Datacasting

A new market driver that combines aspects of digital TV and World Wide Web is gaining the attention of both the broadcasting and the Internet industries. The service, called datacasting, is the broadcast delivery of data over broadcast TV media, such as over-the-air terrestrial broadcast or cable TV.

Datacasting provides a means to reduce signaling problems evidenced by the Web. For many applications, going to push-mode form of delivery provides an opportunity for scaling to RBB proportions and providing important new revenue sources for the Web.

Datacasting is a bandwidth reduction and signaling reduction technique, which permits greater scaling of the servers and networks, which provide content. The tradeoff in both cases (push-mode data and nVoD) is reduced user control and flexibility. For many applications, such as stock quotes and news and software updates, the tradeoff for push mode makes sense.

The basic idea is that data content providers will distribute data over broadcast media (over the air, cable, and satellite) within DTV channels. This is an opportunity for a new type of ISP. Whereas most Internet folks view video being transported inside IP packets on the Internet, broadcasters have a different idea. They believe that IP packets can be transported like TV program signals. The user's digital set top merely tunes to the data channel, decodes the data, and diverts it to a data port on the set top. A set top box would have both an Ethernet and an ATM port for data and TV interface, such as an RGB cable.

Data distribution over TV is not new. For more than 20 years, text information has been transmitted over analog TV spectrum using spare analog bandwidth in each TV channel, called the vertical blanking interval (VBI). The VBI was originally required as a guard band for receivers to solve vertical hold problems. As TV receivers got better, it became possible to use this bandwidth (up to 96 Kbps) for other purposes. In fact, in older or cheaper TV receivers, the VBI is still necessary for video, so data reception over the VBI may be impaired for these older TV sets.

Some companies such as Wavephore (Nasdaq:wavo) have attempted to make a business of data distribution over the VBI, but with little success so far. One would expect that this is mainly due to the limited amount of bandwidth available in VBI.

With the advent of DTV—specifically, channel multiplexing—much more bandwidth is available than what was formerly available over VBI. DTV offers 19.39 Mbps per 6 MHz channel, ostensibly to support full HDTV. However, it is technically possible to transmit NTSC-quality pictures and sound in 3 Mbps or even lower, depending on the screen size, the distance the viewer is from the screen, and the nature of the picture.

If the original picture can be transmitted in 3 Mbps, what is to become of the other 16.3 Mbps? Media conglomerates can transmit multiple TV programs. For example, Disney owns (completely or a majority of) ABC, ESPN, and the Disney Channel. It would be possible for Disney to simulcast all three channels in digital form in the 19.39 Mbps. Similarly Rupert Murdoch owns Fox, FX, Fox Sports, and Fox News; NBC can do the same with CNBC and MSNBC.

But this won't happen because the broadcasters collect fees from cable and satellite operators for the extra channels. Disney, for example, collects $1 per sub per month just for ESPN. This is more than $700 million a year, just for rights fees.

So ESPN will stay on cable/satellite. Channel multiplex exposes the lack of content at the broadcaster disposal. Distribution of popular Web pages or the contracted distribution of software updates, such as Windows 20xx, represents a way to use that extra bandwidth. Because there are more than 1500 broadcast affiliates in the United States, each with a potential of 16 Mbps of data capacity, several gigabits are available to the nation's broadcasters, representing significant new revenue streams. FCC Chairman William Kennard put it succinctly when he said that DTV is the broadcasters' access network to the home.

Of course, there are technical, marketing, and regulatory impediments to be discussed in due course. One interesting problem is how to preserve VBI text when a program converts to digital transmission without reauthoring the text. But the FCC removed an important regulatory hurdle when it ruled that broadcasters need only pay a minimal charge for money received for such services. That ruling relieved the broadcasters of the concern that if they charged a subscription fee for use of their free over-the-air spectrum, they would need to go to auction. The potential of the Internet (and the lack of programming to fill all those channel multiplexes) gives rise to the interest in pushing data over the airwaves.

Applications for Datacasting

Datacasting is particularly well suited for applications which require the distribution of common data to multiple users without the need for interactivity. These applications, therefore, differ from Internet applications in that Internet applications are typically interactive and point to point, whereas datacasting applications are not interactive and point to multipoint. Also, datacasting does not use the Internet for transport. There is the possibility that widespread success of datacasting could siphon substantial amounts of traffic off of the Internet. That, of course, would depend on the attractiveness of datacasting applications. Some of these are covered in the following sections.

Virtual Channels

TV channels are normally pictures sent from the broadcaster. For suitable content, the broadcaster can send sprites or scripts with which the set top box can render the entire program. This works for cartoon channels and some news and weather channels.

Software Distribution

One potential application of datacasting is software updates. Many popular software programs are retrieved from Web servers by millions of users. For example, to extract the latest version of Netscape browsers, the user goes to www.netscape.com and asks for the download. The user is then presented with a list of servers, from which he selects the source of the update. Because of the popularity of Netscape browsers, the company needs to have multiple servers distributed worldwide, and the user picks one that presumably is closest in proximity. The user chooses a site, hoping it is not too busy at that time. (This is a kind of user-initiated load balancing). Having done so, a connection is set up to that server, and the download is sent.

This process imposes a number of problems. First, hundreds of requesters may be converging on a single server at once. When you pick your server, you do not know the usage on that site. Perhaps a geographically more distant site has less congestion and can therefore offer better service.

More importantly, to retrieve your update, a connection is established with the server, and a dedicated bit stream is created between you and the server. If your colleague in the same building is retrieving the same update at the same time from the same server, you two will be duplicating use of server and network resources unnecessarily.

Eutelsat (Paris, France) is undergoing a trial of data distribution services over satellite. Other software can be downloaded, such as updates to set top boxes. Other home networking devices, such as residential gateways, can similarly be updated. Among the applications would be encryption key distribution fault management of the set top box and computers and software updates.

Datacasting bypasses the wired, terrestrial Internet and is a cheaper way to distribute software than pressing and mailing CDs.

Web Caching at Home

Users could have mass data storage at home that can be updated overnight. They can interact with a local data cache rather than going to the public Web.

Real-Time Data Services

Stock quotes, emergency broadcasts, and weather updates are well-known forms of live information update that can be distributed economically by datacasting.

This list is not exhaustive. Some broadcasters envision customized viewer profiles, which allow for a form of customized broadcast. But these give an idea of some of the potential of datacasting.

Problems Posed by Datacasting

Datacasting can be unidirectional or bidirectional (using a separate, non-broadcast return path, such as the Internet). In the downstream path, the bit rate can be constant or variable (opportunistic, in the parlance of the DTV world). In all these cases, content authoring problems also arise, due to the noninteractive nature of datacasting.

In the case of unidirectional transmission, there are the usual questions of framing, flow control, and error detection. The new question arises as to what hyperlinking means in a broadcast or channel multiplex setting. Even in the case of a slow return path, potentially hundreds of thousands of viewers may communicate with the broadcaster at any instant—what new approaches are required for congestion management and access control? And, in either case, there is a whole new class of HTML authoring required. From WebTV, it is apparent that just putting Web pages on a TV monitor doesn't cut it. Viewers want something that looks like TV on their TV. That means pixel-accurate placement, transparency, translucency, wipes, fades, and dissolves.

Another issue for datacasting is that HDTV may be the killer application its supporters hope it is. If that happens, the entire 19.39 Mbps would be used for HDTV. Datacasting would be pushed back until such time as HDTV could be transmitted on less than 19.39 Mbps so that some bandwidth can be freed up.