Objective Measurement of Speech Quality in VoIP over

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Objective Measurement of Speech Quality in VoIP over Wireless. LAN during Handoff,A Writing Project,Presented to,The Faculty of the Department of Computer Science. San Jose State University,In Partial Fulfillment,of the Requirements for the Degree. Master of Science,Nidhi Marwaha Gambhir,Copyright 2009. Nidhi Marwaha Gambhir,All Rights Reserved, Quality of Service is a very important factor to determine the quality of a VoIP. call Different subjective and objective models exist for evaluating the speech quality in. E model is one of the objective methods of measuring the speech quality it considers. various factors like packet loss delay and codec impairments The calculations of E. model are not very accurate in case of handovers when a VoIP call moves from one. wireless LAN to another This project conducted experimental evaluation of performance. of E model during handovers and proposes a new approach to accurately calculate the. speech quality of VoIP during handovers A detailed description of the experimental. setup and the comparison of the new approach with E model is presented in this report. ACKNOWLEDGEMENTS, I would like to thank Dr Soon Teoh for his support and valuable suggestions all through.
my research work I would not have been able to complete this project without his. guidance I would also like to thank Dr Robert Chun and Professor Frank Butt for being. a part of my committee and taking out time to review my project Lastly I would like to. thank my family for motivating me to complete the project. Table of Contents,1 Introduction 1,1 1 Problem Description 1. 1 2 Related Work 2,1 3 Outline 2,2 VoIP Networks 4. 2 1 Introduction to VoIP 4,2 2 VoIP Network Connections 4. 2 3 TCP IP Protocol 5,2 3 1 Transport Layer 6,2 4 Real Time Protocol 7. 2 4 1 RTP Packet Format 7,2 4 2 RTCP RTP Control Protocol 9.
2 5 Codec 10,2 5 1 Sampling 10,2 5 2 Internet Low Bit Rate Codec iLBC 11. 2 5 3 G 711 Codec 12,2 6 Summary 12,3 Quality of Service 13. 3 1 Factors Affecting VoIP Quality 13,3 1 1 Packet Loss 13. 3 1 2 Jitter 13,3 1 3 Delay or Latency 14,3 1 4 Tradeoff 16. 3 2 Measurement of Speech Quality 16,3 2 1 Mean Opinion Score MOS 17.
3 2 2 PESQ 18,3 2 3 E model 19,3 3 Summary 21,4 Impact of Handoff on VoIP 22. 4 1 Handoff in VoIP 22,4 2 Quality of Service during Handover 23. 4 2 1 Subjective MOS test 23,4 2 2 E model Calculations 23. 4 3 New Objective Approach 27,4 4 Summary 29,5 Analysis and Design 30. 5 1 Test Setup 30,5 2 VoIP Client 31,5 3 Wireshark 33.
5 4 MOS Score Calculator 34,6 Implementation Results 39. 6 1 Scenario without Handover 39,6 1 1 MOS score objective for G 711 39. 6 1 2 MOS score objective for iLBC 40,6 2 Scenario with Handover 42. 6 2 1 Subjective MOS Score 42,6 2 2 E model calculations for G 711 42. 6 2 3 E model calculations for iLBC 43,6 3 Calculations using New Approach 43.
6 3 1 New E model calculation for iLBC 43,6 3 2 New E model calculation for G 711 44. 6 4 Comparisons 44,6 5 Correlation between G 711 and iLBC 45. 6 5 1 Comparison of Jitter 46,6 5 2 One Way Delay 47. 6 5 3 Bandwidth 48,7 Conclusion and Future Work 49. 7 1 Conclusion 49,7 2 Future Work 49,8 References 50.
List of Tables,Table 1 iLBC Codec Specifications 12. Table 2 G 711 Codec Specification 12, Table 3 MOS rating based on Listening Quality LQ and Listening Effort LE 17. Table 4 MOS Ratings 18, Table 5 Fitting Parameters for codec G 711 and iLBC 21. Table 6 Average MOS Scores for G 711 and iLBC during handover 42. List of Figures,Figure 2 1 PC to PC Architecture 5. Figure 2 2 TCP IP Protocol Stack 6,Figure 2 3a RTP Datagram for VoIP 7.
