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Quality of Service Analysis of Real Time Applications in Ad Hoc Networks

This research analyzes the quality of service (QoS) of real time applications in ad hoc networks, specifically focusing on real time audio management and the comparison of two ad hoc routing protocols. The study includes designing and testing a VoIP software client, recording QoS factors, and evaluating the performance of proactive (OLSR) and reactive (AODV) routing protocols. The results provide insights for improving real time communication in ad hoc networks.

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Quality of Service Analysis of Real Time Applications in Ad Hoc Networks

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  1. Quality of Service Analysis of Real Time Applications in Ad Hoc Networks Mohammad Ayyash Supervisor: Prof. Raimo Kantola Networking laboratory

  2. Table of Contents • Introduction • Objectives • Steps • Real Time Audio management • VoIP Software Client • Testing • Results • Future Work Networking laboratory

  3. Introduction • Voice over IP (VoIP) is telephone over packet switched networks. • The future of voice communications. • Utilizes the existing wide deployment of the Internet. • Can be applied to any packet switched network. WLAN is an example. Networking laboratory

  4. Objectives • Perform real time audio conversations over an ad hoc WLAN network. • Record the Quality of Service (QoS) factors. • Compare between the two ad hoc routing protocols families: proactive routing (OLSR) and reactive routing (AODV Networking laboratory

  5. Steps • Design and Implement a VoIP software client. • Test cases are designed and executed: • The effect of increasing number of hops. • The effect of the type of intermediate nodes. • The effect of network topology change. • Every test case is executed for AODV and OLSR. Networking laboratory

  6. VoIP Software RTP/SIP UDP/TCP IP Link Layer Physical VoIP protocols • Signaling: Session Initiation Protocol (SIP) • Media Transport: Realtime Transport Protocol (RTP) • Routing: OLSR and AODV • Network Transport: IP • MAC: 802.11b Networking laboratory

  7. VoIP protocols Networking laboratory

  8. SIP Networking laboratory

  9. RTP header 32 bytes GSM audio frame 33 bytes GSM audio frame 33 bytes GSM audio frame 33 bytes RTP Header 0 8 16 24 324 V P X CC M PT Sequence Number Time stamp Synchronization Source identifier (SSRC) Contributing source identifier (CSRC) Refer to RFC 1889 [5] for detailed explanation of header fields RTP Networking laboratory

  10. OLSR vs AODV • Ad hoc networks topology is dynamic with changing topology. • AODV has higher cost of initial link establishment. (File sharing) • OLSR has higher share of bandwidth. (Chatting) • VoIP tolerates initial link establishment (AODV), but need fast re-establishment (OLSR) Networking laboratory

  11. Audio basics • Audio is sampled at 8000 Hz sampling rate and 16 bits per sample • GSM Codec is used. Networking laboratory

  12. Delay Budget • ITU-T recommends the delay budget to be under 150 msec, but not more than 400 msec Networking laboratory

  13. Realtime audio Management Networking laboratory

  14. Quality factors • Packet loss. • Jitter. • End to End delay. • Out of order packet delivery. • Routing Protocol. Networking laboratory

  15. VoIP Software client Networking laboratory

  16. Testing • 3 major test cases: • Effect of number of hops • Effect of intermediate node type • Effect of topology change. Networking laboratory

  17. Test Bed Environment • 4 iPAQs running Familiar linux, and equipped with CompactFlash WLAN 802.11b cards, operating at 2.457GHz 11Mbps. • 2 Laptops, running Fedora Core Linux. Both are Intel Centrino 1.6 GHz, 512 MB RAM and Intel PRO Wireless 2200 BG. Networking laboratory

  18. Environment Difficulties • Unstable iPAQs. Unstable CompactFlash cards. • Noisy WLAN environment (all channels!) • iPAQs clocks are not fixed (software clocks). No time reference. • Topology re-discovered 50’s of times during a test case! Networking laboratory

  19. Test Case Example Inter-arrival (Jitter) Distribution Inter-arrival (Jitter) Highest peak around 66 msec Networking laboratory

  20. Test Case Example (Cont.) End to End Delay. End to End Delay distribution Networking laboratory

  21. Test Case Example (Cont.) Networking laboratory

  22. Results – Test Case 1 • OLSR has less average end to end delay, but wider delay distribution. • AODV has higher processing demand. • OLSR needs more time re-discovering a broken link. • AODV has higher bandwidth share. (but unstable test bed environment) Networking laboratory

  23. Results – Test Case 2 • Using powerful intermediate nodes will reduce the network delay, and eventually the end to end delay. • Using powerful intermediate nodes means larger scale ad hoc network. Networking laboratory

  24. Results – Test case 3 • OLSR requires more processing power when discovering an alternate route. • AODV consumes more share of the bandwidth. • Both protocols discover the new route after almost the same delay. • AODV adds an additional end to end delay after discovery! Networking laboratory

  25. Future Work • Testing on a larger scale Ad Hoc network. • Testing other routing protocols. • Using other audio codecs. • Including video. • Conference calls. • Distributed SIP infrastructure for ad hoc networks. Networking laboratory

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