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Essay - "IEEE 1394: A Future in Home Theater!" - January, 1999


Scott Evans

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Introduction

Let's face it, the audio industry is slow to change. What major innovations have we had in audio and home theater in the last decade or so? CD, LD, DVD, soon to have DVD audio, Dolby Digital, DTS, HDTV, and soon to have MLP. Ok, so it hasn't been exactly void of change. But if you look at the computer industry, new technologies come and go constantly. For example, when was the last time you saw a new digital bus for audio? S/PDIF has been around forever. Computers however… RS-232, Parallel, IDE, ATAPI, endless flavors of SCSI, USB, Ethernet, etc . . . . The audio industry might get a nice push by computers, because now for the first time, we have a new digital bus technology being developed that could have wide implications in both the Consumer Electronics AND the computer industry.

Today's most widely deployed serial technology is RS-232, which is a point to point technology designed to run typically in the 9.6 kbps range, but can be driven up to 115 kbps. This standard cannot scale to more than 2 devices, and falls far short of meeting the needs of today's high bandwidth devices. Alternate serial technologies such as Ethernet (10baseT) are very popular in computer applications, however this bus doesn't work well with time critical multimedia applications such as streaming video/audio.

How would you like to connect all your hi-fi components together by simply daisy-chaining one cable? What if any device, by any manufacturer, could work together flawlessly with no complicated control issues? What if you could watch a movie in your home theater and finish it in the bedroom by pressing one button - without any proprietary or exotic equipment? What if you could program your VCR to record "The Simpsons" with one click, from a web page, while you are a 1000 miles from home? OK, OK, what is it, you ask, this IEEE 1394 stuff, known by some as "Firewire"?

About 1394

IEEE 1394 is a plug and play, multi node bus topology designed to operate at 100, 200, or 400 Mbps (Megabits per second), and much more in the future (as in Gigabits). The name "Firewire" was trademarked by Apple computer, despite that 1394 is an open standard - so for our discussions, we will stick to the more general term 1394.

There are several fundamentals that make 1394 very attractive to the audio and home theater industries. First and foremost is the high bandwidth. Digital audio and video suck up bandwidth, but 400 Mbps is a LOT more bandwidth than we have ever been used to getting. Today's PC modems access the Internet at a maximum of 56 Kbps or 0.056 Mbps, but such new items as cable modems will allow much more data to be sent and received in short time spans (1 Mbps). The problem is getting it in and out of our computers.

IEEE 1394 standard defines two twisted pairs of conductors utilizing differential signaling. Each pair is individually shielded along with overall shielding of the entire bundle. The pairs are crossed over in each cable to yield a transmit/receive configuration. IEEE 1394 Cable Cross SectionOf special note is the existence of power conductors. This allows the 1394 drivers to retain power even if a connected device loses its standard power source. Connected devices with modest power requirements can be powered exclusively by the 1394 bus. (8 to 40VDC, 1.5A) For smaller battery powered devices, an alternate 4-conductor format is defined which lacks the power conductors and has a smaller cable diameter and connector size. Sony is already using this format in digital video recorders. 28 AWG size conductors are standard for a maximum cable length of 4.5 meters between nodes. 24 AWG conductors are also defined for a maximum length of 10 meters. However companies have already announced transceivers to convert 1394 to run on plastic optical fiber for even longer runs.

So from an architecture viewpoint, 1394 can support multiple simultaneous video and audio streams, along with standard point-to-point commands, responses and data transfer. Up to 127 devices or "nodes" can be connected to the bus. The bus itself is plug-and-play with autodiscovery AND a built-in DC power supply - very convenient for small battery powered devices. IEEE 1304 ConnectorThe connector design for 1394 may look a bit familiar to some people - as the design is is from Nintendo - consisting of a small, inexpensive, yet highly reliable plug-in connector (see diagram at right).

The connector defined for 1394 devices had robustness and consumer applications in mind. The connector design was inspired from the cable connector on the Nintendo GameBoy, designed to be resilient in the hands of children. It is a multi node bus with up to 63 devices per subnet and up to 1023 subnets per bus. The bus must be non-cyclical (no loops between any points on the bus) and can support a maximum of 16 hops between devices. This design yields a tree-like structure featuring both daisy-chaining and branching. The concept of a 1394 bridge has been introduced to route traffic and isolate bandwidth from a highly saturated bus such as a home theater and the rest of the 1394 bus.IEEE 1394 Cable and Home Components Currently there are three bandwidth speeds defined, 98.304, 196.608 and 393.216 Mbits/s (megabits per second), referred to as S100, S200 and S400. The bus auto-configures to the speed of the slowest device on the bus, but allows devices to communicate point to point at a higher speed. Work is under way to define 800 Mbps and even multi-gigabit speeds for the future. Plug & play is supported, and when a device is added or removed from the bus device, node re-enumeration occurs. These capabilities help position 1394 for consumer use with diverse devices with no switches or IDs to manage.

Isochronous?

1394 also supports multiple simultaneous "streams" of content referred to as isochronous channels, in addition to more common asynchronous, or sporadic, data. This means that a 1394 device can reserve a specified amount of bandwidth and open an isochronous channel for the purpose of sending a continuous video stream to another component. This is very hard to do in most existing high bandwidth serial technologies such as Ethernet. With Ethernet , the device just throws the data onto the bus, and the parts that don't get through are sent again. The amount of time it takes for the data to get to the recipient depends on how busy the bus is, and there is no guarantee that the parts of data will get there in the same order they were sent. This makes streaming media such as audio and video very difficult. The isochronous channel assures delivery of the content with a predicable and defined maximum latency.

