Transcript
5-10-2010
Challenge the future
DelftUniversity ofTechnology
RoutingRouting Without Routes:The Backpressure Collection Protocol
Steffan Karger
Moeller et al.
2Routing without Routes: The Backpressure Collection Protocol
Presentation outline
• Introduction
• Backpressure routing
• Adjustments for BCP (Backpressure Collection Protocol)
• The weight function
• Queue optimization
• Implementation
• Results
• Conclusion
3Routing without Routes: The Backpressure Collection Protocol
Introduction
• Network assumptions
• Sensor nodes
• Data sinks
• Collection Tree Protocol
• Beaconing
• Builds MST’s
4Routing without Routes: The Backpressure Collection Protocol
Backpressure routingRouting without routes
Data packets flow to the sink in a natural fashion
Monticello Dam in northern California
5Routing without Routes: The Backpressure Collection Protocol
Backpressure routingRouting without routes
Data packets flow to the sink in a natural fashion
• Link weight
• Transmission threshold
6Routing without Routes: The Backpressure Collection Protocol
Backpressure routingRouting without routes
• Use ETX as link usage penalty:
• Minimizes ETX -> fast delivery
7Routing without Routes: The Backpressure Collection Protocol
Backpressure routingRouting without routes
8Routing without Routes: The Backpressure Collection Protocol
Adjustments for BCPFIFO vs LIFO (1)
• Under FIFO, the average source-to-sink delay grows with decreased loading, why?
9Routing without Routes: The Backpressure Collection Protocol
Adjustments for BCPFIFO vs LIFO (2)
• Under LIFO, data packets cascade towards sink
• Average source-to-sink delay does not grow under low load
10Routing without Routes: The Backpressure Collection Protocol
Adjustments for BCP
• Problem: Queue size grows with distance to the sink
• Large networks -> large queues
• Solution: introduce virtual queue
• Discard oldest packet in real queue
• Record virtual queue size
• Null packets
Floating queues
11Routing without Routes: The Backpressure Collection Protocol
Adjustments for BCP
• With fixed queue size algorithm
breaks down
• Floating queue preserves
gradient
Floating queues
12Routing without Routes: The Backpressure Collection Protocol
Implementation
• 23 KB footprint (vs 27 KB for CTP)
• Weight recalculation parameter τ = 50ms• Performance/processor load tradeoff
• Link metric estimation (ETXi->j and Ri->j )• Based on data transmissions and ACK’s
• Advertize queue size in data header• Neighborhood snoops headers
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BCP vs CTP
BCP CTP
Forwarding policy Gradients fromneighborhood
ETX from neighborhood
Setup cost Initial packetloss -
Perturbation cost - Rebuilding MST
Gradient advertizing Header snooping Beaconing
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Results
• Tutornet• 40 nodes, indoor• IEEE 802.15.4-based Tmote Sky devices• -18 dBm transmit power• Poisson traffic
• Static network tests
• External interference
• Highly mobile sinks
Experiment details
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Results
• BCP performs comparable to CTP on delay and delivery order
Static network – Delay performance
Source to sink delay CDF at 0.25 PPS for motes 4 and 40
The Reordering Distance for BCP under FIFOand LIFO servicing priorities.
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Results
• BCP performs better then CTP with higher loads
Static network – Goodput
Goodput against load
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Results
• 802.11 interference• Alternating: 20s on, 20s off
• CTP: 55% - 84% delivery ratio• BCP: 88% - 96% delivery ratio
External interference
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Results
• Sink ‘moves’ every second
Highly mobile sinks
19Routing without Routes: The Backpressure Collection Protocol
Results
• Sink ‘moves’ every second
• BCP adjust very good and even profits from mobile sinks
Highly mobile sinks
MobilityBCP CTP
StaticBCP CTP
Delivery ratio 0.996 0.590 0.969 0.999
Average Tx/packet
1.73 9.5 2.39 2.65
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ResultsHighly mobile sinks
A 200 second window of sink time versus source mote for sinks 8, 18 and 26
• Data is ‘dumped’ when sink
is nearby
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Conclusion
• In static networks:
• BCP performs comparable to CTP on delay and efficiency
• BCP can cope with hihger loads
• Robust to external interference
• Very good performance with highly mobile sinks
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Discussion
• What happens when we use a duty cycle operation?
• BCP should work quite well with synchronized duty-cycle MAC’s like S-MAC
• A-synchronous duty-cycle MAC’s like LPL MAC need adjustments for packet snooping
Duty cycled operation
23Routing without Routes: The Backpressure Collection Protocol
Discussion
• How about transmission count?
• Comparable to CTP
Transmission count
Per source average per packet transmission count to the sink
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