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  1. 1. Capacity Estimation of VOIP Channels on Wireless Networks Baek, Seung Jun Cui, Ningzhuo Ogale, Vinit Park, Ryoungsun Patel, Tanmay
  2. 2. Project Overview <ul><li>Project Goal </li></ul><ul><ul><li>Estimation of channel capacity with VoIP applications over wireless networks(802.11b) </li></ul></ul><ul><ul><li>Measurement of channel characteristics (delay, jitter, packet loss) contributing to QOS for varying number of nodes </li></ul></ul>
  3. 3. VoIP Voice Voice Encoder Network (Internet) Voice Decoder Introduction
  4. 4. VoIP <ul><li>Economical </li></ul><ul><li>Convergence of wired and wireless data networks with PSTN and cellular networks </li></ul><ul><li>Issues with VoIP over Wireless Links </li></ul><ul><ul><li>Is the QOS comparable to traditional PSTN ? </li></ul></ul><ul><ul><li>How many simultaneous users can the network support ? </li></ul></ul>Introduction Cellular Wired LANs PSTN Wireless LANs VoIP
  5. 5. QoS <ul><li>What is QoS : </li></ul><ul><ul><li>A metric which tries to measure the satisfaction level of the user </li></ul></ul><ul><ul><li>Dependent on application </li></ul></ul><ul><ul><li>Mean Opinion Score (MOS) </li></ul></ul><ul><ul><ul><li>A score of 1 to 5 </li></ul></ul></ul>
  6. 6. Voice Samples <ul><li>MOS = 4.5 </li></ul><ul><li>MOS = 3.7 </li></ul><ul><li>MOS = 3.2 </li></ul><ul><li>MOS = 2.5 </li></ul>
  7. 7. Factors Affecting QoS <ul><li>Throughput </li></ul><ul><li>Delay </li></ul><ul><li>Packet losses </li></ul><ul><li>Jitter </li></ul>
  8. 8. Approach <ul><li>Measurement of capacity using the NetIQ Chariot network analysis tool </li></ul><ul><li>Validation and extension of measurements by ns2 simulations of the wireless network </li></ul>
  9. 9. Capacity Measurements <ul><li>Capacity: </li></ul><ul><ul><li>Small scale </li></ul></ul><ul><ul><li>Interference limited </li></ul></ul><ul><ul><li>Determined by acceptable call quality </li></ul></ul><ul><li>Call quality: </li></ul><ul><ul><li>Latency, jitter, packet loss </li></ul></ul><ul><ul><li>MOS (Mean Opinion scores) </li></ul></ul>
  10. 10. Chariot with VoIP Test Module <ul><li>Measures end-to-end performance </li></ul><ul><li>Tests with real application loads </li></ul><ul><li>Tests the capacity of the network </li></ul><ul><li>Overall voice quality (MOS) </li></ul>
  11. 11. Measurement Setup Network (Internet)
  12. 12. MOS, Throughput, and Delay
  13. 13. VoIP Capacity Measurement
  14. 14. Network Simulator NS2 <ul><li>NS version2 is a discrete-event driven and object-oriented network simulator </li></ul><ul><ul><li>Type of simulation: continuous, discrete event, and combined </li></ul></ul><ul><li>NS is an Object-oriented Tcl(OTcl) script interpreter that has a simulation event scheduler and network component object libraries, and network setup module libraries. </li></ul><ul><li>The current NS version is written in C++ and Tcl. </li></ul>
  15. 15. NS2 – User’s View <ul><li>This is an overview of NS2 </li></ul><ul><li>Tcl commands translates into </li></ul><ul><ul><li>A series of object creations </li></ul></ul><ul><ul><li>Plumbing of these objects </li></ul></ul>
  16. 16. NS2 Simulation Parameters <ul><li>Network Interfaces - The model approximates the DSSS radio interface. </li></ul><ul><li>The mac layer – 802.11b </li></ul><ul><li>Radio Propagation model – The two ray ground bounce model. </li></ul><ul><li>Antenna – Omni-directional antenna having a unity gain. </li></ul>
  17. 17. Simulation Setup(1) <ul><li>Random Call Model </li></ul><ul><ul><li>Poisson Call Arrivals </li></ul></ul><ul><ul><li>Exponential Call Holding Time </li></ul></ul><ul><li>Generates a file ‘Call Profile’ </li></ul>Call_Profile.cfg Format: s1 d1 start end s2 d2 start end … MATLAB C++ Generate Poisson and Exponential RVs Randomly Set Non-overlapping Source-Destination Nodes Pair
  18. 18. Simulation Setup(2) <ul><li>15~20 VOIP Clients on 200x200m 2 </li></ul><ul><li>Single Access Point on Center </li></ul><ul><li>Codec G.723.1(6.3kbps) </li></ul><ul><ul><li>24 Payload at every 30ms </li></ul></ul><ul><ul><li>No Silence Suppression Assumed </li></ul></ul><ul><ul><li>Full-duplex Traffic </li></ul></ul><ul><ul><li>RTP( Real Time Protocol) on UDP </li></ul></ul>
  19. 19. Simulation Setup(3) <ul><li>Random Arrangement </li></ul>Random Select UDP CBR Of Codec Uniform Random Position On(500x500) Call Profile AP Clients NS2
  20. 20. Utilizing the Trace files <ul><li>NS2 generates a trace file which contains the simulated data. </li></ul><ul><li>This data needs to be sieved through using applications like XGraph or NAM </li></ul><ul><li>Another way - by making the tools in AWK or C++ which harness the trace file’s data. </li></ul><ul><li>We have implemented a tool in C++ to search the data generated by NS2 for information regarding the throughput and lost data. </li></ul>
  21. 21. Statistical Results of the Simulations:
  22. 22. Simulation Results(Contd.)
  23. 23. Comparison between the Simulation and the actual Measurement:
  24. 24. Conclusion <ul><li>The measurements done using Chariot give us a good estimate of the maximum number of VOIP sessions that can be supported by one access point (using the 802.11 mac layer protocol) </li></ul><ul><li>However due to the probabilistic modeling of the call arrival times and the call duration times the NS simulations give us a realistic estimate of the capacity. </li></ul><ul><li>Thus we conclude that the 802.11b protocol can support 14-18 simultaneous VOIP sessions using the G.723.1 codec and 8-10 VOIP sessions using the G.711 codec. </li></ul>
  25. 25. Future Work <ul><li>The queue length - packet drop rate trade-off </li></ul><ul><ul><li>We tried various simulations with upto 20 times increase in the queue length. </li></ul></ul><ul><li>Shortfalls of the existing 802.11b protocol. </li></ul><ul><ul><li>If the physical layer is implemented using CDMA, performance upgrade could be dramatic. </li></ul></ul>
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