Early implications for home theater

The most pressing problem in home theater that 1394 will be rolled out to solve is that of cable hell. Most newbie home theater owners are completely overwhelmed by the task of connecting all the parts of a home theater together. You need tons of speaker cable, piles of interconnects, composite, component, S-Video cables, digital cables, power cords, and whatnot. To make it all worse, the connectors are mostly the same, and you really have no idea what should plug where. As for the audio and home theater gurus, we have hundreds of dollars invested in cables: 75 Ohms for video, 110 Ohms for line level audio, 75 Ohms for digital. Analog cables can attenuate the signal and introduce all kinds of nasties, and S/PDIF is a jitter-prone format (even though it will handle up to 2 Gigahertz with BNC connectors). Not to mention that a peek behind the equipment rack looks like an all you can eat spaghetti bucket.

1394 to the rescue

In one early application, equipment manufactures can add IEEE 1394 connectors to the back of hi-fi components, allowing, easy, no-decision one-cable hookup. Connection from DVD player to Receiver would flow DD or DTS compressed audio stream, and control-messages such as skip or pause could be sent from the receiver up to the DVD player (a one remote life looks a bit closer). The video stream could flow directly from the player to the DLP projector. Who needs video switchers anymore, just send a command, and a different source starts streaming! SCSI and USB (Universal Serial Bus) are also designed for daisy chaining, but they are used in computers only. 1394 will be for computers AND consumer electronics.

1394 to the extreme

One of the factors that ensures 1394 acceptance, is its high appeal to the mass market consumer electronics devices (the manufacturers and users, actually). Companies like Sony and Pioneer have a large incentive to include this technology in their high volume product lines. But what will this technology do for high performance, low volume (compared to the mass market) home theater in the near future?

Picture the arranging of your new digital speakers around the room, and connecting an AC power and 1394 cable between each speaker and the wall. The wall plate hosting the 1394 jack contains a fiber optic transceiver which connects the speaker to the entire house 1394 optical bus (optical cable removes the length barrier for homes). Your newly upgraded surround processor has a 1394 cable which you simply plug into another nearby 1394 wall jack. Digital VCRs and DVD players from various manufactures also plug into wall jacks, or a convenient 1394 hub. Even your computer has a 1394 jack and connects to the entire house bus. This paints a picture where audio and home theater components are just elements that plug together in a seamless fashion, along with other things in your home such as the telephone, computer, fax machine, lighting controls, heating controls . . . i.e., everything. Are you excited yet? Me too!

Digital Harmony and 1394 standards

Luckily, 1394 is a complete standard and has been proven and used for some time now. However, the standard defines a wire level protocol and transport only. It says nothing about how the connected devices should talk to each other. There are lots of questions out there: How should newly plugged devices identify themselves to the network, and what questions does a receiver need to ask other devices in order to automatically configure itself? How does a remote control base tell a speaker to lower its volume or tell a DVD player to pause? Remember, the promise here is for devices from any manufacture to interoperate automatically. How do devices perform jitter reduction (the info passed along 1394 is all digital), and what types of encoding are used for digital data? All of these are important questions that need to be answered to ensure a uniform experience from owning one manufacturer's products vs. another.

Welcome Digital Harmony (DH) to the plate. DH has designed a system-level protocol to address the above issues and more. They are also working with chip manufactures to make this technology a reality soon. Unfortunately, you have to be a DH licensee in order to get all the detail about the DH magic, but what it means to consumers is clear. If you buy gear with the DH logo, you will be ensured of a set level of interoperability between your various equipment pieces. DH is focusing on getting big companies like Sony and Phillips on the bandwagon to make this a high volume standard. Meridian is already a licensee, and the top technical engineer for DH is the head of engineering for Spectral! Already we see lots of high end roots and ties for Digital Harmony, which means good things for the home theater industry.

I visited Digital Harmony in downtown Seattle, and they were demonstrating a working set of converter boxes. A box interfaced through S/PDIF and RS-232 to a CD player, converted the control signals and audio stream to 1394 Digital Harmony digital data, sent it over a 1394 cable to another converter box that changed the digital information back to S/PDIF and RS-232 control signals for the connected Meridian 565 decoder. And this all worked! Hopefully we should start seeing the DH logo not too long from now.

Convergence

1394 is already becoming a reality from another angle: the computer industry. 1394 is being adopted for tasks such as interfacing with drives and digital camcorders. With 1394 being adopted in parallel by computers and consumer electronics, new convergence opportunities are starting to arise. These include streaming content from the Internet to home theater, upgrading equipment firmware automatically, and even integrating intelligent control functions with the computer. Who doesn't see the value in programming a VCR from a web page? Just as long as it does not look like this: 12 o'clock Blink

Conclusion

The next year or so will be an exciting time as we see 1394 begin to be integrated into the consumer electronics space. Consider it as an opportunity to convert our homes into little Intranets, with a central control hub, and much simpler connections. The short term benefit alone makes me excited, but to think about the possibilities into the deep future . . .

Scott Evans

Graphics used in this article are copyright Adaptec and Skipstone.


© Copyright 1999 Secrets of Home Theater & High Fidelity
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