Recommendation ITU-T G.781 (01/2024) Synchronization layer functions for frequency synchronization based on the physical layer
Summary
History
FOREWORD
Table of Contents
1 Scope
2 References
3 Definitions
     3.1 Terms defined elsewhere
     3.2 Terms defined in this Recommendation
4 Abbreviations and acronyms
5 Synchronization principles
     5.1 Network synchronization
     5.2 Synchronization distribution trails
     5.3 Synchronization interfaces
          5.3.1 Overview
               5.3.1.1 Option I synchronization networking
               5.3.1.2 Option II synchronization networking
               5.3.1.3 Option III synchronization networking
          5.3.2 STM-N
          5.3.3 2 Mbit/s
          5.3.4 2 MHz
          5.3.5 34 Mbit/s and 140 Mbit/s with 125 (s frame structure
          5.3.6 1.5 Mbit/s
          5.3.7 64 kHz
          5.3.8 6312 kHz
          5.3.9 100 Mbit/s, 1 Gbit/s, 10 Gbit/s, 40 Gbit/s, 100 Gbit/s
          5.3.10 OTN interfaces without OSC
          5.3.11 OTN interfaces with OSC
          5.3.12 FlexE interfaces
          5.3.13 MTN interfaces
     5.4 Clock-source quality-level
          5.4.1 Clock-source quality-level definitions
               5.4.1.1 Option I synchronization networking
               5.4.1.2 Option II synchronization networking
               5.4.1.3 Option III synchronization networking
               5.4.1.4 Squelching
          5.4.2 Hierarchy of clock-source quality-levels (QL) or (CS_QL)
               5.4.2.1 Option I synchronization networking
               5.4.2.2 Option II synchronization networking
               5.4.2.3 Option III synchronization networking
          5.4.3 Forcing and defaulting of clock-source quality-levels
               5.4.3.1 Option I synchronization networking
               5.4.3.2 Option II synchronization networking
               5.4.3.3 Option III synchronization networking
          5.4.4 Application of quality level "Unknown"
               5.4.4.1 Option I synchronization networking
               5.4.4.2 Option II synchronization networking
               5.4.4.3 Option III synchronization networking
          5.4.5 Application of quality level "provisioned"
     5.5 Synchronization status messages (SSMs), extended QL TLV, and timing marker (TM) channels
          5.5.1 SSM, eSSM, and TM message sets
               5.5.1.1 Option I synchronization networking
               5.5.1.2 Option II synchronization networking
               5.5.1.3 Option III synchronization networking
          5.5.2 SSM and TM code word generation
               5.5.2.1 Option I synchronization networking
               5.5.2.2 Option II synchronization networking
               5.5.2.3 Option III synchronization networking
          5.5.3 SSM and TM code word interpretation
               5.5.3.1 Option I synchronization networking
               5.5.3.2 Option II synchronization networking
               5.5.3.3 Option III synchronization networking
     5.6 Selection process
     5.7 Signal fail
     5.8 Hold-off time
     5.9 Wait-to-restore time
     5.10 Synchronization source priorities
     5.11 External commands
          5.11.1 External commands per nominated synchronization source
               5.11.1.1 Set_Lockout#p command
               5.11.1.2 Clear_Lockout#p command
          5.11.2 External commands per selection process
               5.11.2.1 Clear command
               5.11.2.2 Forced switch #p command
               5.11.2.3 Manual switch #p command
     5.12 Automatic reference selection process
          5.12.1 QL-enabled mode
          5.12.2 QL-disabled mode
     5.13 Timing loop prevention
          5.13.1 Station clock input used as a source for station clock output
          5.13.2 Between NEs with SEC type clocks
          5.13.3 Between NEs with an SEC clock and an NE or SASE/BITS with an SSU/ST2 clock and only one link
               5.13.3.1 QL/SSM processing not supported between SASE/BITS and NE
               5.13.3.2 QL/SSM processing supported between SASE/BITS and NE (option II)
          5.13.4 Between NEs with an SEC clock and an NE or SASE/BITS with an SSU clock and several links
     5.14 Delay times for NEs with SEC/ST3/SIC
          5.14.1 Delay times for NEs with SEC in option I and III synchronization networks
          5.14.2 Delay times for NEs with ST3/SMC in option II synchronization networks
     5.15 Delay times for NEs with SSU/ST2 or for SASE/BITS
     5.16 Synchronization layer functions
     5.17 Overview of the processes performed within the atomic functions
