Rec. ITU-T G.8261/Y.1361 Amendment 2 (10/2020) Timing and synchronization aspects in packet networks
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 Conventions
6 General
     6.1 Packet network synchronization requirements
     6.2 TDM timing requirements
          6.2.1 PDH timing requirements
          6.2.2 Synchronization interfaces requirements
          6.2.3 SDH timing requirements
     6.3 Synchronization network engineering in packet networks
     6.4 Timing requirements at edge versus timing requirements in core networks
     6.5 PNT domain and CES domain
7 Reference timing signal distribution over packet networks (PNT domain)
     7.1 Plesiochronous and network synchronous methods
          7.1.1 Synchronous Ethernet networks
     7.2 Packet-based methods
8 Timing recovery for constant bit rate services transported over packet networks (CES domain)
     8.1 Network synchronous operation
     8.2 Differential methods
     8.3 Adaptive methods
     8.4 Reference clock available at the TDM end systems
9 Network limits
     9.1 CES network limits
          9.1.1 Network model underlying the network limits
      Deployment Case 1
      Deployment Case 2
      Deployment Case 3
     9.2 PNT network limits
          9.2.1 Synchronous equipment clock interface network limits
      Synchronous equipment clock Option 1 interface network wander limits
      Synchronous equipment clock Option 2 interface network wander limits
      Synchronous equipment clock interface network jitter limits
      Enhanced synchronous equipment clock interface network limits
           Network limits for a full chain of up to 20 clocks
           Network limits for a short chain of up to 4 clocks
          9.2.2 PEC interface network limits
      Network model underlying the PEC network limits
10 Impact of impairments in the packet network on timing distribution and service clock recovery
     10.1 Packet transfer delay and delay variation
          10.1.1 Differential methods
          10.1.2 Adaptive methods
      Random delay variation
      Low frequency delay variation
      Systematic delay variation
      Routing changes
      Congestion effects
      Topology-dependent blocking mechanisms in packet networks
     10.2 Impacts from packet impairments
          10.2.1 Packet error and packet loss
      Impact on TDM service
      Impact on IWF clock recovery process
      Impact on service clock recovery
          10.2.2 Packet severe loss block outcomes
11 Impact of the reference clock impairment on the service clock recovery
     11.1 Impairments for the network synchronous operation methods
     11.2 Impairments for the differential method
12 Results and consequences of the different synchronization methods over packet network reference models
     12.1 CES domain recommendations
          12.1.1 Recommendation for the timing recovery of a TDM service (Deployment Case 1)
          12.1.2 Recommendation for the timing recovery of a TDM service (Deployment Case 3)
          12.1.3 Recommendation for the timing recovery of a TDM service (Deployment Case 2 Application A)
          12.1.4 Recommendation for the timing recovery of a TDM service (Deployment Case 2 Application B)
     12.2 PNT domain recommendations
          12.2.1 Recommendations for reference timing signals distribution over synchronous Ethernet
          12.2.2 Recommendations for reference timing signals distribution over packets
      Recommendations for Deployment Case 1
      Recommendations for Deployment Case 2
Annex A  Proposed network architecture for synchronous Ethernet
     A.1 PRC Location
     A.2 Limiting jitter and wander of synchronous Ethernet
     A.3 Considerations on the design of synchronization network based on synchronous Ethernet
     A.4 Example of timing distribution via synchronous Ethernet
     A.5 Interworking of Ethernet and synchronous Ethernet interfaces
          A.5.1 Interface type and operation mode definitions
          A.5.2 Interworking requirements
          A.5.3 Interworking in frequency
          A.5.4 Interworking in noise
          A.5.5 Related jitter measurement
          A.5.6 Related wander measurement
Annex B  IWF functional partitioning into CES and PNT IWF and network examples
     B.1 General
     B.2 IWF clocks
     B.3 Network examples
Annex C  CES IWF synchronization related requirements
     C.1 Traffic interfaces
