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TCP over Bluetooth multihop:

TCP over Bluetooth multihop:. hardware implementation and performance modeling. Tutor: Rohit Kapoor. Member: Ling-Jyh Chen WeiChih Kuo. Outline. Motivation Development Evaluations Discussion Future work References. Motivation. Why TCP over Bluetooth

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TCP over Bluetooth multihop:

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  1. TCP over Bluetooth multihop: hardware implementation and performance modeling Tutor: Rohit Kapoor Member: Ling-Jyh ChenWeiChih Kuo

  2. Outline • Motivation • Development • Evaluations • Discussion • Future work • References

  3. Motivation • Why TCP over Bluetooth • Bluetooth is expected to become a ubiquitous solution for providing short range, low power, low cost wireless connectivity • A lot of data applications need TCP or UDP to transmit packets • Evaluation the performance of TCP over bluetooth in a real implementation

  4. Bluetooth • a short-range radio technology operating in the unlicensed 2.4GHz ISM frequency band • Frequency Hopping: 1600 hops per second • Piconet & Scatternet Cordless headset Cell phone Cordless headset Cordless headset Cell phone Cell phone

  5. DM1 DH1 DM3 DH3 2/3 FEC DM5 DH5 No FEC Bluetooth Data Packet Type Asymmetric Symmetric Asymmetric Symmetric

  6. Applications IP SDP RFCOMM Control Data Audio L2CAP Link Manager Baseband RF Development • Hardware • Ericsson Bluetooth Application Tool Kit • Software • Microsoft Visual C++ 6.0 • Ericsson Bluetooth Stack

  7. Application Programming Interface Application Application COM Server interface Windows COM Server HOST STACKby Ericsson serial interface (COM/USB) Desktop System Description

  8. Some Features and limitations • Features • Support point-to-multipoint connection • Well-designed API • Limitations • COM Server is not reliable • The stack will crash if we fill the memory buffer too often=>Andus Chan, et al., “Bluetooth Evaluation Project”, http://www.ece.uvic.ca/499/2001a/group19/BT_evaluation_report.pdf

  9. TCP – Retransmission Timeout • RFC 1122 • Jacobson's algorithm for computing the smoothed round- trip ("RTT") time incorporates a simple measure of the variance • Karn's algorithm for selecting RTT measurements ensures that ambiguous round-trip times will not corrupt the calculation of the smoothed round-trip time

  10. TCP Tahoe Initialize: State <-- Slow Start; Case of: ACK received in Slow Start: cwnd <-- cwnd +1; /* “exponential ” increase of cwnd */ If cwnd > Threshold Then State= Congestion Avoidance; ACK received in Congestion Avoidance: If # Acks received = cwnd Then cwnd <-- cwnd +1; /* “linear” increase of cwnd */ Timeout: Threshold <-- cwnd/2; cwnd <-- 1; State <-- Slow Start;

  11. TCP Reno Initialize: State <-- Slow Start; Case of: ACK received in Slow Start: cwnd <-- cwnd +1; If cwnd > Threshold Then State= Congestion Avoidance; ACK received in Congestion Avoidance: cwnd <-- cwnd +1/cwnd; Timeout: Threshold <-- cwnd/2; cwnd <-- 1; State <-- Slow Start; 3 duplicate ACKs: Threshold <-- cwnd/2; cwnd <-- Threshold; State <-- Slow Start;

  12. TCP Westwood • When three duplicate ACKs are detected: • Set ssthresh = BSE*RTT/Packet_Size • If (cwin > ssthresh) Set cwin=ssthresh • When a TIMEOUT expires: • Set ssthresh=BSE*RTT/Packet_Size and cwin=1 Note: RTT = min round trip delay since connection set up

  13. Evaluations • Point to point • Packet size vs Throughput • TCP- Tahoe/Reno/Westwood • Congestion window & RTO • Multihop (not yet)

  14. 1. Packet size vs Throughput • Using TCP Tahoe with different packet size (200bytes ~ 30000bytes) in each connection mode • Ericsson’s COM server will crash if we fill the buffer too often, i.e. with high transmit rate or with small packet size

  15. 1. Packet size vs Throughput

  16. 2. TCP- Tahoe/Reno/Westwood

  17. 2. TCP- Tahoe/Reno/Westwood

  18. 3. Congestion window & RTO

  19. 3. Congestion window & RTO

  20. 3. Congestion window & RTO

  21. Discussion • Our implementation performs well and much close to the maximum throughput • Throughput increases as the packet size increases, and decreases after exceeding a certain amount • Without 3 duplicate ACKs, TCP Tahoe/Reno/Westwood performs almost the same

  22. Future work • Multihop in the same piconet • Multihop across scatternet • Multiple data flows • Connection with interference

  23. References • The Bluetooth Specification v1.1http://www.bluetooth.com • Ericsson Bluetooth Development Kithttp://www.comtec.teleca.se/ • J. C. Haartsen, "The Bluetooth radio system", IEEE Personal Communications , Volume: 7 Issue: 1 , Feb. 2000, Page(s): 28 –36 • M. Gerla, et al., “TCP westwood: congestion window control using bandwidth estimation”, GLOBECOM '01. IEEE , Volume: 3 , 2001, Page(s): 1698 –1702 • B. Braden, ed., "Requirements for Internet Hosts - Communication Layers," RFC 1122, Oct. 1989. • W. R. Stevens, "TCP/IP Illustrated, Volume 1: The Protocols", Addison-Wesley, 1994.

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