Differences Between USH And 1394.

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.

The USB master-slave architecture uses a "call-and-response" scheme where the PC or master queries its plugged-in peripherals or slaves to determine if they have data to transfer. Each peripheral then responds, which results in a two-way communication between the host PC and its associated peripheral devices.

1394 supports the serial bus protocol (SBP), which allows for data transfers to PC peripherals. Rather than utilizing streaming real-time audio/video data, this SBP allows for bigger files to be sent asynchronously across the bus. Another major 1394 feature is its support for content or copy protection. Motion picture companies are concerned about digital content being transmitted, pirated, and duplicated illegally. Copy protection, specifically 5C.protocols are supported by 1394 structures. In 5C, two users are first authenticated as being valid, then data is encrypted or ciphered so that the data being carried on the 1394 bus/cable is only understood by the authenticated users. During this process the cipher secret key is never transmitted on the network.

As far as distance is concerned, the current 1394.a standard recommends a maximum cable length of 4.5 meters. The 1394.b standard extends those distances by supporting optical cable lengths of 50 meters for plastic optical fiber and 100 meters for glass optical fiber and hard polymer clad, as well as 100 Mbps operation over lengths of up to 100 meters on Category 5 The USB 1.1 specifies 5 meters as the standard distance of a peripheral to a PC.

1394 Infrastructure

The 1394 infrastructure is an attribute that should also be noted. Over the past five years, the work of hundreds of engineers has created a massive amount of supporting infrastructure. There now exists numerous protocol standards and specifications for many types of consumer and PC devices, including printers, scanners, and hard-disk drives, as well as AV equipment that needs IEC61883 support such as DTVs and STBs.

New standards like Universal Plug and Play (UPnP) and HAVi make networks easy to construct. UPnP allows devices to describe capabilities in a declarative fashion using XML and export user interfaces in HTML. Relying on these two Internet technologies makes the construction of UPnP devices easy for system designers and removes the need for users to configure individual devices or add device, drivers to systems. In contrast, HAVi allows the product designer to export user interfaces and driver-like control code written in Java to recipient devices. Although different approaches, both UPnP and HAVi will simplify the configuration of connectivity between 1394 devices for system designers.

Targeted Applications

As stated above, USB2.0 extends the speed of the connection from 12 Mbps on USB 1.1 up to 480 Mbps. This provides an attachment point for next-generation peripherals, which complement higher performance PCs and user applications. USB2.0 is both forward and backward compatible with USB1.l, which results in a seamless transition process for the end user. USB2.0 uses the same cables and connectors as USB1.1. USB2.0 offers a compelling opportunity for peripheral vendors to migrate their USB peripherals to higher performance, while still being able to sell the same peripherals into the huge installed base of USB-capable PCs. USB2.0 is also expected to lead to the development of higher performance peripherals that bring new applications to the PC.

USB1.1's data rate of 12 Mbps is sufficient for many PC peripherals such as telephones, keyboards, mice, digital joysticks floppy drives, digital speakers, and low end printers. These peripherals will continue to operate with no change in USB2.0 systems. The higher bandwidth of USB2.0 will permit PC peripherals with more functionality, including higher resolution video conferencing cameras, next generation scanners and printers, fast storage units, and faster broadband Internet connections.

It will make today's user applications more productive, such as taking the time to download a roll of digital photos from a few minutes on USB 1.1 down to a few seconds on USB2.0. Also, the higher bandwidth will support the most demanding PC user applications, such as digital image creation and interactive gaming, where multiple high-speed peripherals will be running simultaneously. The higher data rate of USB2.0 will also open up the possibilities of new and exciting peripherals.

Industry plans are underway now to have USB2.0 incorporated in chipsets. Once these chipsets reach high volume, it is expected that USB2.0 will be about the same cost as USB1.1 is today. Because of this, USB2.0 is expected to supersede USB1.1. Also, like USB1.1, USB2.0 will satisfy the peripheral-interface needs of desktops, mobile systems, and other classes of host platforms. To satisfy the needs of power-sensitive applications such as notebook computers, USB2.0 will provide the same power-management mechanisms as USB1.l to allow the aggressive management of I/O power consumption. This is expected to allow USB2.0 to find use even in demanding low-power systems.

In the 1394 camp, the applications run far and wide. Existing and potential uses for 1394 span a wide range of applications. Consequently, it is difficult to say that any particular applications are the targeted ones for 1394. As 1394 continues to proliferate, an extended network of diverse end equipment will become a reality. 1394 is now being used in such applications as:

* Laptops, PCs, workstations, and servers

* PC peripherals

* Consumer electronics and audio/video home networking

* Telecom/networking

* Automotive and industrial

* Audio/Video home, networking backbone

Bhupender Virk is the international product marketing manager at Philips Semiconductors (San Jose, CA) and Dave Sroka is the 1394 marketing manager at Philips Semiconductors (Albuquerque NM).

Fig
1394 vs. USB2.0 Technologies with Different Strengths
                     1394 strength lies in    USB strength lies in
                     real time A/V transport  PC and PC peripherals
                     1394                     USB 2.0
Availability of 400  Now                      2002
Mbps
PC Host Required     No                       Yes
Network Topology     Peer to Peer             Master/slave
Video Protocol       Yes                      No
Support 1
Net Efficiency 2     A/V                      PC
Comparative Cost 3   $6-$8/node               TBD
(1)1394 includes support for the DV/MPEG protocols and 5C copy
protection.
(2)1394 devices can communicate directly with one another with
guaranteed bandwidth and fair arbitration. A USB device communicates
through the PC. Requiring hubs and the necessity to address latency
issues.
(3)Pricing is volume dependent.