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Performance Analysis for VoIP System

This performance analysis explores the challenges and solutions in VoIP systems, including modeling VoIP traffic, VoIP in Ethernet and Wireless LAN, and addressing critical performance issues like latency, jitter, packet loss, and echo.

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Performance Analysis for VoIP System

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  1. PerformanceAnalysis for VoIP System B92902088 邱柏儒 B92902093 紀忠毅 B92902106 莊典融 B92902120 孟昭宏

  2. Agenda • Modeling VoIP (莊典融) • VoIP in Ethernet (紀忠毅) • An Example in Performance Analysis • VoIP in Wireless LAN (孟昭宏) • Solutions to Performance Problems in VoIP over a 802.11 Wireless LAN • Summary (邱柏儒)

  3. Agenda • Modeling VoIP • VoIP in Ethernet • An Example in Performance Analysis • VoIP in Wireless LAN • Solutions to Performance Problems in VoIP over a 802.11 Wireless LAN • Summary

  4. Modeling VoIP • How to model VoIP traffic • Modeling by distribution • Modeling by state diagram • Pros and Cons

  5. Modeling by Distribution(1) • Modeling data traffic • The data size distribution of Internet traffic which uses the TCP (many smaller files, few larger ones) seen as approximately Pareto-distributed.

  6. Modeling by Distribution(2) • Modeling data traffic • Choose appreciate environment

  7. Modeling by Distribution(3) • Run Simulator • Analysis and diagnosis • Delay • Packet loss • Jitters

  8. Modeling by State Diagram(1) • Modeling speech process

  9. Modeling by State Diagram(2) • Modeling speech process

  10. Pros and Cons • Inaccurate on modeling • Variant and complex • Simulator is different from real world • Unexpected problems on hardware • Low cost • We can implement solution after getting good simulation.

  11. Agenda • Modeling VoIP • VoIP in Ethernet • An Example in Performance Analysis • VoIP in Wireless Lan • Solutions to Performance Problems in VoIP over a 802.11 Wireless Lan • Summary

  12. Critical VoIP Performance Challenges • Latency • Jitter • Packet Loss • Echo

  13. Latency • Good: < 80ms Acceptable: 150~180ms (each way) • Must be addressed with VoIP protocols. Eg, SIP, H.323 • Commonly associated with network congestion and poor bandwidth management. Not in LAN but at LAN/WAN boundary.

  14. Latency • Minimize delay/latency • Queuing techniques • Eq, DiffServ, 802.1p/q • Voice packet priority over other traffic • More stringent, intelligent bandwidth management/QoS • Guaranteed amount of bandwidth to each traffic type.

  15. Jitter • Tolerance range: 20~30ms • Possible solutions • Jitter buffer • Temporarily store • Smooth out the delivery of voice packet • Router queue

  16. Jitter • Prevent jitter • TCP rate control (for data traffic) • UDP rate control (for voice traffic) • Eq, Packeteer’s Application Traffic Management System • Policy-based bandwidth management or QoS strategy

  17. Packet Loss • Loss rate < 1%: OK • Loss rate > 3%: conversation seems “breaking up” • IP: best effort • Serious packet loss may cause dropped calls or even system failure

  18. Packet Loss • Prevent packet loss • Apply more control • IP: best effort predictable

  19. Solution to Improve Quality • PLC (Packet Lost Concealment)  Packet Lost • Dynamic Jitter Buffer  Jitter • Bandwidth Reservation / Packet Priorities / Queuing  Delay • G.168 Echo cancellation  Echo • VAD (Voice Active Detection)  Save Bandwidth

  20. An Example in Performance Analysis • Testing coverage • Testing environment • Testing Equipment & Software • REDCOM performer • QPro • MediaPro

  21. Testing Coverage • Functionality • e.g VoIP/PSTN call, QoS, SIP/Phone Setting • Performance • e.g QoS/RTP measurement • Stress • e.g VoIP call with data integration

