Consumers want ever more content in their television experience, which is one of the reasons that over-the-top (OTT) services like Netflix and LOVEFiLM are enjoying such popularity. They also want more out of their living room remote. But in the managed video world, adding content means adding usage to the network; each channel comes with an impact on bandwidth utilization for the pay-TV operator. So, providing a universe of channels to meet any taste, at any time becomes a unique networking challenge.
This article is part of the inaugural V2M digital magazine issue on Better Broadband, which you can view here as a free PDF.
The need to reclaim more bandwidth is spurred on even further by the space race between operators to reach the 200 HD channels mark. HD tuner penetration has reached more than 50 percent, service providers are offering many of their channels in HD and continue to expand this offering as more content becomes available. In parallel, time-shifted television, HD video-on-demand (VOD), DOCSIS 3.0 high-speed data service and recently 3D HD are putting additional pressure on the available spectrum.
Cable MSO Cox Communications set out to see if there could be an architectural solution to the conundrum, and conducted a long-term field trial of Switched Digital Video (SDV) technology with BigBand Networks. And it found that it was able to support a nearly infinite number of channels while mitigating pressure on bandwidth utilization: a state it calls "Switched Infinity."
In current hybrid fiber-coaxial systems, a fiber-optic network extending from the operator's central office carries all video channels out to a fiber-optic node which services any number of homes ranging from 1 to 2000. From this point, all channels are sent via coaxial cable to each of the homes. But only a percentage of these homes are actively watching channels at a given time. Rarely are all channels being accessed by the homes in the service group (SG).
Unlike legacy broadcast systems that broadcast all programs to all subscribers all the time, in an SDV network, video programming is only transmitted to subscribers within a SG that specifically requests such programming; the unwatched channels do not need to be sent. Cable spectrum becomes a dynamic pool of digital transmission resources that are applied to a subscriber only when needed.
Also, if a subscriber wants to watch a program that is currently being delivered to other subscribers within the same node, the new viewer simply joins the existing switched session. As a result, no additional capacity is consumed by the incremental subscriber.
In cable TV systems in the United States, equipment in the home sends a channel request signal back to the distribution hub. If a channel is not currently being transmitted on the coaxial line, the distribution hub allocates a new QAM channel and transmits the new channel to the coaxial cable via the fiber optic node. For this to work, the equipment in the home must have two-way communication ability. Switched video uses the same mechanisms as video on demand and may be viewed as a non-ending VOD show that any number of users may share.
The idea, of course, is to be able to quickly respond to competitive pressures by introducing new and revenue generating services. With virtually unlimited bandwidth, service providers have a means to rapidly introduce additional SD and HD programming, personalized services and IP video delivery to multiple devices and associated advertising all while leveraging existing SDV and broadcast infrastructure and without having to add bandwidth capacity.
In the Cox trial, simulations based on the collected viewership data during the trial showed that by appropriately reducing the number of tuners per SG, virtually unlimited bandwidth becomes available. In other words, the lineup size, and more specifically the number of HD channels, could be further increased without requiring additional spectrum.
Cox found that knowing which channels should be pushed all the time via traditional broadcast (popular channels, top primetime broadcast networks) and which could be placed in the SDV tier (niche and long-tail content) is the key. Very popular channels offer no over-subscription gain with SDV.
Cox achieved the "Switched Infinity" state where, for a given SG size and number of SDV QAMs combination, the over-subscription rate is controlled by the demand side rather than the supply side, e.g. no matter what the size of the lineup offered, there can only be so many channels watched simultaneously in any given SG. In practice, operators are not necessarily looking to achieve this theoretical infinite capacity target, they are essentially looking to support their channel lineup on the available spectrum while meeting their internal quality of service targets, namely maximum allowed rate of blocking events.
Usage data from the trial showed that only two HD channels appear in the top 25 most popular broadcast channels, and only six showed up in the top 50. This is typical of most SDV systems analyzed to date, according to BigBand, despite HD tuner penetration being about 50 percent. The top 60 broadcast channels have at least one viewer in all SGs over 80 percent of the time and the top 37 channels have at least one viewer in all SGs monitored during the trial at least 90 percent of the time. Additionally, since these channels are always on at peak time (7 p.m.-11 p.m.), there would be no bandwidth gain if they were moved to the SDV tier.
The 25 least popular broadcast channels are watched less than 50 percent of the time and should be moved to SDV reducing the overall broadcast QAM requirements.
This article is part of the inaugural V2M digital magazine issue on Better Broadband, which you can view here as a free PDF.
