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.8273.2/Y.1368.2 TELECOMMUNICATION STANDARDIZATION SECTOR OF ITU Amendment 2 (08/2015) SERIES G: TRANSMISSION SYSTEMS AND MEDIA, DIGITAL SYSTEMS AND NETWORKS Packet over Transport aspects Synchronization, quality and avail
2、ability targets SERIES Y: GLOBAL INFORMATION INFRASTRUCTURE, INTERNET PROTOCOL ASPECTS AND NEXT-GENERATION NETWORKS Internet protocol aspects Transport Timing characteristics of telecom boundary clocks and telecom time slave clocks Amendment 2 Recommendation ITU-T G.8273.2/Y.1368.2 (2014) Amendment
3、2 ITU-T G-SERIES RECOMMENDATIONS TRANSMISSION 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 TELEPHO
4、NE SYSTEMS ON METALLIC LINES G.300G.399 GENERAL 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 CHARACTE
5、RISTICS G.600G.699 DIGITAL TERMINAL EQUIPMENTS 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 GE
6、NERIC ASPECTS G.7000G.7999 PACKET OVER TRANSPORT 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,
7、 please refer to the list of ITU-T Recommendations. Rec. ITU-T G.8273.2/Y.1368.2 (2014)/Amd.2 (08/2015) i Recommendation ITU-T G.8273.2/Y.1368.2 Timing characteristics of telecom boundary clocks and telecom time slave clocks Amendment 2 Summary Amendment 2 to Recommendation ITU-T G.8273.2/Y.1368.2 (
8、2014) introduces the following changes: adds Recommendation ITU-T G.703 as a normative reference in clause 2 adds TDEV requirements in clauses 7.1.2 and C.2.1.2 adds note in clauses 7.3.1 and C.2.3.1 replaces clause 7.4.2 and subclauses 7.4.2.1 and 7.4.2.2 replaces Annex B replaces clause C.2.4.2 an
9、d subclauses C.2.4.2.1 and C.2.4.2.2 adds clause C.2.6 replaces Appendix II removes Appendices IV and V. History Edition Recommendation Approval Study Group Unique ID* 1.0 ITU-T G.8273.2/Y.1368.2 2014-05-14 15 11.1002/1000/12196 1.1 ITU-T G.8273.2/Y.1368.2 (2014) Amd. 1 2015-01-13 15 11.1002/1000/12
10、395 1.2 ITU-T G.8273.2/Y.1368.2 (2014) Amd. 2 2015-08-13 15 11.1002/1000/12543 _ * To access the Recommendation, type the URL 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. IT
11、U-T G.8273.2/Y.1368.2 (2014)/Amd.2 (08/2015) FOREWORD The International Telecommunication Union (ITU) 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 permanen
12、t organ of ITU. ITU-T is responsible for studying technical, operating and tariff questions and issuing 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
13、 the topics for study by the ITU-T study groups which, in turn, produce Recommendations on these topics. 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
14、 are prepared on a collaborative basis with ISO and IEC. NOTE In this Recommendation, the expression “Administration“ is used for conciseness to indicate both a telecommunication administration and a recognized operating agency. Compliance with this Recommendation is voluntary. However, the Recommen
15、dation may contain certain mandatory provisions (to ensure, e.g., interoperability or applicability) and 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
16、used to express requirements. The use of such words does not suggest that compliance with the Recommendation is required of any party. INTELLECTUAL PROPERTY RIGHTSITU draws attention to the possibility that the practice or implementation of this Recommendation may involve the use of a claimed Intell
17、ectual Property Right. ITU takes no position concerning the evidence, validity or applicability of claimed 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 not receive
18、d notice of intellectual property, protected by patents, which may be required to implement this Recommendation. 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/.
