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Question 13

​​Question 13/15 – Network synchronization and time distribution performance

(Continuation of Question 13/15)

Motivation
Network synchronization performance specifications are essential for successful operation of digital transmission networks including the support of, for example, mobile networks. Network timing performance standards are necessary to define the feasibility and most effective means of implementing a time reference distribution service. This includes the distribution of both precision time and frequency.
Continuing effort needs to be put into the study of synchronization issues in packet based networks. 

Requirements for the related OAM and Management functions need to be studied. 

Requirements from new network architectures and applications should be considered (e.g. as related to the IoT, IMT2020 (5G), etc.).
Robust and reliable network synchronization solutions (e.g. as related to GNSS (Global Navigation Satellite System) backup) need to be addressed.

SDN/NFV implications on the synchronization networks should also be studied.

New transmission technologies, services and facilities are regularly being introduced. Inter-operator links need to be efficiently installed, commissioned, brought into service and maintained. Test and measurement instrumentation is required for the installation, commissioning, bringing into service and maintenance of telecommunications equipment and networks. The measurement of the same parameter made with different measuring instruments should give reliable, repeatable and comparable results. Test equipment specification needs continuous review to take account of technology changes and improvements of jitter, wander and precision time measurement.

The following major Recommendations, in force at the time of approval of this Question, fall under its responsibility:
  • Definitions and Architecture: G.781, G.810, G.8260, G.8264, G.8265, G.8275
  • PTP Profiles: G.8265.1, G.8275.1.
  • Network Performance: G.8251, G.822, G.823, G.824, G.825, G.8261, G.8261.1, G.8271, G.8271.1.
  • Clocks: G.811, G.812, G.813, G.8262, G.8263, G.8272, G.8273, G.8273.2.
  • Test equipment: O.171, O.172, O.173, O.174 and O.182.
Question
Study items to be considered include, but are not limited to:
  • What are the requirements for jitter and wander for the future OTN interfaces e.g. beyond 100Gbit/s?
  • What is the network functionality required to provide real-time distribution of absolute time-of-day reference services and/or phase synchronization? What network capabilities are required to support the performance levels necessary to satisfy a selected set of time-of-day and/or phase synchronization user applications?
  • How can network synchronization performance be enhanced through the use of synchronization status messages or other techniques?
  • What network synchronization characteristics, for both normal and degraded mode, should be recommended for services carried over packet networks? What is the dependence on synchronization of performance of various methods of service clock recovery with respect to service requirements (e.g., jitter, wander, time error, etc.)?
  • How can robust and reliable network synchronization solutions be provided (e.g. as related to GNSS backup)?
  • What network synchronization characteristics should be recommended for services carried over packet based networks?
  • What jitter and wander requirements are needed for wireless network applications (e.g., radio relay, satellite)?
  • Synchronization aspects related to supporting mobile network operations: what synchronization requirements are related to supporting the operation of the mobile network (e.g. backhaul and fronthaul) and of the related applications (e.g., LTE, LTE-A, IMT2020 (5G))? What solutions are suitable to meet these requirements? How can the accuracy be improved?
  • What jitter and wander requirements are needed for access networks (e.g. DSL, PON, Microwave)?
  • What jitter and wander specification requirements are needed in the evolution of OTN?
  • Synchronization aspects (frequency, phase and time) of packet networks, e.g. Ethernet, MPLS, IP networks.
  • Synchronization aspects related to new applications, e.g. as related to the Internet of things (IoT).
  • Synchronization aspects with regard to transport via satellite networks.
  • What are the synchronization related requirements for OAM and Management functions.
  • What are the implication of SDN/NFV concepts to the synchronization network architectures and requirements.
  • What manual and automatic test and measurement instrumentation and techniques to assess transmission performance need to be specified by ITU-T and what should be the specifications?
The following are examples of instrumentation and techniques which may be studied:
  • measurement and evaluation of error performance parameters and objectives;
  • test instrumentation and techniques associated with various technologies (e.g. PON, OTN PNT, Submarine systems and beyond 100G);
  • test instrumentation and techniques associated with Layer 1 Transmission technologies for metallic and optical media like 1G access, beyond 100G;
  • jitter and wander test instrumentation and techniques associated with various technologies (e.g. , PON, OTN,PNT and beyond 100G);
  • test instrumentation and techniques associated with Optical Phase modulations (e.g. ODB, DQPSK and DP-QPSK);
  • keeping O-Series Recommendations up to date.
Tasks
Tasks include, but are not limited to:
  • Continue development of recommendations related to the transport of frequency through packet networks, G.826x-series including G.8260, G.8261, G.8261.1, G.8262, G.8262.1, G.8263, G.8264, G.8265, G.8265.1, and G.8266.
  • Continue development of recommendations related to the transport of phase and time through packet networks, G.826x- and G.827x-series including G.8260, G.8271, G.8271.1, G.8271.2, G.8272, G.8272.1, G.8273, G.8273.1, G.8273.2, G.8273.3, G.8273.4, G.8275, G.8275.1, G.8275.2.
  • Revisions and enhancements to Recommendations G.825 and G.8251.
  • Maintenance and enhancement of G.81X-series.
  • Continue work on the transport of clients through OTN e.g. PTP, etc.
  • Consider need for new Recommendation on jitter and wander instrumentation for packet-based networks (O-series), e.g. O.175.
  • Consider need for new Recommendation on physical layer test instrumentation associated with Optical Phase modulations (ODB, DQPSK and DP-QPSK).
  • Work on Recommendation for Frequency and Time Synchronization Layer Functions (G.781, G.781.1).

Relationships


Recommendations:
  • Q.551, G.783, G.798, G.800, G.805, G.80XX series, G.81XX series
  • G.783
Questions:
  • Q2/15, Q4/15, Q6/15, Q8/15, Q9/15, Q10/15, Q11/15, Q12/15, Q14/15 and Q15/15
Study Groups:
  • ITU-T SG2 on telecommunication management
  • ITU-T SG13 on MPLS, OAM, IP and NGN requirements, SDN, IMT 2020 (5G)
  • ITU-T SG9
  • ITU-T SG20 on IoT
  • ITU-R SG4 on satellites
  • ITU-R SG6 on broadcasting
  • ITU-R SG7 on Science Services
  • ITU-R SG8 on mobile
  • ITU-R SG9 on radio relay
Standardization bodies, forums and consortia:
  • ATIS COAST-SYNC
  • IETF TICTOC
  • IETF NTP
  • MEF on circuit emulation over Ethernet and frame delay measurements
  • MEF mobile backhaul
  • IEEE 1588
  • IEEE 802.3
  • IEEE 802.1
  • IEEE 802.16 (Wireless MAN)
  • 3GPP
  • Broadband Forum
  • IEC TC86
  • Optical Interworking Forum (OIF)
  • ETSI
  • ONF
  • CPRI

 

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