Real-time Interaction over the Internet
Christophe Salzmann, Denis Gillet
Overview
Remote experimentation is an effective e-learning paradigm for supporting hands-on education using laboratory equipment at distance. The current trend is to enable remote experimentation in mobile and ubiquitous learning. While the current Internet bandwidth allows remote experimentation to work flawlessly on fixed connections such as LANs, mobile users suffer from both the versatile nature of wireless communications and the limitation of the mobile access devices. These conditions impose that the remote experimentation software should integrate adaptation features.
For effective remote experimentation, it should ideally be guarantee that the information representing the state of the remote equipment is rendered (to the end user) at the same pace at which it has been acquired, yet possibly at the cost of a minimal time delay between the acquisition and rendering phases. In this respect, an end-to-end adaptation scheme is proposed that explicitly handles the inherent variability of the connection and the versatility of the mobile devices considered in remote experimentation. Instead of relying on a stochastic approach, the proposed adaptation scheme relies on a deterministic mass-balance like model.
Keywords : Interaction ; end-to-end adaptation ; network ; remote experimentation
Real-Time Interaction over the Internet
Objectives
Provide the user with the best possible experience
– defined by the RTI2 QoS
Context: remote experimentation of mechatronic systems
– challenging systems: fast dynamics, rich visual content, intrinsic dynamics in the order of magnitude of the information transmission time
Contrains: ubiquitous, adaptable
RTI2 is a new Internet Service
We consider the E2E system at the application level
– this is different than E2E network level
– client and server applications are also considered
– required since the client component can be the bottlenck
We propose a solution that is fair, ubiquitous and adaptable
– compatible with the Internet best practices (TCP friendly)
– transmission protcols independance (TCP, UDP, etc)
– infrastructures independence
– adapt in real-time to the E2E characteristics variations
– no reservation mechanism involved
– the sementic information can be represented with a few bytes to hundreds of kBytes
We control the round trip time of the information (block)
– we can guaranty the level of interaction
– we can ensure that the equivalent E2E buffer stays empty
– we can compensate/reconstruct missing information
Current technologies
– Video streaming: use buffers to smooth playback
– Video conferencing: symetrical transmission, sound emphasis
– Channel with guaranties QoS: require specific infrastructure/software
QoS
The level of interaction: how quickly feedback is provided to the user
The dynamics perception: how accurately in time the behavior of the remote system is perceived
The semantic content: how well the distant system state and conditions of operation can be perceived by the client
Abstractions
E2E infrastructure at the application level
Streams of information aggregated in Blocks
Metrics
d: E2E round trip time at the application level
τ (timeliness) and ε (integrity): characterize the capacity of E2E structure to handle the current block
Adaptation
Track the block round trip time d at the application level
Modify the block size and/or pace to follow a d ref
Real-time model estimation (bandwidth and propagation delay)
Exemple
Desktop computer <-> Palm T3
Bluetooth transmission using TCP
Track round trip time d at the application level
reference round trip time 200 ms
At some point the user move away from the BT access point
– the block round trip time increase
– the controller reduce the block size S
See a 30 sec QuickTime movie(1.7 MB) [epfl_infoscience url=”http://”]