Quality aspects of Internet telephony

Internet telephony has had a tremendous impact on how people communicate. Many now maintain contact using some form of Internet telephony. Therefore the motivation for this work has been to address the quality aspects of real-world Internet telephony for both fixed and wireless telecommunication. The focus has been on the quality aspects of voice communication, since poor quality leads often to user dissatisfaction. The scope of the work has been broad in order to address the main factors within IP-based voice communication. The first four chapters of this dissertation constitute the background material. The first chapter outlines where Internet telephony is deployed today. It also motivates the topics and techniques used in this research. The second chapter provides the background on Internet telephony including signalling, speech coding and voice Internetworking. The third chapter focuses solely on quality measures for packetised voice systems and finally the fourth chapter is devoted to the history of voice research. The appendix of this dissertation constitutes the research contributions. It includes an examination of the access network, focusing on how calls are multiplexed in wired and wireless systems. Subsequently in the wireless case, we consider how to handover calls from 802.11 networks to the cellular infrastructure. We then consider the Internet backbone where most of our work is devoted to measurements specifically for Internet telephony. The applications of these measurements have been estimating telephony arrival processes, measuring call quality, and quantifying the trend in Internet telephony quality over several years. We also consider the end systems, since they are responsible for reconstructing a voice stream given loss and delay constraints. Finally we estimate voice quality using the ITU proposal PESQ and the packet loss process. The main contribution of this work is a systematic examination of Internet telephony. We describe several methods to enable adaptable solutions for maintaining consistent voice quality. We have also found that relatively small technical changes can lead to substantial user quality improvements. A second contribution of this work is a suite of software tools designed to ascertain voice quality in IP networks. Some of these tools are in use within commercial systems today.

[1]  J. Forgie.  Speech communication in packet‐switched networks , 1976 .

[2]  B. Gold,et al.  Digital speech networks , 1977, Proceedings of the IEEE.

[3]  Danny Cohen,et al.  Issues in transnet packetized voice communication , 1977, SIGCOMM.

[4]  William Edward Naylor.  Stream traffic communication in packet switched networks. , 1977 .

[5]  G. Barberis,et al.  Analysis and Optimal Design of a Packet-Voice Receiver , 1980, IEEE Trans. Commun..

[6]  J. Gruber,et al.  Delay Related Issues in Integrated Voice and Data Networks , 1981, IEEE Trans. Commun..

[7]  G. Barberis.  Buffer Sizing of a Packet-Voice Receiver , 1981, IEEE Trans. Commun..

[8]  Nuggehally Sampath Jayant,et al.  Effects of Packet Losses in Waveform Coded Speech and Improvements Due to an Odd-Even Sample-Interpolation Procedure , 1981, IEEE Trans. Commun..

[9]  C. Goodwin.  Conversational Organization: Interaction Between Speakers and Hearers , 1981 .

[10]  D. Mitra,et al.  Stochastic theory of a data-handling system with multiple sources , 1982, The Bell System Technical Journal.

[11]  L. Kleinrock,et al.  Stream Traffic Communication in Packet Switched Networks: Destination Buffering Considerations , 1982, IEEE Trans. Commun..

[12]  Warren A. Montgomery,et al.  Techniques for Packet Voice Synchronization , 1983, IEEE J. Sel. Areas Commun..

[13]  Clifford J. Weinstein,et al.  Experience with Speech Communication in Packet Networks , 1983, IEEE J. Sel. Areas Commun..

[14]  S.A. Mahmoud,et al.  Design and performance evaluation of a packet voice system , 1983, IEEE Transactions on Vehicular Technology.

[15]  Nobuhiko Kitawaki,et al.  Speech-quality assessment methods for speech-coding systems , 1984, IEEE Communications Magazine.

[16]  Hideo Miyahara,et al.  Performance Evaluation of a Packetized Voice System - Simulation Study , 1984, IEEE Transactions on Communications.

[17]  Johnny W. Wong,et al.  Analysis of playout strategies for voice transmission using packet switching techniques , 1984, Perform. Evaluation.

[18]  Manfred R. Schroeder,et al.  Code-excited linear prediction(CELP): High-quality speech at very low bit rates , 1985, ICASSP '85. IEEE International Conference on Acoustics, Speech, and Signal Processing.

[19]  J. Gruber,et al.  Subjective Effects of Variable Delay and Speech Clipping in Dynamically Managed Voice Systems , 1985, IEEE Trans. Commun..

