Examples of Cloud CDN services

Economies of scale, in terms of cost effectiveness and performance for both providers and end-users, may be achieved with the utilization of pre-existing ‘Storage Cloud’ infrastructure, instead of investing large amounts of money in their own content delivery platform or utilizing one of the incumbent operators like Akamai.

Such examples of services already available are: CloudFare [78], CloudLayer [79], Cloud Files [80] , HP Cloud CDN [81] .

CloudFlare [78] provides a Cloud based CDN that currently comprises of 23 data centers around the world. The content delivery overlay network is designed to reduce hops and minimize network latency. On average, a request is fewer than 10 hops and takes less than 30ms. CloudFlare does not bill customers for bandwidth usage. The customer pays a flat rate per plan, which is based on functionality. The

more expensive plans provide Service Level Agreements for high availability, dedicated support and customization.

CloudLayer® Content Delivery Network (CDN) currently distributes content through a network with 24 nodes throughout the cloud, in an effort to put content geographically closer to end-users of small to middle range enterprises CloudLayer CDN includes robust tools for digital rights management and content monetization.

Cloud Files, powered by OpenStack®, provides an integrated solution of online storage for files and media and content delivery through Akamai's CDN. Cloud Files uses 213 of Akamai's edge locations in an effort to satisfy demand in a worldwide level, while keeping costs as low as possible. Cloud Files is in essence an alliance between a Cloud provider and a CDN provider in an effort to minimize costs while achieving low network latency. The drawback of this solution, compared to CloudFare and CloudLayer is that customers are charged for both storage and outgoing bandwidth.

HP Cloud CDN is another integrated solution of online storage for files and media and content delivery. It provides static data delivery from HP Cloud Object Storage to users around the world by caching user data across the HP and Akamai global networks. As in the case of Cloud Files, customers are charged for both storage and outgoing bandwidth.

It is obvious that solutions such as CloudFlare and CloudLayer provide a

"poor man's CDN" solution, since they lack major operating expenses for the maintenance of a global infrastructure of caches, but do not provide control of the service from end to end, as the transfer of content is done through third party networks.

On the other hand, solutions such as HP Cloud CDN and Cloud Files provides an integrated solution of online storage for files and media and content delivery through Akamai's CDN. They are more expensive solutions, but provide control of the service from end to end.

5. Conclusions

Caching services provide the basic operation of copying popular content from a source server to a local server, thereby reducing the distance between the user and the requested content and thus accelerating the process of delivery. Moreover, caching reduces bandwidth consumption, since the requested content is delivered locally. On the other hand, content delivery networks are distributed systems of interconnected servers that form an overlay network. In addition, content delivery systems add another layer of functionality, offering advanced services such as streaming media distribution, data tracking, content personalization and localization, content synchronization with the source server, load balancing, etc.

Caching services are typically passive, that is a caching server downloads updated content from the source server upon user request, or when it has been modified since the last save. Alternatively, active caching systems make assumptions about the life expectancy of content according to frequency of changes or other factors. On their part, content delivery systems proactively forward content to edge servers at regular predesigned intervals, thus ensuring the validity of the content.

Usually, the content owner provides the content distributor with a list of updated objects to be copied and forwarded to the edge servers.

Caching servers are typically installed at the premises of ISPs, because end users are directly connected to ISPs. A content provider, however, may not come in contact with all ISPs to meet the wide range of customers. The role of the content distribution service is to act as middleware between the ISP and the content provider. So in essence it is a mechanism for the collection and subsequent distribution not only of the content but also of the cash flow. The content distributor collects fees from content providers and pays a fee to backbone network operators for data transfer and to ISPs for hosting their machines (if not free of charge in exchange for the use of stored content).

Each of the CDN business models analyzed earlier in this model has its pros and cons. The "traditional" content-centric CDN operating model has positive elements, such as peering agreements with ISP for free installation of caches, but also weaknesses. The main one is the major operating expenses for the maintenance of a

global infrastructure of caches, and also the lack of control of the service from end to end, as the transfer of content is done through third party networks. For this the companies adopting this model must develop strong alliances and cooperation agreements with suppliers of network services, the effectiveness of which depends to a large extent their own performance.

To solve the problem of full control of the content delivery service, some alternative models have been suggested, such as the Content Bridge, which rely on the cooperation of many entities to provide an integrated service. The drawbacks of these models are mainly the complexity and the difficulty of managing partnerships and individual agreements between the parties involved.

Since CDNs charge high fees for their high quality services, they are targeted towards large organizations-content providers who need to efficiently distribute content globally. Independent individuals or small organizations that cannot meet the financial requirements for using the services of a CDN are still forced to rely on traditional caching to efficiently distribute their content.

For these reasons, the Cloud content distribution model appears as an ambitious and promising answer to the problems of content delivery. The Cloud can provide a rather inexpensive coupling of web hosting services with content delivery. The services provided by the CDN can be considered as a distributed extension of a centralized hosting service. Since Cloud providers usually possess various data centers across the globe, it is possible to provide content distribution services. The Cloud may be a "poor man's CDN" solution, since it lacks major operating expenses for the maintenance of a global infrastructure of caches, but does not provide control of the service from end to end, as the transfer of content is done through third party networks. On the other hand, hybrid solutions that provide integration of the Cloud for online storage and content delivery through traditional CDNs are targeted to medium enterprises. They are more expensive solutions, but provide control of the service from end to end.

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