Figure 2 3b RTP Packet Format 8, Figure 2 4 Sampling of Signal from Analog to Digital 11. Figure 2 5 Quantized form of a Signal 11,Figure 3 1 Jitter in Network 14. Figure 3 2 Latency in Network 16, Figure 3 3 Relationship among speech quality delay and increasing Echo 17. Figure 3 4 PESQ Testing 19, Figure 3 5 R factor Rating with MOS score mapping and user satisfaction 20. Figure 4 1 Stages of Handover during a VoIP call 22. Figure 4 2 Comparison of MOS objective and MOS subjective during handover 24. Figure 4 3 Scenario during handover 24, Figure 4 4 Screenshot of wireshark before handoff 25.
Figure 4 5 Screenshot of Wireshark during handover phase 26. Figure 4 6 Screenshot of Wireshark after handover process is complete 27. Figure 4 7 Flowchart of Handover Process 28,Figure 5 1 Seven layers of OSI model 30. Figure 5 2 Test Setup Scenario 31,Figure 5 3 VoIP Client 32. Figure 5 4 Wireshark Screenshot 34,Figure 5 5 MOS Score Calculator 35. Figure 5 6 Screenshot of MOS calculator when handoff is selected 36. Figure 5 7 Screenshot for calculation of R factor 37. Figure 5 8 Screenshot for calculation of MOS score 38. Figure 6 1 Individual comparison of MOS subjective and MOS emodel for G 711 40. Figure 6 2 Individual comparison of MOS subjective and MOS emodel for iLBC 41. Figure 6 3 Comparison of MOS for G 711 and iLBC codec without handover 41. Figure 6 4 Comparison of iLBC and G 711 for handover 43. Figure 6 5 Comparison of New Emodel with E model and Subjective MOS 45. Figure 6 6 Correlation between jitter for iLBC and G 711 during handover 46. Figure 6 7 Correlation between delay for iLBC and G 711 during handover 47. Figure 6 8 Correlation between bandwidth for iLBC and G 711 during handover 48. 1 Introduction, Voice over IP VoIP services has become very popular since the advent of internet and is now. replacing the traditional PSTN networks and the cellular networks The main reason for choosing. VoIP calls over cellular calls is its inexpensive nature Long distance cellular calls tend to be. very expensive to setup whereas the same call can be setup at no cost over the internet Google. Talk Skype and Yahoo Messenger provide free voice services over the internet and thus are. banned in some countries Nowadays VoIP phones are available that can be used even when the. user is travelling to setup a call to another VoIP phone land line or a mobile number at a bare. minimal cost,1 1 Problem Description, Voice over IP services uses the traditional Internet Protocol IP to send the voice packets It.
breaks the voice call into small packets that are routed over the internet Due to the unreliable. nature of the internet these packets might get lost in the network which results in missing. packets at the receiver end As a result the receiver would hear the speaker s sentence. incomplete and may not understand it It is very essential to monitor the quality of these voice. calls to achieve user satisfaction, To measure the speech quality various network factors like delay packet loss jitter etc are. considered The measured speech quality is then mapped to a user satisfaction level Nowadays. many people make VoIP calls when they are travelling thus moving from one network to. another It is very important that the user experiences a good call quality when the VoIP call gets. handed off from one network to another The process of handoff consists of temporarily. disconnecting from one network and then establishing a connection with the new network this. could result in dropped calls or heavy packet loss if not performed smoothly Thus it is very. important to measure the speech quality of VoIP during handovers to achieve high user. satisfaction,1 2 Related Work, Speech quality has always been a concern for VoIP calls The traditional subjective method to. measure the speech quality is by performing the Mean Opinion Score MOS tests To replace. the expensive subjective test objective methods are developed that base the calculations by. considering varied network parameters The most popular objective methods to calculate speech. quality are Perceptual Evaluation of Speech Quality PESQ and E model The effect of handoff. on voice quality of VoIP is studied in 4 the paper studies the various network parameters that. are affected during a call handover, In this project a new approach is proposed to measure the speech quality of VoIP calls during. handover based on the existing E model method,1 3 Outline. The brief outline of the report is below, Chapter 2 provides information on VoIP networks The Transport Control Protocol TCP.