  22. Testing Coverage • Reliability • e.g Long term VoIP / Continuous VoIP call • Interoperability • e.g Cisco ATA/IP Phone/SoftPhone

  23. Testing Environment (1/2)

  24. Testing Environment (2/2) • Pure Environment • Direct connection • Congestion Environment • Smart-bit tools

  25. Testing Equipment & Software EXCEL 9000 • PSTN simulator RADCOM Performer • QPro –Voice quality measurement • MediaPro – VoIP protocol analysis ProLAB • SIP Proxy server / H.323 Gateway • SIP UA simulator / H.323 Client VoIP Phone • Cisco 7940 IP Phone • XTEN / Windows Messenger Analysis Tool • Ethereal / CoolEdit

  26. REDCOM Performer • QPro • Provide voice quality measurement • MediaPro • Provide VoIP protocol flow analysis

  27. QPro – Line Configuration

  28. QPro – Phone Configuration

  29. QPro – Call Setting

  30. QPro – Test Result (1/2)

  31. QPro – Test Result (2/2)

  32. QPro - Summary

  33. Agenda • Modeling VoIP • VoIP in Ethernet • A Case Study in Performance Analysis • VoIP in Wireless LAN • Solutions to Performance Problems in VoIP over a 802.11 Wireless LAN • Summary

  34. VoIP in Wireless LAN - outline • Introduction • VoIP Multiplex Multicast Scheme • Capacity Analysis • Conclusion

  35. The Problems faced by WLAN • System CapacitySystem capacity for voice can be quite low • Other data trafficData from traditional App can interfere with each other

  36. VoIP in 802.11b • VoIP in WLAN can potentially support more than 500 sessions in theory • In practice, only 12 are supported due to various overhead

  37. VoIP in 802.11b • Support data rate up to 11Mb/s • A VoIP stream typically requires less than 10kb/s • The number of simultaneous VoIP streams that can be supported by an 802.11b in theory is around 11M/10K = 1100 • About 550 VoIP sessions

  38. VoIP in 802.11b • In practice, no more than a few VoIP sessions • If GSM 6.10 codec is used, the maximum is 12 • The result is mainly due to added packet header overheads as well as the inefficiency inherent in the WLAN MAC

  39. VoIP in 802.11b • IP + UDP + RTP header = 40bytes • VoIP payload ranging from 10 to 30 bytes • The transmission time:30 * 8 / 11 = 22 us40 * 8 / 11 = 29 us • Efficiency drops to less than 50%

  40. VoIP in 802.11b • Physical layer have additional overhead more than 800 us • Attributed to the Physical preamble, MAC header, MAC backoff time, MAC ACK, Inter-transmission time • Overall efficiency drops to less than 3%

  41. VoIP in 802.11b • TCP connection will cause unacceptably large increase in the delay and packet loss rate of VoIP traffic

  42. VoIP in Wireless LAN - outline • Introduction • VoIP Multiplex Multicast Scheme • Capacity Analysis • Conclusion

  43. Multiplex-Multicast Scheme • An 802.11 WLAN is referred to as the basic service set (BSS) in the standard specification • There are two types of BSSs: Independent BSS and Infrastructure BSS.

  44. Ad Hoc (Independent) BSS

  45. Infrastructure BSS

  46. Multiplex-Multicast Scheme • Focus on infrastructure BSS • Assume that all voice streams are between stations in different BSS • Each AP has two interfaces, an 802.11 interface, and an Ethernet interface which is connected to the voice gateway.

  47. Multiplex-Multicast Scheme

  48. Multiplex-Multicast Scheme • Within a BSS, there are two streams for each VoIP session. • M-M Scheme idea : Combine the data from several downlink streams into a single packet for multicast over the WLAN to their destinations

  49. Multiplex-Multicast Scheme

  50. Multiplex-Multicast Scheme • The voice multiplexer resides in the voice gateway for H.323 • The MUX can also resides in a specially designed AP or a server between the voice gateway and AP

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