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Experimental Results on IP-layer Enhancement to Capacity of VoIPv6 over IEEE 802.11b WLAN

Experimental Results on IP-layer Enhancement to Capacity of VoIPv6 over IEEE 802.11b WLAN. Presented for WiNMee’05 April 3, 2005 Youngjune Gwon , James Kempf, Raghu Dendukuri, and Ravi Jain gyj@docomolabs-usa.com DoCoMo USA Labs. Summary. Motivation Limited VoIP capacity of wireless LAN

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Experimental Results on IP-layer Enhancement to Capacity of VoIPv6 over IEEE 802.11b WLAN

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  1. Experimental Results on IP-layer Enhancement to Capacity of VoIPv6 over IEEE 802.11b WLAN Presented for WiNMee’05 April 3, 2005 Youngjune Gwon, James Kempf, Raghu Dendukuri, and Ravi Jain gyj@docomolabs-usa.com DoCoMo USA Labs

  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. Outline • Motivation • Related work • Capacity enhancement • Hole and Tobagi upper-bound • Experimental methodology • Results • Conclusion

  4. Motivation • Today’s 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. Related Work Our work Our work (*) IEEE 802.11 Task Group E (TGe)formed to define 802.11e

  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. Hole and Tobagi Upper-bound • N = upper-bound VoIP capacity in 802.11 • R = generated voice packets / sec • Tvoice = voice packet transmission time over wireless link • SIFS = short interframe space • TACK = acknowledgment frame time • DIFS = DCF interframe space • TSLOT = slot duration • CWMIN = number of minimum random slots picked during backoff Total voice packet transmission timeover WLAN link from caller/callee CSMA/CA wireless mediumaccess time

  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

  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 (ICNP’99) • Observed peak per client data rate of 30 kbps • Carried over HTTP/TCP/IPv6 ROHC Comp/decomp ROHC Comp/decomp

  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) Note: values in ( ) represent analytical upper-bound

  11. 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) Obtaining Experimental Capacity

  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 %

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