Internet Protocol IP and Real Time Protocol RTP are discussed in detail It also discusses the. coding technology used in VoIP namely codec s G 711 and iLBC. Chapter 3 covers the various factors that affect the Quality of Service in VoIP The method of. measuring the speech quality using Mean Opinion Score MOS Perceptual Evaluation of. Speech Quality PESQ and E model are discussed, Chapter 4 discusses the impact of handovers on VoIP It studies the performance of E model. during handoff and introduces the new proposed method to measure the speech quality during. Chapter 5 covers the whole test setup which includes screenshots of the VoIP client Wireshark. tool and the software developed, Chapter 6 shows the implementation results suing the traditional E model and the new proposed. model It correlates subjective MOS test experiment results with E model and the new objective. model It also compares the two speech codec s iLBC and G 711 for various network parameters. 2 VoIP Networks,2 1 Introduction to VoIP, With the growth of Internet technology the traditional PSTN Public Switched Telephone. Network is now being replaced by the Voice over IP VoIP network A call in a traditional. telephone network is established using circuit switching where a dedicated channel is setup. between the callers The advantage of this approach is that once a call is setup between the. callers the voice quality is very good but on the other end regular telephone calls requires a lot. of resources like network capacity that makes it expensive to setup 18. Voice over IP establishes a call between the users using the Internet protocol It breaks the voice. data into packets and transfers them over the internet On the other hand the receiver reassembles. those packets to establish a voice call VoIP calls utilize the bandwidth more efficiently as. compared to the PSTN calls and hence are cheaper to setup This is one of the major advantages. of using VoIP over telephony now a days VoIP calls can be established PC to PC PC to. telephone or telephone to PC and is also referred as Internet Telephony or IP Telephony. 2 2 VoIP Network Connections, A common VoIP connection is established between phone to phone phone to PC or PC to PC as. shown in figure 2 1 20,Fig 2 1 PC to PC Architecture 20.
The basic process of VoIP includes the following steps. 1 Conversion of analog voice into digital packets, 2 Conversion of digital packets into Internet protocol packets. 3 Transmission of the packets over IP based network. 4 Conversion of digital packets into analog voice at receiver s end. The process of compression is carried out by a voice encoding algorithm called Codec which. allows the call to be transmitted over the IP network. 2 3 TCP IP Protocol, Transmission Control Protocol and Internet Protocol is a stack of protocols that sets up an. agreement for two computers to communicate TCP IP protocol consists of four layers as shown. in figure 2 2,Figure 2 2 TCP IP Protocol Stack 9, Application layer is the uppermost layer of the TCP IP protocol stack it is used by programs like. SMTP for email HTTP web browsing and FTP file transfer protocol After processing the. request at the Application layer the protocol at the Application layer now interacts with. Transport layer also referred as Transmission Control Protocol TCP TCP gets data from the. Application layer and breaks it into packets and sends it to the Internet Layer 9. The Internet layer also known as Internet protocol adds a virtual address known as IP address to. the data packets The IP address of the sender and that of the receiver is added to the data packet. The lowest layer is the Network layer and the data is sent as datagram s in this layer 9. 2 3 1 Transport Layer, The Transmission Control Protocol TCP is responsible for sending the packets over the Internet. protocol and also reassembling the packets at the receiver end If the packets arrive out of order. then TCP reorders the packets and incase of lost or corrupted packet received it sends an. acknowledgement to the transmitter The packet is then resend by the transmitter The TCP. protocol ensures reliable delivery of packets over the internet. Quality of Service is a very important factor to determine the quality of a VoIP call Different subjective and objective models exist for evaluating the speech quality in VoIP E model is one of the objective methods of measuring the speech quality it considers various factors like packet loss delay and codec impairments The calculations of E

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