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Diversity dictates in pervasive computing

Posted: 01 Apr 2001 ?? ?Print Version ?Bookmark and Share

Keywords:pda? x86? arm? set top box? bluetooth?

Unlike the one-size-fits-all PC, the emerging market for Net-centric pervasive computing devices is extremely diverse, including PDAs, set-top boxes, screen phones, in-vehicle computing platforms, smart phones and home gateways. As the market matures, this list of devices will continue to expand into areas that we cannot even imagine today.

Pervasive computing devices must appear to be appliances, not computers. This means that such requirements should be evident on user interfaces that match the function of the appliance. For instance, a network-enabled set-top box's first priority is to deliver high-quality audiovisual content. They must support heterogeneous hardware, networks and content.

Pervasive computing devices target a broad range of price points, form factors and hardware capabilities. For instance, requirements vary across user interface models (including a range for audible as well as small, medium and large manual/visual), power requirements (battery life versus ac power), processor families (ARM, x86, PPC, mips, Hitachi SH, etc.) and network capabilities.

Net factors

The explosion of short-range ad hoc networking (for example, Bluetooth, HomePNA, 802.11, etc.) is commensurate with the explosion of pervasive computing devices. This connectivity capability has implications on the device architecture requiring seamless support for transparent, appliance-like, ad hoc collaboration among these devices themselves.

To be successful, new pervasive computing devices cannot wait for entirely new custom content to be created. A cogent content architecture must address existing devices and lower the entry barrier for future devices seamlessly for all content providers in the value chain. This end-to-end content architecture must also ensure that new devices can be added while still supporting the network scalability demanded by millions of connected devices.

Four classes of pervasive device configurations are necessary to define a simple taxonomy of capability that addresses the complete landscape of requirements. They are thin terminals with no local state information; thick terminals that support applications using a programming model native to the device; gateways and full configuration. The last supports the combination of gateway, thin-terminal and thick-terminal capabilities to allow, in a single device, hosted services, device-specific applications and content rendering for network-delivered data.

The benefit of such a common taxonomy is that it leads to a reusable common device architecture and a small set of programming models for all device and network types to allow for the construction and deployment of device classes across the complete device taxonomy. To be viable, this infrastructure must have 10 essential requirements: use of open standards; end-to-end scalability; support for a variety of device interactions; synchronous user request-response; asynchronous user messaging and notification; remote access from network; support for end-to-end systems for management of users, devices, network-delivered applications and content; enable the integration of third-party components and products; and reuse end-to-end network programming models.

Five categories of integrated components (subsystems) make up the pervasive architecture we are proposing: core, user interface, communications, security and application. The pervasive computing device software architecture supports three basic application models, including both networked and standalone capability.

Pervasive computing devices violate many of today's technology assumptions like html, JavaScript, etc. in the area of user interfaces, networking bandwidth, and connection availability. A full HTML4.0/JavaScript browser, while supported as one of the components in the architecture, is only viable for a subset of the total pervasive computing device domain.

Because of device and network bandwidth and latency constraints, other forms of markup languages are emerging (for example, WML/WMLScript, CompactHTML, VoiceXML, ATVEF). Additionally, the devices that can render these markups come in a variety of form factors (portrait, landscape, various color depths and vocabularies, etc.). For these other form factors and markups, the pervasive computing content delivery architecture can support legacy HTML by the use of transcoding services in the network.

One way to use this transcoding service is to convert HTML or JavaScript into an appropriate markup language for the targeted device. For markup languages that provide a similar user experience to that of HTML, this will have some limited success.

Content in control

Enabled applications are the device-side portion of a consistent end-to-end pervasive computing content-delivery architecture that enables a scalable solution for network-delivered content to the heterogeneous and evolving set of pervasive computing devices. This architecture allows service providers and application programmers to develop and deploy network-based applications to address devices with similar requirements.

Enabled applications use the well-known Java servlet-programming model in conjunction with an embedded HTTP server and a local rendering engine (browser) on the device.

? Jim Colson

Senior Technical Staff Member

IBM Pervasive Computing

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