1、 ETSI TR 103 010 V1.1.1 (2007-03)Technical Report Speech Processing, Transmission and Quality Aspects (STQ);Synchronization in IP Networks -Methods and User PerceptionETSI ETSI TR 103 010 V1.1.1 (2007-03) 2 Reference DTR/STQ-00068 Keywords multimedia, quality, speech, synchronization, VoIP ETSI 650
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6、 copyright and the foregoing restriction extend to reproduction in all media. European Telecommunications Standards Institute 2007. All rights reserved. DECTTM, PLUGTESTSTM and UMTSTM are Trade Marks of ETSI registered for the benefit of its Members. TIPHONTMand the TIPHON logo are Trade Marks curre
7、ntly being registered by ETSI for the benefit of its Members. 3GPPTM is a Trade Mark of ETSI registered for the benefit of its Members and of the 3GPP Organizational Partners. ETSI ETSI TR 103 010 V1.1.1 (2007-03) 3 Contents Intellectual Property Rights4 Foreword.4 Introduction 4 1 Scope 5 2 Referen
8、ces 5 3 Definitions and abbreviations.7 3.1 Definitions7 3.2 Abbreviations .7 4 IP-based Services and Network Configurations.8 4.1 Network models .8 5 Timestamp methods .9 5.1 RTP based media transport.10 5.1.1 RTP Control Protocol .10 5.1.2 Functionality of RTP timestamps .11 5.2 Network Time Proto
9、col or NTP .12 5.2.1 Possible sources of errors in NTP.15 5.2.2 Achievable performance with NTP.15 5.3 Precision Time Protocol or IEEE 1588 16 5.3.1 Protocol Implementation of PTP 18 5.3.2 Limitations of PTP Protocol .19 5.3.3 Possible Sources of Error in PTP20 5.3.4 Achievable performance with PTP
10、.20 5.4 Clock rate and state based synchronization20 5.4.1 Positive and negative features of SyncUTC .21 5.4.2 Achievable Performance in SyncUTC21 6 Perception-based application requirements22 6.1 Audio23 6.2 Video23 6.2.1 Animation .23 6.2.2 Audio and Video.23 6.2.2.1 Conversational Service23 6.2.2
11、.2 Distribution service .24 6.2.2.3 Conferencing Service 24 6.3 Data and Audio.24 6.3.1 Pointers and Audio .24 6.3.2 Still pictures and audio .24 6.3.3 Text and Audio .24 6.4 Data and video24 6.4.1 Text and video 24 6.4.2 Still pictures and audio .25 7 Analysis of timestamp methods .25 7.1 Clock fre
12、quency stability25 7.2 Timestamp reading errors.26 8 Media synchronization in services offered over a combination of TDM and IP networks27 History 28 ETSI ETSI TR 103 010 V1.1.1 (2007-03) 4 Intellectual Property Rights IPRs essential or potentially essential to the present document may have been dec
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15、 referenced in ETSI SR 000 314 (or the updates on the ETSI Web server) which are, or may be, or may become, essential to the present document. Foreword This Technical Report (TR) has been produced by ETSI Technical Committee Speech Processing, Transmission and Quality Aspects (STQ). Introduction Tra
16、ditionally, TDM voice networks have had service performance requirements based on meeting the end users quality of service expectations. In the TDM network, synchronization is a physical layer parameter that has to be designed to meet specific performance standards. Without proper clock synchronizat
17、ion, a service offered over the TDM network experiences errors, i.e. missing data that contributes to reduced service quality and availability. More and more real-time services are now being offered over internet-based networks, where timestamp based synchronization is utilized for billing, maintena
18、nce, call control, one way delay measurements and intra/inter-media stream synchronization. Real-time applications offered over the internet include voice, video and data that have been traditionally carried over circuit switched networks. These services are offered by utilizing new equipment and ne
19、w protocols exclusively designed for this purpose. The protocols permit integration of previously dissimilar voice and data services, creating new applications such as integrated voice mail and email, white boarding that combines voice call with data transfer, desktop video calling etc., from the us
20、e of a single integrated network. An entity to perform data/signalling conversion is required when these services are supported across disparate networks. Internet services can also be offered by connecting existing TDM islands using Internet Protocol (IP) network (TDMoIP or Circuit Emulation over I
