Database Reference
In-Depth Information
In the days before cloud, the main way to address issues regarding performance,
availability and scale in CDN was for companies to physically replicate existing
infrastructure in other geographical locations in order to decrease the physical distance
between the end user and content servers. For example, deploy servers close to ISP
gateways. This approach was not only expensive but companies had to determine the
best replicate and server placement strategy [ 26 ]. The cloud model offers companies an
alternative and less expensive way to expand infrastructure, in particular the ability to
virtually scale across unlimited resources on demand without the need to buy expensive
hardware. The cloud and CDN have both evolved to be complimentary utility plat-
forms. The cloud provides virtually unlimited access to computational resources
(processing, storage and network infrastructure) via array of physical servers deployed
globally. Conversely, CDN provides an optimised repeatable delivery of content from
servers to end users (one-to-many). Using the cloud and CDN together can deliver a
holistic agile system that meets CDN demands and is economically viable. A cloud-
based CDN architecture can provide the following advantages [ 27 ]:
￿
An elastic platformwith ability to dynamically and easily scale capacity up and down.
￿
Hides the infrastructure complexity from CDN applications and content provides.
￿
Enable a QoS driven performance management.
￿
Open standard approach to tap into the capabilities of public clouds to scale during
peak demand.
32 ] in the past have investigated CDN presenting over-
view and technical challenges in designing and implementing effective CDNs. Most of
the work has focused on commercial CDNs that work over private data centres. With
the current trends and advances in cloud computing and the mutual advantages that can
be leveraged by cloud and CDN, in this paper, we present a comprehensive study of
Cloud CDNs. We present a state-of-the art survey on current commercial and research
driven Cloud CDNs. We then present an analysis of current Cloud CDN based on a
comprehensive taxonomy. We
A few studies [ 4 , 23 , 28
-
nally identify the opportunities in the Cloud CDN area.
2 Content Delivery Network and Cloud Computing
2.1 Content Delivery Network
An overview of a typical CDN architecture is presented in Fig. 1 . Depending on appli-
cation and content type the architecture of CDNs may vary However, all CDN
architectures mainly comprise of an origin server, a request redirecting mechanism and a
large number of surrogate cache servers namely Point of Presence (POP).
1. Origin server: is a powerful storage system that contains all the content and/or the
metadata of all the content. To achieve high performance of the whole CDN, the
content in the origin server are pushed to the POP servers (surrogate servers) that
are located at different geographical locations across the globe.
2. POP servers: are distributed in a large numbers at diverse areas in a CDN. The main
function of pop server is to offer the content based on user request. When the content
is not available locally, the pop server should pull it from the origin server and store it
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