Protocol (SCTP) on mobile devices. We present optimisations of the SCTP implementation along with a mobility framework, which simplifies the introduction of mobility functionality in an existing SCTP application. We show that by using this combination, it is possible to perform seamless vertical handover between WiFi and 3G cellular networks. In the third part, we focus on Quality of Information in Delay Tolerant Wireless Sensor Networks (DT-WSN). We study how it is possible to improve the quality of the measurements obtained under conditions where bandwidth and storage capacity are limited, forcing the network to discard a significant fraction of the data. We introduce the SmartGap algorithm, a buffer management algorithm for DT-WSNs, and demonstrate that this algorithm can provide significantly improved QoI over a wide range of network configurations.
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| 7. |
- Söderman, Pehr, 1982-, et al.
(författare)
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Evaluating Buffer Management Algorithms for Delay Tolerant Wireless Sensor Networks
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- One of the challenges in Delay Tolerant Wireless Sensor Networks (DT-WSN), is to handle situations where the available buffer space is insufficient. This is the buffer management problem. In this work, we the buffer management problem, with focus on algorithms to decide what data to discard when buffers are full. We simulate a wide range of network configurations, using a full factorial experiment design. The simulations let us investigate both the relative performance of four buffer management algorithms and the effect of different factors on buffer management performance. The four algorithms we investigate are the two well-known algorithms FIFO and Random Discard, and two Quality of Information based algorithms: an exponential moving average forecasting-based algorithm and the SmartGap algorithm. Our results indicate that certain factors, including mobility model and routing algorithm, have larger influence on relative performance than factors such as link speed and lifetime of data. We also find that the SmartGap buffer management algorithm provides significantly better QoI compared to the alternative algorithms.
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| 8. |
- Söderman, Pehr, et al.
(författare)
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Handover in the Wild : The feasibility of vertical handover in commodity smartphones
- 2013
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Ingår i: Communications (ICC), 2013 IEEE International Conference on. - : IEEE conference proceedings. - 9781467331227 ; , s. 6401-6406
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Konferensbidrag (refereegranskat)abstract
- Today commodity mobile devices are equipped withmultiple wireless access technologies. To enable continuous connectivityit is vital that these terminals provide for vertical handover between different technologies. Particularly, they should provide a vertical handover that complies with the timeliness requirements of soft real-time applications. Considering aspects such as cost- and ease-of-deployment, application neutrality, and, not least, the emergence of transport protocols that support multi-homing such as mobile SCTP and multi-path TCP, we think it would be beneficial to handle vertical handover in thetransport layer of the mobile terminal. This paper demonstrates through several real-world experiments, the feasibility of using a lightweight vertical handover scheme in smart mobile terminals for live video streaming. The vertical handover criteria is basedon the received signal strength. Our experiments suggest that thescheme indeed provides for seamless vertical handover at walking speed – our target scenario. However, the experiments also suggest that the scheme gives significant reductions in handovertime, as compared to mobile SCTP without improvements, at higher speeds.
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| 9. |
- Söderman, Pehr, et al.
(författare)
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Mind the Gap : A Simple and Effective Buffer Management Algorithm for Delay Tolerant Wireless Sensor Networks
- 2014
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Ingår i: Tenth Swedish National Computer Networking Workshop (SNCNW 2014), Västerås, June 2-3, 2014.
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Limited memory capacity is one of the major constraints in delay tolerant wireless sensor networks. Efficient management of this limited resource is critical to the performance of the network. This paper proposes a novel buffer management algorithm, SmartGap, that contrary to most other algorithms does not consider the priority of packets in isolation. Instead, SmartGap is a so-called Quality of Information (QoI) focused buffer management algorithm. That is, in a wireless sensor network that continuously measures some parameter, the value of a single packet is governed by an estimation of its importance in the reconstruction of the sampled signal. Attractive features of SmartGap include a focus on QoI, low computational complexity and simplified reconstruction of the original signal. Simulations in which the performance of SmartGap is compared with the performance of several commonly used buffer management algorithms in wireless sensor networks are provided in the paper. The outcome of these simulations suggest that SmartGap frequently provides improved QoI compared the other simulated algorithms, and upholds fairness between competing data flows.
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| 10. |
- Söderman, Pehr, 1982-, et al.
(författare)
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Mind the SmartGap : A Buffer Management Algorithm For Delay Tolerant Wireless Sensor Networks
- 2015
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Ingår i: Wireless Sensor Networks. - Cham : Springer. - 9783319155821 - 9783319155814 ; , s. 104-119
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Konferensbidrag (refereegranskat)abstract
- Limited memory capacity is one of the major constraints in Delay Tolerant Wireless Sensor Networks. Efficient management of the memory is critical to the performance of the network. This paper proposes a novel buffer management algorithm, SmartGap, a Quality of Information (QoI) targeted buffer management algorithm. That is, in a wireless sensor network that continuously measures a parameter which changes over time, such as temperature, the value of a single packet is governed by an estimation of its contribution to the recreation of the original signal. Attractive features of SmartGap include a low computational complexity and a simplified reconstruction of the original signal. An analysis and simulations in which the performance of SmartGap is compared with the performance of several commonly used buffer management algorithms in wireless sensor networks are provided in the paper. The simulations suggest that SmartGap indeed provides significantly improved QoI compared the other evaluated algorithms.
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