1、 International Telecommunication Union ITU-T G.8263/Y.1363TELECOMMUNICATION STANDARDIZATION SECTOR OF ITU (02/2012) SERIES G: TRANSMISSION SYSTEMS AND MEDIA, DIGITAL SYSTEMS AND NETWORKS Packet over Transport aspects Quality and availability targets SERIES Y: GLOBAL INFORMATION INFRASTRUCTURE, INTER
2、NET PROTOCOL ASPECTS AND NEXT GENERATION NETWORKS Internet protocol aspects TransportTiming characteristics of packet-based equipment clocks Recommendation ITU-T G.8263/Y.1363 ITU-T G-SERIES RECOMMENDATIONS TRANSMISSION SYSTEMS AND MEDIA, DIGITAL SYSTEMS AND NETWORKS INTERNATIONAL TELEPHONE CONNECTI
3、ONS AND CIRCUITS G.100G.199 GENERAL CHARACTERISTICS COMMON TO ALL ANALOGUE CARRIER-TRANSMISSION SYSTEMS G.200G.299 INDIVIDUAL CHARACTERISTICS OF INTERNATIONAL CARRIER TELEPHONE SYSTEMS ON METALLIC LINES G.300G.399 GENERAL CHARACTERISTICS OF INTERNATIONAL CARRIER TELEPHONE SYSTEMS ON RADIO-RELAY OR S
4、ATELLITE LINKS AND INTERCONNECTION WITH METALLIC LINES G.400G.449 COORDINATION OF RADIOTELEPHONY AND LINE TELEPHONY G.450G.499 TRANSMISSION MEDIA AND OPTICAL SYSTEMS CHARACTERISTICS G.600G.699 DIGITAL TERMINAL EQUIPMENTS G.700G.799 DIGITAL NETWORKS G.800G.899 DIGITAL SECTIONS AND DIGITAL LINE SYSTEM
5、 G.900G.999 MULTIMEDIA QUALITY OF SERVICE AND PERFORMANCE GENERIC AND USER-RELATED ASPECTS G.1000G.1999 TRANSMISSION MEDIA CHARACTERISTICS G.6000G.6999 DATA OVER TRANSPORT GENERIC ASPECTS G.7000G.7999 PACKET OVER TRANSPORT ASPECTS G.8000G.8999 Ethernet over Transport aspects G.8000G.8099 MPLS over T
6、ransport aspects G.8100G.8199 Quality and availability targets G.8200G.8299Service Management G.8600G.8699 ACCESS NETWORKS G.9000G.9999 For further details, please refer to the list of ITU-T Recommendations. Rec. ITU-T G.8263/Y.1363 (02/2012) i Recommendation ITU-T G.8263/Y.1363 Timing characteristi
7、cs of packet-based equipment clocks Summary Recommendation ITU-T G.8263/Y.1363 outlines requirements for timing devices used in synchronizing network equipment that operates in the interworking function (IWF) and other network elements as defined in Recommendation ITU-T G.8261/Y.1361. This Recommend
8、ation defines the requirements for packet-based equipment clocks. History Edition Recommendation Approval Study Group 1.0 ITU-T G.8263/Y.1363 2012-02-13 15 Keywords Clock, jitter, synchronization, wander. ii Rec. ITU-T G.8263/Y.1363 (02/2012) FOREWORD The International Telecommunication Union (ITU)
9、is the United Nations specialized agency in the field of telecommunications, information and communication technologies (ICTs). The ITU Telecommunication Standardization Sector (ITU-T) is a permanent organ of ITU. ITU-T is responsible for studying technical, operating and tariff questions and issuin
10、g Recommendations on them with a view to standardizing telecommunications on a worldwide basis. The World Telecommunication Standardization Assembly (WTSA), which meets every four years, establishes the topics for study by the ITU-T study groups which, in turn, produce Recommendations on these topic
11、s. The approval of ITU-T Recommendations is covered by the procedure laid down in WTSA Resolution 1. In some areas of information technology which fall within ITU-Ts purview, the necessary standards are prepared on a collaborative basis with ISO and IEC. NOTE In this Recommendation, the expression “
12、Administration“ is used for conciseness to indicate both a telecommunication administration and a recognized operating agency. Compliance with this Recommendation is voluntary. However, the Recommendation may contain certain mandatory provisions (to ensure, e.g., interoperability or applicability) a
13、nd compliance with the Recommendation is achieved when all of these mandatory provisions are met. The words “shall“ or some other obligatory language such as “must“ and the negative equivalents are used to express requirements. The use of such words does not suggest that compliance with the Recommen
14、dation is required of any party. INTELLECTUAL PROPERTY RIGHTS ITU draws attention to the possibility that the practice or implementation of this Recommendation may involve the use of a claimed Intellectual Property Right. ITU takes no position concerning the evidence, validity or applicability of cl
15、aimed Intellectual Property Rights, whether asserted by ITU members or others outside of the Recommendation development process. As of the date of approval of this Recommendation, ITU had received notice of intellectual property, protected by patents, which may be required to implement this Recommen
16、dation. However, implementers are cautioned that this may not represent the latest information and are therefore strongly urged to consult the TSB patent database at http:/www.itu.int/ITU-T/ipr/. ITU 2012 All rights reserved. No part of this publication may be reproduced, by any means whatsoever, wi
