بررسی شبکه های تحویل محتوا
Abstract
1- Introduction
2- Background
3- Introduction to Taxonomy for Surveying PA-CDNs
4- Heterogeneity Challenges
5- Technical Challenges
6- Commercial Feasibility Challenges
7- Commercial Peer-Assisted CDNs
8- Conclusion and Vision on Direction of Research in the Future
References
Abstract
Peer-assisted content delivery networks have recently emerged as an economically viable alternative to traditional content delivery approaches: the feasibility studies conducted for several large content providers suggested a remarkable potential of peer-assisted content delivery networks to reduce the burden of user requests on content delivery servers and several commercial peer-assisted deployments have been recently introduced. Yet there are many technical and commercial challenges which question the future of peer-assisted solutions in industrial settings. This includes among others unreliability of peer-to-peer networks, the lack of incentives for peers’ participation, and copyright issues. In this paper, we carefully review and systematize this ongoing debate around the future of peer-assisted networks and propose a novel taxonomy to characterize the research and industrial efforts in the area. To this end, we conduct a comprehensive survey of the last decade in the peer-assisted content delivery research and devise a novel taxonomy to characterize the identified challenges and the respective proposed solutions in the literature. Our survey includes a thorough review of the three very large scale feasibility studies conducted for BBC iPlayer, MSN Video and Conviva, five large commercial peer-assisted CDNs - Kankan, LiveSky, Akamai NetSession, Spotify, Tudou - and a vast scope of technical papers. We focus both on technical challenges in deploying peer-assisted solutions and also on non-technical challenges caused due to heterogeneity in user access patterns and distribution of resources among users as well as commercial feasibility related challenges attributed to the necessity of accounting for the interests and incentives of Internet Service Providers, End-Users and Content Providers. The results of our study suggest that many of technical challenges for implementing peer-assisted content delivery networks on an industrial scale have been already addressed in the literature, whereas a problem of finding economically viable solutions to incentivize participation in peer-assisted schemes remains an open issue to a large extent. Furthermore, the emerging Internet of Things (IoT) is expected to enable expansion of conventional CDNs to a broader network of connected devices through machine to machine communication.
Introduction
Recent years have witnessed tremendous growth in video traffic on the Internet as a result of higher broad-band data rates, proliferation in smart handheld devices [24] [95] and affordable unlimited data plans offered by Internet Service Providers [51]. An estimated one-third of all online activities on the Internet is spent watching video according to the recent report [100]. Netflix alone is reportedly streaming over 1 billion hours of video each month which is equivalent to almost 7,200,000 Terabytes of video traffic [37], and this figure is rising constantly. The skyrocketing demand for serving video traffic have questioned the effectiveness of the traditional solution of employing special purpose Content Delivery Networks (CDNs), to serve such content. Invented at the turn of the century [96], CDNs now constitute the backbone for serving content [25] [80]. Yet, as several recent studies suggest [60] [109], even CDNs are being stressed by the demands placed by video users during peak hours. Thus, there is a prodigious interest in searching for alternative content delivery methods that mitigate the stress on CDNs without losing its core objectives. As a first available solution, CDN operators could (and have) deployed more servers across the globe, in order to maintain a balance among user requests and system services. But this requires major investments both in infrastructure and administrative domain [67]. Recently, an alternative approach has been suggested – to employ peer-to-peer technology (P2P) to assist CDN servers and thereby solve scalability and cost issues of traditional CDNs.