Recent Developments in Content Delivery Network: A Survey

Along with the continuing evolution of the Internet and its applications, Content Delivery Networks (CDNs) have become a hot topic with both opportunities and challenges. CDNs were mainly proposed to solve content availability and download time issues by delivering content through edge cache servers deployed around the world. In our previous work, we presented a novel CDN architecture based on a Fog computing environment as a promising solution for real-time applications. In such architecture, we proposed to use a name-based routing protocol following the Information Centric Networking (ICN) approach, with a popularity-based caching strategy to guarantee overall delivery performance. To validate our design principle, we have implemented the proposed Fog-based CDN architecture with its major protocol components and evaluated its performance, as shown through this article. On the one hand, we have extended the Optimized Link-State Routing (OLSR) protocol to be content aware (CA-OLSR), i.e., so that it uses content names as routing labels. Then, we have integrated CA-OLSR with the popularity-based caching strategy, which caches only the most popular content (MPC). On the other hand, we have considered two similar architectures for conducting performance comparative studies. The first is pure Fog-based CDN implemented by the original OLSR (IP-based routing) protocol along with the default caching strategy. The second is a classical cloud-based CDN implemented by the original OLSR. Through extensive simulation experiments, we have shown that our Fog-based CDN architecture outperforms the other compared architectures. CA-OLSR achieves the highest packet delivery ratio (PDR) and the lowest delay for all simulated numbers of connected users. Furthermore, the MPC caching strategy shows higher cache hit rates with fewer numbers of caching operations compared to the existing default caching strategy, which caches all the pass-by content.

Internet delivery infrastructures are traditionally optimized for low-latency traffic, such as the Web traffic. However, in recent years we are witnessing a massive growth of throughput-oriented applications, such as video streaming. These applications introduce new tradeoffs and design choices for content delivery networks (CDNs). In this paper, we focus on understanding two key design choices: (1) What is the impact of the number of CDN's peering points and server locations on its aggregate throughput and operating costs? (2) How much can ISP-CDNs benefit from using path selection to maximize its aggregate throughput compared to other CDNs who only have control at the edge? Answering these questions is challenging because content distribution involves a complex ecosystem consisting of many parties (clients, CDNs, ISPs) and depends on various settings which differ across places and over time. We introduce a simple model to illustrate and quantify the essential tradeoffs in CDN designs. Using extensive analysis over a variety of network topologies (with varying numbers of CDN peering points and server locations), operating cost models, and client video streaming traces, we observe that: (1) Doubling the number of peering points roughly doubles the aggregate throughput over a wide range of values and network topologies. In contrast, optimal path selection improves the CDN aggregate throughput by less than 70\%, and in many cases by as little as a few percents. (2) Keeping the number of peering points constant, but reducing the number of location (data centers) at which the CDN is deployed can significantly reduce operating costs.

With the increasing popularity of the Internet video streaming services (e.g. YouTube and Netflix), content delivery networks (CDNs) are heavily used to stream video contents to users, and consume more and more power and bandwidths in recent years. In this paper, we investigate the problem of saving a video streaming CDN’s operating expense, including both its energy cost and the traffic cost. From our measurement study on the CDN infrastructure of Youku, which is the largest video site in China, we find that there exists an inherent conflict between improving a video streaming CDN’s energy efficiency for power saving, and maintaining the CDN’s ISP-friendly server selection policy. To address this problem, we propose a cost-aware capacity provisioning algorithm, which dynamically plans the service capacities of a CDN’s server clusters in numerous ISPs, and optimizes its overall operating cost regarding both the energy consumptions and the cross-ISP traffics. By using the workload derived from real-world measurement and applying actual power and bandwidth price parameters, we show with experiments that our approach can significantly reduce a video streaming CDN’s overall operating cost, and avoid frequent server switches effectively. To our best knowledge, this work is the first one that identifies and resolves the inherent conflict between a CDN’s energy efficiency and its ISP-friendly policy.

Broadband network technologies have improved the bandwidth of the edge of the Internet but its core is still a bottleneck for large file transfers. Content Delivery Networks (CDNs), built at the edge of the Internet, are able to reduce the workload of network backbones but their scalability and network reach is often limited, especially in case of QoS-bound delivery services. By using the emerging CDN internetworking, a CDN can dynamically exploit resources of other cooperating CDNs to face peak loads and temporary malfunctions without violating QoS levels negotiated with content providers. This paper proposes an architectural schema and an algorithm to minimize transfer time of large files taking into account the SLA constraints agreed between the CDN in charge of content delivery and the content provider, while respecting the maximum budget that the CDN can pay to peer CDNs to ensure its revenue. The experimental analysis confirms the benefits of applying the proposed algorithm in CDN internetworking to enforce SLA guarantees of CDN services.