21、P) that enables backward compatibility. In TDMoIP, data and signalling from TDM islands will be encapsulated or de-encapsulated in the inter-working functions situated at the interfaces of TDM and IP networks. Service quality requirements are expected to be the same as those for TDM service as the e
22、nd user is not aware of the IP transport. The same argument can be extended to physical layer synchronization requirements. The IP network is an asynchronous network with no knowledge of the physical layer and it was solely used for data transport until recently. With the introduction of real-time I
23、P services, the need arose to set specifications for QoS related parameters - delay, delay variation and packet loss. Main sources of packet loss are bandwidth limitations at the edges, network congestion, clock related impairments and large delay variations that cause the jitter buffer to drop or a
24、dd. ITU-T has published ITU-T Recommendation Y.1541 1 on performance objectives for Layer 3 based network parameters - end-to-end packet delay, packet delay variation and packet loss - based on different classes of service. Efforts are ongoing to set additional service classes with reduced packet lo
25、ss objectives. However, synchronization at the physical layer is a topic of discussion only for TDMoIP services in ITU-T 2 and ANSI 3 standard bodies. The present document reviews the time stamping methods available in IP networks and assesses the performance of these in achieving satisfactory servi
26、ces as perceived by end user. ETSI ETSI TR 103 010 V1.1.1 (2007-03) 5 1 Scope The purpose of the present document is to examine whether accuracies achievable by currently available synchronization methods in IP networks are adequate to ensure end users quality of service expectations are met for a p
27、articular multimedia service. The present document will discuss the issues related to inter-stream synchronization when all the concerned media are offered using: IP networks from end-to-end. A combination of TDM and IP networks. Services that will be covered, but not limited to: Video conferencing:
28、 uses video and voice. White boarding: uses data and voice. When a multimedia service is offered in an IP-based network, the play-out mechanism involves de-multiplexing of different media in end node and subsequent play-out of the media based on the timing information carried over by the media. Depe
29、nding on this timing information, one media may precede the other resulting in user dissatisfaction. For each media, the timing relationship between different packets (intra-stream synchronization) is preserved by proper presentation at the end user in which play-out buffer management plays a crucia
30、l part. Size of the play-out buffer can be a fixed value or can be adaptively set based on one way delay measurement using timestamps. The present document gives an overview of synchronization methods by time stamping and the other means that are available to IP-based real-time applications and the
31、effect of these methods on service performance as experienced by end user. However, actual implementation of time stamping is outside the scope of the present document. The reference point at which inter-stream synchronization will be examined is considered to be at the interface of the end device i
32、nvolved, where the play-out buffers are normally located. 2 References For the purposes of this Technical Report (TR) the following references apply: NOTE 1: While any hyperlinks included in this clause were valid at the time of publication ETSI cannot guarantee their long term validity. NOTE 2: The
33、 following standards contain provisions, which, are referenced in the present document. At the time of publication, the editions indicated were valid. All standards are subject to revision, and parties to agreements based on the present document are encouraged to investigate the possibility of apply
34、ing the most recent editions of the standards indicated below, or their successors. ANSI and TIA maintain registers of currently valid national standards published by them. 1 ITU-T Recommendation Y.1541 (2006): “Network performance objectives for IP-based services“. 2 ITU-T Recommendation G.8261/Y.1
35、361 (2006): “Timing and synchronization aspects in packet networks“. 3 ANSI T1 draft technical report OPTXS-SYNC-2006-007R4.doc: “Synchronization of Packet Networks“. 4 IETF RFC 3388: “Grouping of Media Lines in Session Description Protocol (SDP)“. 5 IETF RFC 3261: “SIP: Session Initiation Protocol“
