Peiya Liu Standards Siemens Corporate Research

IEEE 1394: Changing the Way We Do Multimedia Communications

he mark of a good design is to be general- dard provides a way to move high-bandwidth Tpurpose enough so that its use expands to video and audio digital traffic among peer applications beyond those for which it was origi- devices— recorders, DVD, cam- nally intended. Compare the narrowly defined corders, and high-speed/high-resolution printers EISA (Extended Industry Standard Architecture) and scanners. It supports hot-swapping and plug- David Thompson specification and the now-defunct MicroChannel and-play to improve the experience of consumers Bell Labs bus to the vibrant IEEE 1394 standard, which has who want to use 1394-enabled products. In addi- numerous specifications built around it already, tion, IEEE 1394b is waiting in the wings with and many more under development. speeds up to 1,600 Mbps and 3,200 Mbps on the This article highlights some of the many appli- horizon. cations made possible—or made better—by One of the advantages of choosing a serial expanding on the 1394 standard. It also directs over a parallel interface is the reduced you to the key specifications that have developed size of the required connectors and cables—an for each of the application areas. important consideration in portable consumer products where the IEEE 1394 first made inroads. What is the 1394 specification? The 1394 spec calls for six wires—two differential First introduced as Firewire by Apple Comput- pairs plus power and ground. The protocol defines er in the late 1980s, the now-approved IEEE 1394 two connectors. The four-pin 1394 connector has standard was designed to support high-bandwidth the size advantage: at 5 mm × 3 mm, it’s about requirements of devices such as digital video half the size of a universal serial bus (USB) con- equipment and high-performance . nector. The six-pin connector measures 10 mm × The original specification, IEEE 1394-1995, was 5 mm and includes power and ground wires in ratified in 1995. An updated specification, IEEE addition to the signal wires. Figure 1 shows a Std. 1394a-2000, was approved in March 2000. cross-section of 1394 cable and the relative sizes IEEE 1394a describes a serial bus that supports of the four- and six-pin connectors. speeds of 100 Mbytes per second, 200 Mbps, and Throughout the history of the 1394 standard, up to 400 Mbps with much improved traffic con- there has been great debate over the connector. trol and features. The stan- Some groups opposed a four-pin connector

Figure 1. IEEE 1394 six- Power pair wire cable and space- saving plug (six-pin version).

Signal pairs: (2X)

94 1070-986X/00/$10.00 © 2000 IEEE because of its lack of power and ground wires. However, its size has made it one of the key rea- Transaction layer Isochronous sons for the spec’s rapid acceptance. channels The four-pin connector was so much smaller Packets than the USB connector that it was the connector t n e

of choice for many consumer electronics products. m e

Products such as —the first market g Link layer a n where the 1394 spec achieved broad acceptance— a

m Cycle control Packet transmitter Packet receiver will always be self-powered, as will any portable s u b

