CS-350-1: Computer Organization and Architecture

FireWire

CS-350-1: Computer Organization and Architecture

Spring 2004

Justin Garcia

Michael Ripley

Stefani Ryan

Nathan Wilkinson

Table of Contents

1. Introduction………………………….………………………………………………..3

2. The Past, Present, and Future of FireWire……………………………….………...3

3. How FireWire Works………………………………………………………………...4

3.1 The Basics of FireWire……………………………………………………….4

3.2 The Transport Modes of FireWire…..………………………………………..5

3.3 The Advantages of FireWire.....………………………………………………6

7. Uses of FireWire……………………………………………………………..………..6

8. Comparison of FireWire to Similar Devices………………………………………..6

9. Conclusion……………...……………………………………………………...……...7

10. Bibliography…………………………………………………………………………8
Introduction

FireWire is the Apple trademark for the IEEE 1394 standard, while Sony refers to their implementation as i.Link. Apple created this technology in the mid 1990’s. FireWire is used for connecting digital devices to computers and other digital devices. (1394 TA, 2004) It has become the established industry standard for high-performance device connections.

The Past, Present, and Future of FireWire

In 1995, the original version of the FireWire specification was approved by the IEEE as 1394-1995. In 2000, the standard was revised to clean up portions of the power management, and to make the system more efficient. This standard was known as 1394a. Two years later, the 1394b standard was released. This revision provided for transport speeds up to 3.2 Gbps and alternative cabling methods. Currently, only speeds up to 800 Mbps are implemented. The new cabling standards allow for a new FireWire proprietary cable, Category 5 unshielded twisted pair, and glass or plastic fiber optic cables to be used, which extends the reach of the cable from 4.5 meters to 100 meters. The new FireWire cable has a nine-pin connector, and is easily adapted to work with earlier revisions of the 1394 standard. (Apple, 2004) IEEE 1394b also included provisions for a new line code, known as 8B10B, which is the same system used in other high-speed connections, such as gigabit Ethernet, and fibre channel. (Wikipedia, 2004)

With the introduction of RFC2734, FireWire also supports TCP/IP transmission. To many, this appears to be an attractive setup. It is now possible to use an Ethernet protocol over an Ethernet cable, but have a system that is capable of automatically organizing itself, and provides a link-level standard for guaranteeing bandwidth. (Microsoft, 2001)

IEEE 1394b is fully backward compatible with earlier versions of the standard. In fact, it can be used to improve the quality of a lesser FireWire setup, by bridging an IEEE 1394a connection over a new long-run, 100 meter connection.

How FireWire Works

The Basics of FireWire

At the most basic level, FireWire is a high-speed peripheral connection system. Like USB, the cable is capable of providing both a data connection and electrical power for the connected devices. The cable provides for up to 45 watts, with a maximum of 15 amps, and 30 volts. The first two iterations of the FireWire specification called for the use of a proprietary cable and connector. While the cable was identical, the connector could either have four or six pins, the latter containing two pins for power. Traditionally, battery powered devices used the four-pin, because it was smaller, and the device did not need the bus power. Manufacturers of newer devices, such as the Apple iPod, are realizing that the power can be convenient for reducing cable clutter by using the bus power to charge the battery. Sony has abandoned bus power altogether, with its i.Link implementation of the IEEE 1394 standard.

The FireWire bus requires 64 bit addresses for each node. This is defined by the IEEE 1212-1991 standard. The 64 bit addressing scheme allows for a 10 bit bus identifier (1023 buses max), 6 bit node identifier (63 nodes/bus max), and 48 bits for addressing within a device. (Rowe, 1996)

