Jun 2003 Eid Son

John EidsonJuly 16, [email protected]

IEEE-1588 Standard for a Precision Clock Synchronization Protocol for Networked Measurement and Control Systems

I&M Society IEEE1588 July 16,, 2003

Page 2

Overview

•Objectives of 1588

•A bit of history

•Where is it being used?

•Comparison with other protocols

•What the 1588 standard defines

•Technical overview

•Prototype results


Page 3

Objectives of 1588

• Sub-microsecond synchronization of real-time clocks in components of a networked distributed measurement and control system

• Intended for relatively localized systems typical of industrial automation and test and measurement environments.

• Applicable to local areas networks supporting multicast communications (including but not limited to Ethernet)


Page 4

•Simple, administration free installation

•Support heterogeneous systems of clocks with varying precision, resolution and stability

•Minimal resource requirements on networks and host components.

Objectives of 1588 (continued)


Page 5

A bit of History

Status of IEEE 1588

•Approved by the IEEE-SA Review Committee on 12 Sept. 2002

•Published on November 8 2002

•Available from the IEEE http://standards.ieee.org


Page 6

Members of the IEEE-1588 working groupVolker Arlt-Lenze AG

Scott Carter-GE Medical

John Eidson-Agilent

Richard Hambly-CNS Systems

Bruce Hamilton-Agilent

Steve Jennings-Bosch-Rexroth

Robert Johnson-Telemonitor

Bill Kneifel-KUKA

Jurgen Knopke-Lenze

Kang Lee- NIST

Judah Levine-NIST

Anatoly Moldovansky-Rockwell

Ed Powers-Naval Observatory

Jim Read-Hyperfine

Richard Schmidt-Naval Observatory

Steve Smith-ORNL

Joe White-NRL

Stan Woods-Agilent


Page 7

Where is it being used?(presentations scheduled for Sept. 24 workshop)

NETWORK DEVICES:

IEEE 1588 and Network Devices: Dirk S. Mohl, Hirschmann Electronics

Boundary Clock implementation: Øyvind Holmeide, Managing Director, OnTime Networks AS.

Extending IEEE 1588 to fault tolerant synchronization with a worst-case precision in the 100 ns range: Nikoaus E. Keroe, Oregano Systems


Page 8


Page 9


TELECOMMUNICATIONS:

Proposal for IEEE1588 use over Metro Ethernet Layer 2 VPNs: Glenn Algie, Senior Advisor, Wireless Technology Labs, Nortel Networks

INDUSTRIAL AUTOMATION:

Impact of Switch Cascading on Time Accuracy: Prof. Thomas Mueller, University Wintherthur, Suisse, Karl Weber, SIEMENS Automation and Drives

Consequences of Redundant Structures PTP: Ludwig Winkel, SIEMENS Automation and Drives

Application of 1588 for Distributed Motion Control: Kendal R. Harris, Sivaram Balasubramanian and Anatoly Moldovansky, Rockwell Automation


Page 10

HZx Wrappers

Courtesy of SIG Pack Systems AG


Page 11

Control of multiple robots


Page 12

Mulit-stand Printing Press

60mph =

1 inch/millisecond =

1 mil/microsecond


Page 13


MILITARY FLIGHT TEST:

Time Correlation using network based data acquisition on-board a Military Test Vehicle: Jiwang Dai, Ph.D, Senior Software Engineer, L3 Communications Telemetry East, Thomas DeSelms, Senior Network Systems Engineer, Veridian Engineering, and Edward Grozalis, Senior Engineer, L3 Communications Telemetry East

POWER SYSTEMS:

Implementation of IEEE Std.-1588 in a Networked I/O Node: Mark Shepard, GE Drives & Controls, Inc., Salem, VA


Page 14


Page 15

Comparison with other protocols

1588: Target is groups of relatively stable components, locally networked (a few subnets), cooperating on a set of well defined tasks.

NTP: (Network Time Protocol, RFC 1305). Target is autonomous systems widely dispersed on the Internet.

