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Joint ITU-T/IEEE Workshop on The Future of Ethernet Transport (Geneva, 28 May 2010). Q13 Activities on Time Synchronization. Jean-Loup Ferrant, Calnex, Q13 Rapporteur Stefano Ruffini Ericsson, Q13 Associated Rapporteur. Transport of frequency in Q13/15. 2.

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q13 activities on time synchronization

Joint ITU-T/IEEE Workshop

on The Future of Ethernet Transport(Geneva, 28 May 2010)

Q13 Activities on Time Synchronization

Jean-Loup Ferrant,

Calnex, Q13 Rapporteur

Stefano Ruffini

Ericsson, Q13 Associated Rapporteur

transport of frequency in q13 15
Transport of frequencyin Q13/15

2

  • In 2004, Q13 started working on transport of timing on PSN
    • Interworking with TDM was required
    • FDD was the mostly deployed mobile technology (only frequency sync required)
  • Focus on Frequency synchronization
    • 1- Transport of frequency in CES applications
    • 2- Transport of frequency via SyncE
    • First series of recommendations: G.8261, G.8262, G.8264
  • Initial discussion on time synchronization
    • Transport of time on SyncE was also proposed, but 1588 was preferred
transport of time in q13 15
Transport of time in Q13/15

3

  • Transport of time became important with TDD and new applications (e.g. MBSFN)
    • Q13 has chosen to focus on 1588-2008 for the transport of time and frequency (NTP also briefly mentioned)
  • Q13 worked on a first « telecom profile » (consent planned next week)
  • Q13 workplan has been rearranged to align frequency and time recommendations
example in wireless application
Example in Wireless Application

+/- 1.5 ms

+/- 1.5 ms

+/- 3 ms

eNodeB

eNodeB

  • Phase Sync needed to Synchronize transmission from different base stations
    • To optimize bandwidth usage and enhance network capacity
    • In TDD mode uplink and downlink are separated in time
  • LTE-TDD: 3 ms time difference between Base Stations (small cell)
    • “phase synchronization” requirement of 1.5 ms between the master and the slave, according to ITU-T definitions (see G.8260)

6

g 8271
G.8271

The G.8271, Time and Phase synchronization aspects in packet networks

First Q13 recommendation in the G.827x series;

Draft already available

Scope

Overall performance objectives (see applications in previous slide)

Methods to distribute phase synchronization and/or time synchronization (GNSS, Packet-based)

Network Model

Initial focus: Ethernet physical layer

Detailed Network Limits are proposed to be included in a separate document (to be defined, e.g. G.8271.1)

7

ieee1588 telecom profiles
IEEE defines a profile as

“The set of allowed precision time Protocol (PTP) features applicable to a device”

The first purpose of a profile is to allow interworking between PTP master and slaves

ITU-T Q13/15 agreed to define telecom profiles based on IEEE 1588-2008

First profiles will address the transport of frequency

Next profiles will address the transport of phase, time and frequency

IEEE1588 Telecom Profiles

8

frequency telecom profile
Frequency telecom profile

9

  • First profile for end to end application, no support from intermediate nodes
    • Frequency synchronization only
    • PDV is not controlled in intermediate nodes
    • Absolute delay is not an issue for frequency
      • No asymmetry issue
    • Network architecture as per G.8265
frequency distribution without timing support from the network unicast mode
Frequency distribution without timing support from the network (Unicast mode)

10

  • Selected options
      • Unicast is the selected mode
        • Mix unicast and multicast mode is for further study and may be specified in future profiles
      • Mapping:IEEE-2008 annexD (UDP over IPV4)
      • One-way vs two ways
        • Masters must support both
        • Slaves may select one
      • One-step vs two-steps
        • Both allowed
      • BMCA (best master clock algorithm)
        • Definition of a specific BMCA by ITU-T
ieee1588 time profile
IEEE1588 Time Profile
  • The distribution of accurate time/phase (e.g. < 1 microsecond) can be challenging without timing support from the network
    • PDV impacting accurate frequency distribution
    • Asymmetry due to different traffic load on forward and reverse direction
    • Asymmetry due to particular transport technologies
  • A network with timing support is generally required
    • E.g. Boundary Clock in every node

11

related aspects
Related Aspects
  • Several aspects need to be addressed by Q13
    • Telecom Profile (e.g. PTP mapping, Unicast vs. Multicast, packet rate, BMC, etc.)
    • Is the Transparent Clock allowed in Telecom ?
    • Performance aspects (e.g. Clock characteristics, Holdover, etc.)
    • Architecture (e.g. Sync Reference chain), redundancy
    • Combination with SyncE
    • Interworking with the access technologies

12

phase and time
Phase and Time

Relevant Terms are defined in G.8260

Phase: significant events occur at the same instant

Time: nodes get information about time and share a common timescale and related epoch

Time

Phase

14