Time Sync Network Limits: Status, Challenges - PowerPoint PPT Presentation


Title: Time Sync Network Limits: Status, Challenges


1
Time Sync Network LimitsStatus, Challenges
Joint IEEE-SA and ITU Workshop on Ethernet
  • Stefano Ruffini,
  • Ericsson
  • Q13/15 AR

2
Contents
  • Introduction on G.8271 and G.8271.1
  • Definition of Time sync Network Limits
  • Challenges for an operator
  • Next Steps

3
Time Sync Q13/15 Recommendations
  • Analysis of Time/phase synchronization in Q13/15
  • G.8260 (definitions related to timing over packet
    networks)
  • G.827x series

Phase/Time
Frequency
General/Network Requirements Architecture and
Methods PTP Profile Clocks
G.8261 G.8261.1 G.8264 G.8265 G.8265.1 G.8262 G.82
63
G.8271 G.8271.1 G.8275 G.8275.1,
G.8275.2 G.8272 G.8273,.1,.2,.3
G.8271.2
4
Target Applications
Level of Accuracy Time Error Requirement(with respect to an ideal reference) Typical Applications
1 500 ms Billing, Alarms
2 100 ms IP Delay monitoring
3 5 ms LTE TDD (cell gt3km)
4 1.5 ms UTRA-TDD, LTE-TDD (cell ? 3Km)Wimax-TDD (some configurations)
5 1 ms Wimax-TDD (some configurations)
6 lt x ns (x ffs) Location Based services and some LTE-A features(Under Study)
Geneva, Switzerland, 13 July 2013
4
5
Time sync Network Limits
  • Aspects to be addressed when defining the Network
    Limits
  • Reference network (HRM) for the simulations
  • Metrics
  • Network Limits Components (Constant and Dynamic
    Time Error)
  • Failure conditions
  • Network Rearrangements
  • Time Sync Holdover

6
Noise (Time Error) Budgeting Analysis
Common Time Reference (e.g. GPS time)
N
Network Time Reference (e.g. GNSS Engine)
R5
R4
R3
R2
R1
Packet Slave Clock(T-TSC)
Packet Network
PRTC
PacketMaster(T-GM)
End Application Time Clock
T-BC Telecom Boundary Clock PRTC Primary
Reference Time Clock T-TSC Telecom Time Slave
Clock T-GM Telecom Grandmaster
7
Rearrangements and Holdover
  • The full analysis of time error budgeting
    includes also allocating a suitable budget to a
    term modelling Holdover and Rearrangements
  • Time Sync Holdover Scenarios
  • PTP traceability is lost and and the End
    Application or the PRTC enters holdover using
    SyncE or a local oscillator
  • PTP Master Rearrangement Scenarios
  • PTP traceability to the primary master is lost
    the T-BC or the End Application switches to a
    backup PTP reference

8
MAX TE based Limits
  • The Constant Time Error measurement was initially
    proposed as could be easily correlate to the
    error sources (e.g. Asymmetries), however
  • Complex estimator (see G.8260)
  • Different values at different times (e.g. due to
    temperature variation)
  • Max TE has then been selected
  • The measurement might need to be done on
    pre-filtered signal (e.g. emulating the End
    Application filter, i.e. 0.1 Hz). This is still
    under study.

Max TEC (t) maxTE TEREA TEEA lt TED
9
Time Error Budgeting
  • Dynamic Error (dTE (t))
  • simulations performed using HRM with SyncE
    support
  • It looks feasible to control the max TE in the
    200 ns range
  • Constant Time Error (cTE)
  • Constant Time Error per node 50 ns
  • PRTC (see G.8272) 100 ns
  • End Application 150 ns
  • Rearrangements 250 ns (one of the main examples)
  • Remaining budget to Link Asymmetries (250 ns)

10
Stability Requirements
  • Additional requirement on stability of the timing
    signal is needed and is under study
  • Applicable to the dynamic component (d(t))
  • In terms of MTIE and TDEV
  • Possible Jitter requirements
  • Important for End Application Tolerance

