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Building the Next Generation Digital Video Network

White Paper


Building the Next Generation Digital Video Network


As video on demand (VOD) services are deployed, cable operators will experience a fundamental shift in their business, moving from broadcast to unicast content delivery. Another significant change is the introduction of Gigabit Ethernet into their network, which is providing an unprecedented opportunity to turn the cable operator's infrastructure into a sustainable competitive advantage. However, Gigabit Ethernet is more than just transport; it's the foundation of the Next-Generation Digital Video Network.

The Next-Generation Digital Video Network:

  • Enables cable operators to more easily and economically deliver content to where it is needed, when it is needed.
  • Scales from small networks to large with a pay-as-you grow capital profile.
  • Protects your investment by providing a flexible video networking system which embraces evolving architectures and services.
  • Reduces operational costs and complexity by building intelligence into the network.

With the expertise of being the industry leader in Gigabit Ethernet networking, Cisco is driving towards multi-vendor interoperability, reminiscent of what we did with Data over Cable Service Interface Specification (DOCSIS), and we are committed to the success of our customers by providing unsurpassed support, reflected in our proven track record during the @Home transition. Cisco is uniquely qualified to enable cable operators in delivering a sustainable competitive advantage. The content in this paper summarizes Cisco's view of the opportunity before the cable operators and the value Cisco can bring to aid in seizing it.

Market Dynamics

Cable operators are being challenged for customer loyalty with a real competitor, the satellite companies. One reason cable operators are losing their video subscribers to satellite service is because satellite service can offer more channels at a lower price. Thus cable operators are now more motivated than ever before to address this primary threat to their core business by taking advantage of their best asset—their cable plant as a key competitive advantage.

From a market perspective, cable operators have considered their competitive advantages and have determined that their networks offer two benefits that they can leverage as advantages to beat the competition. First, they can deliver far more differentiated bandwidth than the satellite providers can. Clearly, satellite providers can deliver a lot of bandwidth too, but it is the same bandwidth with no differentiation per subscriber. Second, cable operators can offer a viable return channel for interactivity. Combining these two advantages, the cable operators have determined that if they can offer a service whereby their subscribers can watch on television what they want to watch, when they want to watch it (in other words, "on demand"), the turnover in their subscriber base will end. From their perspective, it is about changing the way the world views entertainment and watches television; this is the differentiator that gives them the competitive advantage they seek over satellite service.

Cable operators are now experiencing the beginning of this fundamental shift, which requires the network to deliver a unicast stream for each video request and they are starting to recognize the enormity that this will have on the network as service demand increases. It is also an opportunity for the cable operators to free themselves from the proprietary equipment that limits their capability and regain control of their network. The search for better solutions that helps them move to an open, standards-based system is now possible with the introduction of an intelligent Gigabit Ethernet switched infrastructure that enables scalability and growth of new services without the limitations apparent in legacy architectures.

Limitations with Early Deployments

Early deployments of VOD services used the video-industry-specific DVB/ASI protocol for transport. As DVB/ASI is a point-to-point transport protocol, this lead to an architecture where the VOD servers were directly connected to the QAM modulators, typically over an optical network using wavelength division multiplexing (WDM). There was a one-to-one correspondence from the video server port to the QAM. In some cases, the VOD servers were installed at the distribution hub, with local QAMs sending the video signals out over the hybrid fiber-coaxial (HFC) network.

These early deployments had several issues and limitations, however. First was simply scaling the system. As more users came onto the system, more QAM modulators needed to be deployed to support the additional channels. And since the QAMs were directly connected to the video server, this in turn meant it was necessary to deploy additional VOD server ports, stream capacity, and network bandwidth configured on a one-to-one ratio. This direct connection also causes another limitation around dealing with failures in the system. If an edge QAM failed, the VOD server port it was connected to essentially became useless, and the stream capacity was stranded from use by other QAMs. Another issue was population of content. As each video server could only stream video to QAMs that were directly connected to it, to make a new piece of content available to all users this meant individually populating it on every video server in the system, a time consuming and expensive process.

In general, this architecture was costly to operate and the network did not scale. But, in its defense, this was the only viable technology at the time. DVB/ASI was the industry standard for video transport and widely supported across platforms from numerous vendors.