17、thout the prior written permission of ITU. Rec. ITU-T G.8263/Y.1363 (02/2012) iii Table of Contents Page 1 Scope 1 2 References. 1 3 Definitions 2 4 Abbreviations and acronyms 2 5 Frequency accuracy 4 5.1 Packet-based equipment clock slave frequency . 4 6 Noise generation . 4 6.1 PEC-S-F 5 7 Packet
18、delay variation noise tolerance 6 7.1 PEC-S-F 6 8 Long-term phase transient response (holdover) . 6 8.1 PEC-S-F 6 9 Phase response to packet timing interruptions 7 10 Interfaces. 8 Annex A Packet-based clock functional model 9 Appendix I Packet delay variation noise tolerance testing methodology 10
19、Appendix II Considerations on packet rates . 11 Appendix III Considerations on PEC-S-F time constant 12 Rec. ITU-T G.8263/Y.1363 (02/2012) 1 Recommendation ITU-T G.8263/Y.1363 Timing characteristics of packet-based equipment clocks 1 Scope This Recommendation outlines minimum requirements for the ti
20、ming functions of the packet slave clocks as defined in ITU-T G.8265. It supports frequency synchronization distribution when using packet-based methods. This Recommendation allows for proper network operation when a packet slave clock is timed from a packet master clock as defined in ITU-T G.8265.
21、This Recommendation focuses on mobile applications, and in particular on the delivery of frequency synchronization for end applications such as mobile base stations. It supports the architecture defined in ITU-T G.8265. Other applications are for further study. This Recommendation focuses on two dif
22、ferent deployment cases for the packet slave clock: Packet slave clock embedded in a device co-located with the end application, as shown after the connection C1 in Figure 3 of ITU-T G.8261.1. Packet slave clock embedded within the end application, as shown after the connection C2 in Figure 3 of ITU
23、-T G.8261.1. This second case is for further study for the first version of this Recommendation. Other deployment cases for the packet slave clock are for further study. This Recommendation focuses on the types of networks corresponding to the HRM-1 and HRM-2 as defined in ITU-T G.8261.1. NOTE For l
24、ong observation intervals, the PEC-S-F is expected to compensate for temperature variation effects; therefore, the output of the PEC-S-F will converge to the 1 ppb slope. The HRM-2 type of network is for further study for the first version of this Recommendation. Other types of networks are out of t
25、he scope of this Recommendation. This Recommendation defines the minimum requirements for the packet slave clocks. These requirements apply under the normal environmental conditions specified for the equipment. This Recommendation includes clock accuracy, packet delay variation (PDV) noise tolerance
26、, holdover performance and noise generation. The start-up conditions (e.g., variable filtering bandwidth at start-up, stabilization period, etc.) are for further study. 2 References The following ITU-T Recommendations and other references contain provisions which, through reference in this text, con
27、stitute provisions of this Recommendation. At the time of publication, the editions indicated were valid. All Recommendations and other references are subject to revision; users of this Recommendation are therefore encouraged to investigate the possibility of applying the most recent edition of the
28、Recommendations and other references listed below. A list of the currently valid ITU-T Recommendations is regularly published. The reference to a document within this Recommendation does not give it, as a stand-alone document, the status of a Recommendation. ITU-T G.810 Recommendation ITU-T G.810 (1
29、996), Definitions and terminology for synchronization networks. ITU-T G.811 Recommendation ITU-T G.811 (1997), Timing requirements at the outputs of primary reference clocks suitable for plesiochronous operation of international digital links. 2 Rec. ITU-T G.8263/Y.1363 (02/2012) ITU-T G.823 Recomme
30、ndation ITU-T G.823 (2000), The control of jitter and wander within digital networks which are based on the 2048 kbit/s hierarchy. ITU-T G.824 Recommendation ITU-T G.824 (2000), The control of jitter and wander within digital networks which are based on the 1544 kbit/s hierarchy. ITU-T G.8260 Recomm
31、endation ITU-T G.8260 (2012), Definitions and terminology for synchronization in packet networks. ITU-T G.8261 Recommendation ITU-T G.8261 (2008), Timing and synchronization aspects in packet networks. ITU-T G.8261.1 Recommendation ITU-T G.8261.1 (2012), Packet delay variation network limits applica
32、ble to packet based methods (Frequency synchronization). ITU-T G.8265 Recommendation ITU-T G.8265 (2010), Architecture and requirements for packet-based frequency delivery. ITU-T G.8265.1 Recommendation ITU-T G.8265.1 (2010), Precision time protocol telecom profile for frequency synchronization. 3 D
33、efinitions Definitions related to synchronization are contained in ITU-T G.810 and ITU-T G.8260. 4 Abbreviations and acronyms For the purposes of this Recommendation, the following abbreviations and acronyms are used: ATM Asynchronous Transfer Mode BS Base Station CBR Constant Bit Rate CDMA Code Div