11
Challenges for an operator
  • Distribution of accurate time synchronization
    creates new challenges for an operator
  • Operation of the network
  • Handling of asymmetries (at set up and during
    operation)
  • Planning of proper Redundancy (e.g. Time sync
    Holdover is only available for limited periods
    (minutes instead of days). Exceeding the limits
    can cause service degradation
  • New testing procedures
  • Network performance and Node performance requires
    new methods and test equipment
  • Some aspect still under definition (e.g.
    G.8273.x)

12
Sources of Asymmetries
  • Different Fiber Lengths in the forward and
    reverse direction
  • Main problem DCF (Dispersion Compensated Fiber)
  • Different Wavelengths used on the forward and
    reverse direction
  • Asymmetries added by specific access and
    transport technologies
  • GPON
  • VDSL2
  • Microwave
  • OTN
  • Additional sources of asymmetries in case of
    partial support
  • Different load in the forward and reverse
    direction
  • Use of interfaces with different speed
  • Different paths in Packet networks (mainly
    relevant in case of partial support)
  • Traffic Engineering rules in order to define
    always the same path for the forward and reverse
    directions

13
Next Steps
  • Work is not completed
  • Dynamic components in terms of MTIE and TDEV
    Jitter?
  • Testing methods (G.8273 provides initial
    information)
  • Partial Timing support

14
Partial Timing Support
  • HRM for G.8271.2

Need to define new metrics (e.g. 2-ways FPP)
15
Summary
  • G.8271.1 consented this week
  • Max TE Time sync limits are available
  • The delivery of accurate time sync presents some
    challenges for an operator
  • Asymmetry calibration
  • Handling of failures in the network
  • Still some important topics need to be completed
  • Stability requirements
  • Partial timing support (G.8271.2)

16
Back Up

17
Time Synchronization via PTP
  • The basic principle is to distribute Time sync
    reference by means of two-way time stamps
    exchange
  • Symmetric paths are required
  • Basic assumption t2 t1 t4 t3
  • Any asymmetry will contribute with half of that
    to the error in the time offset calculation (e.g.
    3 ms asymmetry would exceed the target
    requirement of 1.5 ms)

M
S
t1
Time Offset t2 t1 Mean path delay Mean path
delay ((t2 t1) (t4 t3)) /2
t2
t3
t4
18
Metrics
  • Main Focus is Max Absolute Time Error (Max TE)
    (based on requirements on the radio interface for
    mobile applications)
  • Measurement details need further discussion
  • Stability aspects also important
  • MTIE and TDEV
  • Related to End Application tolerance
  • Same Limits in Reference point C or D !
  • Same limits irrespectively if time sync is
    distributed with SyncE support or not ?

TE (t)
Max TE
t
19
Measurement of Newtork Limits at ref. Point C
Option a
C
End Application
...
T-TSC
T-BC
PRTC
T-GM
T-BC
Direct comparison of PRTC Time with 1 PPS
1pps
Test Equipment
PRTC
In alternative the 4 timestamps could be
used TE (TM2 T1 T4 TM3)/2
20
Measurement of Newtork Limits at ref. Point C
Option c
from the two-way PTP flow via an active
measurement probe (e.g. prior to the start of
the service, or connecting the active monitor to
a dedicated port of the T-BC).
C
End Application
...
T-TSC
T-BC
PRTC
T-GM
T-BC
Monitoring method (active probe)
PTP Probe
Test Equipment
PRTC
21
Example of Time Error Accumulation
Accumulation of maximum absolute time error over
a chain of boundary clocks for different values
of asymmetry bias. The physical layer assist
involves SEC/EEC chain with bandwidth 10Hz.
Source WD25 (Anue), York, September 2011
v max asymmetry per hop
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Time Sync Network Limits: Status, Challenges