device. However, many PC such as con- l a i ferencing cameras and portable disk drives can take r Symbols e advantage of bus power from a six-pin connector— S and they do. By having power and ground wires in the connector, designers can produce bus-powered peripherals at considerably lower cost than a bat- Encode/decode Arbitration Media interface tery-powered portable model of the same periph- eral. Therefore, the six-pin connector is more Interface to 1394 cable desirable when size isn’t the primary consideration. Hardware In addition to providing low-cost, high-speed, peer-to-peer communications with huge amounts of memory-mapped address space, the IEEE 1394 protocol is highly scalable. More importantly, for well, allowing to pass from one device to Figure 2. The link and multimedia applications IEEE 1394 supports both another without passing through the link. For physical layers provide asynchronous and isochronous communications. example, if a PC has two 1394 ports—one con- the hardware Asynchronous transport is the traditional mem- nected to a and the other to a — connectivity for IEEE ory-mapped, load-and-store interface that ensures and the PC is designed to keep the physical 1394. error-free delivery of data, but its error-checking interface device powered, traffic can still pass protocols introduce time delays that make it between the printer and the camcorder, even if unsuitable for multimedia. On the other hand, the PC is turned off. error-checking is crucial for such tasks as writing The transaction layer implements the request- data to disks. Isochronous data guarantees response protocol specified in the International throughput at a predetermined rate, making it ideal Organization for Standardization/International for the transmission of time-critical multimedia Electrotechnical Commission (ISO/IEC) 13213: data where some error can be tolerated. IEEE 1394 1994 Standard Control and Status Register (CSR) manages the packeting process, whereby space can Architecture for Buses (see be reserved for the transmission of both schemes. http://standards.ieee.org/catalog/bus.html#gen18). The transaction layer can be implemented in IEEE 1394 building blocks firmware or hardware. The link and physical layers The IEEE 1394 standard defines three layers: are implemented in digital and mixed-signal hard- physical, link, and transaction (see Figure 2). The ware technology, respectively. link and physical layers are the main building blocks of a 1394 interface. The link layer commu- Physical interface devices nicates with the transaction layer using an Physical interface devices connect PCs, work- acknowledged datagram, a one-way data transfer stations, and peripherals to an IEEE 1394 cable with request confirmation. The link layer handles and implement handshaking for data transfers. At packet transmission and reception, as well as the the same time, physical interface devices define cycle control for isochoronous channels. A trans- the transmission speed. Because of the enormous ceiver (physical interface) provides initialization difficulty of integrating analog and digital tech- April–June 2000 and arbitration services and manages the physical nologies on a physical interface device chip, just layer by ensuring that only one node sends data a handful of manufacturers can design and build at any time. The translates the serial these devices. The design challenge to build these data stream and signal levels before sending them chips is intensified with the step up to 800 Mbps to the link layer. and IEEE 1394b. Physical interface devices can be repeaters as Although all physical interface devices must

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Host Interface (OHCI) standard interface, which dramatically increased the usabil- As portable multimedia and ity of the 1394 standard with PC applications. The third generation of links integrates the physical computing devices become interface device and link functions. These integrat- ed devices further enhance the simplicity of design- increasingly popular, power ing a 1394 interface by reducing part count and cost (see the sidebar “Integrating Layers”). management is becoming Helper specifications increasingly important. While the 1394 specification carefully details physical interface device and link operation, it does- n’t define a standard application system interface. As a result, each vendor of first-generation link products had a different system interface. This fact meet certain standards the IEEE establishes, they limited the portability of early 1394 products across nevertheless differ from one another in various system-level applications. Additional specifications ways, with the number of ports supported repre- were needed to “help” improve the 1394 user expe- senting a key differentiating feature. For example, rience. The OHCI and power management specifi- some physical interface devices may have as few cations are two examples of “helper” specifications. as 48 pins in a 100-Mbps first-generation, one-port thin quad flat pack (TQFP). Others may have as Open Host Controller Interface many as 100 pins to accommodate 800-Mbps OHCI provides a standard operating-system speeds. The thermal characteristics of the physi- interface to the application. It defines common cal interface device chip package and the power register sets and services for a generic host con- dissipation of the physical interface device place troller. The interface targets silicon vendors and potential limits on the maximum number of ports software developers creating operating systems on one physical interface device chip. The IEEE and applications for OHCI-compliant 1394 chips. 1394a specification places a 16-port limit on a sin- OHCI allows communication between any 1394 gle physical interface device chip. controllers that support the standard through an Another important defining factor for physical implementation of the link layer protocol of the interface devices is power considerations. A wide 1394 serial bus, with additional features to support range of power-saving functions are available in the transaction and bus management layers. OHCI different physical interface devices. I’ll further dis- also includes (DMA) engines cuss power management below. for high-performance data transfer, as well as a host bus interface, typically component Links interconnect (PCI). Links are the interface blocks between the appli- OHCI guarantees operating system compati- cation and the transceiver, or physical interface bility over multiple hardware platforms, provides device. Links provide the encoding and decoding clean plug-and-play at the firmware level, and functions that allow a PC to interact with a physi- guarantees that a hardware platform has multiple cal interface device. IEEE 1394 links have gone operating system choices. through three generations to date. First-generation OHCI version 1.1 is now in committee. It links came in two flavors. One type provided only updates version 1.0 to include standard power the general-purpose functionality defined in the management mechanisms, refinements to opera- IEEE 1394 specification. At 3,500 gates, these tion, and clarifications. For more information visit devices communicated with a transaction layer ftp://ftp.austin..com/pub/chrptech/1394ohci. that was done in firmware to link physical interface devices to a 32-bit or microcom- Power management puter bus. The second flavor, which linked physi- A wide range of power-saving functions is avail- cal interface devices to a PCI bus, rolled the able in various physical interface devices and also transaction layer into the link hardware to create a various operating systems. Power management is much larger device (150 K gates). Second-genera- a crucial issue, with both hardware and software

