1、INTERNATIONAL TELECOMMUNICATION UNION)45G134 TELECOMMUNICATIONSTANDARDIZATION SECTOROF ITU(08/96)SERIES G: TRANSMISSION SYSTEMS AND MEDIADigital transmission systems Digital networks Designobjectives for digital networks$EFINITIONSG0ANDG0TERMINOLOGYG0FORG0SYNCHRONIZATIONNETWORKSITU-T Recommendation
2、G.810(Previously CCITT Recommendation)ITU-T G-SERIES RECOMMENDATIONS42!.3-)33)/.G03934%-3G0!.$G0-%$)!For further details, please refer to ITU-T List of Recommendations.INTERNATIONAL TELEPHONE CONNECTIONS AND CIRCUITS G.100G.199).4%2.!4)/.!,G0!.!,/5%G0#!22)%2G03934%-GENERAL CHARACTERISTICS COMMON TO
3、ALL ANALOGUE CARRIER-TRANSMISSION SYSTEMSG.200G.299INDIVIDUAL CHARACTERISTICS OF INTERNATIONAL CARRIER TELEPHONESYSTEMS ON METALLIC LINESG.300G.399GENERAL CHARACTERISTICS OF INTERNATIONAL CARRIER TELEPHONESYSTEMS ON RADIO-RELAY OR SATELLITE LINKS AND INTERCONNECTIONWITH METALLIC LINESG.400G.449COORD
4、INATION OF RADIOTELEPHONY AND LINE TELEPHONY G.450G.49942!.3-)33)/.G0-%$)!G0#(!2!#4%2)34)#3$)4!,G042!.3-)33)/.G03934%-3TERMINAL EQUIPMENTS G.700G.799DIGITAL NETWORKS G.800G.899General aspects G.800G.809$ESIGNG0OBJECTIVESG0FORG0DIGITALG0NETWORKS Quality and availability targets G.820G.829Network capa
5、bilities and functions G.830G.839SDH network characteristics G.840G.899DIGITAL SECTIONS AND DIGITAL LINE SYSTEM G.900G.999DEFINITIONS AND TERMINOLOGY FOR SYNCHRONIZATION NETWORKSSummaryThis Recommendation provides definitions and abbreviations used in timing and synchronizationRecommendations.Source
6、ITU-T Recommendation G.810 was revised by ITU-T Study Group 13 (1993-1996) and wasapproved under the WTSC Resolution No. 1 procedure on the 27th of August 1996.KeywordsClock Performance, Jitter Performance, SDH, Synchronization network, Wander Performance.ITU-T RECOMMENDATION G.810ii Recommendation
7、G.810 (08/96)FOREWORDITU (International Telecommunication Union) is the United Nations Specialized Agency in the field oftelecommunications. The ITU Telecommunication Standardization Sector (ITU-T) is a permanent organ ofthe ITU. The ITU-T is responsible for studying technical, operating and tariff
8、questions and issuingRecommendations on them with a view to standardizing telecommunications on a worldwide basis.The World Telecommunication Standardization Conference (WTSC), which meets every four years,establishes the topics for study by the ITU-T Study Groups which, in their turn, produce Recom
9、mendationson these topics.The approval of Recommendations by the Members of the ITU-T is covered by the procedure laid down inWTSC Resolution No. 1 (Helsinki, March 1-12, 1993).In some areas of information technology which fall within ITU-Ts purview, the necessary standards areprepared on a collabor
10、ative basis with ISO and IEC.NOTEIn this Recommendation, the expression “Administration” is used for conciseness to indicate both atelecommunication administration and a recognized operating agency. ITU 1997All rights reserved. No part of this publication may be reproduced or utilized in any form or
11、 by any means,electronic or mechanical, including photocopying and microfilm, without permission in writing from the ITU.Recommendation G.810 (08/96) iiiCONTENTSPage1 Scope. 12 References. 13 Abbreviations 14 Definitions 24.1 General definitions 24.2 Definitions related to clock equipments . 34.3 De
12、finitions related to synchronization networks 44.4 Definitions related to clock modes of operation (applicable to slave clocks) 54.5 Definitions related to clock characterization 54.6 SDH specific definitions. 85 Description of phase variation components 86 Impairments caused by phase variation 86.1
13、 Types of impairments . 86.1.1 Errors . 86.1.2 Degradation of digitally encoded analogue information . 86.1.3 Slips . 86.2 Control of impairments. 96.2.1 Errors . 96.2.2 Degradation of digitally encoded analogue signals. 96.2.3 Slips . 97 Purpose of phase variation specifications. 97.1 Jitter 97.2 W
14、ander 108 Structure of synchronization networks . 108.1 Synchronization modes. 108.2 Synchronization networks. 109 Measurement configurations. 119.1 Synchronized clock measurement configuration 119.2 Independent clock measurement configuration 11Appendix I Mathematical models of timing signals . 12I
15、.1 Total instantaneous phase model of an ideal timing signal 12I.2 Total instantaneous phase model of actual timing signals 12I.3 Time error model 13iv Recommendation G.810 (08/96)PageAppendix II Definitions and properties of frequency and time stability quantities 13II.1 Allan deviation (ADEV). 14I
16、I.2 Modified Allan deviation (MDEV) 15II.3 Time deviation (TDEV) 16II.4 Root mean square Time Interval Error (TIErms) 18II.5 Maximum Time Interval Error (MTIE) 19Recommendation G.810 (08/96) 1Recommendation G.810DEFINITIONS AND TERMINOLOGY FOR SYNCHRONIZATION NETWORKS(Melbourne, 1980; revised in 199
17、6)1 ScopeThis Recommendation provides definitions and abbreviations used in timing and synchronizationRecommendations. It also provides background information on the need to limit phase variation andthe impairments on digital systems.2 ReferencesThe following Recommendations and other references con
