PATRICK SIMS /
06.01.2007
Originally featured on BroadcastEngineering.com
All channels point to IP
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.

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.

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.)

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.

PON cost components

Component and interface costs change over time relative to different network architectures. Today, typical broadband PON (BPON) costs are significantly lower than either gigabit or GigE passive networks simply because of the maturity of the technology and the availability of the chip sets. When comparing the real cost of technology, however, BPON lacks the required bandwidth to support VoIP and video services.

The PON equipment component costs are found in the northbound network interfaces that physically connect the video headend to the PON OLT, the common OLT equipment and the PON interfaces to the outside plant.

A network's central office electronics and installation accounts for only about 8 percent of the network's total cost, whereas the outside plant hardware and labor typically account for about 40 percent of the total cost. (See Figure 3.) The customer premise equipment and installation account for more than 50 percent of the total cost. As one large telco has discovered, the real costs of deployment start at the drop box.

There is a clear positive relationship between technology changes and the interface costs. Higher line rate, higher split ratio and newer technology all lead to a higher PON interface cost.

As stated above, BPON is expected to incur a lower initial cost due to the maturity of the technology and higher volume. Gigabit networks may be expected to have a faster cost reduction rate. This may be partially due to the spreading out of the gigabit PON (GPON) cost over 64 subscribers over time and improvements in MPEG-4 performance. As that happens, the cost differences between BPON and GPON will be reduced.

PON revenues

Before any network design decisions are made, managers and system engineers need to ask themselves the following key questions:

  • Is this a greenfield deployment where, as the incumbent, I can expect a 100-percent take rate where all the service revenues are new?

  • Am I overbuilding with existing subscribers who are already my customers for voice and data, and the only new revenue streams will come from video?

  • Am I overbuilding myself to stem the tide of competition coming into my territory? If so, do I need to implement a copper solution first? Or, can I wait for higher-bandwidth solutions to come down in cost?

Because voice, video and data services represent significant revenues, ultimately there may be a high cost for delaying deployment and potentially losing market share.

Implications for broadcasters

New technology is available to make the implementation of high-bandwidth services easier and less expensive. Even those costs, however, will drop over time. If a service provider can wait, it will gain a cost build-out advantage.

If, on the other hand, the service provider needs to move now, there are copper and copper/fiber network solutions. These can be implemented now and updated to provide more bandwidth without a future forklift renovation.

MPEG-4 will be the compression of choice for these new services. While STB and encoder choices are limited today, more options are coming quickly. This new compression standard offers vast improvements over MPEG-2. The potential downside is that MPEG-4 installations usually require a greenfield.

Broadband service providers are investing billions to build out the infrastructure needed to support IPTV and the delivery of other IP-based services. These companies know that the demand for video is the main driver. Ultimately, the broadcaster must deliver sought-after content or face the risk of losing audiences to other forms of entertainment. While the service providers are laying the pipes, broadcasters have to fill the demand.


Patrick Sims is principal engineer for ADC.



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