Content Distribution Networks (CDN) appeared a decade ago as a method for reducing latencies, improving performance experienced by Internet users, and limiting the effect of flash-crowds, so as balance load in servers. Content Distribution has evolved in different ways (e.g. cloud computing structures and video streaming distribution infrastructures). The solution proposed in early CDN was the location of several controlled caching servers close to clients, organized and managed by a central control system. Many companies deployed their own CDN infrastructure– and so demonstrating the resulting effectiveness. However, the business model of these networks has evolved from the distribution of static web objects to video streaming. Many aspects of deployment and implementation remain proprietary, evidencing the lack of a general CDN model, although the main design concepts are widely known. In this work, the authors represent the structure of a CDN and the performance of some of its parameters, using queuing theory, simplifying the redirection schema and studying the elements that could determine the improvement in performance. The main contribution of the work is a general expression for a CDN environment and the relationship between different variables like caching hit ratios, network latency, number of surrogates, and server capacity; this proves that the use of CDN outperform the typical client/server architecture.

Today’s content delivery networks (CDNs) use large sets of globally distributed servers, advanced routing techniques, and dynamic server selection to provide users with low delay, reliable access to Web, and streaming content. These strategies allow CDNs to extend their reach and performance into large numbers of networks around the globe. However, nearly 20% of Internet users reside in China, where local regulations and network policies make it challenging for global CDNs to serve foreign content from servers in China and limit the effectiveness of their traditional strategies for low-latency content delivery. Recently, a number of China-specific CDNs have partnered with global CDNs to provide service in the country. However, little is known about how CDNs in China are implemented, nor their impact on performance. In this paper, we are the first to investigate the impact of China’s unique policy and networking environment on CDN implementations and deployments. We find that deployments inside China exhibit different client-mapping behavior than global ones, namely, through static server selection for clients given a customer site, and through region-specific clients partitioning and mapping rather than using live network information. We also show that ignoring these properties can significantly impact server selection quality. Our results can be useful for optimization of CDNs in China.

Content-based services are gaining tremendous popularity recently with the proliferation of a wide range of contents. Traditionally, hosting and distribution of these ubiquitous contents are accomplished using content distribution networks (CDNs). CDNs distribute contents in multiple hosting locations for load balancing, availability, and easy access. However, scalability and cost of CDNs are becoming major challenges due to the increase of content-based services. To combat these problems, peer-to-peer (P2P) systems are being considered in combination with CDN to complement each other in a hybrid system. Research works and practical deployments have shown that hybrid CDN–P2P systems are feasible, inexpensive, and scalable. However, P2P-based content distribution systems are known to consume more system-wide energy than traditional CDNs. Hence, energy efficiency of such a hybrid system must be taken into consideration before wider implementation. In our study, we analyze the energy consumption of a hybrid CDN–P2P system in an IP-over-WDM network and show that, due to its hybrid nature, it is possible to exploit the P2P system to significantly reduce load on the CDN and at the same time constrain—and in some cases reduce—energy consumption. We propose energy-aware as well as energy-unaware content source selection mechanisms to help service providers achieve this win–win situation. Using simulations, we show that, for example, in case of a moderately popular content the server load can be reduced by 30%–40% while reducing the system-wide energy consumption by 10%–20% when compared with a traditional CDN.

Over the last years, the content delivery network (CDN) market has been witnessing globally an increase in the development of cloud-based CDNs, as they constitute a viable and cost-effective alternative to traditional commercial CDNs. Towards that direction, Social-Aware Virtual Network Embedding (SAViNE) for wireless content delivery within the OpenLab project aims at establishing, assessing, and prototyping a novel framework for deploying a CDN over the wireless cloud. Specifically, the goal of SAViNE is to provide experimental validation of the efficiency of social network analysis (SNA) - inspired surrogate server placement strategies, devised for fostering content delivery. The proposed framework has been integrated with the OpenLab experimental facilities, providing a run-time environment for CDN deployment, operation, and performance evaluation over the wireless environment. The framework’s feasibility and scalability is experimentally validated. The study is complemented with repeatability evaluation of experimental measurements, related to the resulting CDN’s operational efficiency.

