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- Bjurefors, Fredrik, et al.
(författare)
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A Testbed for Evaluating Delay Tolerant Network Protocol Implementations
- 2008
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Ingår i: Proceedings 5th Swedish National Computer Networking Workshop.
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Konferensbidrag (refereegranskat)abstract
- We present our delay tolerant network testbed and methodology, for testing opportunistic networking protocols and applications, without having to modify the software. To support multiple operating systems running on a single physical computer, virtual machines are at the core of the testbed. Scripted communication opportunities are used to model connectivity in the network. A set of benchmark connectivity models are available to perform evaluations with predictable protocol behavior; dynamic topologies from real-world traces are also supported. Using this environment, we evaluate the testbed with a delay tolerant application and compare the outcome to that of a real-world experiment. Finally, we discuss our results and the limitations of the testbed.
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| 5. |
- Bjurefors, Fredrik
(författare)
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Measurements in opportunistic networks
- 2012
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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.
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| 6. |
- Bjurefors, Fredrik, 1978-
(författare)
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Opportunistic Networking : Congestion, Transfer Ordering and Resilience
- 2014
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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.
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| 7. |
- Bjurefors, Fredrik, et al.
(författare)
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Performance of Pastry in a Heterogeneous System
- 2004
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Ingår i: Proceedings of the Fourth IEEE International Conference on Peer-to-Peer computing.
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Konferensbidrag (refereegranskat)abstract
- In this paper, we study how Pastry performs in a heterogeneous network environment of varying size. The large traffic overhead for management traffic makes the overlay nonfunctional if it grows too large. This can be circumvented by partitioning the routing tables at the cost of increased path lengths and response times.
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| 8. |
- Bjurefors, Fredrik, et al.
(författare)
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Resilience and Opportunistic Forwarding : Beyond Average Value Analysis
- 2014
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Ingår i: Computer Communications. - : Elsevier BV. - 0140-3664 .- 1873-703X. ; 48:SI, s. 111-120
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Tidskriftsartikel (refereegranskat)abstract
- Opportunistic networks are systems with highly distributed operation, relying on the altruistic cooperation of highly heterogeneous, and not always software and hardware-compatible, user nodes. Moreover, the absence of central coordination and control makes them vulnerable to malicious attacks. In this paper, we study the resilience of popular forwarding protocols to a representative set of challenges to their normal operation. These include jamming locally disturbing message transfer between nodes, hardware/software failures and incompatibility among nodes rendering contact opportunities useless, and free-riding phenomena. We first formulate and promote the metric envelope concept as a tool for assessing the resilience of opportunistic forwarding schemes. Metric envelopes depart from the standard practice of average value analysis and explicitly account for the differentiated challenge impact due to node heterogeneity (device capabilities, mobility) and attackers’ intelligence. We then propose heuristics to generate worst- and best-case challenge realization scenarios and approximate the lower and upper bounds of the metric envelopes. Finally, we demonstrate the methodology in assessing the resilience of three popular forwarding protocols in the presence of the three challenges, and under a comprehensive range of mobility patterns. The metric envelope approach provides better insights into the level of protection path diversity and message replication provide against different challenges, and enables more informed choices in opportunistic forwarding when network resilience becomes important.
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| 9. |
- Bjurefors, Fredrik, et al.
(författare)
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Resilience and Opportunistic Forwarding: Beyond Average Value Analysis
- 2013
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Ingår i: CHANTS '13 Proceedings of the 8th ACM MobiCom workshop on Challenged networks.
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Konferensbidrag (refereegranskat)abstract
- Opportunistic networks are systems with highly distributed operation, relying on the altruistic cooperation of heterogeneous, and not always software- and hardware-compatible user nodes. Moreover, the absence of central control makes them vulnerable to malicious attacks. In this paper, we take a fresh look at the resilience of opportunistic forwarding to these challenges. In particular, we introduce and promote the use of metric envelopes as a resilience assessment tool. Metric envelopes depart from the standard practice of average value analysis and explicitly account for the differentiated impact that a challenge may have on the forwarding performance due to node heterogeneity (device capabilities, mobility) and attackers’ intelligence. The use of metric envelopes is demonstrated in the case of three challenges: jamming, hardware/software failures and incompatibilities, and free-riding phenomena. For each challenge, we first devise heuristics to generate worst- and best-case realization scenarios that can approximate the metric envelopes. Then we derive the envelopes of common performance metrics for three popular forwarding protocols under a comprehensive range of mobility patterns. The metric envelope approach enables more informed choices in opportunistic forwarding whenever network resilience considerations become important.
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