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Joint IEEE-SA and ITU Workshop on Ethernet Time Sync Network Limits: Status, Challenges Stefano Ruffini, Ericsson Q13/15 AR Geneva, Switzerland, 13 July 2013 – PowerPoint PPT presentation

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Transcript and Presenter's Notes

Title: Time Sync Network Limits: Status, Challenges


1
Time Sync Network LimitsStatus, Challenges
Joint IEEE-SA and ITU Workshop on Ethernet
  • Stefano Ruffini,
  • Ericsson
  • Q13/15 AR

2
Contents
  • Introduction on G.8271 and G.8271.1
  • Definition of Time sync Network Limits
  • Challenges for an operator
  • Next Steps

3
Time Sync Q13/15 Recommendations
  • Analysis of Time/phase synchronization in Q13/15
  • G.8260 (definitions related to timing over packet
    networks)
  • G.827x series

Phase/Time
Frequency
General/Network Requirements Architecture and
Methods PTP Profile Clocks
G.8261 G.8261.1 G.8264 G.8265 G.8265.1 G.8262 G.82
63
G.8271 G.8271.1 G.8275 G.8275.1,
G.8275.2 G.8272 G.8273,.1,.2,.3
G.8271.2
4
Target Applications
Level of Accuracy Time Error Requirement(with respect to an ideal reference) Typical Applications
1 500 ms Billing, Alarms
2 100 ms IP Delay monitoring
3 5 ms LTE TDD (cell gt3km)
4 1.5 ms UTRA-TDD, LTE-TDD (cell ? 3Km)Wimax-TDD (some configurations)
5 1 ms Wimax-TDD (some configurations)
6 lt x ns (x ffs) Location Based services and some LTE-A features(Under Study)
Geneva, Switzerland, 13 July 2013
4
5
Time sync Network Limits
  • Aspects to be addressed when defining the Network
    Limits
  • Reference network (HRM) for the simulations
  • Metrics
  • Network Limits Components (Constant and Dynamic
    Time Error)
  • Failure conditions
  • Network Rearrangements
  • Time Sync Holdover

6
Noise (Time Error) Budgeting Analysis
Common Time Reference (e.g. GPS time)
N
Network Time Reference (e.g. GNSS Engine)
R5
R4
R3
R2
R1
Packet Slave Clock(T-TSC)
Packet Network
PRTC
PacketMaster(T-GM)
End Application Time Clock
T-BC Telecom Boundary Clock PRTC Primary
Reference Time Clock T-TSC Telecom Time Slave
Clock T-GM Telecom Grandmaster
7
Rearrangements and Holdover
  • The full analysis of time error budgeting
    includes also allocating a suitable budget to a
    term modelling Holdover and Rearrangements
  • Time Sync Holdover Scenarios
  • PTP traceability is lost and and the End
    Application or the PRTC enters holdover using
    SyncE or a local oscillator
  • PTP Master Rearrangement Scenarios
  • PTP traceability to the primary master is lost
    the T-BC or the End Application switches to a
    backup PTP reference

8
MAX TE based Limits
  • The Constant Time Error measurement was initially
    proposed as could be easily correlate to the
    error sources (e.g. Asymmetries), however
  • Complex estimator (see G.8260)
  • Different values at different times (e.g. due to
    temperature variation)
  • Max TE has then been selected
  • The measurement might need to be done on
    pre-filtered signal (e.g. emulating the End
    Application filter, i.e. 0.1 Hz). This is still
    under study.