          C.1.1 Physical, electrical and optical characteristics
          C.1.2 Jitter and wander tolerance
     C.2 Synchronization interfaces
          C.2.1 Physical and electrical characteristics
          C.2.2 Jitter and wander tolerance
     C.3 IWF synchronization function
Annex D  Network applications and requirements for clocks specified  in ITU-T G.8262/Y.1362
Appendix I  Characteristics of Ethernet switches, Ethernet networks, routers and access technologies
     I.1 Characteristics of Ethernet switches and networks
          I.1.1 Delay characteristics of Ethernet switches
               I.1.1.1 Functional operations within an Ethernet switch
               I.1.1.2 Input stage delay
               I.1.1.3 Switch fabric delay
               I.1.1.4 Output queuing delay
               I.1.1.5 Typical delays in the Ethernet switches
          I.1.2 Characteristics of switched Ethernet networks
               I.1.2.1 Topology of Ethernet networks
               I.1.2.2 Traffic patterns and levels
               I.1.2.3 Disruptive events in Ethernet networks
     I.2 Delay characteristics of routers
     I.3 Delay characteristics of access technologies (Microwave nodes, PON, DSL)
Appendix II  Stabilization period
Appendix III  Considerations on packet-based methods
Appendix IV  Applications and use cases
     IV.1 Background
     IV.2 Wireless
          IV.2.1 Applications
          IV.2.2 Examples
               IV.2.2.1 GSM base station (frequency synchronization)
               IV.2.2.2 UMTS FDD base station (frequency synchronization)
               IV.2.2.3 UMTS TDD base station (frequency and phase synchronization)
               IV.2.2.4 3GPP2 CDMA2000 base station (frequency and time synchronization)
               IV.2.2.5 TD-SCDMA base station (frequency and phase synchronization)
               IV.2.2.6 LTE base station (frequency synchronization)
               IV.2.2.7 NR base station (frequency synchronization)
          IV.2.3 Remarks
     IV.3 Infrastructure
     IV.4 Media gateway
Appendix V  Packet networks reference models
     V.1 Ethernet networks models
     V.2 Other network models
Appendix VI  Measurement guidelines for packet-based methods
     VI.1 Measurement reference points
     VI.2 Input traffic characteristics
          VI.2.1 Network Traffic model 1
          VI.2.2 Network Traffic model 2
     VI.3 Test topologies for adaptive methods
          VI.3.1 Baseline test
          VI.3.2 Performance test
               VI.3.2.1 Test Case 1
               VI.3.2.2 Test Case 2
               VI.3.2.3 Test Case 3
               VI.3.2.4 Test Case 4
               VI.3.2.5 Test Case 5
               VI.3.2.6 Test Case 6
               VI.3.2.7 Test Case 7
               VI.3.2.8 Test Case 8
     VI.4 Test Topologies for differential methods
          VI.4.1 Test Case 9
          VI.4.2 Test Case 10
          VI.4.3 Test Case 11
     VI.5 Test for two-way protocols
          VI.5.1 Baseline test
          VI.5.2 Performance test
               VI.5.2.1 Input traffic characteristics
               VI.5.2.2 Test Case 12
               VI.5.2.3 Test Case 13
          VI.5.2.4 Test Case 14
               VI.5.2.5 Test Case 15
               VI.5.2.6 Test Case 16
               VI.5.2.7 Test Case 17
Appendix VII  Wander limits in Deployment Case 1
     VII.1 Limits for the 2048 kbit/s interface
     VII.2 Limits for the 1544 kbit/s interface
Appendix VIII   Synchronization status messaging in synchronous Ethernet PHY
Appendix IX  IWF examples
Appendix X  Considerations on measurement of synchronous Ethernet according to ITU-T methodologies in comparison with IEEE jitter measurements
Appendix XI  Relationship between requirements contained in this Recommendation  and other key synchronization related Recommendations
Appendix XII  Basic principles of timing over packet networks
     XII.1 General
     XII.2 Packet delay variation mitigation by packet selection
     XII.3 Comparison of packet-based and synchronous PHY methods
     XII.4 Existing standards
Appendix XIII  Evaluation of the packet delay variation generation in a network node
     XIII.1 Introduction
     XIII.2 General considerations
     XIII.3  General configuration
          XIII.3.1 General description of the PDV generation tests for a single node
Appendix XIV  Interoperability guidelines for interworking between synchronous equipment clocks and enhanced synchronous equipment clocks