Vendors are finding ways to fine tune switched digital video (SDV) now that it has moved from the realm of being a future technology to real-world deployments. One recent example is the partnership between OpenTV and C-COR, who, at last month’s National Show, rolled out an SDV platform that combines each company’s technology. The demo in Atlanta used OpenTV’s Core 2.0 Middleware solution as the client in Motorola‘s DCT-2000/2500 set-top boxes while C-COR’s nAble global session resource manger (GSRM) provided the session and edge resource management. The result is an open architecture for SDV that can be deployed on legacy, two-way set-top boxes, including Scientific-Atlanta. Because the platform is an extension of the middleware in the set-top box, a program guide doesn’t need to be modified and integrated, which is the current scenario with SDV. "Because we’ve built this as a fundamental piece of the middleware, any program guide, in fact any third-party application, that is running on top of OpenTV’s middleware now has access to the switched digital channels," said Steve Reynolds, CTO of the North American cable division for OpenTV. "The application, or the program guide, doesn’t even know that those channels have been moved into the switched space." One of the primary benefits of SDV is that it frees up bandwidth because it only delivers the channel a customer is viewing. Customers in the same node who are watching the same show are grouped together. Time Warner Cable has been the early frontrunner with SDV, while Cablevision and Cox have trials either planned or deployed. How it works The two companies began working on the project about 18 months ago after Time Warner Cable put out a specification for an end-to-end SDV system. While OpenTV focused on getting it’s Core middleware on Motorola’s set-top box, C-COR found that its VOD software, called nAble, already supported SDV functions such as bandwidth management while also providing reports on what programs were being viewed. "We designed our global resource session manager to work with any of the Motorola or Scientific Atlanta technologies," said Cliff Aaby, C-COR’s VOD Product Architect, "At the (NCTA) booth, we demonstrated that we’re not only able to do switched digital, but that we can do it in an open environment." C-COR’s GSRM interfaces with edge QAM modulators, which is basically the same infrastructure a cable operator would use for VOD or network DVR deployments. The GSRM is the headend device that implements the SDV protocol. In order to deploy switched digital video, streams coming into a headend need to be clamped to make sure the bit rates are pre-established. Once the streams come in, they’re put on multicast-in most cases a GigE multicast-at the headend. The switching is accomplished through a narrowcast edge device that allows multicasts coming into the headend to be targeted down to specific set-top boxes in service groups. In Atlanta, C-COR and OpenTV used Harmonic‘s Narrowcast Services Gateway. "You get all of that headend infrastructure in, and then down on the client side, you have OpenTV’s middleware loaded in the set-top box," Reynolds said. "That switched digital extension resides in a layer in the set-top software stack that is below the program guide." Reynolds said the middleware stack maintains a service list, which includes a flag that establishes whether a channel is in the traditional broadcast space or SDV space. If the particular channel that is requested isn’t being played down to the service group, the C-COR equipment at the headend will send messages to the narrowcast gateway instructing it to join the multicasts and begin transmitting that service down to the service group. Then the switched digital server sends a message down to the set-top box saying the service is now available and where to go to get it. Both Aaby and Reynolds think niche channels, such as foreign language or cooking channels, will be switched since the majority of viewers will already be watching shows on major stations such as CNN or ABC. To that end, Aaby said C-COR’s backoffice reporting system will give cable operators a clearer view of what broadcast channels are actually being viewed, which could help in negotiating packages from programmers. While SDV deployments are expected to pick up steam next year, especially in bandwidth-constrained systems, there’s still some work that needs to be done with standards and technologies. Aaby said that while TWC seems to favor remote procedure calls as the application interface between global session resource managers and modulators, other operators might prefer an XML interface. "It’s a new technology, so there are a lot of opinions about the best way to implement it," Aaby said

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