MPAC 2004Rae Harbird 1 RUBI Adaptive Resource Discovery for Ubiquitous Computing.
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Transcript of MPAC 2004Rae Harbird 1 RUBI Adaptive Resource Discovery for Ubiquitous Computing.
MPAC 2004 Rae Harbird 2
RUBI• Why resource discovery?
• Review of existing protocols
• RUBI, design and evaluation
• Future work
• Conclusions and questions
MPAC 2004 Rae Harbird 3
Ubiquitous Computing • Weiser’s vision becoming reality
– 250 million microprocessors sold monthly, < 2 % destined for PCs
• Ubicomp revenue
– Provision of novel services, low / no ROI from connectivity alone
• Resource discovery and management
– Vital component in the realisation of the ubicomp vision
– Key enabler for revenue stream
MPAC 2004 Rae Harbird 4
• Huge heterogeneity
– Device capabilities and characteristics
• Immense scale
• Dynamic operation and volatility
– Number, types and attributes of services will change fast
• Result: administrative complexity
– Must be hidden from users
Environmental ImplicationsEnvironmental Implications
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• Distributed and highly scalable
– Information available at many points in the network
• Accommodate heterogeneity
– Participants
– Network topologies
• Autonomic
– Function despite the frequent failure of resources, devices and the links between them
Resource Discovery Requirements
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Previous Work • Global, central index of resources
– Jini
• Global, distributed index
– Distributed Hash Tables
• Resources discovered as needed
– Konark, UPnP, SLP
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• Resource Discovery for Ubiquitous Computing
• Overarching adaptive process
– Controlling the way that information is disseminated and retrieved
• Based on local view of the network
• Founded on routing algorithms
– Exchange of routing information more generally applied to the exchange of service details
RUBI
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• Chosen ad hoc routing algorithms for RUBI
• Low, relative mobility: low rate of change
– Proactive routing algorithm (OLSR)
• High, relative mobility: high rate of change
– Reactive routing algorithm (AODV)
• Regions with these characteristics will coexist
– Resource discovery must adapt
Adaption
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Protocol Messages• Resource advertisement (proactive)
• Resource cancellation (proactive)
• Resource requests (proactive and reactive)
• Resource request replies (proactive and reactive)
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• Resource information distributed periodically
– Period length dependent upon whether a node detects change in its locality
• Uses optimised flooding
– Reducing costs as compared with classic flooding
• Subset of neighbours elected as relays
– Used to propagate resource information through the network
Proactive Resource Advertisement
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Proactive Algorithm• Resource requests
– Can be generated by nodes which are not relays
– Used by relays where the resource search should traverse a proactive region
• Resource request replies
– Sent by relays to neighbouring nodes
• Resource cancellation
– Next advertisement will not contain information about the cancelled resource
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Reactive Resource Requests & Replies• All nodes responsible for maintaining their own cache
• Resource information preserved for recently queried resources only
– Deleted from cache if not used after a specified time interval
• Requests are flooded through the network
• Scope is controlled by Time To Live (TTL)
– Uses Expanding Ring Search (ERS) if no resource found
– Overhead of finding a resource is reduced if there is a resource nearby
• Replies are unicast back to the sender
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Algorithm Selection• How does a node determine the type of region it belongs to?
– Assesses this using locally available information.
• Select routing algorithm based on perceived stability
• Link duration is used as a mobility feedback mechanism
– Gleaned from neighbour establishment (NE) process
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Neighbour Establishment• RUBI nodes broadcast HELLO beacons periodically
• HELLO message contains:
– List of that node’s direct neighbours
– Flag indicating whether neighbour has been selected as a relay
– Willingness value (between 0-7)
• Receiver uses HELLO information to build up a picture of local topology
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Relay Selection Rules• Simple heuristic
1. Neighbours advertising maximum willingness
2. Neighbour nodes that are the only nodes through which a 2-neighbour can be reached
3. Neighbours through which the remaining 2-hop neighbour set can be reached
• If there is more than one neighbour that fulfils this role, the one with the greatest number of links is chosen
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Protocol Coexistence• There will be regions where the proactive and reactive areas
border each other
• We must ensure consistent resource discovery behaviour
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Proactive Request Reaches Reactive Region
• Node b sends resource request to its relay A
• Node p will also hear request
• Node p will deal with the request according to the reactive protocol rules
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Proactive Reply Reaches Reactive Region
• Node A, a relay, unicasts a reply to node b
• Node p is within the transmission range of node A
• Node p will hear the reply and may cache the information
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Reactive Request Reaches Proactive Region
• Node p broadcasts a request which reaches node b in a proactive region
• Node b may respond if it has cached relevant information
• Otherwise it can forward the request to its relay set
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Failure Recovery• Resource fails
– Jini-like approach to information currency
– Period in which incorrect information might be served
– Proactive algorithm may be more responsive
• Node fails
– All neighbour information deleted, including resources
– Incorrect information will remain in the network for a period
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Discussion• RUBI represents trade-off between:
– Context-aware operation
– Efficiencies gained by assuming stability
• Greater overhead than the other approaches reviewed
– Neighbour establishment and monitoring
• Will not realise efficiencies gained in other approaches
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Future Plans• Evaluate performance through emulation as part of the
ADAM framework
• Evaluate proposed design improvements
– Border nodes could act as gateways
• Address security issues
– ADAM trust management framework
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Conclusions• Resource discovery
– Key factor in realisation of ubicomp vision
• RUBI designed with ubicomp environment in mind
– Stability of underlying network is not assumed
– Heterogeneity is assumed and exploited where possible
– Routing algorithms ensure the efficient dissemination of information
– Autonomously adapts to prevailing network conditions
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Resource Discovery• Conceptually very simple
– Resource owners register service in distributed directory
– Clients query the directory for services matching a particular set of attributes
• Implementation is more complex
– How to describe resources and express queries?
– What form of distributed directory to use?
– Where to locate information and how to move it around?
– How to control access to that information?
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Effects on Resource Discovery
• Must be distributed
– Available at many points in the network
– Highly scalable
• Must require minimal human interaction
• Must operate on even the most resource-poor devices
• Take advantage of available resources where these are present
– Bandwidth, processor speed, memory
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Routing Algorithms
• Proactive
– Forwarding paths periodically exchanged: OSPF
– Applicable in areas of low, relative mobility
• Reactive
– Route information exchanged as needed: DSR and AODV
– Suited to regions of high, relative mobility
• Hybrid approaches: ZRP
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• Based on two routing algorithms:
– OLSR, suited to stable, fairly dense networks
– AODV, suited to networks that have a fairly high mobility rate
• Algorithms integrate well
– All nodes cache information
– Requests answered by any node with up-to-date information
• RUBI is resilient over wider range of network conditions
Resource Discovery Operation