Technology Shift to Gigabit Ethernet

Today, a technology shift is taking place in the video network infrastructure. The de facto standard for video transport is shifting away from DVB/ASI and being replaced with Gigabit Ethernet as the transport. Gigabit Ethernet is a much more economical transport technology than DVB/ASI, having ridden the tremendous cost reduction curves due to its ubiquitous deployment in modern packet networks. In addition, Gigabit Ethernet switches are being deployed in the head end, connected to the video server, to provide additional transport savings. Many of today's VOD servers can't send out a full Gigabit Ethernet worth of streams on a single port. The Gigabit Ethernet switch aggregates the sub-rate Gigabit Ethernet VOD server ports together so a full Gigabit Ethernet of traffic can be transported across the network saving on fiber and equipment costs.

Because of the point-to-point downstream nature of video on demand traffic, cable operators realized eliminating the components for a return path back to the head end could further reduce capital costs. Thus, most VOD transport networks today are generally designed to be unidirectional. While this unidirectional architecture was fine for DVB/ASI infrastructures, it created operational difficulties in Gigabit Ethernet deployments. The problem in designing the network to be unidirectional is that it breaks the automatic provisioning functionality that relies on bi-directional communication between devices to learn packet forwarding information. Now cable operators had to manually populate the IP and Media Access Control (MAC) addresses in the forwarding tables along with other configuration parameters in the head end switch and the VOD server.

The move to Gigabit Ethernet is about more than just cheap transport, however. It is a fundamental shift in the network architecture. Gigabit Ethernet is about switching and the network control structure that the technology brings with it. Cable operators are moving from a hard-wired DVB/ASI point-to-point configuration to an intelligent, switched infrastructure and all the benefits that this can bring.

The Law of Large Numbers

Clearly, one of the benefits that come with the Gigabit Ethernet switch is the cost reduction for the cable operators. "The law of large numbers" can be applied to the Next-Generation Digital Video Digital Video Network, which factors the expected peak utilization levels of subscribers allowed to access and download movies. Taking into consideration equipment cost, cable operators design their network for a particular, acceptable blocking probability. The resulting calculations will reflect that fewer video server ports are required in the head end than the number of QAMs at the edge of the network.

Traditional legacy network designs require a one-to-one mapping of VOD server ports to QAM channels, but that is no longer necessary with the deployment of the Gigabit Ethernet switch. The Gigabit Ethernet switch directs the requested video stream out to the appropriate QAM. The value of the Gigabit Ethernet switch lies in the fact that it permits a "one-to-many" architecture design that can utilize any VOD server port to send a video stream to any QAM in the network. In other words, because the one-to-one correspondence has been broken between the video server port and the QAM, cable operators can now deploy fewer VOD servers, saving on capital equipment cost by deploying Gigabit Ethernet switching in the head end. This setup pays for itself in the reduction of the
cost-per-stream economics.

The other benefit is from a storage perspective. When cable operators begin to increase the amount of content offered to their subscribers, Gigabit Ethernet switching can save on storage costs. In today's VOD server environments, many can support 2000 to 4000 video streams per cluster of video servers. If a cable operator needs to support 16,000 video streams, that operator would have to replicate all the content that is offered to subscribers four times. A Gigabit Ethernet switch deployed in the head end can send video traffic streams from any video server port out to the QAM. This scenario allows the cable operator to store less frequently accessed movie titles on just one of the clusters and save on storage costs instead of having to replicate the content on all four clusters. By implementing Gigabit Ethernet switching and putting a network in place, cable operators will save not only on the number of video server ports needed to deploy but also on the amount of storage required. The storage savings increases as the amount of content increases. It may not be as significant as with today's content levels, but when they start to compete with the number of titles that Blockbuster offers, about 15,000 hours of content, the amount of savings on storage becomes critical in the overall economics.

VOD Optimized Gigabit Ethernet Solution

Cisco® is committed to providing cable operators with Next-Generation Digital Video Networking solutions that will enable them to easily and cost-effectively offer new, profitable, and scalable digital video services.

