Content Delivery Network(CDN) is a term coined in the late 1990's to describe a system of computers networked together across the Internet that cooperate transparently to deliver content (especially large media content) to end users.

CDN nodes are deployed in multiple locations, often over multiple backbones. These nodes cooperate with each other to satisfy requests for content by end users, transparently moving content behind the scenes to optimize the delivery process. Optimization can take the form of reducing bandwidth costs, improving end-user performance, or both.

The number of nodes and servers making up a CDN varies, depending on the architecture, some reaching thousands of nodes with tens of thousands of servers.

+ Content Networking Techniques

The Internet was designed according to the end-to-end principle. This principle keeps the core network relatively simple and moves the intelligence as much as possible to the network end-points: the hosts and clients. As a result the core network is specialized, simplified, and optimized to only forward data packets. Content Delivery Networks augment the end-to end transport network by distributing on it a variety of intelligent applications employing techniques designed to optimize content delivery. The resulting tightly integrated overlay uses web caching, server-load balancing, request routing, and content services. These techniques are briefly described below. Because closer is better, web caches store popular content closer to the user. These shared network appliances reduce bandwidth requirements, reduce server load, and improve the client response times for content stored in the cache. Server-load balancing uses one or more layer 4–7 switches, also known as a web switch, content switch, or multilayer switch to share traffic among a number of servers or web caches. Here the switch is assigned a single virtual IP address. Traffic arriving at the switch is then directed to one of the real web servers attached to the switch. This has the advantages of balancing load, increasing total capacity, improving scalability, and providing increased reliability by redistributing the load of a failed web server and providing server health checks. A content cluster or service node can be formed using a layer 4–7 switch to balance load across a number of servers or a number of web caches within the network. Request routing directs client requests to the content source best able to serve the request. This may involve directing a client request to the service node that is closest to the client, or to the one with the most capacity. A variety of algorithms are used to route the request. These include Global Server Load Balancing, DNS-based request routing, HTML rewriting, and anycasting. Proximity—choosing the closest service node—is estimated using a variety of techniques including reactive probing, proactive probing, and connection monitoring. Service providers increasingly provide value-added services beyond basic data transport. Features such as virus scanning and parental control are being offered, hoping to increase service attractiveness, user loyalty, revenue, and profit. Web caches and service nodes distributed throughout the content delivery network provide convenient dispatch points for connecting to enhanced services. This handing messages off for further processing is sometimes called vectoring of messages. Two protocols suites are designed to provide access to a wide variety of content services distributed throughout a content network. The Internet Content Adaptation Protocol (ICAP) was developed in the late 1990’s to provide an open standard for connecting application servers. A more recently defined and robust solution is provided by the Open Pluggable Edge Services(OPES) protocol. This architecture defines OPES service applications that can reside on the OPES processor itself or be executed remotely on a Callout Server.

+ Education

STREAMING MEDIA ON THE MOVE
Educational institutions the world over are taking advantage of the latest communications technologies including the high bandwidth I2, 802.11 networks and now, 3g wireless networks to reach their students wherever they are located.

For the first time, Real is providing an integrated media delivery platform for delivering live and on-demand streaming media to all of these networks. The Helix Server is the only multi-format, cross platform streaming server for delivering the highest quality experiences to wired and wireless devices.

So, whether you are delivering distance education to remote students, or recoding lecturers to facilitate exam preparation, Real enables you to reach your students irrespective of where they are located on or off your campus.

+ Enterprise

MOBILE COMMUNICATIONS
Corporations of all sizes across a variety of industries face the challenge of communicating with an increasingly mobile workforce. According to Forrester Research*, companies are adopting mobile applications faster than planned because of advances in technology. In fact, they predict that IT organizations will start thinking of mobility not as a new and emerging technology, but as an integral part of the IT infrastructure.

EXTEND THE REACH OF YOUR CONTENT
Many companies have already embraced the power of streaming media to deliver corporate communications and training directly to their employees desktops rather than making them attend meetings and classes. Now, for the first time, Real is enabling you to extend the reach of your streaming content by delivering it to your employees wherever they are.

+ Government

MOBILE COMMUNICATIONS
Government organizations face the challenge of communicating with an increasingly mobile audience — whether it be employees, special interest groups or the general public. According to Forrester Research*, organizations are adopting mobile applications faster than planned because of advances in technology. In fact, they predict that IT organizations will start thinking of mobility not as a new and emerging technology, but as an integral part of the IT infrastructure.

EXTEND THE REACH OF YOUR CONTENT
Many government organizations have already embraced the power of streaming media to deliver corporate communications and training directly to their employees’ desktops rather than making them attend meetings and classes. More and more state and local governments are streaming a wide variety of meetings to citizens. Now, for the first time, Real is enabling you to extend the reach of your streaming content by delivering it to your audience wherever they are.

+ Churches

JB&A provides full streaming solutions for audio visual professionals.  House of Worship installers, help your clients stream sermons and events onto the web, create DVD’s so members of the congregation can take home and revisit the moments that touched them most deeply and in general expand the walls of their churches to the world.  Allow corporations to reach out to their customer base with targeted    marketing, train their staff at their desks and reach out to employees and clients in different time zones.  Show all kinds of institutions of learning the ease of taking their classes to the internet, creating DVD’s of lecture for study purposes and making distance learning a simple reality.