Bus in motion

Nearly all PCs and associated peripherals on the market have USB ports. This high adoption rate has driven additional adoption of USB in mobile devices like digital cameras, MP3 players, PDAs, and, to some extent, cellular handsets, as these products often require PC connectivity.

Recently, the USB Implementers Forum released USB On-The-Go (OTG) version 1.0, an emerging standard that addresses interconnectivity of mobile devices and other consumer-electronics devices without the involvement of a PC. Under the OTG standard, any device can be either a host or a slave when communicating with other USB-enabled devices, depending on the requirements of the particular communication session.

Market adoption of USB OTG is already underway. Adding USB OTG to a mobile device is as simple as adding a controller and licensing software to support the various peripherals attached. If OTG is integrated into the core logic, the cost of adding USB OTG to a mobile product that already supports USB slave functionality is virtually nothing.

For their cellular-phone chipsets, Qualcomm and Motorola have licensed USB OTG technology from TransDimension, one of several vendors offering OTG as either a chip or intellectual property. In addition, Texas Instruments has incorporated USB OTG into its cellular-phone chipsets. Considering these announcements alone, OTG functionality could find its way into more than 170 million cellular phones per year. In addition, many other yet-to-be-announced mobile products are adopting USB OTG.

The key to USB OTG's success is that it is backward-compatible with all USB hosts and a variety of USB peripherals. With more than 1.4 billion potential connections out there, USB OTG is not waiting around for a market to emerge—it already has one.

People often compare USB OTG to Bluetooth. However, despite the convenience of wireless connectivity, Bluetooth is much slower than USB (700 kbits/sec compared with 12 Mbits/sec), much more expensive to implement, and more power-hungry. The most important factors limiting Bluetooth's success are the fact that few existing products use Bluetooth and the fact that both ends of the connection need to be Bluetooth-enabled. Promoters of Bluetooth are still waiting for the market to develop, while USB is already mature. Even if Bluetooth is successful, many types of peripherals that need connectivity may never adopt the technology.

Meanwhile, the IrDA (Infrared Data Association) standard specifies the wireless transfer of data via infrared radiation. While some laptops, PDAs, and other mobile devices offer it, IrDA is generally not incorporated in many consumer-electronics products and PC peripherals. IrDA suffers from line-of-sight issues and isn't widely used by consumers.

While Bluetooth and IrDA might exist as supplementary wireless connections for some markets, USB OTG will be the standard "baseline" connection method. In the vast majority of cases, USB will be the connection of choice.

See also:Air bus