Cisco is a leader in developing ways in which cable operators can increase VOD service profitability by introducing an architecture that constitutes a VOD optimized Gigabit Ethernet solution (refer to Figure 1). The fully tested and documented solution features the integration of the transponders and lasers directly into the Gigabit Ethernet switch to reduce costs and eliminate some of the network transport components, thereby reducing network complexity and supporting both asymmetrical or unidirectional design architectures.


Figure 1
VOD Optimized Gigabit Ethernet Solution

Evolving Network Architectures

In order to scale with new digital services and growing subscriber demand, networks must evolve. This means cable operators must further enhance and deploy solutions to ease operations by introducing additional network intelligence, even at the edge of network. An intelligent control plane, designed as an open, standards-based control structure, has numerous benefits, one of which provides more efficient network operation of the VOD service. The ability to deploy new equipment in the network and be automatically discovered and configured helps eliminate the challenges of having to manually enter long digit strings into the Gigabit Ethernet switches and other VOD service equipment. Adding more network intelligence empowers the cable operator to offer better support and reduces service outages that may result in customer dissatisfaction.

The enhanced functionality of the control plane allows cable operators to deploy an asymmetrical network that can emulate an architecture that behaves in a fully bi-directional manner. This network intelligence solves one of the major operational challenges in VOD deployments. IP and MAC address tables are automatically configured on the devices and will accept standard network responses received in the network.

The evolutionary progression of the control plane allows the support of multiple services on a shared network infrastructure. As cable operators look to support more than just VOD services, they can begin to consider other digital video services such as a switched broadcast service by enabling network intelligence further out at the edge of the Next-Generation Digital Video Network. There will not be a need to configure certain QAMs only for broadcast and other QAMs only for VOD. The better approach is to have a control plane in place where the control function for the VOD service or for a switched broadcast service simply asks the network if the appropriate resources are available to deliver the service type to a subscriber. The network in turn responds, either confirming or denying the resources to deliver the service, and provisions the network accordingly.

Another benefit would allow cable operators to distribute content into different areas in the network. An example might be to have the most popular content located on VOD servers in the distribution hub. When the next "blockbuster" movie becomes available for their subscribers, cable operators could pre populate the VOD servers at the edge of the network so that more subscribers could access the movie and consume fewer network resources. Thus the benefits of the intelligent control plane from the cable operators' perspective is that they get an efficient network that allows them to scale with subscriber demand and offer profitable digital video services.

Building the Foundation of the Next-Generation Digital Video Network

In summary, when VOD networks were first deployed, cable operators were using DVB/ASI for the transport in their networks. Now there is a transition to Gigabit Ethernet and cable operators need to realize that Gigabit Ethernet is not just a transport replacement. Gigabit Ethernet is also about switching and network control intelligence between devices. Cisco understands the profound implications of going from a hard-wired, point-to-point approach to a fundamental intelligent networking approach. Our expertise in Gigabit Ethernet technology offers considerable value by respecting and protecting the investments inherent in an evolving digital video service, enabling cable operators to discover the advantages of an intelligent switched infrastructure.

Highlighting the intelligent switched infrastructure is the Gigabit Ethernet switch, which continually evolves as the foundation for the Next-Generation Digital Video Network. Initially, the switch integrates the optical transponder with the development of pluggable optics that connects to the Gigabit Ethernet interface of the switch. The addition of an advanced control plane for intelligence and support of new digital video services eases operation and further enhances profitability. The value proposition of an integrated modular chassis is that it delivers an unprecedented amount of flexibility and the ability to grow services and expand upon its capacity. Cisco is developing the network intelligence to reduce complexity, simplifying manageability, and continually deliver the investment protection expected in an emerging service architecture. In addition, the solution will be developed and delivered as part of an standards-based, multivendor, interoperable system that will further drive innovation in the industry. This does not constitute another set of limitations forced upon the cable operators as with other proprietary video systems. Cisco has a proven track record and experience in the cable industry as a primary contributor to the DOCSIS standard and high-speed data solutions.

Our expertise is not about the delivery of another transport solution—it is about getting the most out of your network, and Cisco is the industry leader in Gigabit Ethernet networking. Cable operators are learning how this service will evolve, and Cisco can deliver the network flexibility to scale as their services grow and also deliver the support that they can count on now and into the future.