Introduction

In this article, we will talk about what is most modern in terms of external bus: the Firewire. The Firewire is a very high performance serial bus that makes the connection of different kinds of equipment possible, using a flexible topology and providing very attractive price. Our goal is to show an idea regarding the innovatory characteristics of Firewire, such as concepts of portals, bridges, nodes, virtual connection, etc.. We apologize for having left some gaps, but it is difficult to get technical information about the subject. A good part of the documents available had controlled access, what did not allow us a deeper study.

The FireWire bus, created by Apple in the beginning of the 90's, was adapted, in 1995, and standardized by IEEE 1394 norm. Its communication capacity can reach up to 30 times the USB speed (Universal Serial Bus). Its idea is similar to the USB: it has a simple interface simples capable of receiving up to 63 devices, such as disk drives, digital cameras, digital television, computers, etc, as shown in Figure 1.

Figure 1: Example of equipment arrangements with Firewire.

Sony, Panasonic, Sharp, Canon and JVC were the first companies to release products with Firewire (around 7 million digital video coders - MPEG). The computer market is also supplied with models by Apple, Compaq, Sony and NEC. We have also been waiting for the availability of other models by other leading companies. Nowadays, Castlewood Systems develops a disk drive that directly receives the mass of data from a digital camera, that promises to eliminate the use of tapes in a high quality video studio.

As you can see, the Firewire is not a computer-only bus, since the video applications were the first to be benefited. However, the companies have gradually been adding, in the newer models, Firewire connectors in computers, as it is made for the USB. As in the USB, it is not necessary to initialize the machine to detect the Firewire connected devices, since they are also detected at the time of its physical connection, in application execution time.

The present Firewire products can operate in a rate of 400 Mbps (50 MB/s), against 12 Mbps (1.5 MB/s) of USB. Despite the USB specification revisions allow higher rates (USB 2.0 runs at 480 Mbps or 60 MB/s), the Firewire will not stop there: it should soon reach, with the aid of special fibers or wireless communications, speeds from 800 to 3.200 Mbps. Actually, it can run at 800 Mbps (100 MB/s) under the new IEEE1394b specification.

Firewire is, then, a nickname for a serial bus specified by IEEE, receiving the official name of IEEE 1394. An example of PCI, two or more electrically isolated Firewire buses can be connected by a special circuit, called bridge. Historically, its creation was in 1995 and it was introduced to society in February of 1996, when Peter Johansson, of Congruent Software, presented a work called "Serial Bus to Serial Bus Bridges" to a group of representatives of the big leading companies on the market, such as Philips, Apple, NEC, Seagate, Sony, Sun, Samsung and Texas. This happening started a series of meetings to discuss technical questions not only to define the IEEE 1394-1 pattern (bridge between Firewire buses), but also to specify bridges to be responsible for the interface of the bus being studied with other buses. Those meetings also started to count, afterwards, with representatives of Intel, Microsoft, Canon, Compaq and Panasonic, among others. Although those specifications are not finished yet, the group always keeps a draft of the situation on the site http://grouper.ieee.org/groups/1394/1. So, some details shown here are subject to further revisions.

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