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Switched Digital Video SDV – is the long tail wagging the premium dog? The move towards Switched Digital Video may be driven by an urgent need to reclaim bandwidth, but it will also enable cable to provide access to niche content and deliver personalised services and targeted advertising, says Philip Hunter

able operators have little choice wanting to receive it. It can be seen then IPTV providers that in adopting switched digital video that switching delivers most benefit in can immediately turn C(SDV), as it is the most cost bandwidth terms for content of middling on the long tail, given that effective and constructive way of solving popularity, where there is a reasonable their DSL or occasionally the impending bandwidth crisis imposed chance that it will not be watched by any fibre based access networks by the relentless advance of on-demand customers within a given segment at a given are one-to-one anyway with content. The other principle options, primarily time. Switching is no help for very popular all content unicast. Switching accelerating analogue switch off and channels, such as BBC1 in the UK, because also enables cable to match extending the spectrum from the current level it is almost certain that someone in every IPTV in another important of 860 MHz to 1 GHz or beyond, have their segment will be watching it at any time. respect: by providing a view drawbacks. They will only stem the tide for In this case, switching will save no of what the subscriber is a while, and many cable operators are bandwidth, and so popular channels watching via the return path. coming to the view that retaining analogue will still be broadcast to all subscribers. “That's another reason operators services for delivery to second TV sets can In some ways, it is a similar principle are very interested,” says Adams. be a competitive weapon against IPTV. to mobile TV, where the most popular “Really right now, they don't have SDV, on the other hand, can be a coherent content will be broadcast, while the niche a very accurate way of understanding part of a strategy for delivering personalised content is unicast over cellular networks. what people's usage patterns are. interactive services, opening up the return Switching also does little for very When switching channels, you get path and splitting the coaxial networks unpopular content at the back end of the a lot of information about users' viewing.” into ever smaller segments as fibre is driven long tail, where there is a very low probability deeper towards the consumer. The stampede of it being watched at any one time. Multicast vs unicast SDV towards SDV may be driven by an urgent In this case, the total bandwidth saving However, this aspect of switching raises need to reclaim bandwidth, but it will also over a period would be negligible because some questions. One of them concerns enable operators to provide access to niche the content is only occasionally transmitted privacy, although that is shared also by content both in conventional archives and over the network. The ideal scenario involves IPTV operators and is an issue that will have from Internet sources, while also facilitated intermediate content that is being required to be addressed by the industry as a whole. targeted advertising. within one or two segments at a given In the case of switching, the question is “It's really about the long tail,” says time, but not across the whole network. whether to implement it in such a way that Michael Adams, VP of systems architecture This may include programming for ethnic advertising can be targeted on a one-to-one at Tandberg TV, one of the leading vendors minorities, expatriates or interest groups; basis at individual subscribers rather than of transmission and encoding systems for for example, a cricket channel in the US. just at all people watching a specific channel. cable TV. “It's ideally suited to switching. In this way, cable operators can match This, of course, is possible with IPTV. The idea is you might start off using SDV “In the case of switching, the question to add a fairly small number of niche channels, but over time the number is whether to implement it in such a of channels could be unlimited.” way that advertising can be targeted This is possible because switching in effect on a one-to-one basis at individual takes multicasting beyond the edge QAM into the coaxial loop, delivering content only subscribers rather than just at all to the segment containing at least one user people watching a specific channel.”