Max TEC (t) maxTE TEREA TEEA lt TED
9
Time Error Budgeting
  • Dynamic Error (dTE (t))
  • simulations performed using HRM with SyncE
    support
  • It looks feasible to control the max TE in the
    200 ns range
  • Constant Time Error (cTE)
  • Constant Time Error per node 50 ns
  • PRTC (see G.8272) 100 ns
  • End Application 150 ns
  • Rearrangements 250 ns (one of the main examples)
  • Remaining budget to Link Asymmetries (250 ns)

10
Stability Requirements
  • Additional requirement on stability of the timing
    signal is needed and is under study
  • Applicable to the dynamic component (d(t))
  • In terms of MTIE and TDEV
  • Possible Jitter requirements
  • Important for End Application Tolerance

11
Challenges for an operator
  • Distribution of accurate time synchronization
    creates new challenges for an operator
  • Operation of the network
  • Handling of asymmetries (at set up and during
    operation)
  • Planning of proper Redundancy (e.g. Time sync
    Holdover is only available for limited periods
    (minutes instead of days). Exceeding the limits
    can cause service degradation
  • New testing procedures
  • Network performance and Node performance requires
    new methods and test equipment
  • Some aspect still under definition (e.g.
    G.8273.x)

12
Sources of Asymmetries
  • Different Fiber Lengths in the forward and
    reverse direction
  • Main problem DCF (Dispersion Compensated Fiber)
  • Different Wavelengths used on the forward and
    reverse direction
  • Asymmetries added by specific access and
    transport technologies
  • GPON
  • VDSL2
  • Microwave
  • OTN
  • Additional sources of asymmetries in case of
    partial support
  • Different load in the forward and reverse
    direction
  • Use of interfaces with different speed
  • Different paths in Packet networks (mainly
    relevant in case of partial support)
  • Traffic Engineering rules in order to define
    always the same path for the forward and reverse
    directions

13
Next Steps
  • Work is not completed
  • Dynamic components in terms of MTIE and TDEV
    Jitter?
  • Testing methods (G.8273 provides initial
    information)
  • Partial Timing support

14
Partial Timing Support
  • HRM for G.8271.2

Need to define new metrics (e.g. 2-ways FPP)
15
Summary
  • G.8271.1 consented this week
  • Max TE Time sync limits are available
  • The delivery of accurate time sync presents some
    challenges for an operator
  • Asymmetry calibration
  • Handling of failures in the network
  • Still some important topics need to be completed
  • Stability requirements
  • Partial timing support (G.8271.2)

16
Back Up

17
Time Synchronization via PTP
  • The basic principle is to distribute Time sync
    reference by means of two-way time stamps
    exchange
  • Symmetric paths are required
  • Basic assumption t2 t1 t4 t3
  • Any asymmetry will contribute with half of that
    to the error in the time offset calculation (e.g.
    3 ms asymmetry would exceed the target
    requirement of 1.5 ms)

M
S
t1
Time Offset t2 t1 Mean path delay Mean path
delay ((t2 t1) (t4 t3)) /2
t2
t3
t4
18
Metrics
  • Main Focus is Max Absolute Time Error (Max TE)
    (based on requirements on the radio interface for
    mobile applications)
  • Measurement details need further discussion
  • Stability aspects also important
  • MTIE and TDEV
  • Related to End Application tolerance
  • Same Limits in Reference point C or D !
  • Same limits irrespectively if time sync is
    distributed with SyncE support or not ?

TE (t)
Max TE
t
19
Measurement of Newtork Limits at ref. Point C
Option a
C
End Application
...
T-TSC
T-BC
PRTC
T-GM
T-BC
Direct comparison of PRTC Time with 1 PPS
1pps
Test Equipment
PRTC
In alternative the 4 timestamps could be
used TE (TM2 T1 T4 TM3)/2
20
Measurement of Newtork Limits at ref. Point C
Option c
from the two-way PTP flow via an active
measurement probe (e.g. prior to the start of
the service, or connecting the active monitor to
a dedicated port of the T-BC).
C
End Application
...
T-TSC
T-BC
PRTC
T-GM
T-BC
Monitoring method (active probe)
PTP Probe
Test Equipment
PRTC
21
Example of Time Error Accumulation
Accumulation of maximum absolute time error over
a chain of boundary clocks for different values
of asymmetry bias. The physical layer assist
involves SEC/EEC chain with bandwidth 10Hz.
Source WD25 (Anue), York, September 2011
v max asymmetry per hop
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