1. © Sarvesh 25 November 2015Cross-layer optimization for VoIP over WLAN125 November 20151 Cross Layer optimization for VoIP over WLAN [Yuan Liu Zhu] A Presentation for Resilinets group Sarvesh Kumar Varatharajan Department of Electrical Engineering & Computer Science University of Kansas sarvesh@ittc.ku.edu 25 November 20151

2. © Sarvesh 25 November 2015Cross-layer optimization for VoIP over WLAN225 November 20152 Abstract Problems of VoIP over WLAN Unacceptable voice delays when coexisting with other applications Low voice Capacity due to heavy headers from the above layers Cross layer schemes to improve voice capacity Voice stream enjoys fixed bandwidth. Voice delay is minimum Simulation at various PHY rates over various voice codec Proposed scheme advances throughput of voice stream

3. © Sarvesh 25 November 2015Cross-layer optimization for VoIP over WLAN325 November 20153 Organization of the paper Introduction Background Cross Layer Optimizations Theoretical Analysis Simulation and Results Conclusion 25 November 20153

4. © Sarvesh 25 November 2015Cross-layer optimization for VoIP over WLAN425 November 20154 Introduction VoIP applications Delay Heavy packet headers from upper layers reduces voice capacity 802.11 can support only limited number of VoIP connections Capacity of G.711 VoIP using CBR model and a 20ms packet interval is only 12 calls[2] A scheme is proposed where interaction with application layer reduces delay Time slot reuse method to increase capacity 25 November 20154

5. © Sarvesh 25 November 2015Cross-layer optimization for VoIP over WLAN525 November 20155 Background VoIP Overview Overview of 802.11 and 802.11e Related Work 25 November 20155

6. © Sarvesh 25 November 2015Cross-layer optimization for VoIP over WLAN625 November 20156 VoIP overview 25 November 20156 Variable delay in each hop End to end delay threshold Reference[1]

7. © Sarvesh 25 November 2015Cross-layer optimization for VoIP over WLAN725 November 20157 Overview of 802.11 and 802.11e Distributed Coordination function (DCF) Contention based access Best effort service No QoS support Infeasible option for VoIP Point Coordination function (PCF) When number of polling stations is large then higher the end to end delay Poor performance of VoIP Service Differentiation based on MAC schemes to classify traffic types with relative priorities

8. © Sarvesh Overview of 802.11 and 802.11e 802.11e addresses the problem of 802.11 Hybrid Coordination Function (HCF) –Enhanced Distributed Coordinated Access( EDCA ) Significant time delay –HCF Controlled Channel Access(HCCA) POLL, ACK required. Additional overhead Reference[1] 25 November 2015Cross-layer optimization for VoIP over WLAN825 November 20158 8

9. © Sarvesh Related Work VoIP over PCF[3][4] VoIP over DCF[5] No solutions to improve VoIP performance over HCCA of 802.11e Paper proposes schemes to improve VoIP capacity over HCCA of 802.11e 25 November 2015Cross-layer optimization for VoIP over WLAN925 November 20159

10. © Sarvesh 25 November 2015Cross-layer optimization for VoIP over WLAN1025 November 201510 Organization of the paper Introduction Background Cross Layer Optimizations Theoretical Analysis Simulation and Results Conclusion 25 November 201510

11. © Sarvesh 25 November 2015Cross-layer optimization for VoIP over WLAN1125 November 201511 Cross Layer Optimization Assumption: All nodes of WLAN have fixed and equal PHY rate Slotted TXOP Time Slot reuse Packet-header Compression 25 November 201511

12. © Sarvesh 25 November 2015Cross-layer optimization for VoIP over WLAN1225 November 201512 Slotted TXOP POLL + ACK reduces VoIP capacity in HCCA ACK unnecessary for voice Slotted TXOP –Each node has fixed PHY rate and same voice codec Reference[1] 25 November 201512

13. © Sarvesh 25 November 2015Cross-layer optimization for VoIP over WLAN1325 November 201513 Slotted TXOP (contd) Minimizing time delay Reference[1] Application layer informed about the time slot Packaging is done before the time slot of the node 25 November 201513

14. © Sarvesh 25 November 2015Cross-layer optimization for VoIP over WLAN1425 November 201514 Time-slot reuse Voice Activity Detection(VAD) MAC layer rarely downloads and uploads voice packet at the same time Reference[1] 25 November 201514

15. © Sarvesh Time slot reuse(contd) 25 November 2015Cross-layer optimization for VoIP over WLAN15 Reference[1]

