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November 2006, Volume 9/ Number 11

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Pushing Video Content in Distributed VoD Server Networks

By Chris Riegel


As Video on Demand (VoD) networks grow from the pilot stage to supporting tens of thousands of subscribers, providers face the challenge of managing the flow of movie files throughout the system. Simple VoD models deliver all content from one set of centralized servers, but as networks grow, bandwidth and latency issues will require providers to build distributed networks of edge VoD servers that can locally deliver popular content. This system minimizes overall network bandwidth requirements and eliminates bandwidth and latency issues for subscribers in each edge server�s area, but it complicates the issue of which content should be distributed to which servers, and when.

In this article, we�ll consider the challenges of delivering content in a distributed VoD server network, and look at a new solution that automates and streamlines delivery of popular content while minimizing the time and bandwidth required.

The 80-20 Rule

VoD content libraries may contain hundreds or thousands of titles, but statistically, 80% of VoD subscribers watch 20% of available content. VoD service providers can significantly improve the speed and reliability of consumer access to that popular content by replicating a few dozen titles on regional servers.

Not every regional server will store the same content. Popularity is partly determined by demographics, but other factors include the movie�s release date and the amount of promotion being done for it, and request volume (so as to include older movies that suddenly become popular because of current interest in a particular movie star or the subject matter).

Service providers have developed sophisticated algorithms to determine the popularity of a given movie title based on these factors, but it is one thing to select the right movies for edge distribution and quite another to reliably and cost-effectively distribute the content.

In most cases, regional server updates contain multiple movie titles, running to dozens of gigabytes total. These large file deliveries cause congestion in the network, which reduces the delivery speed of non-popular content being served to a viewer directly from the central content library. Unfortunately, the content distribution systems in place for distributing these files are not wellsuited to the task:

� Most video content management systems use point-to-point file transfers for content distribution, so updating (for example) ten regional server clusters requires ten separate transmissions. This causes network congestion, and can impact the ability of system mangers to perform regional server updates within required time windows.

� Point-to-point file transfer technology offers inefficient error-correction, often retransmitting an entire file if a few bits are dropped or if an edge server temporarily goes offline.

� Traditional content distribution systems often require scripting, manual reporting, and job supervision by the IT staff, increasing operations costs.

Many VoD networks are still small, and these problems may not have cropped up yet for operators of those networks. But larger VoD providers around the world are finding that the cost and complexity of edge server content replication is becoming a key factor limiting their ability to scale the VoD network. As more VoD providers bring on new subscribers, new geographic regions, and an increasing array of content, the replication problem will affect them all.

Intelligent Content Delivery Scales VoD

Recently, VoD providers have begun exploring the use of IP Multicast-based content distribution products to streamline replication of popular movie content. This software promises to eliminate the problems caused by point-topoint file distribution.

Deployment � Multicast-based solutions are easy and cost-effective to deploy. Service providers simply install �master� software on an off-the-shelf server in the central data center along with �slave� clients installed on regional video servers. After installation, the service provider�s staff performs a simple router reconfiguration throughout the network to activate recognition of multicast- based content flows. The �master� software then automatically discovers all regional server points. In addition, the T staff uses a point-and-click interface to set basic parameters for replication jobs such as when the content is distributed, or how much bandwidth can be used for transmitting it to each regional server. Scheduling � Multicast-based software includes APIs that integrate with the VoD provider�s database of popular content. This integration with widelyused subscriber usage databases allows providers to perform content replication automatically. The provider can also perform ad hoc movie distributions to any or all servers in the network at any time.

Distribution � Once the distribution schedule is set, the Multicastbased software uses a single transmission to deliver the appropriate content to each group of servers in the network, based on demographic, release date, and frequency-of-request algorithms. Rather than making redundant point-to-point transfers to individual servers, the software uses one transmission to update the appropriate content to all servers simultaneously. This method greatly reduces the bandwidth and time required to perform replications.

Error-checking � Unlike point-topoint file transfer software, advanced Multicast-based software uses exceptionbased error correction to minimize retransmission. Rather than retransmitting an entire file if a server temporarily goes down or a few bits are dropped, the software maintains a log of which servers are missing which content, and then automatically retransmits only the missing content to the appropriate servers in a single job. Again, this method saves considerable time and bandwidth, and it becomes more important as the VoD network grows. Essentially, multicast-based software guarantees 100 percent delivery of all intended content to all intended servers, automatically and with minimal usage of time and bandwidth.

Reporting and Management � Multicast-based software solutions include full reporting on when the content was delivered, eliminating the need for IT staff to manually create reports of point-to-point transfers. More importantly, however, the Multicast-based software interface gives IT a single console that controls all aspects of the replication function.

VoD service providers face enough challenges with marketing, network operations, and subscriber management without having to worry about whether popular content is being delivered to the right servers at the right time. IP Multicast-based software serves as a reliable, automated, and highly efficient transport vehicle that reduces costs and improves customer satisfaction. It�s a solution worth exploring for every VoD service provider. IT

Chris Riegel, serial entrepreneur, is CEO of Stratacache, his third successful startup in 16 years working with systems and networking technology ventures. For more information, please visit the company online at

If you are interested in purchasing reprints of this article (in either print or PDF format), please visit Reprint Management Services online at or contact a representative via e-mail at [email protected] or by phone at 800-290-5460.


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