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CMPE 259 Sensor Networks
Katia Obraczka
Winter 2005
Routing
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Announcements
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Transport protocols: summary
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Pump Slow Fetch Quickly PSFQPump Slow Fetch Quickly PSFQ
For sink-to-source communication (e.g. network reprogramming)
Reliability via retransmissions
Sequence-driven loss detection
C.Y. Wan, A.T. Campbell, and L. Krishnamurthy. PSFQ: A Reliable Transport Protocol for Wireless Sensor Networks. WSNA'02, September 28, 2002, Atlanta, Georgia, USA.
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RMSTRMST
End-to-end or hop-by-hop repair (the latter is generally better)
Suggests that repair could be done at either MAC layer (ARQ retransmissions) or Transport Layer (requests based on fragment numbers etc.)
Timer-driven loss detection and local data caches Fits with the Directed Diffusion API
F. Stann and J. Heidemann. RMST: Reliable Data Transport in Sensor Networks. IEEE SNPA'03.
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ESRTESRT Aim for overall quality of service rather than node-to-node
reliability
Sankarasubramaniam, Y., Akan, O.B., and Akyildiz, I.F., "ESRT: Event-to-Sink Reliable Transport in Wireless Sensor Networks ", In Proc. ACM MobiHoc`03
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CODACODA
Sankarasubramaniam, Y., Akan, O.B., and Akyildiz, I.F., "ESRT: Event-to-Sink Reliable Transport in Wireless Sensor Networks ", In Proc. ACM MobiHoc`03
Receiver based congestion detection Open loop hop-by-hop backpressure Closed-Loop multi-source regulation
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Summarizing Transport IssuesSummarizing Transport Issues Because of harsh conditions and severe
constraints, it may be better to implement reliability in a hop-by-hop rather than end-to-end manner at either the MAC or transport layer
For energy efficiency, it is best to avoid congestion entirely, or have packet losses occur close to the source. Back pressure is a useful technique.
Where possible, scheduled solutions are preferable.
s
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Routing
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Issues/challengesIssues/challenges
Difficult to pay special attention to any individual node: Collecting information within the specified
region.
Sensors may be inaccessible: Embedded in physical structures. Thrown into inhospitable terrain.
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More issues/challenges…More issues/challenges…
Topological issues: Arbitrarily large scale. No fixed infrastructure. Frequent topology changes
• Battery exhaustion.• Accidents.• New nodes are added.
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More issues/challenges…More issues/challenges…
User and environmental demands also contribute to dynamics: Nodes move. Objects move.
Data-centric and application-centric view: Location. Time. Type of sensor. Range of values…
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More issues/challenges…
Not node-to-node packet switching, but node-to-node data propagation.
High level tasks are needed: At what speed and in what direction was that
elephant traveling? Is it the time to order more inventory?
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Challenges
Energy-limited nodes Computation
Aggregate data Suppress redundant routing information
Communication Bandwidth-limited Energy-intensive
Goal: Minimize energy dissipation
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Challenges
Scalability: ad-hoc deployment in large scale Fully distributed w/o global knowledge. Large numbers of sources and sinks.
Robustness: unexpected sensor node failures
Dynamics: no a-priori knowledge Sink mobility. Target mobility.
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Directed Diffusion
A Scalable and Robust Communication Paradigm for Sensor Networks
C. IntanagonwiwatR. Govindan
D. Estrin
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Application Example: Remote Surveillance
““ Give me periodic report Give me periodic reportss about animal lo about animal lo cation in region A every t seconds” cation in region A every t seconds”..
Tell me in what direction that vehicle in Tell me in what direction that vehicle in region Y is moving?region Y is moving?
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Basic Idea
In-network data processing (e.g., aggregation, caching).
Distributed algorithms using localized interactions.
Application-aware communication primitives. Expressed in terms of named data.
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Elements of Directed Diffusion
Naming Data is named using attribute-value pairs.
Interests A node requests data by sending interests for named
data .