The Transport Modes of FireWire

FireWire defines two transport modes, asynchronous and isochronous. Asynchronous delivery is the standard method for routine data that is less time sensitive, and more in need of reliable delivery. Isochronous delivery is the technique used for streaming data, such as multimedia. The isochronous transport system can guarantee a certain amount of bandwidth, and any current streams will take priority on the bus over asynchronous transfers. Isochronous transfers trade reliability for timely delivery, so that if the bus falls behind, the current packet will be skipped, and the next one will be delivered. Multimedia applications tend to prefer this lossy approach, since most people would prefer to have a stream be kept current, rather then identical to the source data. In applications such as a hard drive, consumers usually prefer that every bit in the data stream be delivered, even if a performance penalty is incurred. A maximum of 64 isochronous channels can be instantiated simultaneously. If the bus is already saturated, the root node will deny channel creation requests. Isochronous channels require a ready-to-send packet from the root node. This packet is sent every 125 microseconds, and each isochronous channel has an opportunity to attach a packet to the leading packet. After the isochronous channels have their opportunity to send, the bus is opened to asynchronous transmissions for the remainder of the time slice. Total bandwidth for isochronous communication is about 1000 bytes/channel/time slice at 100 Mbps, 2000 bytes/channel/time slice at 200 Mbps, or 4000 bytes/channel/time slice at 400 Mbps. (Rowe, 1996)

Advantages of FireWire

One of the advantages of FireWire is its peer-to-peer and autonomous nature. Every time the bus changes, either with a device addition or removal, the bus is reset. During the reset, each node is assigned a device number, and a root node is chosen to coordinate all activities on the bus. The bus reset will occur within 300 microseconds of a change. The ability of the bus to dynamically reconfigure is one of the great advantages of FireWire over USB. USB requires a central controller/host computer, whereas FireWire requires that each device be able to run the bus, if it is chosen. (Rowe, 1996)

Uses of FireWire

FireWire is used predominantly for its speed capabilities, which also entails its capability to send large amounts of data in a relatively short period of time. Real-time applications, such as digital video and audio, use FireWire to capture data as it received with minimal delays. Other types of FireWire compatible hardware besides video and audio equipment includes printers, scanners, external hard drives, external optical disk-writers, repeaters, video game consoles, TVs, and VCRs.

Comparison of FireWire to Similar Devices

Table 1.1, found on Dennis Curtin’s FireWire Web Site, shows the relative speeds of different interfaces computers have available today. In the comparison, FireWire is an extremely fast interface, only possibly outmatched by USB 2.0 when compared to IEEE 1394a (Curtin, 2003). Even though USB 2.0 has a higher overall speed, the IEEE 1394a can arguably keep pace with it because FireWire uses the available bandwidth more efficiently. However, IEEE 1394b is indisputably the fastest device connection available.

Port / Megabits per second
Serial / 0.1125
Parallel / 12
USB 1.1 / 12
SCSI-1 / 40
SCSI-2 / 80
Ultra SCSI / 160
Wide Ultra SCSI / 320
FireWire (1394a) / 400
USB 2.0 / 480
FireWire (1394b) / 800

Table 1.1: A comparison of speeds for different device interconnects.

Conclusion

FireWire is faster, more efficient, and easier to use than most other device interconnects. Because of this it has many applications, ranging from private home use to large corporate needs. With the introduction of IEEE 1394b, it is one of the few standards poised for immense growth in the upcoming years.

Bibliography

1394 Trade Association (2004). “About 1394 Technology.” URL: http://1394ta.org/Technology/About/index.htm

Apple Computer, Inc. (2004). “FireWire 800 Technology Brief.” URL: http://www.apple.com/firewire/

Connell, David (1998). “FIREWIRE: So the Blender Says to the Toaster, He Says...” URL: http://www.satbiznews.com/digi2.html

Curtin, Dennis P. (2003). “A Short Course in Digital Video: FireWire.” URL: http://www.shortcourses.com/video/chapter08.htm

Elen, Richard (2002). “Fire in the Wire -- The Future of Audio Interconnects.” URL: http://www.audiorevolution.com/news/0702/11.firewire.shtml

Microsoft Corporation (2001). “IEEE 1394 and the Windows Platform.” URL: http://www.microsoft.com/whdc/system/bus/1394/1394tech.mspx

Rowe, Lawrence A. (1996). “Multimedia Applications of IEEE 1394.” URL: http://bmrc.berkeley.edu/courseware/cs298/spring96/dscheel/index.htm

Wikipedia (2004). “FireWire.” URL: http://en.wikipedia.org/wiki/Firewire

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