18、tain provisions which, through referencein this text, constitute provisions of this Recommendation. All Recommendations are subject torevision; all users of this Recommendation are therefore encouraged to investigate the possibility ofapplying the most recent edition of the Recommendations and other
19、 references listed below. A list ofthe currently valid ITU-T Recommendations is regularly published.1 ITU-T Recommendation G.707 (1996), Network node interface for the Synchronous DigitalHierarchy (SDH).2 CCITT Recommendation G.811 (1988), Timing requirements at the outputs of primaryreference clock
20、s suitable for plesiochronous operation of international digital links.3 CCITT Recommendation G.812 (1988), Timing requirements at the outputs of slave clockssuitable for plesiochronous operation of international digital links.4 ITU-T Recommendation G.813 (1996), Timing characteristics for SDH equip
21、ment slaveclocks (SEC).5 CCITT Recommendation G.822 (1988), Controlled slip rate objectives on an internationaldigital connection.6 ITU-T Recommendation G.823 (1993), The control of jitter and wander within digitalnetworks which are based on the 2048 kbit/s hierarchy.7 ITU-T Recommendation G.824 (19
22、93), The control of jitter and wander within digitalnetworks which are based on the 1544 kbit/s hierarchy.8 ITU-T Recommendation G.825 (1993), The control of jitter and wander within digitalnetworks which are based on the Synchronous Digital Hierarchy (SDH).3 AbbreviationsFor the purposes of timing
23、and synchronization Recommendations, the following abbreviationsapply:ADEV Allan DeviationAIS Alarm Indication SignalAP Access PointCUT Clock Under TestFFM Flicker Frequency ModulationFPM Flicker Phase Modulation2 Recommendation G.810 (08/96)MC Master ClockMDEV Modified Allan DeviationMRTIE Maximum
24、Relative Time Interval ErrorMST Multiplex Section TerminalMTIE Maximum Time Interval ErrorNE Network ElementPDH Plesiochronous Digital HierarchyPRC Primary Reference ClockPSTN Public Switched Telephone NetworkRWFM Random Walk Frequency ModulationSASE Stand Alone Synchronization EquipmentSC Slave Clo
25、ckSDH Synchronous Digital HierarchySE Synchronization ElementSEC SDH Equipment ClockSETS SDH Equipment Timing SourceSTM Synchronous Transport ModuleSSU Synchronization Supply UnitTDEV Time DeviationTIE Time Interval ErrorTIErms root mean square Time Interval ErrorTVAR Time VarianceUI Unit IntervalUI
26、p-p Unit Interval peak-to-peakUTC Coordinated Universal TimeWFM White Frequency ModulationWPM White Phase Modulation4 DefinitionsFor the purposes of timing and synchronization Recommendations, the following definitions apply.4.1 General definitions4.1.1 alignment jitter: The short-term variations be
27、tween the optimum sampling instants of adigital signal and sampling clock derived from it.4.1.2 bilateral: A synchronization link where the corrective action to maintain locking is active atboth ends of the link.4.1.3 frequency departure: An underlying offset in the long-term frequency of a timing s
28、ignalfrom its ideal frequency.4.1.4 network synchronization: A generic concept that depicts the way of distributing a commontime and/or frequency to all elements in a network.Recommendation G.810 (08/96) 34.1.5 single ended synchronization: A method of synchronizing a specified synchronization nodew
29、ith respect to another synchronization node, in which synchronization information at the specifiednode is derived from the phase difference between the local clock and the incoming digital signalfrom the other node.4.1.6 synchronization chain: An active interconnection of synchronization nodes and l
30、inks.4.1.7 synchronization reference chain: A specific synchronization chain to form the basis forsimulations of jitter and wander in the synchronization network.4.1.8 slip: The repetition or deletion of a block of bits in a synchronous or plesiochronous bitstream due to a discrepancy in the read an
31、d write rates at a buffer.4.1.9 standard frequency: A frequency with a known relationship to a frequency standard.4.1.10 time: Time is used to specify an instant (time of the day) or as a measure of time interval.NOTE The words time or timing, when used to describe synchronization networks, usually
32、refer tothe frequency signals used for synchronization or measurement.4.1.11 time scale: A system of unambiguous ordering of events.NOTE This could be a succession of equal time intervals, with accurate references of the limits ofthese time intervals, which follow each other without any interruption
33、 since a well-defined origin. A timescale allows to date any event. For example, calendars are time scales. A frequency signal is not a time scale(every period is not marked and dated). For this reason “UTC frequency“ must be used instead of “UTC“.4.1.12 (timing) jitter: The short-term variations of
