Wit: Infrastructure for Wireless Palmtop Computing

Terri Watson, UW

One-line summary: Proxy-like system based on ParcTab IRnet, where Tcl is the programming language and Tcl-DP-like IPC the transport. Emphasis on application partitioning between mobile and fixed world, but no uniform architecture/methodology for doing so, and no notion of BW management for high-bw apps.

Overview/Main Points

HP-95LX palmtops connect to Parc IRnet. A "half wit" proxy running in wired network is the liaison to the wired part of the application.
Reliable and unreliable transport, proxy communication, UI, and simple cooperative threading package available to Tcl on palmtop. App-level handlers talk to each other, but Tcl's talk to each other on separate logical channels.
Handoff: as mobile moves, its outgoing packets are routed to a new BS. Application uses RPC to query which BS is the current one, but application is not normally notified of handoff.
Multiple logical streams to same palmtop are separate TCP (or RPC) connections.
Current apps: tty, textual WWW, talk, wireless video. Uses nv to get frames and send them to the palmtop. No compression, so we're talking seconds/frame.

Interesting conclusions (from her quals talk):

Tcl is a good infrastructure choice for app development, but there was no BW management and as a result applications suffered (like video viewer).
Info browsing most popular app
Local (mobility) info rarely used, even though it was available! Contrast to tab and badge systems. Is this a chicken-and-egg problem?
Perhaps exploit UI to give user hints about relative costs (latency) of various operations.

Relevance

Implemented instance of proxy concept: application partitioning using a simple scripting language.

Flaws

Lack of BW management really bit them on the butt. The position paper talks about adapting to connectivity changes, but doesn't say how.
No "tight integration" between palmtop and fixed apps (eg consistent calendar or email,etc ); orthogonal to project
UI/SDK tightly integrated with network -- maybe too tightly?
No uniform architecture or methodology for partitioning apps. See Rover for interesting approach to this. Wit 2 has a data-driven partitioning architecture.
Design is extremely broad: covers everything from IP encapsulation in IR drivers all the way up to "UI color and layout choices"

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