1. Experimental Results on IP-layer Enhancement to Capacity of VoIPv6 over IEEE 802.11b WLAN Presented for WiNMee05 April 3, 2005 Youngjune Gwon, James Kempf, Raghu Dendukuri, and Ravi Jain gyj@docomolabs-usa.com DoCoMo USA Labs

2. © 2005 by DoCoMo Communications Laboratories USA, Inc. Confidential proprietary. All rights reserved. Youngjune Gwon 2 Summary Motivation –Limited VoIP capacity of wireless LAN –Limited availability of experimental measurements Many existing studies based on analytical modeling or simulations –Unstudied impact of IP or higher layer enhancements Most focused on modifying 802.11 MAC Our contributions –One of the first experimental results for VoIPv6 over 802.11b –Proposed use of IP or higher layer enhancement schemes ROHC and Silence Suppression (SS) –Analytical capacity model using ROHC, SS, IPv6, 802.11b, and G.711 parameters –Experimental validation Key technical results –Achieved best-case capacity improvement of 140 % without MAC modification or PCF –Analytical model more optimistic about capacity than the actual by 20%

3. © 2005 by DoCoMo Communications Laboratories USA, Inc. Confidential proprietary. All rights reserved. Youngjune Gwon 3 Outline Motivation Related work Capacity enhancement Hole and Tobagi upper-bound Experimental methodology Results Conclusion

4. © 2005 by DoCoMo Communications Laboratories USA, Inc. Confidential proprietary. All rights reserved. Youngjune Gwon 4 Motivation Todays WLAN is being used not only for data (TCP) but also for voice and other real-time multimedia Maximum capacity of VoIPv4 over WLAN (Vo4WLAN) is 6 –Assuming G.711 with frame duration of 10 msec and 802.11b Higher layer solutions to improve VoIP capacity unstudied –Compared to many existing enhancements by modifying 802.11 MAC Limited availability of experimental measurements –Few in Vo4WLAN –What about VoIPv6 over WLAN (Vo6WLAN)?

5. © 2005 by DoCoMo Communications Laboratories USA, Inc. Confidential proprietary. All rights reserved. Youngjune Gwon 5 Related Work Capacity Evaluation Studies Capacity Enhancement Schemes Analytical/simu lation-based Experimental802.11 MAC modifying * Higher layer enhancing Vo4WLAN Garg and Kappes (ICC03), Hole and Tobagi (ICC04) Anjum et al. (GLOBECOMM03), Newmann (Network World Fusion) Aad et al. (INFOCOM01), Suzuki et al. (PIMRC01), Veeraraghavan et al. (INFOCOM01), Yeh et al. (ICC02), Anjum et al. (GLOBECOMM03) Any work? Vo6WLAN Any work? Our work (*) IEEE 802.11 Task Group E (TGe) formed to define 802.11e

6. © 2005 by DoCoMo Communications Laboratories USA, Inc. Confidential proprietary. All rights reserved. Youngjune Gwon 6 Capacity Enhancement Robust Header Compression (ROHC) – RFC 3095 –60 byte RTP/UDP/IPv6 headers fully compressed to 1 – 2 bytes Silence Suppression (SS) –More than 50 % of telephone speech is silent –Enabled by Speech Activity Detector (SAD) When silence detected, need not transmit packets (perfect SS), or transmit minimal bits only

7. © 2005 by DoCoMo Communications Laboratories USA, Inc. Confidential proprietary. All rights reserved. Youngjune Gwon 7 Hole and Tobagi Upper-bound N = upper-bound VoIP capacity in 802.11 R = generated voice packets / sec T voice = voice packet transmission time over wireless link SIFS = short interframe space T ACK = acknowledgment frame time DIFS = DCF interframe space T SLOT = slot duration CW MIN = number of minimum random slots picked during backoff Total voice packet transmission time over WLAN link from caller/callee CSMA/CA wireless medium access time

8. © 2005 by DoCoMo Communications Laboratories USA, Inc. Confidential proprietary. All rights reserved. Youngjune Gwon 8 Analytical Vo6WLAN Capacity Hole and Tobagi upper-bound capacity for Vo6WLAN –Assume VoIPv6 over 802.11b, G.711 with 10 msec voice frame (80-byte voice payload), ROHC (header = 1.5 byte), perfect SS Vo6WLAN schemes 1 Plain 2 ROHC only 3 SS only 4 ROHC + SS Upper-bound capacity, N 671314 Capacity improvement -17 %117 %133 %

9. © 2005 by DoCoMo Communications Laboratories USA, Inc. Confidential proprietary. All rights reserved. Youngjune Gwon 9 Experimental Methodology Real wireless IPv6 testbed Voice traffic –Speech generation ITU-T Recommendation P.59 –G.711 codec –Carried over RTP/UDP/IPv6 Data traffic –Based on a web traffic model Choi and Limb (ICNP99) Observed peak per client data rate of 30 kbps –Carried over HTTP/TCP/IPv6 ROHC Comp/decomp ROHC Comp/decomp

10. © 2005 by DoCoMo Communications Laboratories USA, Inc. Confidential proprietary. All rights reserved. Youngjune Gwon 10 Results Experimental notes –Started from 5 calls and incrementally add a call to 14 total calls Call = caller/callee pair of one wireless and one wired nodes –Number of web clients matches number of wireless nodes –Captured all transmitted and received packets Measuring packet loss and latency –Computed MOS for each case Used ITU E-model MOS > 3 to determine capacity Validation of analytical model –More optimistic than experimental results by 20 % Capacity improvement –17 % (ROHC) to 140 % (ROHC + SS) Background web traffic Vo6WLAN schemes 1 Plain 2 ROHC only 3 SS only 4 ROHC + SS No6 (6)7 (7)12 (13)13 (14) Yes561012 Note: values in ( ) represent analytical upper-bound

11. © 2005 by DoCoMo Communications Laboratories USA, Inc. Confidential proprietary. All rights reserved. Youngjune Gwon 11 Obtaining Experimental Capacity No ROHC, no SS, no web traffic (I) No ROHC, no SS, with web traffic (II) With ROHC, no SS, no web traffic (III) With ROHC, no SS, with web traffic (IV) No ROHC, with SS, no web traffic (V) No ROHC, with SS, with web traffic (VI) With ROHC, with SS, no web traffic (VII) With ROHC, with SS, with web traffic (VIII)

12. © 2005 by DoCoMo Communications Laboratories USA, Inc. Confidential proprietary. All rights reserved. Youngjune Gwon 12 Conclusions Presented experimental VoIPv6 over 802.11b Proposed use of IP or higher layer enhancement schemes –ROHC and Silence Suppression (SS) Instantiated analytical model for VoIP capacity in wireless LAN –Using ROHC, SS, IPv6, 802.11b, and G.711 parameters Validated experimentally Key technical results –Achieved best-case capacity improvement of 140 % –Vo6WLAN capacity predicted by analytical model is off by 20 %