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Switched Digital Video

But with switching in an HFC network, number on the STB, so the SDV resource though, unicast and multicast SVC can run this one-to-one relationship comes at the manager system has to match programmes in parallel over the same network. Operators expense of bandwidth, in effect giving to channel numbers correctly. can therefore have, for example, three tiers up some of the savings that may have been In some cases though, the programme of content, with the most popular channels the original reason for implementing SDV. requested is already being watched by broadcast, those of intermediate popularity To see why, we have to consider another subscriber in the same service put out in multicast SVC, and those of least how SDV works. It can work group, in which case the resource manage popularity in unicast SVC. This would mean in two ways, multicast or merely has to inform the STB which that the personalised delivery would be unicast mode, the latter being frequency to tune to in order to “join in”. restricted to the latter group, but could be a more recent introduction. “This offers significant bandwidth savings, part of an ongoing migration towards more Multicast mode is still the however does not provide a one-to-one universal one-to-one delivery. predominant form and relation between content and the subscribers Such a strategy could also involve delivers the greatest STB,” says Ramin Farassat, product pushing fibre deeper, extending the edge bandwidth savings. marketing VP at RGB Networks, a vendor QAMs closer to subscribers and creating In this mode, when a of SDV technology. ever smaller service groups, which in turn subscriber switches The other form of SVC, unicast mode, would make it economical to increase the to a certain channel, does afford such one-to-one relationships, number of channels available via first the set-top box because now - when a subscriber's STB multicast and then unicast SDV. It is worth (STB) sends a requests a programme and tunes to it - noting that pushing fibre deeper does request out over nobody else in that group can access it. nothing by itself to ease bandwidth the return path to Therefore any advert delivered with that congestion within the service nodes served the controller programme will come just to that one by coax, because without SDV there is no or resource subscriber and can be personalised way the network can tell which manager located accordingly, as can any other content programmes to deliver. The combination of somewhere in the features. Other subscribers can watch SDV and fibre deployment though is a core network. that programme, but have to receive their potent one because it allows operators to This controller's job own copy, again delivered on a one-to-one progressively increase the amount of is to instruct the edge basis. This is like IPTV, but with the content available, while moving towards QAMs to allocate disadvantage that if, say three people in a one-to-one delivery. bandwidth to channels service group want to watch a programme, and reclaim unused capacity it has to be multicast separately to each VOD and DOCSIS are driving SDV when not needed. So in this subscriber, consuming three times as much Many operators of course have already case, if the requested channel bandwidth within the coaxial segment. deployed video on demand (VOD), is not already available in that VOD is similar, where each subscriber which delivers movies or other archived segment, known as a service group, receives separate unicasts of movies, content on a one-to-one basis, and this the edge QAM would allocate bandwidth although in that case the content may provides the framework for SVC, to it, and the controller would send be streamed at different times rather than by opening up the return path, notes a message telling the STB what frequency as a scheduled broadcast. As Farassat notes, Nick Fielibert, CTO and chief architect to tune to. the bandwidth price may be worth paying for Europe at Scientific Atlanta, Cisco's The key points here are that this for the benefits of personalised content video transmission system subsidiary. process must be transparent to the user delivery. “The choice of multicast or unicast “If you have already built a VOD infra- and must take place quickly, so that is dependant on whether the operator structure, then SDV comes free on top.” channels can be changed within the is interested in building a true personalised Indeed as Fielibert adds, the deployment allotted time, typically about a second. architecture, or just relying on switched video of VOD itself has contributed to the need The actual frequency allocated to a for bandwidth savings,” he says. for SDV by soaking up bandwidth. particular channel will not always be the In unicast mode it is even more imperative Another factor pushing demand for SDV same given that SDV is designed to that the content delivered via SVC is chosen is the deployment of DOCSIS to provide share a given amount of spectrum carefully. If the content is too popular, broadband Internet access and also IP between a much larger number of it will soon soak up more bandwidth than delivery of video content. Alongside channels that it could accommodate a network without SVC, because it would delivering IP and Internet services, simultaneously. But the user must always be transmitted simultaneously across many the original motive for DOCSIS was to receive that content on the same channel or even all the segments. Significantly increase upstream bandwidth, but now, “Recent SDV architectures support as Fielibert points out, DOCSIS is being used increasingly in predominantly a mixture of different constant bit downstream mode to deliver video. rates, but this is still inflexible “There is no longer often just one DOCSIS and fails to exploit the full power channel on the downstream, but maybe ten and perhaps 20 in the next two years, of the latest codecs.” that is 160 MHz of capacity,” says Fielibert.

