Flow Control Mechanisms for the Bundle Protocol in IEEE 802.15.4 - - PowerPoint PPT Presentation

Platzhalter für Bild, Bild auf Titelfolie hinter das Logo einsetzen Wolf-Bastian Pöttner, Lars Wolf CHANTS 2012 (ACM MobiCom), Istanbul, Turkey, August 2012

Flow Control Mechanisms for the Bundle Protocol in IEEE 802.15.4 Low-Power Networks

Lars Wolf | Flow Control for DT-WSN | Page 2 / 9

Motivation

Wireless Sensor Networks (WSNs)

• Battery-powered nodes, limited hardware capabilities
• Wireless communication, usually IEEE 802.15.4
• Unstable links, changing topologies
• Many publications use DTN, but not Bundle Protocol

Delay Tolerant Wireless Sensor Networks (DT-WSNs)

• Sensor Networks using store, carry and forward protocol
• Bundle Protocol allows seamless backend integration

Lars Wolf | Flow Control for DT-WSN | Page 3 / 9

Bundle Protocol in IEEE 802.15.4 Wireless Networks

Bundle Protocol over IEEE 802.15.4 Wireless Links

• Bundle Protocol designed as overlay protocol on Layer 5
• But: Significant overhead

IEEE 802.15.4 Convergence Layer

• Transports bundles inside IEEE 802.15.4 MAC frames
• Avoids network and transport layer, has to handle their tasks
• IEEE 802.15.4 MAC does CRC, ACKs, retransmissions,...
• Flow Control necessary to avoid overrunning receivers
• WSN nodes are slow due to limited resources

Lars Wolf | Flow Control for DT-WSN | Page 4 / 9

Problem Statement

Assumptions

• Persistent bundle storage in flash (not enough RAM)
• Writing a page (0.5 - 5ms) slower than reading (<<1ms)
• File systems and OS make the delay variable over time

Problem Statement

• Ensure inter-packet-delay tD is large enough to give sender

and receiver time.

• Or:

Goal

• Minimize tD

tD ≥ max(TR,TS)

t" t" Sender" Receiver" ACK"

Data"

TX" RX" RX" TX"

tS,1 ACK"

Data"

TX" RX" RX" TX"

tS,2 tR,2 tD tR,1

Lars Wolf | Flow Control for DT-WSN | Page 5 / 9

Four Different Flow Control Mechanisms (1/2)

• Fixed Delay between outgoing packets
• TCP-inspired approximation of processing time

t" t" Sender" Receiver" ACK"

Data"

TX" RX" RX" TX"

tS,1 tR,1 ACK"

Data"

TX" RX" RX" TX"

tS,2 tR,2 Fixed"Delay" t" t" Sender" Receiver" ACK"

Data"

TX" RX" RX" TX"

tS,1 tR,1 ACK"

Data"

TX" RX" RX" TX"

tS,2 tR,2 Variable"Delay"

"" "" "" "" "" "" ""

Delay&tD& Transmissions&

Threshold"

Lars Wolf | Flow Control for DT-WSN | Page 6 / 9

Four Different Flow Control Mechanisms (2/2)

• Application-Layer ACKs when processing is done
• Receiver-feedback on estimated processing time

t" t" Sender" Receiver" ACK"

Data"

TX" RX" RX" TX"

tS,1 tR,1 ACK"

Data"

TX" RX" RX" TX"

tS,2 tR,2 Receiver"Feedback" t" t" Sender" Receiver" ACK"

Data"

TX" RX" RX" TX"

tS,1 tR,1 ACK"

Data"

TX" RX" RX" TX"

tS,2 tR,2 Applica:on"Layer"ACK" App=Layer"ACK"

RX" TX"

Lars Wolf | Flow Control for DT-WSN | Page 7 / 9

Evaluation: Application Layer Throughput

100 200 300 400 500 600 10 20 30 40 50 60 70 80 Application-layer Throughput [bytes/s] Payload Length [bytes] Fixed-Delay TCP-inspired App-Layer ACKs Receiver-feedback

• App-layer ACK & Receiver-feedback show highest throughput

100 200 300 400 500 600 10 20 30 40 50 60 70 80 Application-layer Throughput [bytes/s] Payload Length [bytes] Fixed-Delay TCP-inspired App-Layer ACKs Receiver-feedback 100 200 300 400 500 600 10 20 30 40 50 60 70 80 Application-layer Throughput [bytes/s] Payload Length [bytes] Fixed-Delay TCP-inspired App-Layer ACKs Receiver-feedback 100 200 300 400 500 600 10 20 30 40 50 60 70 80 Application-layer Throughput [bytes/s] Payload Length [bytes] Fixed-Delay TCP-inspired App-Layer ACKs Receiver-feedback

Lars Wolf | Flow Control for DT-WSN | Page 8 / 9

Evaluation: TX Energy Consumption (via transmitted data)

§ App-Layer ACK shows highest energy consumption because additional ACK packets have to be transmitted

15000 30000 45000 60000 10 20 30 40 50 60 70 80 Total Transmitted Data [bytes] Payload Length [bytes] Fixed-Delay TCP-inspired App-Layer ACKs Receiver-feedback

Lars Wolf | Flow Control for DT-WSN | Page 9 / 9

Conclusions

• Delay Tolerant Wireless Sensor Networks (DT-WSN)
• Low-Power nodes built around µC running on batteries
• IEEE 802.15.4 as predominant wireless communication
• IEEE 802.15.4 Convergence Layer
• Operates directly on top of MAC layer to reduce overhead
• Takes care of typical L3+L4 duties. Here: Flow Control
• Flow Control for IEEE 802.15.4 CL
• App-Layer ACK: high throughput and energy consumption
• Receiver-feedback: Energy efficient but platform specific
• µDTN is available as open-source software

Lars Wolf wolf@ibr.cs.tu-bs.de Wolf-Bastian Pöttner poettner@ibr.cs.tu-bs.de http://www.ibr.cs.tu-bs.de/projects/mudtn/