GPS: (Satellite based Global Positioning System of the US Department of Defense): Target is autonomous, widely dispersed systems.

TTP(www.ttpforum.org), SERCOS (IEC 61491): Target is tightly integrated, usually bus or specialized TDMA network based closed systems.


Page 16

ModerateModerateModerate computation footprint

Moderate network and computation footprint

Small network message and computation footprint

Resources

Master/SlaveDistributedClient/serverPeer ensemble

Master/slaveStyle

Sub-microsecond

Sub-microsecond

Sub-microsecond

Few milliseconds

Sub-microsecond

Target accuracy

BusBus or starSatelliteInternetNetworkCommuni-cations

Local busLocal busWide areaWide areaA few subnetsSpatial extent

SERCOSTTPGPSNTP1588


Page 17

Every TDMA cycle, ~ms

Yes

Configured

No

No

SERCOS

Every TDMA cycle, ~ms

~1 second

Varies, nominally seconds

~2 secondsUpdate interval

YesRF receiver and processor

NoFor highest accuracy

Hardware?

ConfiguredN/AConfiguredSelf organizing

Administration

NoNoYesNoProtocol specifies security

ConfiguredYesYesYesLatency correction

TTPGPSNTP1588


Page 18

1588 Defines:

•Descriptors characterizing a clock

•The states of a clock and the allowed state transitions

•1588 network messages, fields, and semantics

•Datasets maintained by each clock

•Actions and timing for all 1588 network and internal events


Page 19

•Critical physical specifications

•A suite of messages for monitoring the system

•Specifications for an Ethernet based implementation

•Conformance requirements

•Implementation suggestions


Page 20

Timing Latency & Fluctuation

msecs of delay and fluctuation

Application layer

Network protocol stack

Physical layer < 100 nsecs of delay and fluctuation

Application layer


Physical layer

Repeater, Switch, or

RouterRepeaters & Switches:fluctuations ~100ns to usecRouters:fluctuations ~ms


Page 21

Reducing Timing Latency & Fluctuation

• Within a node:

• Make timing measurements as close to the physical layer as possible to eliminate protocol stack and operating system fluctuations.

• Use statistical techniques to further reduce residual fluctuations from PHY layer, network and repeaters and switches.

• Routers:

• Use transfer devices (1588 boundary clocks) to reduce router latency and fluctuations


Page 22

Selecting a Master Clock-Single Subnet

Repeater or

Switch

Repeater or

Switch

Typical slave clock

Master clock

Self-configuring based on clock characteristics

• Information contained in ‘Sync’ messages

• All clocks run an identical ‘Best Master Clock’ algorithm

=1588 code & hardware


Page 23

1588 Characterization of Clocks

• Based on primary source of time, e.g. GPS, local oscillator…

• Accuracy

• Variance

• Preferred set membership

• Type: Boundary clock (spans subnets) or ordinary clock

• UUID


Page 24

1588 Timing Related Messages

•Multicast only within a subnet

•Four types of timing messages: Sync, Follow_Up, Delay_Req, Delay_Resp

•Issuing and response to these messages dependent on the ‘state’ of each clock


Page 25

Detection of Sync messages

Application layer


Optional Sync and

Delay_Req message detector

Physical layer

e.g. MII interface in Ethernet


Page 26

IEEE-1588 Code

Network protocol stack & OS

Physical layer

msecs of delay and fluctuation

< 100 nsecs of delay and fluctuation

Repeater, Switch, or

RouterRepeaters & Switches: ~100ns to usecRouters: ~ms

Sync detector & timestamp

generator

Master clock sends:

1. Sync message

2. Follow_up message


Page 27

1588 SynchronizationStep 1:• Sync message sent from

master to slaves• All Sync message

detectors (SMD) note the time on the local clock this message appears at the SMD

• Step 2:• Follow-Up message

containing precise sending time sent from master to slaves

• All slaves compute offset and correct their clock

uProcessor-Aestimated sending time = 9:59.99AM

precise sending time = 10:00AM

SMD-Ameasures Sync message

precise sending time = 10:00AM

Master Clock

uProcessor-Bestimated sending time = 9:59.99AM

receipt time = 10:05AM

SMD-Bmeasures Sync messagereceipt time = 10:05AM

Slave Clock

Sync messageestimated sending time = 9:59.99AM

network

uProcessor-Aprecise sending time =

10:00AM

SMD-A

Master Clock

uProcessor-Bestimated sending time = 9:59.99AM

precise sending time = 10:00AMreceipt time = 10:05AM

SMD-B

Slave Clock

Follow_Up messageprecise sending time = 10:00AM

network

Clockcorrection

circuits

Clock

0:05


Page 28

Synchronization computation

offset = receipt time – precise sending time –one way delay (for a Sync message)

one way delay = {master to slave delay + slave to master delay}/2 (assumes symmetric delay)

master to slave delay = receipt time – precise sending time (for a Sync message)

slave to master delay = Delay_Req receipt time -precise sending time (of a Delay_Req message)


Page 29

Sync messages:

• Issued by clocks in the ‘Master’ state

• Contain clock characterization information

• Contain a estimate of the sending time

• When received by a slave clock the receipt time is noted

• Can be distinguished from other legal messages on the network

• For best accuracy these messages can be easily identified and detected at or near the physical layer and the precise sending (or receipt) time recorded


Page 30

Follow_Up messages:


• Always associated with the preceding Sync message

• Contain the ‘precise sending time’ as measured as close as possible to the physical layer of the network

• When received by a slave clock the ‘precise sending time’ is is used in computations rather than the estimated sending time contained in the Sync message


Page 31

Delay_Req messages:

• Issued by clocks in the ‘Slave’ state

• When received by the master clock the receipt time is noted

• The slave measures and records the sending time

• Can be distinguished from other legal messages on the network

• For best accuracy these messages can be easily identified and detected at or near the physical layer and the precise sending (or receipt) time recorded


Page 32

Delay_Resp messages:


• Always associated with a preceding Delay_Req message from as specific slave clock

• Contain the receipt time of the associated Delay_Req message

• When received by a slave clock the receipt time is noted and used in conjunction with the sending time of the associated Delay_Req message as part of the latency calculation


Page 33

1588 Multiple Subnet Topology

Repeater or

Switch

GPS

Repeater or

Switch

Repeater or

Switch

Repeater or

Switch

Grand Master Clock

Typical Slave Clock

Only Slave Port of Boundary Clock

Typical Master Port of Boundary Clock

=1588 code & hardware

Boundaryclock

Router


Page 34

Multiple Subnet Synchronization &Master Clock Selection

• Boundary clocks do NOT pass Sync, Follow_Up, Delay_Req, or Delay_Resp messages

• Within a subnet a port of a boundary clock acts just like an ordinary clock with respect to synchronization and best master clock algorithm

• The boundary clock internally selects the port that sees the ‘best clock’ as the single slave port. This port is a slave in the selected subnet. All other ports of the boundary clock internally synchronize to this slave port.


Page 35

•Boundary clocks define a parent-child hierarchy of master-slave clocks.

•The best clock in the system is the Grand Master clock.

•If there are cyclic paths in the network topology the best master clock algorithm reduces the logical topology to an acyclic graph.


Page 36

1588 Management Messages

•Management messages are multicast ONLY within a subnet.

•Boundary clocks, not routers, transfer management messages between subnets.

•Management messages allow appropriate query and update of selected database information maintained by each clock.


Page 37

1588 Time Scales

• The time base in a 1588 system is the time base of the Grand Master Clock. All other clocks synchronize (perhaps via boundary clocks) to the grand master.

• The Grand Master Clock time base is implementation dependent.

• If the Grand Master Clock maintains a UTC time base, the 1588 protocol distributes the appropriate leap second information to the slaves.


