Capital Currents: Baseband digital interfaces, revisited

Wed, 07/31/1996 - 8:00pm
Jeffrey Krauss, Interfacing with The Digital World and President of Telecommunications and Technology policy
By Jeffrey Krauss, interfacing with the digital world and President of Telecommunications and Technology policy

This work has run into a major conflict that is almost certain to lead to incompatible, consumer-unfriendly products. And this time, nobody can blame the cable industry. The blame rests with two different groups of TV and VCR manufacturers.


The EIA set out a few years ago to adopt a standard for a baseband digital interface that allows digital TVs, VCRs, cable boxes and other audio- visual media to send signals to one another. Think of this as a local area network connecting these devices within a single room. The EIA decided that the data rate should be at least 50 Mbps in order to carry two digital HDTV signals at the same time.

The EIA 1394 standard was agreed to last year as the physical layer of the network. This was developed by the computer industry and is called "FireWire" by Apple. It can carry packetized data, including digital video or digital audio, at data rates of up to 400 Mbps on twisted pair cables.

The next step is agreement on a command language. This is needed to allow different devices on the network to talk to one another, identify each other and execute the commands that the user sends with his handheld remote control. For example, it allows the cable box to tell the TV which channel it should tune to in order to allow the customer to watch a pay-per-view movie. This example assumes, of course, that there is only one digital tuner, located in the TV and shared by the other devices in the network.

The conflict

Well, it now turns out that there are two command languages on the table, each with a group of proponent companies. The CAL command language, which is used in analog audio/video and home automation products that work on a network called CEBus, is supported by a group of TV and VCR manufacturers headed by Thomson Consumer Electronics.

Other CAL supporters include Intel, Honeywell and AT&T. The AV/C command language was developed by the Digital VCR Conference and is supported by Sony, Mitsubishi and (they claim) more than 50 other companies.

Both of these groups plan to have TV sets and digital VCRs on the market within the next year. Thomson and other companies will have digital VCRs later this year that connect to the RCA DirecTV satellite receiver and record the satellite-delivered digital programming. These products will use the CAL command language. Sony, Mitsubishi and others will have digital VCRs and TVs on the market later this year, and they will talk to one another using the AV/C command language.


Products using the CAL command language and those using the AV/C command language can coexist on a 1394 network. But they can't talk to one another. You won't be able to use a Sony digital VCR with a Thomson DirecTV receiver, or an RCA Digital-VHS recorder with a Sony TV.

Digital cable boxes can be designed to support both the CAL and AV/C languages. This will increase their costs, of course, because it requires additional processing capability. But it doesn't seem likely that boxes that only speak one language will be able to operate in the same network with boxes that only speak the other language.

This is something like the Beta vs. VHS split in the analog VCR market. But there, the video cassettes were physically different and incompatible, and consumers could understand that. Here, the physical 1394 cable will connect into both groups of products. The incompatibility is deep in the electronic signals, hidden from view. Try explaining that to consumers.

What will happen? It's too soon to say. Both sides seem committed to their command language. Neither command language appears to have any significant superiority over the other. This may be a case like driving on the right-hand side of the street, versus driving on the left-hand side. Neither one has any apparent superiority over the other, but there are huge benefits to the public when everyone does it the same way.

A compromise?

Maybe, like the Beta/VHS case, one will win in the marketplace, and the other will wither away, but only after consumers make a huge investment in hardware.

Maybe a market will develop for command language "translators." Because the incompatibility is in the signals, it is easier to build "translators" than if there were physical incompatibilities. Think about the difficulties of playing a VHS tape in a Beta VCR, or a music CD in a cassette player. But running PC software on a Mac is feasible.

Or maybe one side will back off and accept the other's command language. The consumer electronics industry has behaved like this in the past, in order to avoid product incompatibilities. Now's the time for them to work on such a compromise, before there are large consumer investments at stake.


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