| 1. |
- Bastani, Saeed, et al.
(författare)
-
A social node model for realising information dissemination strategies in delay tolerant networks
- 2012
-
Ingår i: Proceedings of the 15th ACM international conference on Modeling, analysis and simulation of wireless and mobile systems. - New york : ACM Press. ; , s. 79-88, s. 78-79
-
Konferensbidrag (refereegranskat)abstract
- In Delay Tolerant Networks (DTNs) as an emerging content dissemination platform, mobile nodes opportunistically exchange content as they meet, with the intent of disseminating content among nodes that share common interests. During a meeting, nodes can exchange both content of direct interest to themselves as well as content that is of interest to a larger set of nodes that may be encountered in the future. The utility of DTN is governed by the content exchange opportunity (the amount of content that can be exchanged during a meeting) as well as the selection of content to be exchanged in order to maximise the interest nodes will have in information they are exposed to. Considering that there is a cost associated with the content exchange (e.g. battery usage, buffer occupancy or consumed transmission opportunity) the aim for nodes participating in content dissemination should be to maximise their payoff. In this paper, we contribute a generic framework for describing the characteristics of content exchange among participating nodes in a network. We incorporate a distributed information popularity measurement and the pairwise interaction of nodes modelled as a bargaining problem. The outcome of this process is the fair split up of dwelling time as a network resource and the selection of which content objects to exchange in order to maximise the nodes’ payoff. The framework is generally intended to be used as a capstone for investigation of content dissemination properties and various content exchange strategies in a DTN, a topic addressed in this paper and experiments conducted to validate the function and correctness of the proposed framework.
|
|
| 2. |
|
|
| 3. |
|
|
| 4. |
|
|
| 5. |
- 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.
|
|
| 6. |
- 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.
|
|
| 7. |
- Bjurefors, Fredrik, et al.
(författare)
-
Resilience and Opportunistic Forwarding : Beyond Average Value Analysis
- 2014
-
Ingår i: Computer Communications. - : Elsevier BV. - 0140-3664 .- 1873-703X. ; 48:SI, s. 111-120
-
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.
|
|
| 8. |
- Bjurefors, Fredrik, et al.
(författare)
-
Resilience and Opportunistic Forwarding: Beyond Average Value Analysis
- 2013
-
Ingår i: CHANTS '13 Proceedings of the 8th ACM MobiCom workshop on Challenged networks.
-
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.
|
|
| 9. |
- Cambazoglu, Volkan, et al.
(författare)
-
The impact of trace and adversary models on location privacy provided by K-anonymity
- 2012
-
Ingår i: Proc. 1st Workshop on Measurement, Privacy, and Mobility. - New York : ACM Press. - 9781450311632
-
Konferensbidrag (refereegranskat)abstract
- Privacy preserving mechanisms help users of location-based services to balance their location privacy while still getting useful results from the service. The provided location privacy depends on the users' behavior and an adversary's knowledge used to locate the users. The aim of this paper is to investigate how users' mobility patterns and adversaries' knowledge affect the location privacy of users querying a location-based service. We consider three mobility trace models in order to generate user traces that cross each other, are parallel to each other and form a circular shape. Furthermore, we consider four adversary models, which are distinguished according to their level of knowledge of users. We simulate the trace and the adversary models by using Distortion-based Metric and K-anonymity. The results show that the location privacy provided by K-anonymity decreases, as users are located closer to each other in the trace models. The impact of the adversary on location privacy is reduced as more users are cloaked together.
|
|
| 10. |
- Cambazoglu, Volkan, et al.
(författare)
-
Towards adaptive zero-knowledge protocols : A case study with Fiat–Shamir identification protocol
- 2013
-
Ingår i: Proc. 9th Swedish National Computer Networking Workshop. ; , s. 67-70
-
Konferensbidrag (refereegranskat)abstract
- Interactive zero-knowledge protocols are used as identification protocols. The protocols are executed in rounds, with security being increased with every round. This allows for a trade-off between security and performance to adapt the protocol to the requirements of the scenario. We experimentally investigate the Fiat–Shamir identification protocol on machines and networks with different performance characteristics. We find that the delay of the protocol highly depends on network latency and upload bandwidth. Computation time becomes more visible, when the protocol transmits little amount of data via a low latency network. We also experience that the impact of the sizes of the variables on the delay of the protocol is less than the number of rounds', which are interior factors in the protocol.
|
|