34、ision Multiple Access CE Customer Equipment CES Circuit Emulation Service DUT Device Under Test EEC synchronous Ethernet Equipment Clock ESMC Ethernet Synchronization Messaging Channel FDD Frequency Division Duplex FE Fast Ethernet GE Gigabit Ethernet GPS Global Positioning System GSM Global System
35、for Mobile communications HRM Hypothetical Reference Model IP DSLAM IP Digital Subscriber Line Access Multiplexer IP Internet Protocol IWF Interworking Function MAC Medium Access Control Rec. ITU-T G.8263/Y.1363 (02/2012) 3 M-CMTS Modular Cable Modem Termination System METROE METRO Ethernet MPEG Mov
36、ing Picture Experts Group MRTIE Maximum Relative Time Interval Error MSAN Multiservice Access Node MTIE Maximum Time Interval Error NE Network Element NTP Network Time Protocol OLT Optical Line Termination OTN Optical Transport Network PDH Plesiochronous Digital Hierarchy PDV Packet Delay Variation
37、PEC Packet-based Equipment Clock PEC-S-F Packet-based Equipment Clock Slave Frequency PHY Physical (layer) PNT Packet Network Timing PNT-F PNT-Function PRC Primary Reference Clock PSC-A Packet-based Service Clock-Adaptive PSC-D Packet-based Service Clock-Differential PSTN Public Switched Telephone N
38、etwork PTP Precision Time Protocol PTS Packet Timing Signal PTSF Packet Timing Signal Fail QL Quality Level SASE Stand Alone Synchronization Equipment SDH Synchronous Digital Hierarchy SEC SDH Equipment Clock SLA Service Level Agreement SNTP Simple Network Time Protocol SRTS Synchronous Residual Tim
39、e Stamp SSM Synchronization Status Message SSU Synchronization Supply Unit STM Synchronous Transfer Mode TCP Transmission Control Protocol TDD Time Division Duplex TDEV Time Deviation 4 Rec. ITU-T G.8263/Y.1363 (02/2012) TDM PW TDM PseudoWire TDM Time Division Multiplex ToD Time of Day UI Unit Inter
40、val UTC Coordinated Universal Time WCDMA Wideband Code Division Multiple Access 5 Frequency accuracy 5.1 Packet-based equipment clock slave frequency Under free running conditions, the output frequency accuracy of the packet-based equipment clock slave frequency (PEC-S-F) should not be greater than
41、4.6 ppm with regard to a reference traceable to an ITU-T G.811 clock. NOTE The time interval for this accuracy is for further study. Values of one month and one year have been proposed. 6 Noise generation The noise generation of a PEC-S represents the amount of phase noise produced at the output of
42、the PEC-S when there is an ideal input reference packet timing signal. Figure 1 illustrates the testing procedure: +G.8263-Y.1363(12)_F01Ideal input packettiming signal (no PDV)Output physical clock withincertain performance limitsPacket masterclock (PEC-M)FRPacket slave clock(PEC-S) - CUTCUTFRClock
43、 under testFrequency reference+Figure 1 Noise generation testing procedure It should be noted that packet-based equipment clocks slave frequency according to the architecture defined in ITU-T G.8265 (see Figure 1 of ITU-T G.8265) are not cascaded; therefore it would not be required to specify noise
44、generation produced at the output of the clock when there is an ideal input reference signal. In fact the applicable noise generation requirement is already covered by the specifications provided in clause 7 of this Recommendation. However, this specification is provided in order to enable network o
45、perators to measure the noise produced by the PEC-S-F under ideal conditions, separately from the scenarios where packet delay variation (PDV) is applied (PDV noise tolerance testing). The maximum time interval error (MTIE) is measured through an equivalent 10 Hz, first-order, low-pass measurement f
46、ilter, at a maximum sampling time of 1/30 seconds. Rec. ITU-T G.8263/Y.1363 (02/2012) 5 6.1 PEC-S-F When the PEC-S-F is in the locked mode of operation, synchronized to a packet delay variation free reference, and its MTIE output is measured using the same reference as the packet master clock which
47、generated the packet timing signal, the MTIE should have the limits described in Table 1, if the temperature is constant (within 1K). Table 1 Wander generation (MTIE) for PEC-S-F with constant temperature MTIE limit (ns) Observation interval (s) 1000 0.1 1000 (Note) NOTE The maximum applicable obser
48、vation interval is for further study. The resultant requirement is shown by the solid line in Figure 2. When temperature effects are included, the allowance for the total MTIE contribution increases by the values in Table 2. Table 2 Additional wander generation (MTIE) for PEC-S-F with temperature ef
49、fects Additional MTIE allowance (ns) Observation interval (s) 1000 0.1 100 (Note) NOTE The maximum applicable observation interval is for further study. The resultant requirements are shown by the dashed line in Figure 2. G.8263-Y.1363(12)_F02MTIE ns100 00010 0001 0000.1 1 10 100 1 000 10 0001 ppb (for constanttemperature)10 ppb (for variabletemperature)Observation interval (s)Figure 2 Wander generat