IEEE MultiMedia tion links were able to take advantage of the Open aspects to consider. Currently, the IEEE 1394 spec-

96 ification doesn’t fully specify power standards. Par- ticularly, very little in the latest version addresses Integrating Layers software power management considerations. As a Physical interface and link devices can simplify the implementation of IEEE consequence, is driving a power man- 1394 applications. A hybrid analog and digital device, the physical interface agement specification that addresses them. device has been on the market for some time. During that period, its func- In the 1394 world, devices can be configured as tionality has increased from basic single-port support at 100 Mbps to a broad either consumers or suppliers of power. For exam- range of products targeted at different types of applications. Like the sup- ple, a with a single port would be a plemental standards that support different applications, the proliferation of power consumer. A set-top box configured as a physical interface devices makes 1394 implementation much faster, easier, home entertainment center with many ports and less expensive. could be a power supplier. Lucent Technologies Microelectronics Group has been a leader in 1394 As portable multimedia and computing devices hardware technology. Bell Labs, Lucent’s research and development arm, become increasingly popular, power management created the technology that first enabled PC and workstation manufactur- is becoming increasingly important. Hardware ers to connect high-end consumer multimedia appliances to a PC and to and software development work is still required to each other at 400 Mbps, the top speed in the 1394a specification. reduce power dissipation. Although IEEE 1394a In designing this technology, Lucent had to overcome three key chal- supports the delivery of up to 60 watts of power lenges. The first was to accommodate clock speeds as high as 400 MHz. The via the power and ground connections inside the second was to incorporate both analog and digital circuitry on a single chip. standard six-pin cable, the four-pin cable most The third was to design the chip to conform to the new power management typically used for small portable devices, as dis- requirements imposed by operating systems. These technical challenges had cussed above, doesn’t include the power and been the choke point for the industry in the development of next- ground lines. It’s important to reduce power generation multimedia PCs and consumer devices. demands wherever possible. Another Lucent innovation was a three-port IEEE 1394a-compliant physical Hardware designers can lower power require- interface device housed in a 64-pin TQFP package that pioneered a round of ments by including automatic device power- smaller footprint designs. These new physical interface devices provided a com- down during suspend, a link interface disable, bination of small size and low power that helps reduce final system costs and and the ability to power-down an inactive port extends the 1394 design options for portable PCs and other compact, battery- automatically. Operating system developers are powered systems. Most recently, Lucent expanded on the Bell Labs technolo- just beginning to take advantage of some of the gy to introduce the first integrated physical interface/OHCI device. The newest hardware features, but much work needs to be level of integration further enhances IEEE 1394 application opportunities by done. By 2001 or 2002, operating systems should enabling smaller, simpler, more efficient and add-in card designs. be taking considerably more advantage of power The 1394 market is an excellent illustration of the benefits of cooperation saving features. in taking advantage of a well-designed general-purpose standard and Some of the specifications under development expanding it to benefit an increasing number of applications. Each innova- by the 1394 Trade Association are covered in the tion builds on those that have gone before. 1394TA Power Spec, which describes a uniform method for power management, including how nodes should supply, limit, pass, and consume for plastic optical fiber, multiple kilometers (km) power; implementation of suspend and resume for glass cables, and 100 meters for power saving mechanisms; and a model for man- category 5 (CAT-5) at 100 Mbps. aging power states. More information is available Some companies are already producing proto- at http://www.1394-pcwg.org/. types and products that meet or surpass the requirements of 1394b. Lucent Technologies 1394b—the next step Microelectronics Group demonstrated the first An enhanced specification, 1394b should be bilingual 1394b physical interface device at finalized this year. IEEE 1394b will extend bus Comdex 1998. This two-port device automatical- speeds to 800 and 1,600 Mbps. The enhancements ly switched from 1394a operation to operation at also include architectural support for 3,200 Mbps, 800 Mbps (a different style for Mbps occurred April–June 2000 although the signaling parameters for 3,200 Mbps when it detected connection to a 1394b physical are not yet available. The IEEE 1394b also supports interface device). forms of cabling not supported in the existing Another example comes from NEC. In a recent 1394a specification, resulting in a dramatic press release, NEC announced a 1394b-like physi- increase in cable lengths—from the 4.5 meters of cal-layer chip. In addition, the company proto- the original standard copper cable to 100 meters typed a bridge device that the company says will

