Autonomous Virtual Mobile Nodes
Shlomi Dolev
Seth Gilbert
Elad Schiller
Alex Shvartsman
Jennifer Welch
Challenges
• Locality
• Unreliable nodes
•
•
••
Nodes only
send
Mobile
nodes
fail,messages to
nearby
nodesand
go to sleep,
Global
coordination
is expensive
get turned
off.
Challenges
• Locality
• Unreliable nodes
• Irregular motion
•
•
•
Mobiletravel
Nodes
nodeswherever
fail,
they want
to
gogo
to sleep, and
get turned off.
Opportunities
• Broadcast
• Wireless broadcast is a powerful
primitive.
• Allows a node to reach all nearby
nodes,
• Ensure they receive the same
messages.
Opportunities
• Broadcast
• Time & Geography
• Nodes are physical entities
– physical time & location
• Use GPS and/or algorithms for
synchronization / location
Related work
• Existing protocols
• Flooding
• Distributed structure
– E.g., TORA [PC97]
• Compulsory movement of nodes
–
[HP99, CNS01]
Related work
• Existing protocols
• Random walk
• Random walk of a single agent
• Coping with chaos by chaos
Related work
• Existing protocols
• Random walk
• Virtual nodes
• Geo-Quorums [DGL03]
• Virtual Stationary Automata
– [DGL05]
• Virtual Mobile Node [DGL04]
Autonomous Virtual Mobile Node
• Automaton
• New programming abstraction
• A virtual general-purpose
computing entity.
Autonomous Virtual Mobile Node
• Automaton
• New programming abstraction
• Distinct location at any time
• Implemented by “real’’ mobile
nodes that happens to be near.
Autonomous Virtual Mobile Node
• Automaton
• New programming abstraction
• Distinct location at any time
• Communicates with:
• other virtual nodes, and
• “real” mobile nodes.
Autonomous Virtual Mobile Node
• Automaton
• Reliability
• Autonomous
• Fault
recovery
On-line
movement decision:
– current state, and
• Self-stabilization
– sensor/environment input.
1any
• Example
Tolerate
starting state:
The group
emulation
enhances
maybe several
(undesired)
robustness:
• If •north-east
area appears
deserted
copies,
or fail, or
•• some
may
go south-west
• none
all.of range.
moveat
out
Autonomous Virtual Mobile Node
• Automaton
• Reliability
• Autonomous
• On-line movement decision:
– current state, and
– sensor/environment input.
Example 2
• Hitchhike with the traffic, or
• Go in the opposite direction
Application Domain
• Vehicular networks
• Traffic control and safety
– E.g., ad hoc traffic light
Application Domain
• Vehicular networks
• Traffic control and safety
– E.g., ad hoc traffic light
Application Domain
• Vehicular networks
• RFID tags
• Very small, cheap and wireless
tagging network.
• Limited power supply.
– Photoelectric gate
• Use flash light to activate the net
• The AVMN follows the light
• E.g.,
• count the number of items
• find an expired item
• Use microwave instead of light.
Application Domain
• Vehicular networks
• RFID tags
• Swarm computing
• Multiple virtual nodes
– Hierarchically originated
– Performing different task
• Collaborating or competing
Implementation
• Exactly 1 instance
Three different schemes
1.
Virtual Stationary Automaton
• alive messages to known location
of a stationary node (VSA)
• VSA keeps track of the AVMN
• No message for too long
• create a new AVMN
• VSA eliminates duplicates
Implementation
• Exactly 1 instance
Three different schemes
1.
2.
Virtual Stationary Automaton
Send alive messages
containing
more
thanreceive
(N+1)/2
Send
alive
messages
in
a an
•IfIf
a real
node
doesn’t
• creates
a
new AVMN
random
walk
fashion.
alive message for too long
• generates a formation token
• carries ids and traverses
in a random walk fashion
• If tokens collide: merge ids’ lists
Implementation
• Exactly 1 instance
Three different schemes
1.
2.
3.
Virtual Stationary Automaton
Send alive messages
Nodes alive messages
• Real nodes periodically send
stay alive messages
• random walk to AVMN
• in order to survive
• AVMN must collect at least
(N + 1)/2 messages.
Implementation
• Exactly 1 instance
• Self-stabilization
<State1, input1>
<State1,
2, input1
2>
• Every emulating real node
– Keeps a replica of the AVMN
– Ensures identical replica
• Buffer input events waiting to be
applied to the state.
• At a fixed interval,
• sends replica to all.
• Predetermined function resolves
conflicts.
<State3, input3>
Implementation
• Exactly 1 instance
• Self-stabilization
• Mobility
• Where and when to move?
– Can be decided by current state
– Ensure the right order of events
– Ensure nodes´ proper join/leave
Esure
that:
move to x
move
t2 <join,
x3• on
tid3 37634>
2 on to
• Old nodes remain participants
• Enough nodes near the new
, input> notification
location<State
can receive
x1
x2
x3
• And, mobile nodes can join
Discussion
• Described how to implement a single AVMN
– Can implement multiple AVMNs using the same
techniques.
• There are a number of ways to optimize
– Use min amount of power to reach everyone.
– Use nodes that are closer to the new AVMN centrum.
– If possible, take advantage of nodes movement.
Thank you
Your attention is appreciated