[20]  Ward Whitt,et al.  Characterizing Superposition Arrival Processes in Packet Multiplexers for Voice and Data , 1986, IEEE J. Sel. Areas Commun..

[21]  Hyeong-Ho Lee,et al.  A Study of On-Off Characteristics of Conversational Speech , 1986, IEEE Trans. Commun..

[22]  Xavier Maitre,et al.  7 kHz audio coding within 64 kbit/s , 1988, IEEE J. Sel. Areas Commun..

[23]  Dinesh C. Verma,et al.  A Scheme for Real-Time Channel Establishment in Wide-Area Networks , 1990, IEEE J. Sel. Areas Commun..

[24]  Mats Carlsson.  Design and implementation of an or-parallel Prolog engine , 1990, RIT / KTH / TRITA-CS.

[25]  P. M. Gopal,et al.  A simulation study of network delay for packetized voice , 1991 .

[26]  D.C. Verma,et al.  Delay jitter control for real-time communication in a packet switching network , 1991, Proceedings of TRICOMM `91: IEEE Conference on Communications Software: Communications for Distributed Applications and Systems.

[27]  Donald F. Towsley,et al.  Approximation Techniques for Computing Packet Loss in Finite-Buffered Voice Multiplexers , 1991, IEEE J. Sel. Areas Commun..

[28]  Hans A. Hansson.  Time and probability in formal design of distributed systems , 1991, DoCS.

[29]  Philip Almquist,et al.  Type of Service in the Internet Protocol Suite , 1992, RFC.

[30]  Stephen E. Deering,et al.  First IETF internet audiocast , 1992, CCRV.

[31]  Henning Schulzrinne,et al.  Voice Communication Across the Internet: A Network Voice Terminal , 1992 .

[32]  Jean-Chrysostome Bolot,et al.  Characterizing End-to-End Packet Delay and Loss in the Internet , 1993, J. High Speed Networks.

[33]  Lars-Henrik Eriksson,et al.  Finitary Partial Inductive Definitions as a General Logic , 1993, ELP.

[34]  Henning Schulzrinne,et al.  Reducing and characterizing packet loss for high-speed computer networks with real-time services , 1993 .

[35]  Jean-Chrysostome Bolot,et al.  End-to-end packet delay and loss behavior in the internet , 1993, SIGCOMM '93.

[36]  Jean-Chrysotome Bolot.  End-to-end packet delay and loss behavior in the internet , 1993, SIGCOMM 1993.

[37]  Scott Shenker,et al.  Integrated Services in the Internet Architecture : an Overview Status of this Memo , 1994 .

[38]  Allan Gut,et al.  An intermediate course in probability , 1995 .

[39]  Kevin Jeffay,et al.  An Empirical Study of a Jitter Management Scheme for Video Teleconferencing , 1995, Multim. Syst..

[40]  Kuldip K. Paliwal,et al.  Speech Coding and Synthesis , 1995 .

[41]  Kuldip K. Paliwal,et al.  Speech Coding and Synthesis , 1995 .

[42]  Per Kreuger.  Computational issues in calculi of partial inductive definitions , 1995, SICS dissertation series.

[43]  Matthijs A. Visser,et al.  Voice and data transmission over an 802.11 wireless network , 1995, Proceedings of 6th International Symposium on Personal, Indoor and Mobile Radio Communications.

[44]  Jean-Chrysostome Bolot,et al.  Analysis of Audio Packet Loss in the Internet , 1995, NOSSDAV.

[45]  S. Shenker.  Fundamental Design Issues for the Future Internet , 1995 .

[46]  Henning Schulzrinne,et al.  RTP: A Transport Protocol for Real-Time Applications , 1996, RFC.

[47]  Annika Waern,et al.  Recognising Human Plans: Issues for Plan Recognition in Human - Computer Interaction , 1996 .

[48]  Klas Orsvarn,et al.  Knowledge Modelling with Libraries of Task Decomposition Methods , 1996 .

[49]  Johan Montelius,et al.  Exploiting fine-grain parallelism in concurrent constraint languages , 1997, Uppsala theses in computing science.

[50]  Bengt Ahlgren,et al.  Improving computer communication performance by reducing memory bandwidth consumption , 1997, SICS dissertation series.

