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FireWire - Linking the DV world together

Copyright Daniel Rutter 1996. All rights reserved.


As soon as the Digital Video (DV) concept surfaced a wonderful image bubbled up in my brain. That wonderful image was of a DV camera pumping perfect, incorruptible video straight into a PC for editing by some simple little adaptor cable. No capturing, no generation losses, nothing more to buy.

That image looks set to become a reality in the next year or so, and the enabling technology, as pony-tailed persons in suits are wont to say, is poetically titled "The IEEE-1394 High Performance Serial Bus".

Because "The IEEE-1394 High Performance Serial Bus" is not a phrase that trips melodically off the tongue, it's usually described using the trademarked Apple Computer name, FireWire.

If you use DV, you'll be using IEEE-1394. FireWire is the standard digital audio/video interface for every DV product. It can be used for all sorts of things, but a major application will be the connection of digital audio and video gadgets to personal computers of every stripe.

FireWire can be used as a general purpose data transfer system for all sorts of computing applications, though whether people will actually end up using it this way is far from certain, thanks to considerable heavyweight competition..


Good stuff

What makes FireWire the way to go? Well, it's small - a FireWire cable is relatively thin (FireWire cable is not unlike 10BaseT thick Ethernet cable) and can be up to 4.5 metres long in each stage without repeater boxes, and even carries power as well as its four data wires. So, it can theoretically be the only cable connected to some devices.

The power supply's really there to keep the signalling interface of the 1394 adaptor on each connected machine powered up even if the host machine's turned off, so any number of devices on a FireWire network can be powered down and leave the rest working fine.

FireWire is baroquely complex in specification - the spec runs to hundreds of pages. But, it is sublimely easy to use. In order to make an IEEE-1394 compliant device work you just plug it in, and you don't have to worry about addresses or termination or the geometry of the setup. It's hot-swappable - you can plug and unplug FireWire devices with everything still turned on and they'll be automatically recognised.

It's fast too, with current chipsets capable of 100MBps (megabits per second), 200MBps chips just around the corner and 400MBps due late this year. You can mix devices of different speeds on the one FireWire network - it's even possible for two fast FireWire devices to communicate at their peak speed on a network which also includes slower devices, as long as the slower devices aren't in between the fast ones. Future speed increases up to 1GBps are on the drawing board.

IEEE-1394's exceedingly flexible in topology - you can run your devices in a SCSI-esque daisychain, or in a star configuration, or as a tree, or any other way you like. And it's not proprietary - nobody has to pay license fees to anybody to include it in their products. And it's even cheap - around $US200 for computer IEEE-1394 interface cards, when they're available.

And you can put a whole LOAD of devices on it. Even the mightiest SCSI-II FAST WIDE device chain can only have 15 units plus the controller on it; FireWire supports 63 devices with, might I remind you, no termination and address setting to worry about.


Used first on DV cameras

A whole slew of products not traditionally thought of as PC peripherals are going to feature IEEE-1394 compatibility. DV cameras are the big news, but IEEE-1394's low price and high specifications means it could show up on VCRs, CD players and digital TV sets, as well as hard drives, printers, scanners, still video cameras and other traditional desktop gadgets.

High speed interface connectors are not renowned for their convenience. Hands up everyone who's gone half mad trying to plug a 50 way Centronics SCSI connector into the back of a computer that can't be moved out because of the mighty cable thicket tethering it to the wall? Those days are over.

The standard connectors used for FireWire are related to the connectors on the venerable Nintendo GameBoy. While not especially glamorous, the GameBoy connectors have proven reliable, solid, easy to use and immune to assault by small children. If a four year old can't break it, you probably won't be able to either.


Mine! Mine!

The problem, technically, with pushing tons of digital audio-video data around is that you either need a completely reliable network that you KNOW is not going to run out of bandwidth, or giant buffers all over the place to take care of the pauses and surges in data delivery that the network produces.

FireWire, of course, has an answer for this too. It can operate in two modes - asynchronous and isochronous.

In asynchronous mode FireWire works like many other data transfer systems - data is sent one way, an acknowledgement's sent back. Isochronous mode, however, sets up a channel with a particular data transfer rate and doesn't let anything else use this bandwidth, even if it's not actually full of data at the moment. So a video player that knows it's going to need, say, 70MBpS of a 100MBpS 1394 network's bandwidth can reserve it for the period it needs it, and nobody needs to throw away 20Mb of RAM to keep the data flowing. Up to 64 isochronous "channels" can be running at once.


Share and share alike

The trouble with network bandwidth is there's never enough of it. Isochronous channels are all very well, but if three systems each want a 50MBps slice of a 100MBps network, you're still in trouble.

