All channels point to IP
Jun 1, 2007 12:00 PM, BY PATRICK SIMS
An IP-based network is the most cost-effective way to deliver HDTV and new multimedia services.
The big picture is clear: Consumers want more entertainment options, faster service and higher quality. Nearly half of U.S. households already own or plan to purchase an HD-enabled television in the next year. Nine million homes purchased HDTVs during the 2006 holiday shopping season alone.
In addition, the FCC has set February 2009 as the deadline for the end of analog television. Over the next two years, many more viewers will likely purchase new TV sets.
Add to this the surging demand for high-speed broadband, and it is obvious that viewers want more, and they want it now.
Broadcasters are ready. Most high-profile programs, including sporting events, prime-time programming and even news, are already broadcast in HD, and more HD programming and channels are being added each month.
All of these factors are driving content service providers, including telco, cable and satellite, to IP-based delivery platforms and networks. IPTV is the first platform being rolled out.
Defining IPTV
IPTV describes a system where a digital television service is delivered using IP over a network infrastructure. Such delivery systems are typically built by a broadband operator using a single infrastructure. Customers are provided total control over their multimedia experience, resulting in an interactive and high-quality service.
Table 1. Typical bandwidth requirements for MPEG-2 standards
Click image to enlarge.
IPTV holds the allure of tapping into new revenue sources by delivering advanced multimedia services over broadband networks. One key element in this development is that, when combined with modern compression such as MPEG-4 AVC, the telcos can begin using their copper distribution system (xDSL) to deliver highly enhanced and profitable services to an eager audience.
As competition grows more fierce, what's the best way to deploy IPTV? There is no single answer. Today, the basic delivery mechanisms include DSL; passive optical networks (PON), such as fiber-to-the-home (FTTH); traditional CATV over hybrid fiber coax (HFC); or a combination. Each has advantages and challenges.
The demand for bandwidth
With current video compression technologies, neither symmetric high-speed digital subscriber line (SHDSL) or asymmetric DSL (ADSL) can provide the bandwidth required for IPTV. With ADSL2+ at 26Mb/s and high-speed DSL (VDSL) at 50Mb/s, more bandwidth is available, but the limitation is delivery distance. Subscribers need to be close to the central office or remote terminal as the available speed of any xDSL network decreases with distance.
Operators often find that IPTV deployment over xDSL is a more attractive option given their existing investments in the copper plant and the need to ramp up to deliver these new services quickly. One of the key problems in xDSL, however, is the ability to deliver SD and HD MPEG-2 content. HD MPEG-2 signals require about 20Mb/s per channel compared with 2.5Mb/s to 3.5Mb/s for SD content. (See Table 1.)
MPEG-4 AVC
Fortunately, MPEG-4 AVC provides a solution. Also called H.264, MPEG-4 AVC is a well-understood compression technology. It is generally considered at least twice as bandwidth-efficient as MPEG-2. In addition, because MPEG-4 is a new technology, even higher compression ratios are likely to be developed in the future.
Table 2. Typical bandwidth requirements using MPEG-4 AVC
Conversely, MPEG-2 is at the end of its compression improvement curve, and little advances are expected in its performance. Typical MPEG-4 AVC data rates for familiar content are shown in Table 2.
Network capacity
The objective when examining network capacity is to determine whether a particular implementation can meet a given service bandwidth requirement. This is important in the southbound PON port capacities, and even more important in the northbound interfaces where multicasting techniques will be initiated. (See Figure 1.)
Figure 1. PON capacities in the northbound and southbound interfaces
Click image to enlarge.
Network capacity must meet maximum usage needs without video blocking for any given take rate. The system architecture must be engineered to handle regular usage by the given take rates and still have sufficient capacity to ensure adequate video service during peak demand times. Maximum network capacity can be estimated by multiplying the number of subscribers by the maximum number of video feeds per subscriber. Another way would be to assign a maximum bit rate or bandwidth per subscriber times the number of subscribers.
In Figure 2, the channel lineup and VOD demand affects the optical line termination (OLT) trunk capacity from the video headend. Depending on the number and type of VOD services offered, channels may use unicast or multicast techniques. Multicast is the ability of one network node to send identical data to several viewers, such as broadcast.
Unicast video is a point-to-point transmission requiring the source to transmit an individual copy of a message to each requester. Multicast is more bandwidth efficient, but unicast offers more options and user control.
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