[51]  Björn Gambäck.  Processing Swedish sentences : a unification-based grammar and some applications , 1997 .

[52]  Luigi Rizzo,et al.  Dummynet: a simple approach to the evaluation of network protocols , 1997, CCRV.

[53]  Vern Paxson,et al.  End-to-end Internet packet dynamics , 1997, SIGCOMM '97.

[54]  Leo Monteban,et al.  WaveLAN®-II: A high-performance wireless LAN for the unlicensed band , 1997, Bell Labs Technical Journal.

[55]  Jean C. Bolot,et al.  The Case for FEC-based Error Control for Packet Audio in the Internet , 1997 .

[56]  Luigi Rizzo.  The FreeBSD Audio Driver , 1997, COST 237 Workshop.

[57]  Isidor Kouvelas,et al.  Overcoming workstation scheduling problems in a real-time audio tool , 1997 .

[58]  J. Rosenberg.  Internet Telephony: a (partial) Research Agenda , 1997 .

[59]  Vern Paxson,et al.  End-to-end routing behavior in the Internet , 1996, TNET.

[60]  Henning Schulzrinne,et al.  A Comparison of SIP and H.323 for Internet Telephony , 1998 .

[61]  David L. Black,et al.  An Architecture for Differentiated Service , 1998 .

[62]  Steven McCanne,et al.  Simulation of FEC-based error control for packet audio on the Internet , 1998, Proceedings. IEEE INFOCOM '98, the Conference on Computer Communications. Seventeenth Annual Joint Conference of the IEEE Computer and Communications Societies. Gateway to the 21st Century (Cat. No.98.

[63]  Henning Schulzrinne,et al.  Real Time Streaming Protocol (RTSP) , 1998, RFC.

[64]  Mark Handley,et al.  SDP: Session Description Protocol , 1998, RFC.

[65]  P. Van Mieghem.  A lower bound for the end-to-end delay in networks: application to voice over IP , 1998 .

[66]  V. Hardman,et al.  A survey of packet loss recovery techniques for streaming audio , 1998, IEEE Network.

[67]  N. K. Shankaranarayanan,et al.  The AT&T Labs broadband fixed wireless field experiment , 1999, WCNC. 1999 IEEE Wireless Communications and Networking Conference (Cat. No.99TH8466).

[68]  M. Handley,et al.  SIP: Session Initiation Protocol , 1999, RFC.

[69]  Ismail Dalgic,et al.  Comparison of H.323 and SIP for IP telephony signaling , 1999, Optics East.

[70]  Gunnar Karlsson.  Providing quality for Internet video services , 1999 .

[71]  Kenneth J. Christensen,et al.  An algorithm for playout of packet voice based on adaptive adjustment of talkspurt silence periods , 1999, Proceedings 24th Conference on Local Computer Networks. LCN'99.

[72]  David Hands,et al.  A Study of the Impact of Network Loss and Burst Size on Video Streaming Quality and Acceptability , 1999, IDMS.

[73]  N. K. Shankaranarayanan,et al.  The AT&T Labs broadband fixed wireless field experiment , 1999, IEEE Commun. Mag..

[74]  Georg Carle,et al.  Framework model for packet loss metrics based on loss runlengths , 1999, Electronic Imaging.

[75]  Olivier Hersent.  IP telephony , 1999 .

[76]  Henning Schulzrinne,et al.  An RTP Payload Format for Generic Forward Error Correction , 1999, RFC.

[77]  Donald F. Towsley,et al.  Adaptive FEC-based error control for Internet telephony , 1999, IEEE INFOCOM '99. Conference on Computer Communications. Proceedings. Eighteenth Annual Joint Conference of the IEEE Computer and Communications Societies. The Future is Now (Cat. No.99CH36320).

[78]  Ashley Saulsbury.  Attacking latency bottlenecks in distributed shared memory systems , 1999 .

[79]  Jussi Karlgren,et al.  Stylistic Experiments for Information Retrieval , 1999 .

[80]  Michel Mandjes,et al.  End-to-end delay models for interactive services on a large-scale IP network , 1999 .

[81]  Hui Zhang,et al.  Endpoint admission control: architectural issues and performance , 2000, SIGCOMM 2000.

[82]  Uyless Black.  Internet Telephony: Call Processing Protocols , 2000 .

