Differences Between USH And 1394 - Technology Information

Computer Technology Review, Dec, 2000 by Bhupender Virk, Dave Sroka

USB works best for PC devices, while 1394 is best suited for video enabled devices sending a constant data stream.

In this era of computing and communications convergence, the Universal Serial Bus (USB) and IEEE 1394-1995 bus architectures are key to interconnectivity for all home, office, and mobile communications devices. USB works best for PC devices such as keyboards, mice, joysticks, digital still cameras, and printers, which have low data requirements. The 1394 specification excels in video applications that require streaming of data such as video cameras, DVD, VCRs, DVRs, and audio and set-top boxes. 1394 also has the flexibility to operate in asynchronous/latent environments such as PCs and disk drives.

These two bus architectures, along with their upcoming advances complement each other, rather than being competitive technologies. They address different sets of applications with some overlap. As combined technologies, they introduce newer connectivity to PCs and consumer electronics products. Philips is a participant in both the USB2.0 Promoter group and the 1394 Trade Association Board of Directors.

Coexisting Standards

In the end, both USB2.0 and 1394 are expected to coexist on many future consumer and PC systems, as well as convergence systems that merge capabilities of both environments. The figure summarizes the different strengths of 1394 and USB2.0. They differ in application focus because of the continuous evolution of the current environment. Today, there is a large and rapidly increasing installed base of USB-capable PCs and hundreds of USB peripherals in the marketplace that connect to the PC. It is a natural evolution to increase the speed of USB and provide an easy migration path for existing USB peripherals. Likewise, 1394 plays a significant role in PC, most notably for DV camcorder applications where digital content can be easily edited and distributed. In 2000, 20% of all PCs will include a 1394 port.

In audio/video consumer electronics systems, 1394 is on its way toward becoming the dominant connector. As a result, 1394 can provide a high speed bus today that connects PCs to entertainment equipment.

USB2.0 continues to use a low cost host-centric connection model, which is the best answer for a PC connection to PC peripherals. USB makes plugging in new peripherals easy with plug and play; it is almost 100 times faster than the original serial port, and it supports multiple device connectivity. USB expands a PC's capabilities via an external port and eliminates the need for users or integrators to open the system chassis. Since USB supports multiple peripheral devices simultaneously, it allows users to run numerous devices such as printers, scanners, digital cameras, and speakers from a single PC. USB also allows for automatic device detection and installation, thus making connectivity a true plug-and-play experience for end users.

The IEEE 1394 spec provides for real time data transfer, which is referred to as "isochronous" data transmission while guaranteeing bandwidth. 1394 combines this with support for asynchronous transmissions, which efficiently exploits a subset of bandwidth. 1394 is a peer-to-peer technology where each node can serve as the network master. In the PC environment an example would be peripheral devices that can send data to each other without first going through the PC. Or in a mixed consumer and PC system, a PC peripheral can interoperate with a VCR and set-top box, without needing a PC in the network.

The 1394 topology supports both daisy chaining and branching with the capability to support 63 nodes/connections for each 1394 bus network. Over 1000 networks can be supported in the 1394 topology. 1394 is designed to enhance ease of use for the end user. All 1394 devices are "hot plug and play" so that new equipment can be added to the network without disturbing current applications that are running. All 1394 devices act as peer-to-peer repeaters, thus removing the need for special devices such as hubs.

USB/1394 Features

USB1.1 has a low asynchronous data transmission rate of 1.5 or 12 megabits per second (Mbps) and 1394.a has a constant isochronous data stream of 100, 200, or 400 Mbps. Released earlier this year, USB2.0 supports up to 480 Mbps or about 40 times the performance currently available from USB 1.1. The higher bandwidth will support such applications as digital image creation and web publishing, where multiple high-speed peripherals run simultaneously.

This high bandwidth USB2.0 spec is the technical launching pad for consumer electronics products with more functionality, including higher resolution videoconferencing cameras, next generation scanners and printers, and faster broadband Internet connections. The 1394 specification will also continue to be more robust with higher bandwidth delivery of 800 to 1,600 Mbps beginning in 2001 and subsequently is expected to move up to 3.2 gigabits per second. The USB and 1394 architectures also differ significantly. USB is based on a master-slave relationship, while 1394 is a peer-to-peer networked environment.