YouTube, AppleTV, ABC.COM, Cinemanow, Movielink, Amazon, unbox and the list goes on. Look at the growing numbers of players in the Internet video space. Believe the recent statistics on video viewed over the Internet. Internet TV has arrived.

A comScore report for July 2007 indicated that nearly 75 percent of U.S. Internet users, 134 million Americans, watched an average of three hours of online video during the month, a total in excess of 9 billion streamed videos. Despite the fact that a large portion of this video is of short duration and marginal quality, the demand for content over the Internet continues to grow month over month. Threat or opportunity? The impact of Internet video on cable operators can be significant. In the current model, the over-the-top video providers generate the revenue, either subscription or ad supported, and the operators pay for the network expansion necessary to support the explosive growth in traffic.

How much network expansion, and at what cost? There are several ways to assess these numbers. Estimating (conservatively) that half of those 9 billion streams measured by comScore were carried via cable access, you’d get 4.5 billion, which then turns into 150 million by the day, or 6.25 million by the hour. Stipulate further that each of these streams averages 15 minutes and, under a linear model, you’d see about 1.6 million separate streams cross cable’s access plant every quarter hour.

Of course, data traffic is not linear, but bursty. Futhermore, translating its impact on a cable access plant involves looking at an additional set of numbers, including service group sizes, penetration rates, simultaneous usage, speed per user, throughput per node, and quadrature amplitude modulation (QAM) channels per node.

Here is an additional difficulty in forecasting the cost of network expansion: In the migration toward DOCSIS 3.0 that is now underway, several of these benchmarks – from throughput to cost per QAM channel – are themselves shifting.

The degree to which the over-the-top providers drive high-speed data subscriptions is another incalculable and possibly offsetting factor. Suffice to say, however, that millions of dollars’ worth of cable infrastructure is underwriting the delivery of increasingly popular video services that are generating revenue for other providers.

This new cadre of Internet video providers relies upon best-effort, high-speed data networks, expensive content distribution networks (CDNs) and access networks (both cable and telco) to deliver their content to the consumer. This delivery model is suitable for consumer demand today, but as popularity grows, so will expectations for higher and more reliable quality. Herein lies the opportunity.

Over the past several years, cable operators have invested millions of dollars to ensure that their digital video and DOCSIS networks are reliable, provide the highest levels of quality, and are designed for expansion, both in capacity and functionality. Combining this infrastructure will enable operators to offer their own high-quality, cost-effective cable IPTV service. Cable will prove a very worthy opponent to those new Internet upstarts. What is IPTV? The term "IPTV" (Internet protocol television) refers to video delivery to an IP device. In cable, the access network used is based on DOCSIS QAM/RF with the home gateway being a cable modem or DOCSIS-capable set-top box. This differentiates it from telco-based IP video services.

A broad range of video services can be enabled using IPTV. Services similar to those provided via the traditional cable system can be delivered using an IP infrastructure, such as linear TV by way of switched digital video (SDV) and traditional video on demand (VOD). More flexible than the traditional system, IPTV is capable of supporting additional applications such as higher video quality and lower bit-rate MPEG-4 AVC (H.264) encoding or personalized mosaic.

Given the argument that the classic cable architecture can address both broadcast and targeted video services so effectively, one might question IPTV over cable and its expense. Yet leveraging existing infrastructure allows operators to minimize the associated overhead and justify the inclusion of cable IPTV into their offerings. Leveraging assets The combination of existing digital video and DOCSIS networks allows for the most efficient means to deliver IPTV by cable operators. Figure 1 provides an overview of a combined cable IPTV delivery network that enables the delivery of VOD and SDV to the PC or IP set-top box. This architecture, which is based upon a modular cable modem termination system (M-CMTS), DOCSIS 3.0, VOD and SDV, consists of the following elements.

• Core CMTS: Cable modem registration, high-speed data and voice over IP (VoIP) delivery
• Cable modem (narrow or wideband): High-speed data, IPTV access
• Cable modem/multimedia terminal adapter (MTA) provisioning server: Cable modem initial registration

Digital Video
• VOD server: Store and stream VOD/time-shifted content
• Multicast video sources: H.264 encoded video source for SDV
• VOD/SDV session manager and middleware: Client to session communication, interface to business systems
• Edge resource manager (ERM): Manage QAM resource allocation
• Conditional access (CA): control access to services for authorized users
• PC/IP set-top client: Communicate to CA and session manager for access and session management

• DOCSIS timing interface server: Synchronizes timing between core CMTS and universal edge QAM modulator
• Universal edge QAM modulator: Delivers DOCSIS encapsulated MPEG stream to the cable modem
• GigE switch

With the exception of the IPTV client and possibly the IPTV session manager, each of the elements mentioned previously is already a key element in the existing architectures. This lets operators leverage existing investments to deliver this new service, maximizing quality and minimizing costs. The delivery elements described are then combined with the session control signaling to tie the entire solution together.