IEEE-1394 gets around this by means of "bridges", adaptors you put inline which prevent devices on one side of the bridge "polluting" the rest of the network with their own traffic. So if you've got five big hairy video editing machines FireWired to each other and to five DV cameras and to five DV record decks, you can set the network up so each computer's got a direct connection to one camera and one recorder, but each is bridged to the others. If one of them makes a specific request for data from one of the machines on the other side of the bridge it'll be sent, and sent no slower than it would be if the bridge wasn't there. But otherwise, their "neighbourhood" of cable won't be carrying megabits of data they don't need.

A FireWire net separated from other nets by bridges is its own personal "bus segment", which can have up to 63 devices. You can connect more than 1000 bus segments with bridges. If you find this restrictive, it's nice to have you reading, Mr Lasseter.

Mind you, FireWire's less cloggable than other networking systems anyway. It uses a "fairness" arbitration system to make sure that bus-hogs not using an isochronous channel give way to other data transmitters.


Prosumer first

"Prosumers", people who use technology in a semiprofessional capacity and for cost or other reasons don't buy the full spec professional hardware, are the major targets for early FireWire gadgets. This is because professionals and lowly "consumers" are hard to sell new technology to - professionals already have a huge investment in the existing technology and aren't going to throw it away for anything that everyone else isn't already using, and consumers need a highly evolved, easy to use product that requires a long development period.

Prosumers are famed for their enthusiasm for new products and their tolerance of flaws. If they find a nonlinear editing system that costs ten times less than the competition but crashes every five hours on the hour, they'll buy it, and an alarm clock. And so the first FireWire-equipped products will be prosumer DV cameras and associated accessories for Macintosh and IBM compatible PCs.

This is not to say these products will have glaring flaws - the first generation DV cameras are very desirable items indeed - but FireWire-related technology can only improve and diversify its appeal over time.


The problem for the solution

There's a real need for a faster-than-SCSI interface, if hard drives' potential data delivery speeds aren't to outstrip the data-moving abilities of their interfaces. Drives currently available manage transfer rates pushing the 10 megabyte per second (Mbps, not to be confused with megabit per second, MBps) mark, so two of these moving data at the same time will choke even a Fast Wide SCSI-II bus.

In the interim, there's the ANSI Fast-20 and Fast-40 protocols, also known as Ultra SCSI, which double SCSI's internal clock speed to offer 20Mbps and 40Mbps transfers for Fast and Fast Wide SCSI-II, respectively. Ultra SCSI is backward compatible with previous SCSIs (provided your total cable length is less than 10 feet...) and the adaptor cards come in at around the $US400 mark, but it can be nothing but a stopgap - Seagate's director of marketing and planning, Craig Frane, says drive performance is improving from 30 to 50 per cent every 15 to 18 months, and at that rate merely doubling your available bandwidth ain't good enough.



The wonderful thing about standards (cue background well-played-record crackling noise) is that there are so many to choose from. And IEEE-1394, despite its marked advantages overall, faces competition from other high speed transfer contenders in the computer data transfer area. Nervous purchasers not eager to repeat the Beta VCR buyers' experience of paying a thousand dollars for a clock will know that the best technology doesn't necessarily win, so it's wise to keep an eye on the other competitors.

Fibre Channel Arbitrated Loop (FC-AL) and Serial Storage Architecture (SSA) are high speed transfer systems designed to replace SCSI, and as such have a fighting chance of elbowing IEEE-1394 out of the computer world.

FC-AL is the frontrunner of the two in specification. It offers 100 megabyte per second data transfer - an 800 megabit per second bandwidth, with double that speed possible in future versions. This colossal speed is needed by serious file servers and specialist video machines today - and, going by past trends, will be needed by ordinary family desktop machines in not very many years.

FC-AL's major claim to fame is that it's built on the existing Fibre Channel system, as used for eyepoppingly expensive fibre optic networks in various monster applications. FC-AL can use pricey fibre cables, but FC-AL also works fine with plain copper cables, which is what ordinary mortals will be using for some time yet.

The networking connection, though, means FC-AL can be used for ALL of your computer connections. Controller to drive, scanner to computer, computer to printer, computer to computer. If you're a big corporation that already has FC networking, this is obviously attractive.

IEEE-1394 and SSA are restricted to connecting boxes to other boxes in non-shared ways, and cannot run network protocols, so you'll still need separate network cards and cable between your computers.

FC-AL supports 126 devices in a chain, doesn't need any manual addressing and can have cables 30 metres long. It does cyclic redundancy check (CRC) error detection instead of SCSI's simple parity check, and it supports hot plugging and unplugging like IEEE-1392.

FC-AL is not for the common or garden computer user. Controllers and drives should start to arrive in bulk later this year, and they'll be aimed at people who need gigantic superfast storage - serious video operators and maintainers of giant file servers, for the most part. FC-AL controllers and drives will be something like one and a half times as expensive as comparable SCSI gear, but that comparable SCSI gear is the top of the range hardware, not $150 Adaptec controllers and $500 drives.