     5.18 Interworking between option I, II and III synchronization networks
6 Synchronization distribution layer atomic functions
     6.1 SD connection function (SD_C)
     6.2 SD trail termination functions
          6.2.1 SD trail termination source function (SD_TT_So)
          6.2.2 SD trail termination sink function (SD_TT_Sk)
     6.3 SD adaptation functions
          6.3.1 SD layer to NS layer SEC quality adaptation source function (SD/NS-SEC-A_So)
          6.3.2 SD layer to NS layer SEC quality adaptation sink function (SD/NS-SEC_A_Sk)
          6.3.3 SD layer to NS layer adaptation source function (SD/NS_A_So)
7 Network synchronization layer atomic functions
     7.1 NS_connection functions (NS_C)
8 Transport layer to SD layer atomic functions
     8.1 STM-n multiplex section adaptation functions
          8.1.1 STM-N multiplex section to SD adaptation source (MSn/SD_A_So)
          8.1.2 STM-N multiplex section to SD adaptation sink (MSn/SD_A_Sk)
     8.2 Pqs adaptation functions
          8.2.1 Pqs to SD adaptation source (Pqs/SD_A_So)
          8.2.2 Pqs to SD adaptation sink (Pqs/SD_A_Sk)
     8.3 P12s layer adaptation functions
          8.3.1 P12s layer adaptation source functions
               8.3.1.1 Type 1 P12s to SD adaptation source for station clock output supporting SSM (P12s/SD-sc-1_A_So)
               8.3.1.2 Type 2 P12s to SD adaptation source for station clock output port not supporting SSM (P12s/SD-sc-2_A_So)
          8.3.2 P12s layer adaptation sink functions
               8.3.2.1 Type 1 P12s to SD adaptation sink for traffic input port (P12s/SD-tf_A_Sk)
               8.3.2.2 Type 2 P12s to SD adaptation sink for station clock input port (P12s/SD-sc_A_Sk)
     8.4 T12 layer adaptation functions
          8.4.1 T12 to SD adaptation source (T12/SD_A_So)
          8.4.2 T12 to SD adaptation sink (T12/SD_A_Sk)
     8.5 P11s layer adaptation functions
          8.5.1 P11s to SD adaptation source (P11s/SD_A_So)
          8.5.2 P11s to SD adaptation sink (P11s/SD_A_Sk)
     8.6 T01 layer adaptation functions
          8.6.1 T01 to SD adaptation source (T01/SD_A_So)
          8.6.2 T01 to SD adaptation sink (T01/SD_A_Sk)
     8.7 T02 layer adaptation functions
          8.7.1 T02 to SD adaptation source (T02/SD_A_So)
          8.7.2 T02 to SD adaptation sink (T02/SD_A_Sk)
     8.8 T21 layer adaptation functions
          8.8.1 T21 to SD adaptation source (T21/SD_A_So)
          8.8.2 T21 to SD adaptation sink (T21/SD_A_Sk)
     8.9 ETH layer adaptation functions
          8.9.1 ETH to SD adaptation source (ETH/SD_A_So)
          8.9.2 ETH to SD adaptation sink (ETH/SD_A_Sk)
     8.10 OTUk layer adaptation functions
          8.10.1 OTUk to SD adaptation source (OTUk/SD_A_So)
          8.10.2 OTUk to SD adaptation sink (OTUk/SD_A_Sk)
     8.11 OSC layer adaptation functions
          8.11.1  OSC to SD adaptation source (OSC/SD_A_So)
          8.11.2 OSC to SD adaptation sink (OSC/SD_A_Sk)
     8.12 FlexO layer adaptation functions
          8.12.1 FlexO to SD adaptation source (FlexO/SD_A_So)
          8.12.2 FlexO to SD adaptation sink (FlexO/SD_A_Sk)
     8.13 FlexE layer adaptation functions
          8.13.1 FlexE to SD adaptation source (FlexE/SD_A_So)
          8.13.2 FlexE to SD adaptation sink (FlexE/SD_A_Sk)
     8.14 MTNS layer adaptation functions
          8.14.1 MTNSy to SD adaptation source (MTNSy/SD_A_So)
          8.14.2 MTNSy to SD adaptation sink (MTNSy/SD_A_Sk)
9 Equipment clock to transport layers clock adaptation functions
     9.1 STM-N layer
          9.1.1 STM-N layer clock adaptation source (MSn-LC_A_So)
     9.2 VC layers
          9.2.1 VC-n layer clock adaptation source (Sn-LC_A_So)
          9.2.2 VC-m layer clock adaptation source (Sm-LC_A_So)
     9.3 Pxx layers
          9.3.1 Pqs layer clock adaptation source (Pqs-LC_A_So)
          9.3.2 P12s layer clock adaptation source (P12s-LC_A_So)
          9.3.3 P11s layer clock adaptation source (P11s-LC_A_So)
     9.4 T12 layer
          9.4.1 T12 layer clock adaptation source (T12-LC_A_So)
     9.5 T01 layer
          9.5.1 T01 layer clock adaptation source (T01-LC_A_So)
     9.6 T02 layer
          9.6.1 T02 layer clock adaptation source (T02-LC_A_So)
     9.7 T21 layer
          9.7.1 T21 layer clock adaptation source (T21-LC_A_So)
     9.8 ETYn layer
          9.8.1 ETYn layer clock adaptation source (ETYn-LC_A_So)
     9.9 ODU layer
          9.9.1 ODUk layer clock adaptation source (ODUk-LC_A_So)
          9.9.2 ODUCn layer clock adaptation source (ODUCn-LC_A_So)
