With wireless connectivity waiting in the wings, a supplement to the USB standard called USB on-the-go has begun to gather momentum as a way to connect mobile devices on a point-to-point basis, without a PC intermediary. This is especially true in the cellular phone market, where Irvine, California-based Transdimension, maker of a USB on-the-go chip, announced a licensing agreement with Motorola in February. The announcement followed a similar agreement made late last year with Qualcomm. In the PDA market, Sony will be using a USB on-the-go product, the ISP1362 from Royal Phillips Electronics, in its Cli handheld devices. Other companies working on USB On The Go technologies include ARC, Hewlett Packard, and Cypress Semiconductors.

While a number of sources say that USB OTG doesn't compete directly with Bluetooth, the fact that Bluetooth has not yet taken off as a short range data exchange medium hasn't hurt USB on-the-go's chances.

"USB OTG might be taking advantage of the relatively slow development of Bluetooth," said Brian O'Rourke, a senior analyst at In-Stat/MDR.

According to Jack Ganssle, an embedded software development expert and columnist for Embedded Systems Programming, the usefulness of USB OTG solutions will depend on whether or not vendors offer software support.

"If they only provide low-level drivers," said Ganssle, "it'll take a ton of work to write the code."

To this end, David Murray, VP of marketing at Transdimension, says that a Transdimension subsidiary called SoftConnex provides all the software necessary to create an off-the-shelf USB on-the-go platform when combined with the company's OTG 243 processor.

USB on-the-go came about because a number of companies saw that the growing intelligence of mobile devices would make exchanging data between them-without a PC playing host-a useful capability. Those companies formed a working group that produced the USB on-the-go supplement to USB 2.0 in late 2001. The supplement specifies small form-factor connectors and cables, lower power requirements than USB, and the ability for devices to dynamically switch between the role of host and peripheral.

In USB on-the-go, there are two kinds of devices: dual-role and peripheral-only. The initial means of communications between both types of devices is the session request protocol (SRP). The dual-role devices can both initiate and respond to the SRP, but the peripheral-only device is only capable of initiating. When two dual-role devices are connected, they use the Host Negotiation Protocol to perform a change of roles. The HNP is typically triggered by user input or by an application running on a dual-role device currently acting as a peripheral.