34、 the significant instants of a timing signal fromtheir ideal positions in time (where short-term implies that these variations are of frequency greaterthan or equal to 10 Hz).4.1.13 unilateral: A synchronization link where the corrective action to maintain locking is onlyactive at one end of the lin
35、k.4.1.14 UTC: The time scale, maintained by the Bureau International des Poids et Mesures (BIPM)and the International Earth Rotation Service (IERS), which forms the basis of a coordinateddissemination of standard frequencies and time signal.NOTE The reference frequency for network synchronization is
36、 the frequency which generates theUTC time scale. It is therefore preferable to use the words “UTC frequency“ instead of “UTC“.4.1.15 wander: The long-term variations of the significant instants of a digital signal from theirideal position in time (where long-term implies that these variations are o
37、f frequency less than10 Hz).NOTE For the purposes of this Recommendation and related Recommendations, this definition doesnot include wander caused by frequency offsets and drifts.4.2 Definitions related to clock equipments4.2.1 clock: An equipment that provides a timing signal.NOTE The word “clock“
38、 generally means, when used for synchronization networks, the generator ofthe frequencies which will be used to synchronize the network.4.2.2 frequency standard: A generator, the output of which is used as a frequency reference.4.2.3 master clock: A generator which generates an accurate frequency si
39、gnal for the control ofother generators.4.2.4 node clock: A clock distributing synchronization to one or more synchronized equipment.4 Recommendation G.810 (08/96)4.2.5 primary reference clock (PRC): A reference frequency standard that provides a referencefrequency signal compliant with Recommendati
40、on G.811.4.2.6 slave clock: A clock whose timing output is phase-locked to a reference timing signalreceived from a higher quality clock.4.2.7 stand alone synchronization equipment (SASE): The stand alone implementation of thelogical SSU function, which incorporates its own management function.4.2.8
41、 synchronization supply unit (SSU): A logical function for frequency reference selection,processing and distribution, having the frequency characteristics given in Recommendation G.812.4.3 Definitions related to synchronization networks4.3.1 asynchronous mode: A mode where clocks are intended to ope
42、rate in free running mode.4.3.2 local node: A synchronous network node which interfaces directly with customerequipment.4.3.3 master slave mode: A mode where a designated master clock is used as a frequencystandard which is disseminated to all other clocks which are slaved to the master clock.4.3.4
43、mutually synchronized mode: A mode where all clocks exert a degree of control on eachother.4.3.5 plesiochronous mode: A mode where the essential characteristic of time scales or signalssuch that their corresponding significant instants occur at nominally the same rate, any variation inrate being con
44、strained within specified limits.4.3.6 pseudo-synchronous mode: A mode where all clocks have a long-term frequency accuracycompliant with a primary reference clock as specified in Recommendation G.811 under normaloperating conditions. Not all clocks in the network will have timing traceable to the s
45、ame PRC.4.3.7 synchronization element: A clock providing timing services to connected networkelements. This would include clocks conforming to Recommendations G.811, G.812 and G.813.4.3.8 synchronization link: A link between two synchronization nodes over whichsynchronization is transmitted.4.3.9 sy
46、nchronous network: A network where all clocks have the same long-term accuracy undernormal operating conditions.4.3.10 synchronization network: A network to provide reference timing signals. In general, thestructure of a synchronization network comprises synchronization network nodes connected bysyn
47、chronization links.4.3.11 synchronization network node: A group of equipment in a single physical location whichis directly timed by a node clock.NOTE A physical location may contain more than one synchronization network node.4.3.12 synchronization sink: The destination of timing in a synchronizatio
48、n trail.4.3.13 synchronization source: The source of timing in a synchronization trail.4.3.14 synchronization traceability: A series of synchronization elements and synchronizationtrails, normally within a single SDH or PDH equipment domain.4.3.15 synchronization trail: The complete connectivity bet
49、ween synchronization element and anetwork element, or between two synchronization elements.Recommendation G.810 (08/96) 54.3.16 transit node: A synchronous network node which interfaces with other nodes and does notdirectly interface with customer equipment.4.4 Definitions related to clock modes of operation (applicable to slave clocks)4.4.1 free running mode: An operating condition of a clock, the output signal of which isstrongly influenced by the oscillating element and not controlled by servo phase-locking techniq
