Latency is an unavoidable fact of distributed systems, and an unrelenting foe of interface usability. I present methods for lessening the impact of latency on distributed haptic, graphic, and collaborative interfaces. These three interfaces are present in the distributed nanoManipulator, a shared tool for remote operation of Atomic Force Microscopes. The work is carried out in the context of the Internet, where best-effort service means that network performance is not guaranteed and that applications must function under a wide range of conditions.
The ability of a distributed control algorithm to tolerate latency is innately tied up with how data or operations in the algorithm are represented for transmission over the network. I introduce two new representations for haptics, the warped plane approximation and local environment sampling, with superior latency tolerance. I show how image-based rendering is a useful representation for transferring the output of a remote graphics engine across the network, yielding a tenfold reduction in mean response time over video-based approaches, and how optimistic concurrency control is a useful representation for transmitting the actions of a remote collaborator across the network, requiring 85% less concurrency control overhead than pessimistic approaches. All of these intermediate representations convey a meaning that is not just true at a single point space and a single point in time, but that is valid across a volume of space or across a range of times. These higher-order representations reduce both the amount of blocking necessary and the rate at which closed feedback loops must run in an algorithm.
I show how techniques used to adaptively deliver multimedia content -- the User Datagram Protocol (UDP), Forward Error Correction (FEC), and Queue Monitoring (QM) -- are applicable to the streams of data transmitted by force feedback tele-operators. UDP alone yields a 35% reduction in latency and a 75% reduction in jitter.
The new algorithms and adaptations for the distributed nanoManipulator's interfaces combined to make this collaborative tool feasible, leading to successful use by experimenters more than 2000 miles apart.
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Last revised Tue Apr 12 9:37:44 EDT 2005 by jeffay at cs.unc.edu.