1 Neighbor Table Message Pool Contains Contains Reference to - - PDF document

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Unifying Link Abstraction for Wireless Sensor Netw orks

Chris Wilson

Tow ards a Sensor Netw ork Architecture: Low ering the Waistline

• Lack of sensor net architecture
• Monolithic protocols
• No abstraction
• No modularity
• No code reuse

Internet Architecture

Application Transport Network Link HTTP, DNS, TFTP, POP3, SMTP… TCP, UDP, DCCP… IP Ethernet, Wi-Fi, PPP, SLIP, FDDI…

Sensor Net Architecture

Network Protocol A Network Protocol B Network Protocol C SP Link A Link B

Challenges

• Efficiency
• Neighbor Management
• Power Management
• Cooperation between Link & Net
• Handle Packets

SP

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Neighbor Table

• Contains

– Neighbor Address – Schedule information – Link quality

• Extensible
• Allows cooperation between

Network and Link layers

Message Pool

• Contains

– Reference to the next packet – Number of packets left – Next packet notification

• Network sets urgency and

reliability bits

• Link set congestion and phase

shift bits

Implementation Link Protocols

• Slotted protocol

– IEEE 802.15.4

• Channel sampling protocol

– B-MAC

802.15.4

• Inserts neighbors with schedule info
• Checks for messages or listen bit on

neighbor frame

• Beacons use broadcast neighbor or

unicasts round robin

• LQI metric for link quality
• Uses Acks for reliability bit

B-MAC

• Added synchronization and source

information to header

• Extracts sync on long preambles
• Use short preamble with sync
• Use long preamble with unknown

destinations or broadcasts or urgent

• Use Acks for reliability bit
• RSSI and packet-error-rate estimate

for link quality

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B-MAC “Piggybacking”

A B C

Long

B-MAC “Piggybacking”

A B C

short

Netw ork Protocols

• Collection Routing

– MintRoute

• Data Dissemination

– Trickle

• Data Aggregation

– Synopsis Diffusion

MintRoute

• Broadcasts route updates and

sends data

• Use “find” for parent selection
• Data sent w/Reliability bit
• Chooses neighbor with best

EXT and hop count as parent

Trickle

• Spreads new data to the entire

network

• Motes occasionally transmit

data description

• When something new is heard

take it and send descriptions more aggressively

Synopsis Diffusion

• Uses order and duplicate

insensitive aggregates

• Robust to changing topology
• Sends aggregates to collection

point

• Requires a gradient to collection

point

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B-MAC Comparison 15.4 Comparison MintRoute results

• Stable
• Lower Duty Cycle than w/o SP
• Benefits from piggybacking

Trickle Results MintRoute + SD

Batching common messages together resulted in 35% power savings

Tenet

• Architecture for multi-tier WSN
• Abstracts away application

specific code on motes

• Not incompatible with SP

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Critique

• Assumes fair play
• What’s a Network Service

Manager?

• Timestamps
• Security