Page 38

Basic Uses of Explicit Time in Measurement and Control

Time stamping (relative or absolute)

• Time stamping system events for debugging

• Time stamping data to allow correlation with other data or events

Coordination of measurement: (sampling and triggering)

Coordination of action (time based behaviors)

• Timed execution scripts

• Temporal mutual exclusion: (time slots)


Page 39

Measurement setup to test prototypes of an earlier version of 1588

Clock-A Clock-B

Agilent 5372AF&T Analyzer

1 PPS signal

1-4 Ethernet repeaters

Agilent Technologies prototype clock


Page 40

Allan frequency deviations for test oscillators

10-1

100

101

102

103

10410

-12

10 -11

10-10

10-9

10 -8

10-7

Averaging Time, seconds

Alla

n D

evia

tion

CTS CB3LV

10811D


Page 41

Switch Connection

Inexpensive oscillator, fast loop

0

10

20

30

40

50

60

70

-49

0

-42

0

-35

0

-28

0

-21

0

-14

0

-70 0 70

14

0

21

0

28

0

35

0

Offset-nanoseconds

Fre

qu

en

cy

10811D, fast loop

0

10

20

30

40

50

60

70

-46

0

-39

5

-33

0

-26

5

-20

0

-13

5

-70 -5 60

12

5

19

0

25

5

32

0

38

5

Offset-nanoseconds

Fre

qu

en

cy

Inexpensive oscillator, slow loop

0

20

40

60

80

-390

-325

-260

-195

-130 -65 0 65 130

195

260

325

390

Offset-nanoseconds

Fre

qu

ency

10811D, slow loop

0

20

40

60

80

100

-26

0

-21

0

-16

0

-11

0

-60

-10

40

90

14

0

19

0

24

0

29

0

34

0

Offset-nanoseconds

Fre

qu

en

cy

s = 138 ns

s = 92 ns

s = 140 ns

s = 123 ns


Page 42

Repeater ConnectionInexpensive oscillator, fast loop

0

20

40

60

80

100

120

-235

-200

-165

-130 -95

-60

-25

10 45 80 11

5

15

0

18

5

Offset-nanoseconds

Fre

qu

en

cy

10811D, fast loop

0

50

100

150

200

-150

-12

5

-10

0

-75

-50

-25 0 25

50

75

10

0

12

5

Offset-nanoseconds

Fre

qu

en

cy

10811D, slow loop

0

50

100

150

200

250

300

-22

0

-18

5

-15

0

-11

5

-80

-45

-10

25

60

95

13

0

16

5

20

0

Offset-nanoseconds

Fre

qu

en

cy


020406080

100120

-30

0

-25

5

-21

0

-16

5

-12

0

-75

-30

15

60

10

5

15

0

19

5

24

0

Offset-nanoseconds

Fre

qu

en

cy

s = 46 ns

s = 42 ns

s = 75 ns

s = 80 ns


Page 43

Direct Connection

10811D, fast loop

050

100150200250

-80 -65 -50 -35 -20 -5 10 25 40 55 70More

Offset-nanoseconds

Freq

uenc

y

Inexpensive oscillator, fast loop

0

50100150200

250

-145

-125

-105 -85 -65 -45 -25 -5 15 35 55 75

Offset-nanoseconds

Freq

uenc

y


0

20

40

60

80

100

120

140

-32

0

-270

-22

0

-17

0

-120 -7

0

-20

30 80 13

0

18

0

23

0

Offset- nanoseconds

Fre

qu

en

cy

1 0 8 1 1 D , s l o w l o o p

0

1 0 0

2 0 0

3 0 0

4 0 0

5 0 0

6 0 0

-35

-25

-15 -5 5 15 25 35 45

O f f s e t - n a n o s e c o n d s

Fre

qu

en

cy

s = 39 ns

s = 15 ns

s = 34 ns

s = 76 ns


Page 44

Seconds tick deviations: connection via a repeater


Page 45

Seconds tick deviations: connection via a repeater

nanoseconds


Page 46

For further information:

John Eidson, chair 1588 committee, [email protected]

September 24, 2003 IEEE1588 Workshop

http://ieee1588.nist.gov

Jun 2003 Eid Son

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