Electronic Design

In Entertainment Networks, 1394 Is The Right Choice

Today's electronics industry is populated with excellent standards for just about any design task. The engineering community has done a terrific job of creating these standards, and engineers should use the best of the bunch for their products.

The IEEE 1394 standard, known commercially as FireWire and i.LINK, is typical. Nothing moves video and audio from one system to another faster and more reliably. FireWire is reliable and easy for the consumer to use, which is important as we move into the exciting new era of the home-entertainment network, with high-definition television and whole-house connectivity.

But just as typically, some engineers insist on using the wrong standard in some products. By trying to cut corners, they deprive end users of optimal performance and consign products to "best effort" rather than "best available" technology. Their products risk being overshadowed by competitors who use the optimal standard.

Consider USB. It has emerged as a great interface between PCs and low-end peripherals. After some early performance challenges, it's ubiquitous in PC peripherals. Some designers, though, use it in camcorders and for high-end hard-disk drives. These design decisions carry performance costs and automatically lower video transmission quality—-definitely not optimal digital video.

The specifications tell the story. FireWire is faster. A series of independent studies last year found that FireWire 800 transmits information at 30 to 54 Mbytes/s compared with USB's 16 to 21 Mbytes/s. Even 1394a, with a throughput of 22 to 26 Mbytes/s, is faster. This is because USB is PC-centric, so it carries administrative overhead that FireWire doesn't.

Comparing 1394 against USB's power-carrying capacity shows another marked difference. USB 2.0 provides 5 V and 500 mA, which is insufficient for advanced hard-disk storage and external DVDs. FireWire delivers a full 30 V and 1.5 A. For the business traveler, that means 1394 can power HDDs and DVDs with no need for bulky add-on power supplies. Even in the home network, the additional power is more convenient.

So, the optimal design choice is to include both interfaces in the PC network. USB and FireWire coexist well in notebooks, which use both to good advantage. But in camcorders, digital cameras, and wherever top quality video is needed, 1394 is the only choice.

This is true for products like TVs, DVD receivers, and set-top boxes, which are at the core of the emerging home-entertainment network. FireWire is pre-eminent, but Ethernet seems to have a dedicated constituency that thinks it can enhance it to be "good enough." This doesn't make sense, as 1394 is designed specifically to move multiple high-definition video streams in real time and to support peer-to-peer networking. Ethernet is not. Multiple devices in an Ethernet network cause collisions that reduce the usable bandwidth at regular intervals, all the way down to as little as 15%. FireWire will never fall below 60% usable bandwidth.

Ethernet fans will have to overhaul it completely, adding lots of buffering to store video up front, so the stream remains continuous during busy periods. But buffering creates a minimum 7-s. delay each time the viewer changes the TV channel—not a recipe for delivering real-time audio or video. It's not even a satisfactory best effort.

Also, consider product-to-product connectivity. FireWire operates using peer-to-peer transmission, so all devices with a 1394 interface can interact. Ethernet needs bulky equipment typically required for data processing.

For an office network, Ethernet is fine, although the FireWire standard can also complete all of an office network's tasks very reliably. Yet as we move from computer to home-entertainment networks, led by the move from analog to digital TV, Ethernet will never do the job without an expensive technical overhaul that carries risk and unnecessary delays in product development and leads to only a best-effort transmission.

USB and Ethernet are model standards that are excellent for data transport. But it's simply bad design to try to force-fit them into real-time audio and video applications, or into home-entertainment networks, where 1394 is the best choice.

TAGS: Components
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