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enable 1-km networks. The physical interface cols that can be used with different multimedia device chip, designated the PD72880, is capable formats such as AV/C, DVC, MPEG, and AMP. of 400 Mbps. NEC claims its architecture is supe- This expandable set of specifications includes not rior in addressing signal delay and thus capable of only protocols widely used today, but also emerg- 500-meter transmission—a fivefold improvement ing protocols such as high-definition digital video. over the 1394b requirement. The chip supports IEC 61883 provides a standard interface for soft- full-duplex transmission as well, also required by ware commands to a camcorder or other device. No the 1394b specification. matter what device and what software application, the commands for play, stop, rewind, and other Specifications for multimedia applications camera functions are the same at the bit level. Implementation of 1394-enabled applications The other critical aspect to the specifications is requires an understanding of the specifications a common definition of headers, the part of a data targeted to the functionality required. Here I’ll dis- transmission that tells the device that the next set cuss four of the most popular multimedia appli- of ones and zeros is a command. It’s necessary to cations: digital video, mass storage, home describe how to send things down a 1394 pipe so networking, and wireless. they come out the other end properly. For further information on IEC 61883 visit http://www.iec Digital video .ch/cs1oi-e.htm. Of particular interest to multimedia systems The AV/C general and enhancement specifica- designers is that IEEE 1394 offers a way to move tions define control and data for audio/video high-bandwidth video and audio digital traffic (A/V) applications. More specifically, they define among peer devices—digital cameras, DVD, cam- general commands used to control consumer corders, and high-speed, high-resolution printers audio/video electronics and specific enhance- and scanners—without a hub or master (PC) in ments for VCR, digital VHS (DVHS), 8mm, and between. For example, a digital camera can send other A/V products. For information on AV/C pictures directly to a printer or a camcorder can specifications visit http://www.1394ta.org connect to a set-top box. The 1394 standard has /Technology/Specifications/. been endorsed in the digital TV market by the A variety of protocol specifications are available Electronics Industries Association and Advanced to cover the wealth of video compression formats, Television Systems Committee (ATSC) in the US, including MPEG2-TS (digital satellite system, or and the Digital Video Broadcasting (DVB) stan- DSS, transport stream) across 1394, which is now dards in Europe. in committee (http://www.1394ta.org), the Con- The IEEE 1394 specification for high-speed data sumer Electronics Manufacturers Association rates has allowed applications that were once only (CEMA) Subcommittee R4.8 digital interface stan- possible in movie and TV studios to be done with dard EIA 775, and the AV/C tuner general model consumer-electronic systems, such as capturing for analog and digital video tuners as well as digi- movies to disk or using a camcorder as a TV sim- tal video broadcast (DVB) and DSS video tuners. ply by “plugging in.” The 1394b spec adds addi- tional value by promising to support multiple Content protection. Multimedia devices must streams of real-time video. include a content protection scheme for copy- A number of specifications have evolved around righted material. Technologies such as 1394 make this area of high-speed digital video and audio. For it easy to transport digital video and . example, the IEC 61883 specifications describe the To address this issue, in 1998 a consortium of five standard for hardware protocols used for Digital companies—, , , , and Video Consortium (DVC) devices. The six volumes Matsushita Electric Industrial—developed the Dig- of IEC 61883-1, -2, -3, -4, -5, and -6 are available ital Transmission Content Protection (DTCP) from http://www.ansi.org or http://www.iec.ch. method, a copy protection method for copyright- Four main subsections to the specifications ed content transferred across digital interfaces. have evolved to support digital video—camera The five companies established the Digital control, content protection, audio/music, and Transmission Licensing Administrator, or DTLA, videoconferencing. to license the content protection system and to generate and distribute cryptographic materials Camera control. The IEC 61883 specifications such as keys and certificates. For a technical white