[83]  Henning Schulzrinne,et al.  Integrating packet FEC into adaptive voice playout buffer algorithms on the Internet , 2000, Proceedings IEEE INFOCOM 2000. Conference on Computer Communications. Nineteenth Annual Joint Conference of the IEEE Computer and Communications Societies (Cat. No.00CH37064).

[84]  Wenyu Jiang,et al.  Modeling of Packet Loss and Delay and Their Effect on Real-Time Multimedia Service Quality , 2000 .

[85]  Anders Andersson.  Capacity Study of Statistical Multiplexing for IP Telephony , 2000 .

[86]  Wenyu Jiang,et al.  Analysis of on-off patterns in VoIP and their effect on voice traffic aggregation , 2000, Proceedings Ninth International Conference on Computer Communications and Networks (Cat.No.00EX440).

[87]  Gunnar Karlsson,et al.  Admission control based on end-to-end measurements , 2000, Proceedings IEEE INFOCOM 2000. Conference on Computer Communications. Nineteenth Annual Joint Conference of the IEEE Computer and Communications Societies (Cat. No.00CH37064).

[88]  Vineet Kumar,et al.  IP Telephony with H.323: Architectures for Unified Networks and Integrated Services , 2001 .

[89]  Gunnar Karlsson,et al.  PBAC: Probe-Based Admission Control , 2001, QofIS.

[90]  David Clark,et al.  A taxonomy of internet telephony applications , 2001 .

[91]  Robert G. Cole,et al.  Voice over IP performance monitoring , 2001, CCRV.

[92]  Hossam Afifi,et al.  Integrating networks measurements and speech quality subjective scores for control purposes , 2001, Proceedings IEEE INFOCOM 2001. Conference on Computer Communications. Twentieth Annual Joint Conference of the IEEE Computer and Communications Society (Cat. No.01CH37213).

[93]  Ashok K. Agrawala,et al.  Measuring Traffic on the Wireless Medium: Experience and Pitfalls , 2002 .

[94]  Krister Svanbro.  Lower Layer Guidelines for Robust RTP/UDP/IP Header Compression , 2002, RFC.

[95]  Scott Pennock,et al.  Accuracy of the Perceptual Evaluation of Speech Quality (PESQ) algorithm , 2002 .

[96]  Roch Lefebvre,et al.  The adaptive multirate wideband speech codec (AMR-WB) , 2002, IEEE Trans. Speech Audio Process..

[97]  Jan Skoglund,et al.  iLBC - a linear predictive coder with robustness to packet losses , 2002, Speech Coding, 2002, IEEE Workshop Proceedings..

[98]  Thiemo Voigt,et al.  Architectures for service differentiation in overloaded Internet servers , 2002 .

[99]  Wenyu Jiang,et al.  Speech recognition performance as an effective perceived quality predictor , 2002, IEEE 2002 Tenth IEEE International Workshop on Quality of Service (Cat. No.02EX564).

[100]  L. Rasmusson.  Network capacity sharing with QoS as a financial derivative pricing problem : algorithms and network , 2002 .

[101]  Wenyu Jiang,et al.  Comparison and optimization of packet loss repair methods on VoIP perceived quality under bursty loss , 2002, NOSSDAV '02.

[102]  Anders Lindgren,et al.  Quality of Service Schemes for IEEE 802.11 Wireless LANs – An Evaluation , 2003, Mob. Networks Appl..

[103]  Walter F. Stenning,et al.  AN EMPIRICAL STUDY , 2003 .

[104]  Joe Armstrong,et al.  Making reliable distributed systems in the presence of software errors , 2003 .

[105]  Olof Hagsand,et al.  Sicsophone: a low-delay Internet telephony tool , 2003, 2003 Proceedings 29th Euromicro Conference.

[106]  Adam Wolisz,et al.  On the Importance of a VoIP Packet , 2003 .

[107]  Ramón Cáceres,et al.  RTP Control Protocol Extended Reports (RTCP XR) , 2003, RFC.

[108]  W. Bastiaan Kleijn,et al.  Rate-distortion comparisons between FEC and MDC based on Gilbert channel model , 2003, The 11th IEEE International Conference on Networks, 2003. ICON2003..

[109]  Gunnar Karlsson,et al.  The Performance of Endpoint Admission Control Based on Packet Loss , 2003, QofIS.

[110]  Xiaoyan Cheng,et al.  Using IEEE 802.11e MAC for QoS over wireless , 2003, Conference Proceedings of the 2003 IEEE International Performance, Computing, and Communications Conference, 2003..

