frequency and time synchronization in packet based networks

Frequency and Time Synchronization in Packet Based NetworksPacket Based Networks

BRKAGG-3000

© 2009 Cisco Systems, Inc. All rights reserved. Cisco PublicPresentation_ID 1

Topic of This SessionTopic of This Session

Transmit high quality frequency and/or time reference from one or multiple sourcesmultiple sources…

… to distinct consumers (applications, users, systems) with specific synchronization requirements thru Service Provider packet

© 2009 Cisco Systems, Inc. All rights reserved. Cisco PublicBRKAGG-3000 2

specific synchronization requirements thru Service Provider packet networks.

Background ExpectationBackground Expectation

This session is an Introductory level session.

It is well suited for Packet experts with slight or no timing expertise.

Timing experts with slight or no packet expertise.

Any person having both expertise is welcome even so ☺To get news about what standardization organizations are doing.


What Will NOT Be DiscussedWhat Will NOT Be Discussed

Products and implementations

Tests and performance results


ConventionsConventions

Slides marked with logo are for Information.

Acronyms are usually given at the bottom of the slide.

Acronyms are also listed in Index.y

References to standards are given throughout the presentation.

List of key references and access links are given at the end of the presentation.


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AgendaAgenda

Synchronization Problem Statement

Overview of the Standardization Works

Frequency Transfer: techniques and deploymentq y q p ySynchronous Ethernet

Adaptive Clock Recovery

Challenges of Precise Time/Phase DistributionTwo-Way Transfer Time Protocols

Overview of IEEE Std 1588-2008 for Telecom

Conclusion & Next steps


p

Problem StatementWhat and Why Do We Care About?


Synchronization Why and How are Packet Switched Networks Involved?Why and How are Packet Switched Networks Involved?

Transition from TDM to Ethernet networks.

Connect consumers requiring Frequency and/or Time (F&T) synchronization.

PSN is built with network elements that

Subscriber Access

TDM / ATM

Mobile TV

May have to support F&T distribution

May be consumers of F&TWiMAX

DVB-T/H3GPP/2

Mobile user

AggregationEthernet

xDSLDSLAM

Backbone

PPE

Peer ISPTDM /

ATM

P P

Femto-cell

MSE

OLTxPON

M-CMTSDOCSIS

Hub & Spoke or Ring P Internet

PEPE

MSA

PE

MeshP

VoDContent Network

TV SIP

ResidentialSoHO


PEnterprise

Synchronization ServiceSynchronization Service

Single domain vs. multiple domainsI t t i lti d i t k

Subscriber Access

M bil Internet is a multi-domain network.

Wholesale Ethernet virtual link

Frequency and time could use different distribution methods.

TDM / ATM

DVB-T/H3GPP/2

Mobile TV

distribution methods.

Operators may provide synchronization services to their customers.

Aggregation

WiMAX

Backbone S

Mobile user

AggregationEthernet

xDSL

DSLAM

Backbone

PPE

Peer ISPTDM / ATM

P P

Femto-cellUTC

PRC

MSE

OLTxPON

M-CMTS

Hub & Spoke or Ring

P

Internet

PEPE

MSA

PE

MeshP

Content Network

ResidentialSoHO


DOCSIS VoD TV SIPEnterprise UTC

PRC

Key ConsumersKey Consumers

FrequencyTDM interoperability and Co-existence: Circuit Emulation, TDM, MSAN (MGW)

Access: Wireless Base Stations PON DSLAccess: Wireless Base Stations, PON, DSL

Time and Phase alignmentWireless Base StationsWireless Base Stations

SLA and Performance Measurements

BS : Base Station


PON : Passive Optical NetworkDSL : Digital Subscriber LineSLA : Service Level Agreement

Why Is Timing Important? The Leading RequirementsThe Leading Requirements

Application Frequency Phase AlignmentTime Synchronization

TDM t ( CES SDHPRC-traceability, jitter & wander

TDM support (e.g. CES, SDH transformation), Access

PRC traceability, jitter & wander limitationsITU-T G.8261/G.823/G.824/G.825

GSM, WCDMA and LTE FDD N/A (except for MBMS and SFN)

