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 www.stratacache.com.
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