21,386 research outputs found
Cooperative Caching for Multimedia Streaming in Overlay Networks
Traditional data caching, such as web caching, only focuses on how to boost the hit rate of requested objects in caches, and therefore, how to reduce the initial delay for object retrieval. However, for multimedia objects, not only reducing the delay of object retrieval, but also provisioning reasonably stable network bandwidth to clients, while the fetching of the cached objects goes on, is important as well. In this paper, we propose our cooperative caching scheme for a multimedia delivery scenario, supporting a large number of peers over peer-to-peer overlay networks. In order to facilitate multimedia streaming and downloading service from servers, our caching scheme (1) determines the appropriate availability of cached stream segments in a cache community, (2) determines the appropriate peer for cache replacement, and (3) performs bandwidth-aware and availability-aware cache replacement. By doing so, it achieves (1) small delay of stream retrieval, (2) stable bandwidth provisioning during retrieval session, and (3) load balancing of clients' requests among peers
Predicting the Impact of Measures Against P2P Networks on the Transient Behaviors
The paper has two objectives. The first is to study rigorously the transient
behavior of some P2P networks whenever information is replicated and
disseminated according to epidemic-like dynamics. The second is to use the
insight gained from the previous analysis in order to predict how efficient are
measures taken against peer-to-peer (P2P) networks. We first introduce a
stochastic model which extends a classical epidemic model and characterize the
P2P swarm behavior in presence of free riding peers. We then study a second
model in which a peer initiates a contact with another peer chosen randomly. In
both cases the network is shown to exhibit a phase transition: a small change
in the parameters causes a large change in the behavior of the network. We
show, in particular, how the phase transition affects measures that content
provider networks may take against P2P networks that distribute non-authorized
music or books, and what is the efficiency of counter-measures.Comment: IEEE Infocom (2011
Academic Performance and Behavioral Patterns
Identifying the factors that influence academic performance is an essential
part of educational research. Previous studies have documented the importance
of personality traits, class attendance, and social network structure. Because
most of these analyses were based on a single behavioral aspect and/or small
sample sizes, there is currently no quantification of the interplay of these
factors. Here, we study the academic performance among a cohort of 538
undergraduate students forming a single, densely connected social network. Our
work is based on data collected using smartphones, which the students used as
their primary phones for two years. The availability of multi-channel data from
a single population allows us to directly compare the explanatory power of
individual and social characteristics. We find that the most informative
indicators of performance are based on social ties and that network indicators
result in better model performance than individual characteristics (including
both personality and class attendance). We confirm earlier findings that class
attendance is the most important predictor among individual characteristics.
Finally, our results suggest the presence of strong homophily and/or peer
effects among university students
The power of indirect social ties
While direct social ties have been intensely studied in the context of
computer-mediated social networks, indirect ties (e.g., friends of friends)
have seen little attention. Yet in real life, we often rely on friends of our
friends for recommendations (of good doctors, good schools, or good
babysitters), for introduction to a new job opportunity, and for many other
occasional needs. In this work we attempt to 1) quantify the strength of
indirect social ties, 2) validate it, and 3) empirically demonstrate its
usefulness for distributed applications on two examples. We quantify social
strength of indirect ties using a(ny) measure of the strength of the direct
ties that connect two people and the intuition provided by the sociology
literature. We validate the proposed metric experimentally by comparing
correlations with other direct social tie evaluators. We show via data-driven
experiments that the proposed metric for social strength can be used
successfully for social applications. Specifically, we show that it alleviates
known problems in friend-to-friend storage systems by addressing two previously
documented shortcomings: reduced set of storage candidates and data
availability correlations. We also show that it can be used for predicting the
effects of a social diffusion with an accuracy of up to 93.5%.Comment: Technical Repor
- …