Chapter 8. FireWire

The FireWire name was originally coined by Apple Computer, Inc., for a high-throughput serial multimedia link to interconnect computer and consumer electronic devices. It was designed to handle both Asynchronous (such as data) and Isochronous (such as video) packet transmissions. That transmission technology was later standardized as the IEEE 1394 serial bus. Many standardization efforts were coordinated at the 1394 Trade Association (1394 TA), a nonprofit trade organization formed in 1994 with earlier strong support from major corporations such as Hewlett-Packard, IBM (through its former printer division now known as Lexmark), Microsoft, SONY, and Texas Instruments, as well as Apple. The first FireWire standards were released during 1995 and were known as IEEE 1394-1995. This first version of 1394 technology is capable of delivering transmission throughputs of 100, 200, and 400 Mbps over a special shielded twisted pair cable of 4.5 meters. These throughputs can also be carried over a backplane internal to an electronic device such as a computer. The 1394 TA membership has grown to more than 100 companies. FireWire plugs, sometimes also known as iLink, can be found on many computer and digital video devices. The new 1394b standards, released during 2001, have made the FireWire technology run faster and go further based on a new media arbitration technique. Via 6B10B encoding and full-duplex transmission, 1394b signals can be carried over a Category 5 unshielded twisted pair cable of up to 100 m, a plastic optical fiber of up to 50 m, a hard polymer clad or glass optical fiber of up to 100 m, and a short shielded twisted pair cable of 4.5 m. Transmission throughputs of up to 1600 Mbps have been defined on glass optical fiber and shielded twisted pair cable. The new FireWire technology holds great potential for Home Network applications for its high throughput and long reach to carry multimedia signals linking computer peripheral and electronics device clusters.

In this chapter, we will examine the traditional as well as the enhanced FireWire technologies by studying their media access protocol and associated signaling techniques. Similar to Ethernet protocol, the 1394 media access arbitration is a distributed process. However, the packet collision is avoided by filtering transmit requests through intermediate nodes and issuing a single transmit permission from a final decision node, the root or the BOSS, depending on whether the enhanced arbitration technique is used. Different time gaps exist between isochronous and asynchronous packets for the traditional 1394 arbitration process [1]. Wider gaps are allocated between asynchronous packets to allow isochronous packets to have a higher priority to access the transmission media. Transmission efficiencies depend on ratios of these gaps to packets lengths. These transmission gaps are eliminated in the new 1394b arbitration procedure to maintain a very high efficiency over longer connecting distances at higher transmission throughputs. Short symbols, instead of signal-level transitions, are used by the 1394b for transmission requests, and they can be delivered while the current packet is still being transmitted. This is made possible by implementing a full-duplex transmission scheme over two pairs, where one pair is always used for transmitting and the other for receiving without echo cancellation. The 8B10B encoding is used to aid signal reception where clock information has to be recovered from the data pair alone instead of being delivered from the STROBE pair as in a traditional 1394 transceiver. These new 1394b transmission techniques can be easily applied on different transmission media by using a different signal driver, either electrical or optical, and a corresponding signal detection device. We limit our discussion only to electrical cable transmission media in this chapter. We first look at bus topology, the arbitration process, the packet format, and the line signal as defined by the IEEE 1394-1995 standards [1]. We then highlight these new 1394b [2] techniques including control and request symbol encoding, full duplex arbitration, and packet encoding and delivery as well as copper transmission media specifications.