Phase alignment between base stations

Mobile Base Stations

Frequency assignment (fractional frequency accuracy) shall be better than• ± 50ppb (macrocells)• ± 100ppb (micro- & pico-cells)• ± 250ppb (femtocells)

UMTS TDDPhase alignment between base stationsmust be < ±2.5µs

TD-SCDMAPhase alignment between base stationsmust be < ±3µs

CDMA2K Time alignment error should be less than 3 μs pp ( )CDMA2K and shall be less than 10 μs

LTE TDD Phase alignment between base stationsfrom ±0.5µs to ±50µs (service degradation)

WiMAX Mobile Shall be better than ± 15 ppb Phase alignment between base stationsmust be < ±1µsmust be < ±1µs

DVB-S/H//T2 SFN TBD Cell synchronization accuracy for SFN supportmust be < ± 3µs

MB SFN Service Phase/time alignment between base stationsrequirement can vary but in order of µs


One-way delay and jitterPerformance Measurement

To improve precision << 1 ms for 10 to 100µs measurement accuracyneed ± 1 µs to ± 10µs ToD accuracy

GPSGPS

Use of GPS (and GNSS alternatives)

Cost

Limited utilization

raises some concerns:

Limited utilizationLocations

Regulatory & Politics

ReliabilityGeography

V lnerabilitVulnerability

https://www.gsw2008.net/files/Civ%20Vulnerabilities GSW2008 pdf


rabilities_GSW2008.pdf

746th Test SquadronGPS : Global Positioning System

GNSS : Global Navigation Satellite System

“GPS provides many benefits to civilian users. It is vulnerable however to interference andIt is vulnerable, however, to interference and other disruptions that can have harmful consequences. GPS users must ensure thatconsequences. GPS users must ensure that adequate independent backup systems or procedures can be used when needed.”

GPS policy, applications, modernization, international cooperation February 01Interagency GPS Executive Board


“The civil transportation infrastructure, seeking the i d ffi i d ibl b GPS iincreased efficiency made possible by GPS, is developing a reliance on GPS that can lead to serious consequences if the service is disruptedserious consequences if the service is disrupted, and the applications are not prepared with mitigating equipment and operational procedures.”

Vulnerability Assessment of the Transport Infrastructure Relying on GPS, Aug. 01U.S. Department of Transportation


“In coordination with the Secretary of Homeland Security, develop,

A Report Requires the Secretary of Transportation to:

In coordination with the Secretary of Homeland Security, develop, acquire, operate, and maintain backup position, navigation, and timing capabilities that can support critical transportation, homeland security, and other critical civil and commercial infrastructure applications within the United States, in the event of a disruption of the Global Positioning System or other space-based positioning, navigation, and timing services…”

U.S. Space-Based Positioning, Navigation, and Timing PolicySigned by the President of the United States on December 8, 2004, and published December 15 2004December 15, 2004.


Alternative to GPSAlternative to GPS

As Replacement or Backup

Alternative Radio NavigationLORAN-C ELORAN

Atomic ClockCheap Scale Atomic Clock

Molecular Clock

Network ClockMain topic of this breakout session!


LORAN : LOng Range Aid to Navigation

Distribution in a PoP (e.g., Intra-CO)Distribution in a PoP (e.g., Intra CO)

IP/MPLS

Central or Remote Office

L1 / L2 L2/L3 Domain

PE-AGG N-PEN-PE

P

MSEPE-AGG P


Synchronization Equipment

Three Areas Of StudyThree Areas Of Study

External Integrated Time and Frequency ServerFrequency Server

Inter-CO/LAN (WAN)

Intra-CO, LAN


Intra-node, -platform

Standardization DevelopmentOrganizationsOrganizationsWho’s doing what?


