Abstract-Recent advances in wireless communications and mobile networking have dramatically increased the popularity of multimedia services for mobile users, with wireless video streaming at their fingertips. To facilitate efficient acquisition of video content, proxy caching has been widely used by wireless service providers (WSPs), which typically deploy cache servers at mobile switching centers (MSCs). However, capacity provisioning of cache servers is challenging, given the dynamic user demands and the limited cache server resources. With increased densities of wireless service deployment, it is increasingly common that mobile users are covered by more than one WSP within an area. This brings opportunities of a collaborative caching paradigm among the cache servers deployed at different MSCs. In this paper, we explore the benefits of collaborative caching in wireless streaming services, addressing both challenges of incentives and truthfulness of selfish WSPs. We propose a collaborative mechanism that maximizes the social welfare in the context of VickreyClarke-Groves (VCG) auctions, in which cache servers cooperate in the trading of their resources in a self-enforcing manner. Experimental results demonstrate that superior performance can be achieved with respect to the quality of video streaming.

A new critical angle refractometer (CAR) for high accuracy refractive index measurement of liquid has been developed. The instrument improves the accuracy by two reflections in an elongated parallelogram prism, and acquires the angular reflectivity without any angle scanning parts through introduction of a point source with a divergent beam and a charge coupled device. In addition, it employs a simple and robust measurement method that gets the critical angle by differentiating the angular reflectivity. Through investigating absorbing media with absorption index κ (the imaginary part of refractive index) from 0 to 10(-2.1), the theoretical calculation shows that the proposed two-reflection CAR would outperform the traditional one-reflection CAR on lowering the principal error from the differentiation method and improving the ability of getting the critical angle. By testing two typical liquids-salt-water solution and milk, the preliminary experiment indicates that this two-reflection divergent differentiating critical angle refractometer is feasible and of high accuracy.

Collaborative ISP caching has been advocated to reduce the otherwise significant amount of costly inter-ISP traffic generated by peer-to-peer (P2P) applications. The fundamental design criteria employed by ISP cache servers are, however, not well understood, with respect to dynamic P2P traffic patterns, ISP peering policies and cache server capacity constraints. In particular, there is a lack of investigations on the design and analysis of resource allocation mechanisms with awareness of inter-ISP traffic and ISP policies in the context of collaborative ISP caching-which is our focus in this study. In this paper, by characterizing practical inter-ISP traffic patterns, we have developed a theoretical framework to analyze representative cache resource allocation schemes within the design space of collaborative caching, with a particular focus on minimizing costly inter-ISP traffic. The optimization framework incorporates both locality-aware and locality-unaware peer selection strategies and ISP peering agreements, in order to examine their respective effects on the design of ISP collaborative caching mechanisms. Our analyses not only help us understand the traffic characteristics of existing P2P systems in light of realistic elements, but also offer fundamental insights into designing collaborative ISP caching mechanisms.