[111]  Giuseppe Pappalardo,et al.  WiFi mobility framework supporting GPRS roaming: design and implementation , 2003, IEEE International Conference on Communications, 2003. ICC '03..

[112]  Rita Puzmanova.  IP Telephony with H.323: Architectures for Unified Networks and Integrated Services , 2003 .

[113]  Christian Huitema,et al.  STUN - Simple Traversal of User Datagram Protocol (UDP) Through Network Address Translators (NATs) , 2003, RFC.

[114]  Ian Marsh,et al.  Modelling the Arrival Process for Packet Audio , 2003, QoS-IP.

[115]  Gunnar Karlsson,et al.  Wide Area Measurements of Voice over IP Quality , 2003, QofIS.

[116]  Erik Hagersten,et al.  Toward Scalable Cache Only Memory Architectures , 2003 .

[117]  Catherine Boutremans,et al.  DELAY ASPECTS IN INTERNET TELEPHONY , 2003 .

[118]  Kristina Höök,et al.  A glass box approach to adaptive hypermedia , 1996, User Modeling and User-Adapted Interaction.

[119]  Enrico Pelletta.  Maximum Throughput of IEEE 802.11 Access Points: Test Procedure and Measurements , 2004 .

[120]  Alexander Raake,et al.  Elements of interactivity in telephone conversations , 2004, INTERSPEECH.

[121]  Claudio Casetti,et al.  Improving fairness and throughput for voice traffic in 802.11e EDCA , 2004, 2004 IEEE 15th International Symposium on Personal, Indoor and Mobile Radio Communications (IEEE Cat. No.04TH8754).

[122]  Fethi Filali.  Dynamic and efficient tuning of IEEE 802.11 for multimedia applications , 2004, 2004 IEEE 15th International Symposium on Personal, Indoor and Mobile Radio Communications (IEEE Cat. No.04TH8754).

[123]  Gunnar Karlsson,et al.  Self-Admission Control for IP Telephony Using Early Quality Estimation , 2004, NETWORKING.

[124]  Thierry Turletti,et al.  IEEE 802.11 rate adaptation: a practical approach , 2004, MSWiM '04.

[125]  I. Claesson,et al.  Analog circuit implementation for speech enhancement purposes , 2004, Conference Record of the Thirty-Eighth Asilomar Conference on Signals, Systems and Computers, 2004..

[126]  Peter Reichl,et al.  Where packet traces meet speech samples: an instrumental approach to perceptual QoS evaluation of VoIP , 2004, Twelfth IEEE International Workshop on Quality of Service, 2004. IWQOS 2004..

[127]  Peter Reichl,et al.  Hot discussion or frosty dialogue? towards a temperature metric for conversational interactivity , 2004, INTERSPEECH.

[128]  Jerry D. Gibson,et al.  Selective bit-error checking at the MAC layer for voice over mobile ad hoc networks with IEEE 802.11 , 2004, 2004 IEEE Wireless Communications and Networking Conference (IEEE Cat. No.04TH8733).

[129]  Sameh El-Ansary.  Designs and Analyses in Structured Peer-To-Peer Systems , 2005 .

[130]  Henning Schulzrinne,et al.  Using dynamic PCF to improve the capacity for VoIP traffic in IEEE 802.11 networks , 2005, IEEE Wireless Communications and Networking Conference, 2005.

[131]  Åsa Rudström,et al.  Co-Construction of Hybrid Spaces , 2005 .

[132]  Kevin Jeffay,et al.  An empirical study of delay jitter management policies , 1995, Multimedia Systems.

[133]  Rickard Cöster,et al.  Algorithms and Representations for Personalised Information Access , 2005 .

[134]  Erik Klintskog,et al.  Generic distribution support for programming systems , 2005 .

[135]  M. Varela.  Studying the Effects of FEC on Voice Traffic Using PSQA , 2005 .

[136]  Markus Bylund,et al.  A Design Rationale for Pervasive Computing: User Experience, Contextual Change and Technical Requirements , 2005 .

[137]  Alexander Raake,et al.  The well-tempered conversation: interactivity, delay and perceptual VoIP quality , 2005, IEEE International Conference on Communications, 2005. ICC 2005. 2005.

[138]  R.M. Gray.  The 1974 origins of VoIP , 2005, IEEE Signal Processing Magazine.

