1. Bhavish Aggarwal 04005018 Guide: Prof. Bhaskaran Raman
Design and Implementation of a VoIP Application over Platform for Rural Deployment
Bhavish Aggarwal
Guide: Prof. Bhaskaran Raman

2. Rural Indian Context 70% of Indians live in 6,00,000 villages.
Most are illiterate and extremely poor.
But need for communication technologies remains high!

3. Existing Technologies
Cellular
High cost of value-added services for average rural consumer.
High infrastructural cost and low returns for companies.
WiMax
Potential yet to be proven.
Again, costly.
VoIP over WiFi
Active research area.
Cheaper hardware and infrastructure.
Cost-priced to lower cost to consumer.

4. Advantages of 802.15.4 radio Low operational power Cheap hardware
Typical consumption of 50 mW with radio on.
Lowers operational cost and maintenance.
Cheap hardware
radio costs only $5.
The tmote platform with the radio costs $70. This can be reduced by customizing and optimizing the platform for our context.

5. To the drawing board Problem statement
Implement VoIP over a mesh of nodes and minimize jitter and end-to-end delay meeting VoIP quality requirements.
Challenges
High throughput across multi-hop connections
Low latency across multi-hop connections
Low power consumption
Platform limitations: tmote sky constraints

6. Assumptions and Approach
Number of simultaneous calls are less.
System design aimed at maximizing call quality; not to support higher number of calls.
Justified in a village context.
Approach
Dual-radio approach.
Transmit and receive simultaneously.
Improve overall throughput and lower latency

7. Contributions
Interconnection of two tmotes to make a dual-radio device.
Mechanism to transfer data encapsulated in AM packets across the wired link between two tmotes.
Proposed mechanism addressing bus contention between radio and UART pins.

8. Previous Work Much research in VoIP over WiFi mesh.
Citymesh - covering entire city of Brussels.
Studies on improving VoIP capacity and call admissions.
Orthogonal to our assumption!

9. Previous Work
Studies in using multi-radio nodes to increase throughput of VoIP over mesh.
Show good improvement in call quality and capacity of network.
We want to apply same logic over mesh.
Some work on VoIP over done; but with single radio nodes.

10. Motivation for dual-radio node
Data rate of 250 kbit/s just enough for VoIP codecs. Techniques to improve throughput across multi-hops needed.
Interfaces on independent channels allows simultaneous transmission and reception.
16 channels - minimize interference in both adjacent and non-adjacent links.

11. Single Radio Node

12. Dual Radio Node

13. Steps in development Connecting two tmotes over expansion connector.
Create interrupt driven communication link.
Data encapsulation within AM packets over wired link.
Protocol to access shared bus between radio and UART reliably.

14. Hardware connection Each mote has two expansion connectors.
UART and I2C interfaces available.
UART is simpler and has less overhead of ACKs.
Tinyos api doesn’t implement UART as interrupt based. We need signaling and interrupt mechanism.
2 more pins used in addition to UART pins.

16. Protocol for Packetized Transfer
RTS/CTS used to signal interrupt and acceptance.
Sender sends the number of bytes the receiver should look out for.
Data transferred.

17. Issues present The bus between UART and radio is shared.
Only one transfer at a time.
Full benefit of two independent radios not achieved.

18. Present Status Mechanism to join two tmotes functional.
Data is transferred between the two tmotes encapsulated within AM packets.
Proposed framing and bus arbitration mechanism to be completed

19. Future Work Analyze performance of VoIP over a single dual-radio node.
Analyze performance of VoIP over multi-hop connections.
Routing calls through the network using low power duty cycling mechanisms.

20. References
R. Burda and C. Wietfeld, "Multimedia over and ZigBee Networks for Ambient Environment Control”, In Proceedings of the 65th IEEE Vehicular Technology Conference, VTC 2007-Spring.
Rahul Mangharam, Anthony Rowe, Raj Rajkumar and Ryohei Suzuki, “Voice over Sensor Networks”, In Proceedings of the 27th IEEE International Real-Time Systems Symposium (RTSS'06).
Xudong Wang, Abhishek Patil and Weilin Wang, “VoIP Over Wireless Mesh Networks: Challenges and Approaches”, WICON 2006.

21. References (contd.)
Dragos Niculescu, Samrat Ganguly, Kyungtae Kim and Rauf Izmailov, “Performance of VoIP in a Wireless Mesh Network”, In Proceedings of IEEE INFOCOM 2006, Apr
Hung-yu Wei, Kyungtae Kim, Anand Kashyap and Samrat Ganguly, “On Admission of VoIP Calls Over Wireless Mesh Network”, In Proc. of ICC Next Generation Mobile Networks, Istanbul, June 2006.
Samrat Ganguly et al, “Performance Optimizations for Deploying VoIP Services in Mesh Networks”, IEEE Journal on Selected Areas in Communications, Vol. 24, No. 11, November 2006.

22. Thank You!
Questions??