Gradients Gradients is set up within the network designed to
“draw” events, i.e. data matching the interest.
Reinforcement Sink reinforces particular neighbors to draw higher
quality ( higher data rate) events.
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NamingNaming
Content based naming. Tasks are named by a list of attribute – value pairs. Task description specifies an interest for data
matching the attributes. Animal tracking:
Interest ( Task ) DescriptionType = four-legged animalInterval = 20 msDuration = 1 minuteLocation = [-100, -100; 200, 400]
RequestRequest
Node dataType =four-legged animalInstance = elephantLocation = [125, 220]Confidence = 0.85Time = 02:10:35
ReplyReply
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Interest
The sink periodically broadcasts interest messages to each of its neighbors.
Every node maintains an interest cache. Each item corresponds to a distinct interest. No information about the sink. Interest aggregation : identical type, completely
overlap rectangle attributes. Each entry in the cache has several fields
Timestamp: last received matching interest. Several gradients: data rate, duration, direction.
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Source
Sink
Interest = Interrogation
Gradient = Who is interested(data rate , duration, direction)
Setting Up Gradient
Neighbor’s choices :1. Flooding 2. Geographic routing3. Cache data to direct interests
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Data Propagation
Sensor node computes the highest requested event rate among all its outgoing gradients.
When a node receives data: Find a matching interest entry in its cache
• Examine the gradient list, send out data by rate.
Cache keeps track of recent seen data items (loop prevention).
Data message is unicast individually to the relevant neighbors.
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Source
Sink
Reinforcing the Best Path
Low rate event Reinforcement = Increased interest
The neighbor reinforces a path:1. At least one neighbor2. Choose the one from whom it first received the latest event (low delay)3. Choose all neighbors from which new events were recently received
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Local Behavior Choices
For propagating interests In the example, floodIn the example, flood More sophisticated behaviors possible: e.g.
based on cached information, GPS
For setting up gradients data-rate gradients are set up towards data-rate gradients are set up towards
neighbors who send an interestneighbors who send an interest.. Others possible: probabilistic
gradients, energy gradients, etc.
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Local Behavior Choices
For data transmission Multi-path delivery with selective quality along Multi-path delivery with selective quality along
different pathsdifferent paths Probabilistic forwarding Single-path delivery, etc.
For reinforcement RReinforce paths based on observed delayseinforce paths based on observed delays Losses, variances etc.
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Initial simulation study of diffusion
Key metric Average Dissipated Energy per event delivered
• indicates energy efficiency and network lifetime
Compare diffusiondiffusion to FFloodinglooding Centrally computed tree (omniscient multicastomniscient multicast)
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Diffusion Simulation Details
Simulator: -2ns-2ns - Network Size: 50 250 Nodes Transmission Range: 40m Constant Density: 1.95x10-3 nnnnnnn2 nnnn(9 .8
s in radius) MAC: Modified Contention-based MAC Energy Model: Mimic a realistic sensor radio [Pottie
2000] nn nnnnnnnnnn nnn 660 , 3 9 5 ,
35mw in idle
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Diffusion Simulation
Surveillance application 5 sources are randomly selected within a 70m x
nnnnnn nn nnn nnnnn70 5 sinks are randomly selected across the field nnnn nn n nnnnnnnnnn2/ nnnnnnnnnn0.02/ Event size: 64 bytes 36Interestsize: byt es All sources send the same location estimate for b All sources send the same location estimate for b
ase experiments ase experiments
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Average Dissipated Energy
0
0.002
0.004
0.006
0.008
0.01
0.012
0.014
0.016
0.018
0 50 100 150 200 250 300
Ave
rag
e D
issi
pat
ed E
ner
gy
(Jo
ule
s/N
od
e/R
ecei
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Eve
nt)
Network Size
DiffusionDiffusion
Omniscient MulticastOmniscient Multicast
FloodingFlooding
Diffusion can outperform flooding and even omniscient multicast.Diffusion can outperform flooding and even omniscient multicast.(suppress duplicate location estimates) (suppress duplicate location estimates)
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Conclusions
Can leverage data Can leverage data processing/aggregation processing/aggregation inside the network.inside the network.