     9.10 OSC layer
          9.10.1 OSC layer clock adaptation source (OSC-LC_A_So)
     9.11 FlexO layer
          9.11.1 FlexO layer clock adaptation source (FlexO-LC_A_So)
     9.12 FlexE layer
          9.12.1 FlexE layer clock adaptation source (FlexE-LC_A_So)
     9.13 MTNS layer
          9.13.1 MTNS layer clock adaptation source (MTNSy-LC_A_So)
10 T12 section layer functions
     10.1 T12 connection function T12_C
     10.2 T12 trail termination functions
          10.2.1 T12 trail termination source (T12-Z_TT_So)
          10.2.2 T12 trail termination sink (T12-Z_TT_Sk)
11 T01 section layer functions
     11.1 T01 connection function T01_C
     11.2 T01 trail termination functions
          11.2.1 T01 trail termination source (T01_TT_So)
          11.2.2 T01 trail termination sink (T01_TT_Sk)
12 T02 section layer functions
     12.1 T02 connection function T02_C
     12.2 T02 trail termination functions
          12.2.1 T02 trail termination source (T02_TT_So)
          12.2.2 T02 trail termination sink (T02_TT_Sk)
13 T21 section layer functions
     13.1 T21 connection function T21_C
     13.2 T21 trail termination functions
          13.2.1 T21 trail termination source (T21_TT_So)
          13.2.2 T21 trail termination sink (T21_TT_Sk)
Annex A  Synchronization selection process
Annex B  SyncPhy data sets
     B.1 Introduction of SyncPhy dataset
     B.2 Derived data type specifications
          B.2.1 ClockIdentity
          B.2.2 QualityLevel
          B.2.3 Boolean
     B.3 defaultDS data set member specifications
          B.3.1 General
          B.3.2 defaultDS.clockIdentity
          B.3.3 defaultDS.qualityLevel
          B.3.4 defaultDS.eqlSel
          B.3.5 defaultDS.syncNetworkOption
          B.3.6 defaultDS.clockModeStatus
          B.3.7 defaultDS.clockModeConfig
          B.3.8 defaultDS.sourceSwitchType
          B.3.9 defaultDS.forcedSource
          B.3.10 defaultDS.manualSource
          B.3.11 defaultDS.revertiveMode
          B.3.12 defaultDS.wtrTime
          B.3.13 defaultDS.qlEnable
     B.4 currentDS data set member specifications
          B.4.1 General
          B.4.2 currentDS.hopsNumber
          B.4.3 currentDS.enhancedHopsNumber
          B.4.4 currentDS.frequencyOffsetFromCkSource
     B.5 parentDS data set member specifications
          B.5.1 General
          B.5.2 parentDS.systemClockSourceID
          B.5.3 parentDS.systemClockSourceQL
     B.6 portDS data set member specifications
          B.6.1 General
          B.6.2 Common attributes
               B.6.2.1 portDS.portName
               B.6.2.2 portDS.portType
               B.6.2.3 portDS.portStatus
               B.6.2.4 portDS.lockOut
               B.6.2.5 portDS.ssmSupp
               B.6.2.6 portDS.eSsmSupp
               B.6.2.7 portDS.localPriorityForSystemClock
               B.6.2.8 portDS.localPriorityForStationClock[portDS.portName]
               B.6.2.9 portDS.ssmSendEnable
               B.6.2.10 portDS.qlReceiverInfo
               B.6.2.11 portDS.qlOverwrite
               B.6.2.12 portDS.qlFixedValue
               B.6.2.13 portDS.ssmInSaBit
               B.6.2.14 portDS.ssmOutSaBit
          B.6.3 Station clock port attributes
               B.6.3.1 portDS.stationClockPortType
          B.6.3.2 portDS.stationClockSsmOutThreshold
               B.6.3.3 portDS.stationClockReferenceForOutput
               B.6.3.4 portDS.stationClockSourceID
               B.6.3.5 portDS.stationClockSourceQL
          B.6.4 Line clock port attributes
               B.6.4.1 portDS.lineClockTmMode
Appendix I  Transport layer models for synchronization information
Appendix II  Examples of synchronization functionality in the NE
     II.1 Examples of synchronization functionality in the NE for option I networks
     II.2 Examples of synchronization functionality in the NE for option II networks
     II.3 Examples of synchronization functionality in the NE for option III networks
Appendix III  Delay time allocation for option I and III networks
     III.1 Delay and processing times for the synchronization selection process
     III.2 Non-switching message delay TNSM
     III.3 Switching message delay TSM
     III.4 Holdover message delay THM
     III.5 Wait-to-restore time TWTR
Appendix IV  Interworking of option II equipment supporting second-generation SSM  and first-generation SSM using a translation function
Appendix V  SDL descriptions
Appendix VI  Clarification of the use of the acronym 'SEC'
Appendix VII  Use cases of mixing SSM and eSSM