SSA is slower and should be cheaper than FC-AL, and SSA devices have actually been shipping from IBM since August 1995. SSA moves a relatively small 80 megabytes per second, and supports 20 metre cables.

Like FC-AL, SSA supports 126 devices per loop, with FireWire bridge-style switches to permit more. It supports cheap copper cables or fibre optics - which extend the device to device distance from 20m to 2.5km! And, like 1394 and FC-AL, you can hot-swap devices and you don't have to set addresses. SSA's special feature is that while it's physically different from SCSI, it uses the same protocol - so existing SCSI devices don't have to have all of their firmware rewritten from the ground up.

And, in case all this isn't complex enough for you, SCSI doesn't look as if it's going to roll over and die as quickly as proponents of new systems might like. A 160 megabyte per second long-cable Ultra SCSI variant is presently being developed by ANSI XT310 Standards Committee.


System support

Apple plans to have FireWire interfaces on all of its products by the end of this year - although this doesn't necessarily mean they'll all come as standard with a FireWire port. Microsoft's promised to include FireWire compatibility with future versions of Windows. Microsoft like it because it makes their Simply Interactive PC (SIPC) idea easier to achieve - IEEE-1394 is inherently perfect for plug and play applications, and its simplicity suits Microsoft's vision of fully integrated home entertainment systems.

Compaq's new line of Presario computers, due out at the end of this year, will feature 1394 interfaces, and Texas Instruments is making the chips now and will be making 1394-ported notebook computers later this year. Sony's two prosumer DV cameras (the DCR-VX1000 and DCR-VX700) both have 1394 ports (they call it DigitalLink), as does their ES-7 Pentium-based nonlinear editing system and upcoming "DVCRs", and Matsushita should have similarly equipped cameras out soon. Panasonic Broadcast & Television Systems Company's DVCPRO professional digital video system will also push data via 1394.

Adaptec has various IEEE-1394 products in the pipeline. Cirrus Logic wants to make the chips. Conner has pledged support, as have DEC and Western Digital.


Will FireWire fly?

It is eminently possible that IEEE-1394 will find a home with Apple as their replacement for the ancient, slow but simple AppleTalk networking system, but will stop there as far as pure computer applications go. FireWire's the only horse in the DV data transfer race and so will definitely not become an orphan format - but there's a big gap between survival and ubiquity. Popularity with notebook makers and designers of unproven home entertainment concept computers is a long way from being as universal as, say, IDE, or even SCSI.

Sure, it'll be nice if everything's 1394 compatible. But the rabid competition that drives computing's mercurial development carries with it an inescapable difficulty in settling on standards, and systems that Deserve To Win frequently don't.

The worst case scenario, fortunately, is my original dream. One way or another, you'll be able to connect a pretty cheap camera to a pretty cheap PC via a pretty cheap interface and do darn good video editing. If that ain't good enough for you, I advise you to lower your standards.



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Of Megabits and Megabytes

One of the most annoying things about researching a story like this is doublechecking every transfer rate statistic you see to find out whether the people that produced the original document meant megabits per second (MBps) or megabytes per second (Mbps). If you believe Prentice Hall's Illustrated Dictionary of Computing, B is the abbreviation for bit, b the abbreviation for byte. It's counterintuitive that the smaller unit have the upper case initial, but that's the way it is, because the bit was invented before the byte and got first dibs on acronyms.

Unfortunately, universal usage among corporate, academic and government bodies appears to have swung solidly to the "big-B-byte, little-b-bit" way of thinking. This is intuitive and a sensible enough way of doing it - but the same darn institutions produce reams of documents in which megabyte is abbreviated Mb. There's no point being precious about a fine point of terminology when the flow of usage is plainly going the other way, but when the flow's going round in circles life gets difficult.

Megabits per second is a common measure of network speed, megabytes per second is the human-language variant. Converting between the two is of easy - MB=Mb/8 - but figuring out exactly how many bits or bytes there are in a mega is trickier.

The Systeme Internationale (SI) prefix "mega" denotes one million (10^6) if it's talking about things that come in tens, like centimetres or dollars. But computers work in binary (base 2), and so their numbers go in powers of two, not powers of ten. The mega prefix, as far as a computer's concerned, denotes 2^20, or 1,048,576. Not one million or, for that matter, the halfway-right 1,024,000. It is downright amazing how many glossaries define a megabyte as 10^6 bytes.



Parallel and serial

All of the new wave interface designs - IEEE-1394, SSA, FC-AL - are serial designs. This means they send data one bit at a time. Parallel interfaces are the old guard - they send their data several bits at a time, down more wires. Ordinary 8 bit SCSI cables have 50 wires, 16 bit cables (for Fast and/or Wide SCSI) have 68 wires. Parallel would be a great way of getting more data down the cable, were it not for the fact that said cable can't be very long, and has to be thick and expensive to get all of those conductors in.


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