19、 ITU 2015 All rights reserved. No part of this publication may be reproduced, by any means whatsoever, without the prior written permission of ITU. Rec. ITU-T G.8273.2/Y.1368.2 (2014)/Amd.2 (08/2015) 1 Recommendation ITU-T G.8273.2/Y.1368.2 Timing characteristics of telecom boundary clocks and telec
20、om time slave clocks Amendment 2 1) Clause 2, References Add the following references in clause 2: ITU-T G.703 Recommendation ITU-T G.703 (2001), Physical/electrical characteristics of hierarchical digital interfaces. ITU-T G.8273 Recommendation ITU-T G.8273/Y.1368 (2013), Framework of phase and tim
21、e clocks. 2) Clause 7.1.2, Dynamic time error low-pass filtered noise generation (dTEL) Renumber NOTE 2 as NOTE, and replace the following text: The applicable time deviation (TDEV) is for further study. NOTE 1 This Recommendation is expected to include a normative TDEV mask similar to that containe
22、d in Appendix IV in order to constrain the frequency distribution of the noise. It is strongly suggested that implementations based on this Recommendation limit dynamic time error noise generation to meet at least the requirements of the TDEV mask contained in Appendix IV. With: For a Class A or Cla
23、ss B T-BC containing an EEC-Option 1 clock and operating in locked mode synchronized to both a wander-free time reference at the PTP input and a wander-free frequency reference at the SyncE/SDH input, the TDEV at the PTP and 1 PPS outputs, measured through a first-order low-pass filter with bandwidt
24、h of 0.1 Hz, should meet the limits in Table 7-5 under constant temperature (within 1K). Table 7-5 Dynamic time error noise generation (TDEV) for T-BC with constant temperature TDEV limit ns Observation interval s 4 m 1000 (Notes 1, 2) NOTE 1 The minimum value m is determined by packet rate of 16 pa
25、cket per second (m=1/16) or 1 PPS signal (m=1) NOTE 2 The values in this table are valid for 1 PPS, 1 GbE and 10 GbE interfaces. Interfaces for rates above 10 GbE are for further study. 3) Clause 7.3.1, PTP to PTP noise transfer Renumber NOTE as NOTE 1 and add the following note after the newly numb
26、ered note: NOTE 2 At all permissible noise input levels, the gain peaking of 0.1dB from PTP to PTP, or 0.2dB from physical layer frequency to PTP is far lower than the permitted noise generation of the clock at the PTP and 1pps outputs. Therefore it may be difficult to verify the gain peaking at eit
27、her the PTP or 1pps outputs 2 Rec. ITU-T G.8273.2/Y.1368.2 (2014)/Amd.2 (08/2015) 4) Clause 7.4.2, Holdover performance Replace clause 7.4.2 and subclauses 7.4.2.1 and 7.4.2.2 with the following text: 7.4.2 Holdover performance When a T-BC loses its PTP input references, it enters the phase/time hol
28、dover state. Under these circumstances, the T-BC may either rely on the holdover of a local oscillator, or on a physical layer frequency assistance reference traceable to a primary reference clock (PRC), or on a combination of both. This requirement reflects the performance of the clock in cases whe
29、n the PTP input is ideal followed by disconnection of the PTP input. For the case of phase/time holdover requirements based on physical layer frequency (T-BC performance with physical layer frequency assistance during loss of PTP input reference), the frequency physical layer input is ideal. This re
30、quirement bounds the maximum excursions in the output timing signal. Additionally, it restricts the accumulation of the phase movement during input signal impairments or internal disturbances. 7.4.2.1 T-BC holdover The phase/time holdover requirements applicable to a T-BC are for further study. 7.4.
31、2.2 T-BC performance with physical layer frequency assistance during loss of PTP input reference The phase/time output will be measured through a first order low-pass filter with bandwidth of 0.1 Hz. The phase/time performance during loss of PTP input reference requirements based on physical layer f
32、requency applicable to a T-BC under constant temperature conditions is shown in Table 7-6. Under constant temperature conditions the maximum observation interval is 1000 seconds. Table 7-6 Performance allowance during loss of PTP input (MTIE) for T-BC with constant temperature MTIE limit ns Observat
33、ion interval s 22 + 40 0.1 1 100 22+ 25.25 0.2 100 1000 The phase/time performance during loss of PTP input reference requirements based on physical layer frequency applicable to a T-BC under variable temperature conditions is shown in Table 7-7. Under variable temperature conditions the maximum obs
34、ervation interval is 10000 seconds. Table 7-7 Performance allowance during loss of packet signal input (MTIE) for T-BC with variable temperature MTIE limit ns Observation interval s 22 + 40 0.1 + 0.5 1 100 72+ 25.25 0.2 100 1000 for further study 1000 10000 5) Annex B Replace Annex B with the follow