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Switched Digital Video

This leaves less for other services, and begs bandwidth saving of this architecture,” What's needed to implement SDV? the question of whether video will migrate says RGB's Farassat. to DOCSIS rather than SDV. Fielibert Of course, a lot of bandwidth can be Staging processor - This equipment, dismisses this question, arguing, “There's saved by migrating from MPEG2 to the located at the hub, converts signals really no value delivering broadcast latest H.264 codec, but this requires new from variable to constant bit rate at content over IP, except to get to multiple STBs. However, SDV can ease this migration 3.75Mbps, and converts multi-program devices, foe example, in the home network by allowing H.264 and MPEG2 services transport streams (MPTSs) to single- or mobile handsets.” to coexist while the STB population program transport streams (SPTSs) IP over DOCSIS will also be used to replacement takes place, according to Bruce Bulk encryptor - Allows for independent provide access to Internet based video Bradley, director of product development scaling of encryption and Edge QAM content, but for the premium broadcast for digital video solutions at Motorola's resources, and is connected to the IP channels, SDV will be more cost effective Connected Home Solutions division. network over Ethernet using GigE ports because it comes effectively free on top “Operators can switch MPEG-2 services QAM modulators - The number of QAMs of VOD. “For CMTS deployment (ie DOCSIS), to the vast majority of currently deployed are primarily driven by the size of the we are talking about $40 to $50 per Mbps set-tops, but take advantage of the advanced service group, the simultaneous number for transport, while for SDV it is zero cost,” compression of MPEG-4 (H.264) to switch of channels being watched, and the says Fielibert. services to newer set-tops that support it,” amount of “gain” designed into the says Bradley. system based on traffic modeling and SDV deployment strategies Another major consideration is, naturally, risk tolerance There is, however, work to be done choice of supplier, and this hinges partly Session Resource Manager (SRM) determining how to deploy SDV. There on whether to go for an end-to-end solution - the master bandwidth controller will be some knock on effect within the from a single vendor or to mix and match. in the system, which governs access core that may determine where to locate Some vendors such as Scientific Atlanta, to content and network resources content, in some cases replicating it close Motorola and Tandberg TV provide total and allows sharing of those resources to each edge QAM, while for less popular solutions, but are increasingly supporting by various applications programmes holding it just in one central open standards that allow different makes SDV server - The “brains” of the SDV server. There is also the issue of bit rate, of video server, edge QAM and other system, it coordinates resources as today's SDV solutions require conversion network components to come from different (the switch, the QAM modulators, of content either to constant bit rate (CBR) vendors. There are other vendors that and the set-top boxes) to enable or capped variable bit rate (cVBR), provide just part of the solution, such as channel changes which amounts to the same thing. This is Arris Networks, which specialises in DOCSIS SDV manager - Contains the user clearly unsatisfactory, for constant bit rate modems and edge QAMs. interface for control of the SDV does not equate to constant quality. The video field is evolving from being servers and system, providing a means Fast action video such as sports, a closed to an open market for networking, for operators to configure the various for example, require a higher bit rate, based ultimately on IP, much as voice and settings for the SDV servers while pictures of somebody reading data has done already, and this is allowing the news can make do with much less. operators to cherry pick, according to Arris 2005, and is now deploying Modern compression techniques can senior director for business development its fourth generation product. exploit these differences, but only if the Jeff Brooks. There is, however, a question According to Ron Wolfe, senior network supports variable bit rates. of whether Arris will be big enough to product marketing manager of For this reason, recent SDV architectures compete, having failed in its bid to acquire cable video at BigBand, one of the support a mixture of different constant Tandberg TV earlier this year. On the other company's recently completed bit rates, but this is still inflexible and fails hand, Arris is well ahead in making edge deployments reaches 2.3 million to exploit the full power of the latest codecs. QAMs that support all services including subscribers in New York City, where Operators are, therefore, awaiting VOD, SDV, data, and network PVR, rather a cable operator used the new technologies that allow SDV to than requiring separate products for each. technology to add international deliver programmes in their native VBR This is important given that a large part programming in nine new format, with RGB promising such a product. of the motivation for SDV lies in relieving languages. Another operator is said “Through this technology, the operators bandwidth congestion without major to be using BigBand's technology to can still manage the delivery of the upgrades such as are required for expand its offering of HDTV without switched video streams, but would spectrum extension. using additional network capacity. deliver them at the highest video quality BigBand Networks has been deploying Wolfe claims that BigBand's possible, while still benefiting from the switched broadcast commercially since deployments of switched broadcast collectively pass more than five “Pushing fibre deeper does nothing million households worldwide. by itself to ease bandwidth As Switched Digital Video evolves congestion within the service nodes beyond early deployments, expect to hear a lot more on the technology served by coax.” outside the US. CSI

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