Cable IPTV is perfectly suited for both VOD and SDV. The control signaling for both of these applications is based upon existing VOD and SDV standards and implementations with minor modifications. Each of these applications is explained later. VOD VOD over cable IPTV is based on a switched network with unicast streaming to a client. A unicast channel is created between the VOD server and the client. This link is created directly to the edge QAM modulator. The system enables the delivery of a VOD asset to an IP set-top or PC connected to cable modem. The session is initiated by a request from a VOD client, which runs on the PC or IP set-top and communicates with the VOD session manager over IP.

The VOD client sends a request for an asset to the session manager. The IPTV session manager receives the session control messages from the client and requests QAM resources for the asset from the ERM. Once the QAM resources have been allocated, the session manager selects the VOD server and sends a message to transmit the asset to the client.

In the case of a wideband cable modem, the cable modem is tuned on its primary QAM channel to one of the core-CMTS downstream channels on which the DOCSIS media access control (MAC) messages and tuning information are exchanged. The VOD traffic is carried on the secondary downstream QAM channels directly associated with the edge QAM modulator, where it is then encapsulated with the appropriate DOCSIS header. The data is then streamed to the cable modem, which strips the DOCSIS header and delivers the stream via IP to the client to render the video to the consumer. (See Figure 2.) Switched digital As the cable industry has already recognized, linear TV is a service well-suited for delivery via IP multicast and results in greater network efficiency.

With IP multicast delivery of linear TV, devices in the headend encode one or more video channels into an MPEG transport stream, which is carried in the network via IP multicast.

In the cable IPTV system, the multicast service flows directly from the headend to the edge QAM modulator. A client that resides on the PC or IP set-top initiates the SDV session. The client sends messages to the SDV session manager requesting a channel change. The SDV session manager is configured with the list of channels and their multicast addresses along with a list of QAM channels that can service each client.

The SDV manager then replies with the frequency of the QAM channel that carries the multicast service. The cable modem tunes to the QAM channel and receives the multicast service. If the client sends a channel change request and the channel is not available on any of the QAM channels in its group, the SDV session manager will set up a new multicast session. The SDV session manager sends a setup request to the ERM for a new multicast session with multicast address, client information and list of QAM channels. The ERM allocates a QAM channel and sends a response to the SDV session manager, which in turn sends a response to the client with the tune parameters.

The EQAM modulator joins the multicast service and encapsulates the traffic with DOCSIS frames and, as in the VOD description earlier, forwards the stream to the cable modem, which receives the multicast streams directly from the edge QAM modulator on the secondary channels, strips the DOCSIS header and delivers the stream via IP to the client to render the video to the consumer. (See Figure 3) Conclusion First satellite, then telco and now Internet – cable operators continue to fight a highly competitive battle to grow and maintain their video subscriber base. Fortunately, the investments made in the DOCSIS and digital video infrastructure over the past several years have prepared them well.

The emergence of Internet video should not generate fear but excitement. A report detailing a six-month study commissioned by CTAM and based on Nielsen data concluded that Internet viewing actually increased consumers’ overall TV viewing. This opportunity, not crisis, presents numerous new possibilities for operators, whether it be a new, independent, revenue-generating service, a tool to be used to upsell to premium video and/or data packages, or a new vehicle to generate revenue from targeted advertising.

Cable’s competitors are comparatively ill-equipped to compete against the leveraging of cable’s existing infrastructure and relationships with content providers. By creating new and compelling service offerings, cable can keep the lead. The industry has the experience, tools and innovation to fend off these foes, old and new.

Tom Kennedy is director, cable strategy and business development, for Harmonic. Reach him at

The Daily


Ad Market Sizzles for Online Video

Zenith predicts that online video advertising will be the fastest-growing digital channel in 2021, rising by 26% to reach $63 billion. Overall, the firm predicts digital advertising will take 58% share of the

Read the Full Issue
The Skinny is delivered on Tuesday and focuses on the cable profession. You'll stay in the know on the headlines, topics and special issues you value most. Sign Up


Sep 10
Most Powerful Women – 2021 Nominations Due: Sept 10, 2021
Dec 7
Most Powerful Women CelebrationSave the Date!
Full Calendar


Seeking an INDUSTRY JOB?

Hiring? In conjunction with our sister brand, Cynopsis, we are offering hiring managers a deep pool of media-savvy, skilled candidates at a range of experience levels and sectors, The result will be an even more robust industry job board, to help both employers and job seekers.

Contact for more information.