35、ing text: Rec. ITU-T G.8273.2/Y.1368.2 (2014)/Amd.2 (08/2015) 3 Annex B Control of transient due to rearrangements in the synchronous Ethernet network (This annex forms an integral part of this Recommendation.) A T-BC shall properly limit the generation of phase/time error due to a rearrangement of
36、the physical layer frequency transport (e.g., SyncE, SDH) by using ingress QL information (e.g., ESMC message). In the worst-case, the input SyncE frequency will experience a re-arrangement transient as detailed in Figure 12 of ITU-T G.8262 and Figure 12 of ITU-T G.813. When a SyncE/SDH rearrangemen
37、t occurs, the T-BC may experience an initial output transient when the SyncE/SDH loses PRC-traceability and a second output transient when or after the SyncE/SDH again becomes PRC-traceable. The absolute value of T-BC output phase error shall meet the following requirements when these transients occ
38、ur: a) The T-BC output phase error at the PTP and 1 PPS outputs shall not exceed the mask of Figure B.1 and Table B.1 below. NOTE The mask of Figure B.1 assumes that the SyncE signal loses PRC traceability at time zero and becomes traceable again at 15 s (i.e., the SyncE transient is completed by 15
39、 s). The re-establishment of PRC-traceability will be earlier in smaller rings; the exact time depends on the number of EECs/SECs in the ring and the exact values of the SSM message delays. The mask is extended to 50 s to allow time for the T-BC to either re-acquire the SyncE signal or begin using t
40、he T-BC filter again after PRC-traceability has been re-established. The SyncE transient test is done without a measurement filter and should exclude any constant time error. Ideally, the absolute value of unfiltered dTE is desired. See Appendix II for background on the assumptions and derivations f
41、or the masks of Figure B.1 and Table B.1. Figure B.1 Phase error limit for output phase error transient after the start of the SyncE/SDH rearrangement 4 Rec. ITU-T G.8273.2/Y.1368.2 (2014)/Amd.2 (08/2015) Table B.1 T-BC output phase transient mask for output transient after start of SyncE/SDH rearra
42、ngement (at and just after loss of PRC-traceability by the SyncE/SDH signal) Time S after start of SyncE/SDH rearrangement (s) T-BC output absolute phase error (ns) 0 S 2.4 200 + 50S 2.4 S 14.25 50 + 270 e 2(0.05)(S 2.4) 14.25 S 15.5 180 15.5 S 25.5 115 25.5 S 50 50 + 65 e 2(0.05)(S 25.5) NOTE As pe
43、r ITU-T G.8264 SSM might be disabled by the operator. The impact on the mitigation of time error due to SyncE/SDH rearrangement when not using SSM is under the responsibility of the operator and is for further study. 6) Clause C.2.1.2, Dynamic time error low-pass filtered noise generation (dTEL) i)
44、Replace the following text: The applicable TDEV is for further study. NOTE 1 This Recommendation is expected to include a normative TDEV mask similar to that contained in Appendix V in order to constrain the frequency distribution of the noise. It is strongly suggested that implementations based on
45、this recommendation limit dynamic time error noise generation to meet at least the requirements of the TDEV mask contained in Appendix V. With: For a Class A or Class B T-TSC containing an EEC-Option 1 clock, and operating in locked mode synchronized to both a wander-free time reference at the PTP i
46、nput and a wander-free frequency reference at the SyncE/SDH input, the TDEV at the 1 PPS output, measured through a first-order low-pass filter with bandwidth of 0.1 Hz, should meet the limits in Table C.5 under constant temperature (within 1K). Table C.5 Dynamic time error noise generation (TDEV) f
47、or T-TSC with constant temperature TDEV limit ns Observation interval s 4 1 1000 ii) Renumber NOTE 2 as NOTE 7) Clause C.2.3.1, PTP to 1 PPS noise transfer Renumber NOTE as NOTE 1 and add the following note after the newly numbered note: NOTE 2 At all permissible noise input levels, the gain peaking
48、 of 0.1 dB from PTP to 1 PPS, or 0.2 dB from physical layer frequency to 1 PPS is far lower than the permitted noise generation of the clock at the PTP and 1 pps outputs. Therefore it may be difficult to verify the gain peaking at either the PTP or 1 pps outputs. 8) Clause C.2.4.2, Holdover performa
49、nce Replace clause C.2.4.2 and subclauses C.2.4.2.1 and C.2.4.2.2 with the following text: Rec. ITU-T G.8273.2/Y.1368.2 (2014)/Amd.2 (08/2015) 5 C.2.4.2 Holdover performance When a T-TSC loses its PTP input references, it enters the phase/time holdover state. Under these circumstances, the T-TSC may either rely on the holdover of a local oscillator, or on a physical layer frequency assistance refere