SDO’s Working ItemsSDO s Working Items

1. Frequency Distribution Purpose: transition from TDM to Carrier Ethernet networks

TDM interoperability and co-existence: CES, Access, MSAN (MGW)

Target: High Quality Frequency: PRC-traceabilityTarget: High Quality Frequency: PRC-traceability

Mobile base stations

Target: Accuracy and stability of radio interface

2. Time DistributionPurpose: get better result than with current NTP

Wi l b t ti < 1 h li tWireless base stations: < 1 µs phase alignment accuracy

Performance measurement: minimum 100 µs accuracy

Over constrained network (Service Provider domain)


Over Internet, over NGN CES : Circuit Emulation ServiceMSAN: Multi Service Access Node

Technical AlternativesTechnical Alternatives

Frequency transferParallel (overlay) SDH/SONET network

Radio Navigation (e.g., GPS, LORAN)

PHY-layer mechanisms

Packet-based solutions

f ( )Time transfer (relative and absolute)Radio Navigation (e.g., GPS, LORAN…)

P k t b d l tiPacket-based solutions


Overview and Status of SDO WorksOverview and Status of SDO WorksSDO Techno Status Scope Market

G.8261(2008)Service Provider

ITU-TSG15 Q13

Synchronous Ethernet

G.8262(2007)+Amend.1G.8264(2008)G.781 (2008)

PHY-layer frequency transfer

Service Provider (SP) Metro & Core

Ethernet

G 8261 (2006) CES performancePacket-based timing

G.8261 (2006)

Multiple working items: profile, metrics,

modeling…

CES performance

Packet-based frequency, phase and time transfer

Service Provider (SP)

IEEE1588 PTP

IEEE1588-2002IEEE1588-2008

No “Telecom” profile

Precise time distribution

Enterprise: TimeSP: Frequency, phase and time

ITU-T & IETF

802.1AS Based on PTP Ballot Precise time

distribution Residential

NTP NTPNTPv3 Standard

NTPv4: WIP (CY08)Time distribution

InternetSP domain


IETF( )

TICTOCNTPv5PTP Profile(s)

New WG approved by March 08

Frequency and time transfer

InternetSpecific SP areas

IEEE1588-2008 and Telecom SDO’s RelationshipsRelationships

ProfiNet: IEC 61158 Type10 DeviceNet: IEC 62026-3

ControlNet: IEC 61158 Type2IETFNTP

yp

IEC Profiles

IETFTICTOC

IEEE1588-2008

(PTPv2)IEEE

802.1AS( )AVB

Profile(s)Telecom Profile(s)On-going

ITU-TATIS

g g

IEEE 802.3


Q13/15Telcordia Timestamping

Frequency TransferDistribution of Frequency Reference


Frequency Transfer: The Two OptionsFrequency Transfer: The Two Options

Physical layer optionsEx: SONET/SDH, SDSL, GPON, Synchronous Ethernet

Pros: “carrier-class”, well defined, guaranteed results

Cons: node by node link bit timing, requires HW changes

Packet-based optionsEx: SAToP, CESoPSN, NTP, PTP (protocol of IEEE Std 1588)

Pros: flexible, looks simple, some can do time as well

C th t k d th t k t ffi t i l !Cons: the network and the network traffic, not so simple!


Timing Network Engineering PrinciplesTiming Network Engineering Principles

The task of network synchronization is to distribute the reference signal from the PRC to all network elements requiring synchronization.

The method used for propagating the reference signalThe method used for propagating the reference signal in the network is the master-slave method.

Slave clock must be slaved to clock of higher (or equal)Slave clock must be slaved to clock of higher (or equal) stability. hierarchical model


PRC : Primary Reference Clock

Source: ETSI EG 201 793 “Synchronization network engineering”

Hierarchical Physical Timing DistributionHierarchical Physical Timing Distribution

PRS : Primary Reference Source


PRS : Primary Reference SourceBITS : Building Integrated Timing System

Source: Telcordia GR-436-CORE “Digital Network Synchronization Plan”

Centralized Timing Network ArchitectureCentralized Timing Network ArchitecturePRC : Primary Reference Clock (≈ PRS)SSU : Synchronization Supply Unit (≈ BITS)SEC : SDH Equipment Clock

Core Network

SEC : SDH Equipment Clock

Aggregation and Access Networks



Distributed Timing Network ArchitectureDistributed Timing Network Architecture

R i fReceiver for synchronization reference signal



Timing (Frequency) ArchitectureTiming (Frequency) Architecture

Synchronization equipmentsPRC (PRS) and SSU (BITS) do not belong to the Transport network.