[139]  Olivier Hersent,et al.  IP Telephony: Deploying Voice-over-IP Protocols , 2005 .

[140]  Mattias Dahl,et al.  Speech Enhancement Implementations in the Digital, Analog, and Hybrid Domain , 2005 .

[141]  Per Brand,et al.  The design philosophy of distributed programming systems : the Mozart experience , 2005 .

[142]  Jonathan Rosenberg.  Traversal Using Relay NAT (TURN) , 2005 .

[143]  Y. Oie,et al.  Handover management based on the number of retries for VoIP on WLANs , 2005, 2005 IEEE 61st Vehicular Technology Conference.

[144]  S. Murphy,et al.  An approach to transport layer handover of VoIP over WLAN , 2006, CCNC 2006. 2006 3rd IEEE Consumer Communications and Networking Conference, 2006..

[145]  Magnus Sahlgren,et al.  The Word-Space Model: using distributional analysis to represent syntagmatic and paradigmatic relations between words in high-dimensional vector spaces , 2006 .

[146]  Ravi Jain,et al.  An Experimental Study of the Skype Peer-to-Peer VoIP System , 2005, IPTPS.

[147]  Miguel A. Garcia-Martin,et al.  The 3G IP multimedia subsystem IMS - merging the internet and the cellular worlds (2. ed.) , 2006 .

[148]  Volodya Grancharov,et al.  Human Perception in Speech Processing , 2006 .

[149]  Alexander Raake,et al.  Speech Quality of VoIP - Assessment and Prediction , 2006 .

[150]  Ian Marsh,et al.  A Systematic Study of PESQ's Performance (from a Networking Perspective) , 2006 .

[151]  Jörg Ott,et al.  Extended RTP Profile for Real-time Transport Control Protocol (RTCP)-Based Feedback (RTP/AVPF) , 2006, RFC.

[152]  Marie Sjölinder,et al.  Age-related cognitive decline and navigation in electronic environments , 2006 .

[153]  Alan B. Johnston,et al.  Internet Communications Using SIP: Delivering VoIP and Multimedia Services with Session Initiation Protocol , 2006 .

[154]  Ian Marsh,et al.  The Design and Implementation of a Quality-Based Handover Trigger , 2006, Networking.

[155]  Gonzalo Camarillo,et al.  The 3G IP Multimedia Subsystem (IMS): Merging the Internet and the Cellular Worlds, Second Edition , 2006 .

[156]  Ali Ghodsi,et al.  Distributed k-ary System: Algorithms for Distributed Hash Tables , 2006 .

[157]  Christian Hoene,et al.  Internet Telephony over Wireless Links , 2006 .

[158]  Mark Handley,et al.  Reliable Audio for Use over the Internet , 2006 .

[159]  Donald F. Towsley,et al.  Characterizing and Detecting Skype-Relayed Traffic , 2006, Proceedings IEEE INFOCOM 2006. 25TH IEEE International Conference on Computer Communications.

[160]  Henning Schulzrinne,et al.  An Analysis of the Skype Peer-to-Peer Internet Telephony Protocol , 2004, Proceedings IEEE INFOCOM 2006. 25TH IEEE International Conference on Computer Communications.

[161]  Dan Sahlin,et al.  An Automatic Partial Evaluator for Full Prolog , 2007 .

[162]  Adam Dunkels,et al.  Programming Memory-Constrained Networked Embedded Systems , 2007 .

[163]  Stina Nylander,et al.  Design and Implementation of Multi-Device Services , 2007 .

[164]  Jarmo Laaksolahti,et al.  Plot, Spectacle, and Experience: Contributions to the Design and Evaluation of Interactive Storytelling , 2008 .

[165]  Fredrik Olsson,et al.  Bootstrapping Named Entity Annotation by Means of Active Machine Learning: A Method for Creating Corpora , 2008 .

[166]  Dan Wing,et al.  Session Traversal Utilities for NAT (STUN) , 2020, RFC.

[167]  H. Schulzrinne,et al.  A Transport Protocol for Real-time Applications , 2010 .

[168]  Olivier Hersent.  H.323: Packet‐Based Multimedia Communications Systems , 2010 .

[169]  J. Holtzman,et al.  The Interaction between Queueing and Voice Quality in Variable Bit Rate Packet Voice Systems , 2011 .