1、 I n t e r n a t i o n a l T e l e c o m m u n i c a t i o n U n i o n ITU-T G.8263/Y.1363 TELECOMMUNICATION STANDARDIZATION SECTOR OF ITU (08/2017) SERIES G: TRANSMISSION SYSTEMS AND MEDIA, DIGITAL SYSTEMS AND NETWORKS Packet over Transport aspects Synchronization, quality and availability targets
2、SERIES Y: GLOBAL INFORMATION INFRASTRUCTURE, INTERNET PROTOCOL ASPECTS, NEXT-GENERATION NETWORKS, INTERNET OF THINGS AND SMART CITIES Internet protocol aspects Transport Timing characteristics of packet-based equipment clocks Recommendation ITU-T G.8263/Y.1363 ITU-T G-SERIES RECOMMENDATIONS TRANSMIS
3、SION SYSTEMS AND MEDIA, DIGITAL SYSTEMS AND NETWORKS INTERNATIONAL TELEPHONE CONNECTIONS 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 G
4、ENERAL CHARACTERISTICS OF INTERNATIONAL CARRIER TELEPHONE SYSTEMS ON RADIO-RELAY OR SATELLITE 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 EQUIP
5、MENTS G.700G.799 DIGITAL NETWORKS G.800G.899 DIGITAL SECTIONS AND DIGITAL LINE SYSTEM 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 TR
6、ANSPORT ASPECTS G.8000G.8999 Ethernet over Transport aspects G.8000G.8099 MPLS over Transport aspects G.8100G.8199 Synchronization, quality and availability targets G.8200G.8299 Service Management G.8600G.8699 ACCESS NETWORKS G.9000G.9999 For further details, please refer to the list of ITU-T Recomm
7、endations. Rec. ITU-T G.8263/Y.1363 (08/2017) i Recommendation ITU-T G.8263/Y.1363 Timing characteristics 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 fun
8、ction (IWF) and other network elements (NEs) as defined in Recommendation ITU-T G.8261/Y.1361. Recommendation ITU-T G.8263/Y.1363 defines the requirements for packet-based equipment clocks. History Edition Recommendation Approval Study Group Unique ID* 1.0 ITU-T G.8263/Y.1363 2012-02-13 15 11.1002/1
9、000/11524 1.1 ITU-T G.8263/Y.1363 (2012) Amd. 1 2013-08-29 15 11.1002/1000/12014 1.2 ITU-T G.8263/Y.1363 (2012) Amd. 2 2014-05-14 15 11.1002/1000/12191 2.0 ITU-T G.8263/Y.1363 2017-08-13 15 11.1002/1000/13320 Keywords Clock, jitter, synchronization, wander. * To access the Recommendation, type the U
10、RL http:/handle.itu.int/ in the address field of your web browser, followed by the Recommendations unique ID. For example, http:/handle.itu.int/11.1002/1000/11830-en. ii Rec. ITU-T G.8263/Y.1363 (08/2017) FOREWORD The International Telecommunication Union (ITU) is the United Nations specialized agen
11、cy 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 issuing Recommendations on them with a view
12、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 topics. The approval of ITU-T Recommendatio
13、ns 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 “Administration“ is used for concisenes
14、s 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) and compliance with the Recommendation
15、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 Recommendation is required of any party. INTEL
16、LECTUAL PROPERTY RIGHTSITU 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 claimed Intellectual Property Rights, whe
17、ther 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 Recommendation. However, implementers are cauti
18、oned 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 2017 All rights reserved. No part of this publication may be reproduced, by any means whatsoever, without the prior written permission of I
19、TU. Rec. ITU-T G.8263/Y.1363 (08/2017) iii Table of Contents Page 1 Scope . 1 2 References . 1 3 Definitions 2 4 Abbreviations and acronyms 2 5 Frequency accuracy 3 5.1 Packet-based equipment clock slave frequency . 3 6 Noise generation . 3 6.1 Packet-based equipment clock slave frequency . 4 7 Pack
20、et delay variation noise tolerance 5 7.1 Packet-based equipment clock slave frequency . 5 8 Long-term phase transient response (holdover) . 5 8.1 Packet-based equipment clock slave frequency . 6 9 Phase response to packet timing interruptions 6 10 Interfaces . 7 Annex A Packet-based clock functional
21、 model 8 Appendix I Packet delay variation noise tolerance testing methodology 9 I.1 Testing set-up for packet delay variation noise tolerance testing . 9 I.2 Test methodologies . 10 Appendix II Considerations on packet rates . 24 Appendix III Considerations on a packet-based equipment clock slave f
22、requency time constant . 25 Appendix IV Variable temperature testing methodology . 26 Bibliography. 27 Rec. ITU-T G.8263/Y.1363 (08/2017) 1 Recommendation ITU-T G.8263/Y.1363 Timing characteristics of packet-based equipment clocks 1 Scope This Recommendation outlines minimum requirements for the tim
23、ing 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. T
24、his 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
25、ferent deployment cases for the packet slave clock as follows. 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 Figu
26、re 3 of ITU-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 hypothetical reference models, HRM-1 and HRM-
27、2, defined in ITU-T G.8261.1. NOTE For long observation intervals, the packet-based equipment clock slave frequency (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 s
28、tudy for the first version of this Recommendation. Other types of networks are outside the 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. T