Recently, large-volume contents distributed by a content delivery network (CDN) on the Internet increase the load of content delivery servers and networks, which may degrade the quality of service. To overcome this problem, some mirror servers providing the same content are located on a network, and a request is navigated to one of the mirror servers. It is important to locate the mirror servers on the appropriate place in a network, as it affects the performance of the CDN. In this paper, we address the server location problem, which determines the location of the mirror servers satisfying the following two constraints: the number of the paths to the servers in a link is small, and the number of the nodes whose nearest mirror server is the same is small. The former constraint corresponds to the alleviation of the network load, and the latter constraint corresponds to the alleviation of the server load. First, we prove that this new server location problem is NP-complete. Next, we present a heuristic algorithm and evaluate it by applying to some actual network topologies. The results show that the algorithm can determine a good server location.

On the energy consumption computation in Content Delivery Networks

Content Delivery Networks (CDNs) have emerged as a dominant mechanism to deliver content over the Internet. Despite their importance, to our best knowledge, large-scale analysis of CDN cache performance is lacking in prior literature. A CDN serves many content publishers simultaneously and thus has unique workload characteristics; it typically deals with extremely large content volume and high content diversity from multiple content publishers. CDNs also have unique performance metrics; other than hit ratio, CDNs also need to minimize network and disk load on cache servers. In this paper, we present measurement and analysis of caching workload at a large commercial CDN. Using detailed logs from four geographically distributed CDN cache servers, we analyze over 600 million content requests accounting for more than 1.3 petabytes worth of traffic. We analyze CDN workload from a wide range of perspectives, including request composition, size, popularity, and temporal dynamics. Using real-world logs, we also evaluate cache replacement algorithms, including two enhancements designed based on our CDN workload analysis: N-hit and content-aware caching. The results show that these enhancements achieve substantial performance gains in terms of cache hit ratio, disk load, and origin traffic volume.

The Internet architecture, based on end-to-end connections, had difficulties to efficiently deliver the always increasing number of contents. Content Delivery Networks (CDN) have been deployed to improve the delivery. Recent research works propose a new networking architecture, much more adapted to the current Internet usage (end-users just care about the contents they want and not about the endpoints that provide them). The Content-Centric Networking (CCN) aims at replacing the IP paradigm. CCN has been investigated by the research community for few years, and some demonstrators have proved its feasibility. However, less works have addressed the CDN use-case so far. In this paper, we show that the current CCN design, which does not allow negative reply, is not suitable for interconnection with the CDN service. We then propose the use of two new tables in the CCN nodes that are interconnected to the CDN servers, in order to detect possible misses in the CDN servers and subsequently forward the requests for missing contents toward the original servers instead of the CDN surrogates. The evaluations we have performed highlight that the integration of both new tables does not incur an increase of the memory requirement and thus a cost in the node. The proposed solution is thus a viable solution to make CCN network work in close cooperation with CDN networks, each one keeping its specific business models and functions: transport for CCN, storage for CDN.

The contribution of this paper is a novel peer-to-peer (P2P) middleware solution for extending the reach, scale and functionality of content delivery networks (CDNs). The research problem of extending legacy CDN functionality towards user-to-user content networking and enhancing the CDN quality attributes of reach and scale are addressed. The proposed P2P middleware solution extends the reach and scale of CDNs to cover the digital home environment via specialized virtual multimedia home gateways and extends the legacy CDN functionality by enabling user-generated content sharing via the P2P extended CDN infrastructure.

Internet-scale services like YouTube are provisioned by large Content Delivery Networks (CDNs), which push content as close as possible to the end-users to improve their Quality of Experience (QoE) and to pursue their own optimization goals. Adopting space and time variant traffic delivery policies, CDNs serve users' requests from multiple servers/caches at different physical locations and different times. CDNs traffic distribution policies can have a relevant impact on the traffic routed through the Internet Service Provider (ISP), as well as unexpected negative effects on the end-user QoE. In the event of poor QoE due to faulty CDN server selection, a major problem for the ISP is to avoid being blamed by its customers. In this paper we show a real case study in which Google CDN server selection policies negatively impact the QoE of the customers of a major European ISP watching YouTube. We argue that it is extremely important for the ISP to rapidly and automatically detect such events to increase its visibility on the overall operation of the network, as well as to promptly answer possible customer complaints. We therefore present an Anomaly Detection (AD) system for detecting unexpected cache-selection changes in the traffic delivered by CDNs. The proposed algorithm improves over traditional AD approaches by analyzing the complete probability distribution of the monitored features, as well as by self-adapting its functioning to dynamic environments, providing better detection capabilities.

Building a peer-to-peer content distribution network with high performance, scalability and robustness