Technical universities, especially in Europe, are facing an important challenge in attracting more diverse groups of students, and in keeping the students they attract motivated and engaged in the curriculum. We describe our experience with gamification, which we loosely define as a teaching technique that uses social gaming elements to deliver higher education. Over the past three years, we have applied gamification to undergraduate and graduate courses in a leading technical university in the Netherlands and in Europe. Ours is one of the first long-running attempts to show that gamification can be used to teach technically challenging courses. The two gamification-based courses, the first-year B.Sc. course Computer Organization and an M.Sc.-level course on the emerging technology of Cloud Computing, have been cumulatively followed by over 450 students and passed by over 75% of them, at the first attempt. We find that gamification is correlated with an increase in the percentage of passing students, and in the participation in voluntary activities and challenging assignments. Gamification seems to also foster interaction in the classroom and trigger students to pay more attention to the design of the course. We also observe very positive student assessments and volunteered testimonials, and a Teacher of the Year award.

Abstract-The main purpose of many current peer-to-peer (P2P) networks is off-line file sharing. However, a potentially very promising use of such networks is to share video streams (e.g., TV programs) in real time. In order to do so, the peers in a P2P network who are interested in the same video stream may employ Application Level Multicasting (ALM). In existing P2P networks, peers may exhibit behavior which is problematic for ALM: they are not always willing to donate resources (free-riding), and they may arrive and depart at a high rate (churn). In this paper we propose the Orchard algorithm for creating and maintaining ALM trees in P2P networks, which deals with both these problems. By employing a technique called Multiple Description Coding, we split a video stream into several substreams. Orchard creates a dynamic spanning tree for each of these substreams in such a way that in the resulting forest, no peer has to forward more substreams than it receives. Based on an analysis of the expected performance of Orchard and on experiments in a real system, we find that Orchard is capable of maintaining a multicast forest, even when peers join and leave the forest at a high rate.

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Lightning, the prevailing solution to Bitcoin's scalability issue, uses onion routing to hide senders and recipients of payments. Yet, the path between the sender and the recipient along which payments are routed is selected such that it is short, cost efficient, and fast. The low degree of randomness in the path selection entails that anonymity sets are small. However, quantifying the anonymity provided by Lightning is challenging due to the existence of multiple implementations that differ with regard to the path selection algorithm and exist in parallel within the network. In this paper, we propose a general method allowing a local internal attacker to determine sender and recipient anonymity sets. Based on an in-depth code review of three Lightning implementations, we analyze how an adversary can predict the sender and the recipient of a multi-hop transaction. Our simulations indicate that only one adversarial node on a payment path uniquely identifies at least one of sender and recipient for around 70% of the transactions observed by the adversary. Moreover, multiple colluding attackers can almost always identify sender and receiver uniquely. CCS CONCEPTS• Security and privacy → Distributed systems security; • Networks → Network simulations.

The nature of wireless multihop ad-hoc networks makes it a challenge to offer connections of an assured quality. In order to improve the performance of such networks, multipath routing in combination with Multiple Description Coding (MDC) has been proposed. By splitting up streams of multimedia traffic into several substreams (called descriptions), by sending these substreams along different paths from the source to the destination, and by reassembling them again at the destination, the quality of the received stream may be improved as compared to the single-description, single-path case. In this paper we present a simulation study of the combination of MDC and multipath routing from a network perspective with a realistic medium access control protocol (IEEE 802.11) and a widely used routing protocol (Dynamic Source Routing with our own multipath extensions). Our simulations show that for most of the cases considered, the combination of multipath routing and MDC does not perform better than single-path routing and a single description in IEEE 802.11-based networks.