29、his Recommendation includes clock accuracy, packet delay variation (PDV) noise tolerance, holdover performance and noise generation. The start-up conditions (e.g., variable filtering bandwidth at start-up and stabilization period) are for further study. 2 References The following ITU-T Recommendatio
30、ns and other references contain provisions which, through reference in this text, constitute 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
31、encouraged to investigate the possibility of applying the most recent edition of the 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-alon
32、e document, the status of a Recommendation. ITU-T G.703 Recommendation ITU-T G.703 (2016), Physical/electrical characteristics of hierarchical digital interfaces. 2 Rec. ITU-T G.8263/Y.1363 (08/2017) ITU-T G.810 Recommendation ITU-T G.810 (1996), Definitions and terminology for synchronization netwo
33、rks. ITU-T G.811 Recommendation ITU-T G.811 (1997), Timing characteristics of primary reference clocks. ITU-T G.823 Recommendation 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),
34、 The control of jitter and wander within digital networks which are based on the 1544 kbit/s hierarchy. ITU-T G.8260 Recommendation ITU-T G.8260 (2015), Definitions and terminology for synchronization in packet networks. ITU-T G.8261 Recommendation ITU-T G.8261/Y.1361 (2008), Timing and synchronizat
35、ion aspects in packet networks. ITU-T G.8261.1 Recommendation ITU-T G.8261.1/Y.1361.1 (2012), Packet delay variation network limits applicable to packet-based methods (Frequency synchronization). ITU-T G.8265 Recommendation ITU-T G.8265/Y.1365 (2010), Architecture and requirements for packet-based f
36、requency delivery. ITU-T G.8265.1 Recommendation ITU-T G.8265.1/Y.1365.1 (2014), Precision time protocol telecom profile for frequency synchronization. 3 Definitions Definitions related to synchronization are contained in ITU-T G.810 and ITU-T G.8260. 4 Abbreviations and acronyms For the purposes of
37、 this Recommendation, the following abbreviations and acronyms are used: CBR Constant Bit Rate CES Circuit Emulation Service CUT Clock Under Test EEC synchronous Ethernet Equipment Clock FPP Floor Packet Percentageool FR Frequency Reference GM Grandmaster HRM Hypothetical Reference Model IWF Interwo
38、rking Function MAFE Maximum Average Frequency Error MTIE Maximum Time Interval Error NE Network Element PDV Packet Delay Variation PEC-M Packet-based Equipment Clock Master PEC-S Packet-based Equipment Clock Slave Rec. ITU-T G.8263/Y.1363 (08/2017) 3 PEC-S-F Packet-based Equipment Clock Slave Freque
39、ncy PHY Physical (layer) PRC Primary Reference Clock PSD Power Spectral Density PTP Precision Time Protocol PTS Packet Timing Signal PTSF Packet Timing Signal Fail SEC Synchronous digital hierarchy Equipment Clock SSM Synchronization Status Message TDEV Time Deviation 5 Frequency accuracy 5.1 Packet
40、-based equipment clock slave frequency Under free running conditions, the output frequency accuracy of the PEC-S-F should not be greater than 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 1 month and 1 y
41、ear have been proposed. 6 Noise generation The noise generation of a packet-based equipment clock slave (PEC-S) represents the amount of phase noise produced at the output of the PEC-S when there is an ideal input reference packet timing signal (PTS). Figure 1 illustrates the testing procedure: +G .
42、 8 2 6 3 - Y . 1 3 6 3 ( 1 2 ) _ F 0 1I de a l i np ut p a c ke tt i m i ng s i gn a l ( no PD V )O ut pu t p hy s i c a l c l oc k w i t hi nc e r t a i n pe r f or m a nc e l i m i t sP a c ke t m a s t e rc l oc k ( P E C - M )FRP a c ke t s l a ve c l oc k( P E C - S ) - C U TC U TFRC l oc k un
43、de r t e s tF r e qu e nc y r e f e r e nc e+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, specification of noise gene
44、ration produced at the output of the clock is not required 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 ena
45、ble network operators to measure the noise produced by the PEC-S-F under ideal conditions, separately from the scenarios where 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 filter, at a
46、maximum sampling time of 1/30 s. 4 Rec. ITU-T G.8263/Y.1363 (08/2017) 6.1 Packet-based equipment clock slave frequency When the PEC-S-F is in the locked mode of operation, synchronized to a PDV free reference, and its MTIE output is measured using the same reference as the packet master clock which
47、generated the PTS, the MTIE should have the limits described in Table 1, if the temperature is constant (within 1 K). Table 1 Wander generation (maximum time interval error) for packet-based equipment clock slave frequency with constant temperature MTIE limit (ns) Observation interval (s) 1 000 0.1
48、1 000 (Note) NOTE The maximum applicable observation interval is for further study. The resultant requirement is shown by the solid line in Figure 2. Figure 2 Wander generation (maximum time interval error) for packet-based equipment clock slave frequency NOTE For long observation intervals, the PEC
49、-S-F is expected to compensate for temperature variation effects; therefore, the output of the PEC-S-F will converge to the 1 ns/s slope. When temperature effects are included, the limits are given in Table 2. Table 2 Wander generation (maximum time interval error) for packet-based equipment clock slave frequency with temperature effects Additional MTIE allowance (ns) Observation interval (s) 10