16. © Sarvesh 25 November 2015Cross-layer optimization for VoIP over WLAN1625 November 201516 Packet-header compression 25 November 201516 Typical VoIP packet at MAC layer 40 –byte IP/UDP/RTP headers while payload only 10 to 30 bytes Packet Header Compression(PHC) –Casner’s Algorithm[6] –Most of the fields in the IP,UDP and RTP headers do not change over the lifetime of RTP session(Represent by fewer bits) –RTP header fields such as sequence number and time stamp are increased by a constant amount for successive packets –Differential coding –This algorithm can compress the header to 2 bytes

17. © Sarvesh 25 November 2015Cross-layer optimization for VoIP over WLAN1725 November 201517 Cross Layer Optimization Assumption: All nodes of WLAN have fixed and equal PHY rate Slotted TXOP Time Slot reuse Packet-header Compression 25 November 201517

18. © Sarvesh 25 November 2015Cross-layer optimization for VoIP over WLAN1825 November 201518 Theoretical Analysis 25 November 201518

19. © Sarvesh 25 November 2015Cross-layer optimization for VoIP over WLAN1925 November 201519 Theoretical Analysis 25 November 201519

20. © Sarvesh 25 November 2015Cross-layer optimization for VoIP over WLAN2025 November 201520 Theoretical Analysis 25 November 201520

21. © Sarvesh 25 November 2015Cross-layer optimization for VoIP over WLAN2125 November 201521 Theoretical Analysis 25 November 201521 TRST with PHC increases network capacity compared to original TRST If p sil is large enough the network capacity of VoIP increases compared with STXOP, let alone the original HCCA scheme

22. © Sarvesh 25 November 2015Cross-layer optimization for VoIP over WLAN2225 November 201522 Organization of the paper Introduction Background Cross Layer Optimizations Theoretical Analysis Simulation and Results Conclusion 25 November 201522

23. © Sarvesh 25 November 2015Cross-layer optimization for VoIP over WLAN2325 November 201523 Simulation and Results 25 November 201523 Reference[1]

24. © Sarvesh 25 November 2015Cross-layer optimization for VoIP over WLAN2425 November 201524 Simulation and Results 25 November 201524 Reference[1]

25. © Sarvesh 25 November 2015Cross-layer optimization for VoIP over WLAN2525 November 201525 Simulation and Results 25 November 201525 Reference[1]

26. © Sarvesh 25 November 2015Cross-layer optimization for VoIP over WLAN2625 November 201526 Simulation and Results 25 November 201526 Reference[1]

27. © Sarvesh 25 November 2015Cross-layer optimization for VoIP over WLAN2725 November 201527 Simulation and Results 25 November 201527 Reference[1]

28. © Sarvesh 25 November 2015Cross-layer optimization for VoIP over WLAN2825 November 201528 Simulation and Results 25 November 201528 Reference[1]

29. © Sarvesh 25 November 2015Cross-layer optimization for VoIP over WLAN2925 November 201529 Simulation and Results 25 November 201529 Reference[1]

30. © Sarvesh 25 November 2015Cross-layer optimization for VoIP over WLAN3025 November 201530 Simulation and Results 25 November 201530 Reference[1]

31. © Sarvesh Conclusion STXOP utilizes slotted TXOP and discards POLL and ACK to system capacity Every voice stream enjoys fixed bandwidth Interaction with application layer reduces delay TRST scheme proposed reutilizes silent slots to advance system performance and reduce CFP duration Proposed scheme better than HCCA scheme System capacity better for codec G 723.1 25 November 2015Cross-layer optimization for VoIP over WLAN31

32. © Sarvesh 25 November 2015Cross-layer optimization for VoIP over WLAN3225 November 201532 References [1]YUAN Wen-peng, LIU Gan, ZHU Guang-xi,Cross-layer optimization for VoIP over WLAN,June 2007 Volume 1,No 1,Computer Technology and Application,ISSN1934-7332,USA [2]LIN Y.-B. and Chlamtac, I. Wireless and Mobile Network Architectures, New York:Wiley,2001 [3]Chen D., Garg S., Kappes. And M. and Trivedi K. Supporting VBR VoIP traffic in IEEE 802.11 WLAN in PCF mode. Avaya Laboratories, Basking Ridge, NJ Tech. Rep. ALR-2002-026, 2002 [4]Veeraraghavan, M., Cocker, N. and Moors, T. Support of voice services in IEEE 802.11 wireless LANs Proc. INFOCOM ‘01 Apr. 2001, 1:488-497 25 November 201532

33. © Sarvesh 25 November 2015Cross-layer optimization for VoIP over WLAN3325 November 201533 References [5]Baldwin, R.O. Davis IV, N.J.Midkiff, S.F and Raines, R.A. Packetized voice transmission using RT-MAC, a wireless real- time medium access control protocol. Mobile Comput Commun. Rev 2001, 5(3):11-25 [6] Casner,S. and Jacobson, V. Compressing IP/UDP/RTP headers for low speed serial links. Proc. IETF RFC 2508, Feb 1999. 25 November 201533