USB OTG - On-The-Go / miniUSB

The new OTG specification will effectively eliminate the role of the PC as a go-between.

With all kinds of digital electronics devices coming out left and right, users would become more productive if they can mix and match the functionality of their portable devices. There's a growing need for devices to communicate to each other as we are moving away from a PC-centric world. If our digital cameras can directly connect to cell phones to send images over the Internet, our 7lb. laptops can rest at home. However, this capability to sharing data among consumer electronics is offset by the lack of an industry standard and the complexity involved in implementing proprietary solution in the devices.

Where USB On-The-Go Comes in?
With vast majority of peripherals communicating with a computer through Universal Serial Bus, USB is naturally the candidate for mobile point-to-point connectivity. Though, the major obstacle associated with this proposal is that USB employs a master-slave protocol, which relies on the intelligence of the host. Implementing the entire USB host on any portable electronics will be an over-kill for any dedicated devices. Not only will a standard USB host significantly cripple the battery life of a low-powered device, the connectors are also too large for the form factor of those miniature devices.

To address these problems, a new supplement to USB 2.0 specification has been finalized in December 2001. The new standard, called USB On-The-Go, defines new mini connectors, negotiation rules and power requirements used in both host and peripheral. The specification also calls for a new type of device called 'dual-role peripheral' in which it can act as either host or peripheral depending on how users connect the cable to its unique mini-AB receptacle. When the dual-role device is connected to the mini-A plug, it turns into a host. When the mini-B plug is connected instead, the device becomes a peripheral. The OTG peripheral can also determine the power consumed the by host during a connection in order to preserve battery power.

To complete the picture, the USB Promoter Group requires all OTG dual-role devices to come with a 'Targeted Peripheral List' of supported hardware. This list basically helps consumers to find peripherals to connect to their dual-role devices. In near future, USB OTG dual-role devices will be able to support a large class of peripherals without having individual driver for each device on the ‘Targeted Peripheral List.

The Opposing Forces
To sum up the last paragraph, the USB OTG specification simply upgrades the current peripherals to feature limited host functions to interconnect a certain number of devices. USB OTG controllers will likely to reside on devices like digital cameras, smart phones and handheld computers whose natures of their applications generally require some forms of expansions. To speed up the adoption, Philips is already shipping a developer’s kit for Intel xScale, which is touted as the next-generation platform for smart phones and handheld computers.

USB OTG is not alone in this market as there’s already a line-up of competitors in this category. These rivals include Bluetooth and FireWire. Currently in version 1.1, Bluetooth is a designed from ground up to connect consumer electronics. It already has a head start, and the appeal to connect peripherals wirelessly has created a niche market for Bluetooth products. Bluetooth might cut the wires, but USB OTG High Speed and Full Speed easily outrun Bluetooth in the speed. Even so, some are skeptical whether the extra bandwidth is necessary for the market USB OTG is targeting.

FireWire or IEEE 1394a has totally given a face-lift to the digital video industry since its inception, and it is by far the most versatile among all the standards covered in this article. It offers solid isochronous transfer, multiple bandwidth modes, ultra-high speed and most important of all, peer-to-peer architecture that USB 2.0 lacks. The main drawback is that a FireWire controller demands electricity several times higher than USB OTG to be practical on tiny electronics products. For this reason, FireWire has a different application focus than USB On-The-Go. A low-powered version of FireWire is currently in works to overcome this barrier.

USB OTG isn’t without its own problems. To consumers, the additional OTG USB cables are rather confusing. Users would be using one cable for exchanging data between their PDA and MP3 player, and another for hooking them up to a PC. Consumers will also have to learn how to plug the cables correctly to suit their needs. Moreover, early adopters of the new OTG products will find the 'Targeted Peripheral List 'to be somewhat lacking.

Where USB OTG is Heading?
There's not much USB, originally designed to converge phones and computers, hasn’t accomplished, including simplifying the ways of which people work with computers and inspiring new ideas for business opportunities. Following the success of USB 2.0 and with the compatibility of 500 million devices, the new On-The-Go is ready to push mobile computing to the next level.