36、. 6 IETF RFC 3550: “A Transport Protocol for Real-Time Applications“. 7 IETF RFC 3551: “RTP Profile for Audio and Video Conferences with Minimal Control“. 8 IETF RFC 2250: “RTP Payload Format for MPEG1/MPEG2 Video“. ETSI ETSI TR 103 010 V1.1.1 (2007-03) 6 9 IETF RFC 3016: “RTP Payload Format for MPE
37、G-4 Audio/Visual Streams“. 10 IETF RFC 3497: “RTP Payload Format for Society of Motion Picture and Television Engineers (SMPTE) 292M Video“. 11 IETF RFC 3984: “RTP Payload Format for H.264 video“. 12 IETF RFC 1305: “Network Time Protocol (version 3) - Specification, Implementation and Analysis“. 13
38、IEEE Std 1588-2002: “Standard for Precision Time Synchronization Protocol for Networked Measurement and Control Systems“. 14 IETF RFC 4330: “Simple Network Time Protocol (SNTP) Version 4 for IPV4, IPV6 and OSI“. 15 David L. Mills: “Internet Time Synchronization: The Network Time Protocol“, IEEE Tran
39、sactions on Communications, Vol. 39, No.10, October 1991, pp 1482 - 1493. 16 David L. Mills: “Adaptive Hybrid Clock Discipline Algorithm for the Network Time Protocol“, IEEE Transactions on Networking, Vol. 6, No. 5, October 1998, pp 505 - 514. 17 David L. Mills: “NTP Performance Analysis“, www.eeci
40、s.udel.edu/mills/ntp.html. 18 Nelson Minar, MIT Media Lab: “A Survey of the NTP Network“, http:/www.media.mit.edu/nelson, December 9, 1999. 19 John C. Eidson and Kang Lee: “Sharing A Common Sense of Time“, IEEE Instrumentation and Measurement Magazine, March 2003. 20 Dirk S. Mohl: “IEEE 1588 - Preci
41、se Time Synchronization as the Basis for Real Time Applications in Automation“, http:/www.l- 21 Hans Wiebel: “PTP Timestamping Methods“, 2004 Conference on IEEE 1588, September 2004. 22 Dave Tonks: “IEEE 1588 in Telecommunications Applications“, 2004 Conference on IEEE 1588, September 2004. 23 Eidso
42、n, J.C and Hamilton, Bruce: “IEEE-1588 Node Synchronization Improvement by High Stability Oscillators“, NIST workshop on IEEE 1588, September 2003. 24 Martin Horauer: “Clock Synchronization in Distributed Systems“, Ph.D. dissertation, Department of Computer Technology, University of Technology, Vien
43、na, February 2004. 25 Kero N.E., Muhr H., Gaderer G., Holler R., Sauter T., Horauer M.: “Embedded SyncUTC and IEEE 1588 clock synchronization for Industrial Ethernet“, NIST workshop on IEEE-1588 standard, September 2003. 26 Gaderer G., Holler R., Sauter T. and Muhr H.: “Extending IEEE 1588 to Fault
44、Tolerant Clock Synchronization“, Proceedings of International Workshop on factory communication systems, September 2004, pp 353-357. 27 ITU-T Recommendation G.114 (2003): “One way transmission time“. 28 ITU-T Recommendation F.700 (2000): “Framework Recommendation for multimedia services“. 29 Ralf St
45、einmetz: “Human Perception of Jitter and Media Synchronization“, IEEE Journal on Selected Areas In Communications, Vol. 14, No.1, January 1996. 30 Yadavalli G., Masry M., Hemami S.: “Frame Rate Preference in Low Bit Rate Video“, IEEE International Conference on Image Processing (ICIP 2003), Barcelon
46、a, 14-17 September 2003. 31 ANSI T1 technical report TR-45 (1995): “Speech Packetization“. 32 ITU-R Recommendation BT.1359-1 (1998): “Relative timing of sound and vision for broadcasting“. 33 ETSI ETR 297 (1996): “Human Factors (HF); Human Factors in Videotelephony“. ETSI ETSI TR 103 010 V1.1.1 (200
47、7-03) 7 34 ANSI T1.522 (2000): “Quality of Service for Business Multimedia Conferencing“. 35 ETSI TR 102 479 (V1.1.1): “Telecommunications and Internet converged Services and Protocols for Advanced Networking (TISPAN); Review of available material on QoS requirements of Multimedia Services“. 36 ATSC
48、 Implementation Subcommittee Finding - Doc. IS-191 (June 2003): “Relative Timing of Sound and Vision for Broadcast Operations“. 37 ETSI TS 122 228 (V7.5.0): “Digital cellular telecommunications system (Phase 2+); Universal Mobile Telecommunications System (UMTS); Service requirements for the Interne
49、t Protocol (IP) multimedia core network subsystem (IMS); Stage 1“. 38 ITU-T Recommendation Y.1401 (2000): “General requirements for interworking with Internet protocol (IP)-based networks“. 3 Definitions and abbreviations 3.1 Definitions For the purposes of the present document, the following terms and definitions apply: drift: variation in skew or the second derivative of offset between two clocks with time IP multimedia application: app
