Content distribution over cable systems

From its origin as Community Antenna TV (CATV), a solution to poor over-the-air reception in the late 1940s, cable distribution is now the dominant delivery method for all TV programming. Even with the loss of subscribers to DBS satellite services, cable TV systems reach more than 60 percent of American households.

Superstations pave the way

Cable systems were little more than local aberrations in the broadcast universe until satellites were brought into the picture. In the late 1970s, Ted Turner had the idea of distributing WTCG in Atlanta via C-Band across the United States. Available evrywhere across the country, WTCG became the first "superstation."

The FCC defines a “nationally distributed superstation'” in 47 CFR 76.120. The general requirement is that the station is “not owned or operated by or affiliated with a television network,” offers “interconnected program service on a regular basis for 15 or more hours per week to at least 25 affiliated television licensees in 10 or more states” and is retransmitted by a satellite carrier.

The significance of Turner’s conceptual innovation was that when CNN was launched in 1981, it followed the same national distribution paradigm, satellite up link and national distribution via down link to domestic cable headends. So, in a sense, superstations morphed into national cable TV broadcasting.

The cable plant grows

Aided by government deregulation, by the end of the 1980s, nearly 53 million households subscribed to cable, and cable program networks had increased from 28 in 1980 to 79 by 1989. The growth continued, and in 1995, there were 139 cable programming services available nationwide, in addition to many regional programming networks. By the spring of 1998, the number of national cable video networks had grown to 171. At the turn of the millennium, more than 65 million households, roughly 70 percent of all TV viewers, subscribed to cable.

As the Internet exploded in the late 1990s, cable operating companies began upgrades of their distribution networks, investing $65 billion between 1996 and 2002 to build higher capacity hybrid networks of fiber optic and coaxial cables. These “broadband” networks provide multichannel video, two-way voice and high-speed Internet access.


The primary means of making programming available to MSOs and regional cable systems is via satellite. There is a certain kind of irony in that cable and DBS are battling for subscribers and cable is completely dependent on satellites for content distribution to headends.

Established by AT&T Broadband and operational since 1994, Headend In The Sky, (HITS) in Littleton, CO, delivers more than 170 digitally compressed video and audio TV programming signals to more than 3,000 cable operation sites across America. In 2001, Comcast acquired AT&T Broadband, HITS and AT&T’s cable TV business, and now reaches more than 22 million customers.

HITS Total Digital service consists of:

  • Basic: More than 60 basic and expanded basic networks on up to six transponders delivered via satellite on SES AMERICOM's AMERICOM2Cable AMC-4 satellite;
  • Expanded: More than 150 video and 50 audio services on 15 transponders, with the upgraded video quality of Pure Pixel Plus technology from Motorola;
  • High Definition: 6 HD channels on two transponders.

MPEG-2 video is encoded with redundancy using DigiCipher II encryption. The Main satellite footprint covers the continental U.S. (CONUS), while Alaska, Hawaii and Puerto Rico have spot beams. Programming is received via Ku and C band. The turnkey service includes a disaster recovery plan and around-the-clock headend maintenance and monitoring.

On the wire

Once content is received at the headend, the programming is distributed over the plant, cable that has been deployed either underground or overhead. Cable operators are granted franchises to specific geographic areas and have to negotiate right of way for each of these territories.

A tree and branch topology is used until reaching the customers’ homes. A detailed description of cable system topologies can be found in the report, “Technical Analysis of Open Access and Cable Television Systems.

Distribution from the headend is moving toward an IP-based methodology. DTV transport streams and other data packets travel the distribution network. At the “edge,” a QAM modulator facilitates program delivery to a cable ready receiver or set top box (STB).

There are three communication channels between the cable distribution network and the customer’s premises:

  • An upstream channel between 5 and 40MHz uses QSPK modulation to send information back to the service provider.
  • An out-of-band channel is used to deliver STB upgrades.
  • Distribution of cable TV signals is done over dedicated frequency bands on a single wire. QAM and a standard 6MHZ bandwidth channel are used. All “services” are available to the consumer all the time.

The Society of Cable Telecommunication Engineers (SCTE) addresses technical issues and sets standards for cable systems.

SCTE 07 2006 “Digital Transmission Standard For Cable Television” defines the technical methods used for DTV delivery on cable systems. The parameters of various processing blocks are tweaked for a cable environment.

ANSI/SCTE 43 2005 is the Digital Video Systems Characteristics Standard for Cable Television. The document specifies particular constraints and extensions to MPEG- 2 and other incorporated standards when used in cable systems.


The broadcast paradigm of delivering all channels simultaneously to a viewer has been carried over into cable systems. But with the transition to DTV, and in particular HDTV, bandwidth on cable systems is in demand. After the upgrade of cable systems to bidirectional capabilities and with the successful deployment of VOD, cable operators are now migrating toward a paradigm similar to the Internet. Deliver only the program the subscriber desires.

Switched Digital Video (SDV) broadcasting enables dynamic bandwidth allocation for infrequently used channels, rather than allocating bandwidth to lesser-used channels all the time. So, by delivering only the desired program to a customer, bandwidth is freed for more HD broadcasting and video-on-demand services.

An SDV solution

OpenTV and C-COR have developed an open architecture switched digital video system that integrates an interactive program guide based on OpenTV Core 2.0 Middleware that runs on Motorola's DCT-2000/2500 set-top boxes. C-COR's nABLE global session and resource manager (GSRM) provides session and edge resource management.

C-COR's nABLE GSRM is a core component of the nABLE On Demand Management Platform. It facilitates management of both On Demand and switched digital broadcast from the same application. OpenTV Core 2.0 provides a common operating environment across different hardware and software digital TV platforms.

Turnaround is fair play

The build out and use of back channel capabilities by MSOs has enabled a lucrative business opportunity for cable broadband service providers. It seems like everyday a new off-air show is being offered by a network for download and viewing.

VOD and PPV services don’t require human intervention, with downloading and billing being completely automated. Long anticipated convergence of TV and Internet functionality is finally becoming a reality in these first generation iTV features.

Last-mile bandwidth is the limiting factor. Fiber to the curb (FTTC) and home (FTTH) seeks to enlarge the data capacity “pipe” into consumer homes and offices.

Trying to get a bigger piece of the pie, MSOs have introduced VoIP telephony service in direct competition with telcos. Telcos have not taken the attack lightly.

A very real threat to cable operators is the emergence of ADSL+ and FiOS. With the advent of improved codecs and bigger DSL pipes, TV may become big business for traditional telecommunication companies. This means trouble for CATV operators.

The next T2D will discuss IPTV.