Achieve desired global behavior through localized interactions.
Empirically adapt to observed environment.
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Energy-efficient multipath routing
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Energy-efficient multipath routing Based on directed diffusion. In directed diffusion:
Sink broadcasts interest. Sensors periodically (low rate) sends back
data (e.g., event detection reports). Sink sends reinforcement on preferred path. Reverse path is established. Upon missing reports, sink re-broadcasts
interest and sink reinforces.
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Problem?
Periodic flooding of interests and events in the presence of failures.
Solution?
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Solution: multiple paths
Multipath routing: Load balancing. Reliable delivery (by sending duplicates). Robustness.
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Observations
Primary path: “best” path. Data sent at lower rate on alternate
paths. Upon failure on primary path,
reinforcement on alternate path. If all altremate paths fail, flooding for
path re-establishment. Overhead: alternate path maintenance. Resilience measured as how often path
re-establishment is needed.
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Approach
Disjoint versus “braided” paths. How to build multiple paths with local
information only?
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Localized disjoint multipaths
Sink establishes primary path. Sink selects “next best” neighbor “A”. A propagates “alternate path”
reinforcement to its “best” neighbor “B”.
If B is already on a path between sink and source, B sends back a “negative reinforcement”.
Access to local information only may lead to longer paths.
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Braided multipath
Partially disjoint. For each node on primary path, find
best path from source to sink that does not contain that node.
Paths in the braid expend equivalent energy.
Reinforcement to “best” node and alternate reinforcement to “next best” node.
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Evaluation
Energy efficiency. Overhead.
Resilience to failures. Isolated versus patterned failures.
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Results
Braided multipaths are more energy efficient. Especially at lower densities.
Disjoint multipaths have better resilience to patterned losses.
Braided multipaths exhibit better resilience to isolated failures.
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Geographic routing
Deliver packets to nodes or regions based on their geographic location.
Typically, nodes know their position and immediate neighbors.
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Basic Geographic ForwardingBasic Geographic Forwarding
B. Karp and H.T. Kung. GPSR: Greedy Perimeter stateless Routing for Wireless Networks. MobiCom2000.
Greedy: send packet to neighbor that is closest to destination
Can get stuck in voids. GPSR proposes a perimeter routing mode to avoid this.
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Trajectory Based ForwardingTrajectory Based Forwarding
D. Niculescu and B. Nath, Trajectory Based Forwarding and Its Applications. MOBICOM 2003.
Pre-encode arbitrary geographic trajectory; packet goes through nodes closest to this trajectory.
Particularly well suited for large networks with high density.
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Geographic routing without location information (Rao et al.) Apply geographic routing when (most)
nodes do not have position information. Approach: “virtual coordinates”.
Use local connectivity information.
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Assumptions
Nodes know their own coordinates. Nodes know coordinates of nodes in the
2-hop neighborhood.
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Routing
Greedy: forward to neighbor closest to destination.
When packet arrived to destination, stop.
If stuck, do expanding ring search until closer node found.
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Coordinate construction
A node’s coordinates is the average of its neighbors’ coordinates.
Finding perimeter nodes’ coordinates. Beacon nodes flood “Hello” message. Perimeter nodes discover distance in hops
to other perimeter nodes. Perimeter nodes broadcast their perimeter
vector. Perimeter nodes use triangulation to find
coordinates of all perimeter nodes.
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Coordinate construction (cont’d) Deciding whether a node is on
perimeter: Use distance to beacon nodes. If node is the farthest away from beacon
node compared to all its 2-hop neighbors, then it’s on the perimeter.
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Evaluation
Comparison between greedy routing using real- versus virtual coordinates.
Metrics: Success rate: number packets reaching
destination using purely greedy routing. Average path length. Routing load. Overhead.
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Results
Scalability. Network size. Density.
Mobility. Losses. Obstacles. Trade-offs.
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