IEEE MultiMedia describe a variety of isochronous transport proto- paper describing the DTCP method and licensing

98 information from the DTLA, visit the DTLA Web site at http://www.dtcp.com. Other organizations such as the Copy Protec- Multimedia devices must tion Technical Working Group (CPTWG), the Dig- ital Transmission Discussion Group (DTDG), the include a content protection CEMA 1394 Interface Committed, the DVD Forum, and the Secure Music Initiative are explor- scheme for copyrighted ing copy protection schemes. CEMA’s R4.8 1394 Interface Subcommittee cre- material, since it’s easy to ated a report documenting amendments neces- sary to EIA 775, 761, and 762 to support each of transport digital files. the copy protection approaches. It provides a valuable set of comparisons of the different copy protection schemes available.

Audio/music. Oddly enough, audio/music a technical committee of the National Committee seems to fall under the general category of digital of Information Technology Standards. Draft spec- video. Because audio—and music in particular—has ifications are available at ftp://ftp.t10.org/t10 some special characteristics, the 1394 Trade Associ- /drafts/sbp2/. More general information is avail- ation has a set of specifications specifically for audio able at http://www.T10.org. functions. These specifications include audio and The Device Bay specification defines a uniform super-audio CD control models, and a tape recorder set of mechanical and electrical requirements for subunit. More information is available at PC peripherals. Aimed at devices such http://www.1394ta.org/Technology/Specifications. as readable/writeable CD and DVD drives, hard dri- ves, and high-capacity devices, as Videoconferencing. Uncompressed digital well as more esoteric multimedia devices, Device videoconferencing has special requirements that Bay is the answer to customer requests to make the 1394 Digital Video Conferencing Camera Spec- upgrading and customizing PCs easy. A Device Bay ification defines. Specification 1.2 is the most slot in a PC allows any Device-Bay-compatible prod- recent set of functions, services, and register defin- uct to be quickly plugged in, used, and removed, itions that the 1394 Trade Association has accept- without lengthy software installation procedures. It ed. Updates have been proposed and are under supports both casual use and hot-swapping for fast consideration. For more information, check out repairs. For more information on Device Bay, see: http://www.1394ta.org/Technology/Specifications http://www.devicebay.org. /index.htm. The T10 also monitors the RBC. Draft specifi- cations are available at ftp://ftp.t10.org/t10 Mass storage /drafts/rbc. For more general information visit Although many mass storage devices have taken http://www.t10.org. advantage of IEEE 1394a, the move to IEEE 1394b The AV/C specifications include mass storage is particularly accommodating to hard-disk manu- models including minidisks, hard disks, and com- facturers, who need the higher data transfer rates. pact disks, plus a descriptor for storage-class The principal specifications for mass storage are the devices. More information can be found at Serial Bus Protocol 2 (SBP-2) and the Device Bay. In http://www.1394ta.org/Technology/Specifications. addition, there exist a variety of subspecifications, including the Reduced Block Commands (RBC) Home networking Command Set and a variety of AV/C descriptions. High-bandwidth home networking is approach- SBP-2 describes a transport protocol for asyn- ing reality for the general population. The Home chronous commands or data and is widely adopt- Audio Video interoperability (HAVi) architecture April–June 2000 ed by peripherals manufacturers. SPB-2 defined software protocols and application pro- is not just for disk drives—it’s also used for scan- gramming interfaces (APIs), as well as addressing, ners and printers. Examples include the newly versioning, and management of isochronous announced scanners from Epson, Umax and a streams for consumer electronics and computing printer from Epson. devices. The 1394 Trade Association accepted the The specification is released through the T10, HAVi, and a definition of allowable command set

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Asychronous connection management is Resources defined by an AV/C document that the 1394 The IEEE 1394 protocols are complex and on Trade Association has accepted. Currently, a rapid evolutionary path. If you’re interested in updates are being proposed. Visit http://www keeping up on the latest developments in this .1394ta.org/Technology/Specifications/index.htm area you may want to access the following: for more information.

❚ The 1394 Trade Association’s Web site: Wireless http://www.1394TA.org Although the current 1394 specification does- n’t include a specification for wireless transmis- ❚ A PC99 developer’s guide for 1394, co- sion, some companies are working on it. authored by Microsoft, Intel, and : Semiconductor and Wi-LAN showed a demo of http://www.eu.microsoft.com/hwdev wireless IEEE 1394 on two prototype /xpapers/pc99/08PC99.htm at the 1999 Internationale Funkausstellung (IFA, or International Radio Exhibition) in Berlin. Two ❚ Zayante sites with links to a wealth of MPEG-2 streams were sent to two set-top boxes for resources: “1394 Community” at http:// decoding, then into a pair of TV sets. The raw data www.zayante.com/html/IEEEinfo/IEEEcom rate reported was 48 Mbps, resulting in a 30-Mbps .html and “P1394b (Gigabit 1394)” at burst transfer rate, which can ultimately deliver http://www.zayante.com/p1394b/index up to six MPEG-2 streams in two directions simul- .shtml. The complete draft of the 1394b pro- taneously. Similar wireless demonstrations of posal in PDF format: http://www.zayante.com 1394 have been shown by companies such as /p1394b/drafts/p1394b_rev100.pdf. Sony (at Comdex 99) and NEC (at CES 2000).

Conclusion codes is now in committee. First demonstrated run- With the demonstration of 1394 over wireless ning over 1394 at Comdex 1998, HAVi enables media, it’s clear that Apple’s Firewire has satisfied many of the rich multimedia transfer and manipu- the definition of a good bus design—it has expand- lation functions gaining in popularity in the home ed far beyond its original intent. As consumer mul- market. For more information, check http://www timedia and computing applications continue to .1394ta.org/Technology/Specifications/index.htm merge, the peer-to-peer flexibility and the serial and http://www.havi.org. bus advantages of the IEEE 1394 standard will The Video Electronics Standards Association become increasingly popular. As demonstrated by (VESA) is developing a document that describes the increasing bandwidth of 1394b, there’s no the physical and data link layers and midlayer immediate end in sight to the amount of perfor- protocols required for a home network. The white mance that can be extracted from this protocol. paper is now complete, and the first draft home With backward compatibility in mind, contribu- network specification was released for VESA mem- tors to the evolving standard are opening up a new bership review last August. The proposed specifi- way of computing that will provide increasing cation will make it possible for consumers to flexibility and portability of applications. MM access all networked appliances through a device in the home such as a TV or PC. It takes advantage Thompson is Manager of Technology Development, IEEE- of the longer distance capabilities of the 1394b 1394 Transceivers, Lucent Technologies Microelectronics specification. The VESA Home Network Commit- Group at Bell Labs. Readers may contact him at Lucent Tech- tee has successfully completed a test of the home nologies, 1247 South Cedar Crest Blvd., Rm. 2E356, Allen- networking concept with several companies, and town, PA 18103, e-mail [email protected]. portions have been demonstrated at trade shows including Comdex and the Consumer Electronics Contact Standards editor Peiya Liu, Siemens Corporate Show. For more information, see http://www Research, 755 College Road East, Princeton, NJ 08540, e- .vesa.org/committees.html. mail [email protected]. IEEE MultiMedia

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