SEC (SDH/SONET Equipment Clock) belong to Transport network.


They are embedded in Network Element : NE.

Network Synchronization TrailNetwork Synchronization Trail

Synchronization information is transmitted through the network via synchronization network connectionssynchronization network connections.

Synchronization network connections are unidirectional and generally point-to-multipoint.

Stratum 1 level CO

Stratum 2 level

CO

NE(Stratum level ≥ 3)


CO Timing DistributionCO Timing Distribution

NE’s External NE’s

External Timing

External Timing Input g

Outputa.k.a. BITS IN

Figure 4-2. Recommended BITS Implementation with SONET Timing Distribution


Source: Telcordia GR-436-CORE . Digital Network Synchronization Plan

PHY-Layer Transfer SummaryPHY Layer Transfer Summary

PRC/PRS

SSU/BITS SSU/BITS

Intra-office

Intra-officeInter-office Inter-office

NE NENE NE NE NE

Intra-office

PRS PRS

Intra- Intra- Inter-officeInter-office

BITS BITS

Intraoffice

Intraoffice

Intra-office


NE NE NE NENE NE

Network Synchronization Trail : SSMNetwork Synchronization Trail : SSM

What clock quality

Stratum 1 level

do I get? Is that the best source I

can use?Stratum 2 level

NE level

can use?

NE level

Some of these synchronized trail contain a communication channel, the Synchronization Status Message (SSM) transporting a quality identifier, the QL (quality level) value.

This is a 4 bit field in SDH/SONET frame overhead


This is a 4-bit field in SDH/SONET frame overhead.

Purpose: Traceability (and help in prevention of timing loops)

Synchronization Connection ModelSSM Allows Source TraceabilitySSM Allows Source Traceability

Representation of the PRC pnetwork connection

Fault Representation of the synchronization network connection in case of f ilX failure

Example of restoration of the synchronization


PRC synchronization network connection

SSU synchronization network connectionSEC synchronization network connection

ITU-T Synchronous Ethernet (SyncE)ITU T Synchronous Ethernet (SyncE)

PHY-layer frequency transfer solution for IEEE802.3 linksAnalogy: licensed vs. unlicensed radio frequency

Well-known design rules and metricsBest fit for operators running SONET/SDHBest fit for operators running SONET/SDH

Fully specified at ITU-T Working Group 15 Question 13For both 2.048 and 1.544 kbps hierarchiesp

Expected to be fundamental to high quality time transfer

Drawback : hardware upgradesAll timing chain shall be SyncE capable.


ITU-T Synchronous Ethernet SupportITU T Synchronous Ethernet SupportITU-T G.8262 (EEC):

Synchronous Ethernet Equipment ClockExternal

Equipment

PRC-traceable signal from BITS/SSU

ITU-T G.781: Clock Selection Process

Equipment BITS/SSU)

External timing interface outputs

IEEE802.3 ± 100ppm

ITU-T G.8261SyncE interface Frequency

External timing interface inputs

External timing interface inputs

SyncE interface jitter & wander

Frequency distribution

traces

PLL Synchronous Ethernet capable

Line Card


Synchronous Ethernet capable

Line Card

ITU-T G.8264ESMC and SSM-QL

Synchronous Ethernet capable Equipment

G.8264: ESMCG.8264: ESMC

Ethernet Synchronization Messaging ChannelUse OSSP from IEEE802.3ay (a revision to IEEE Std 802.3-2005)

Key purpose: transmit SSM (QL)Outcome: Simple and efficient

But designed to support extensions

Protocol model: Event-driven with TLVs

Two message typesTwo message typesEvent message sent when QL value change

Information message sent every second

TLVsQL-TLV is currently the unique defined TLV.

Other functions can be developed.


pOSSP : Organization Specific Slow Protocol

G.8264: ESMC Format0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1

|-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-|| Slow Protocols MAC Address |

G.8264: ESMC Format

|-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-|| Slow Protocol MAC Addr (cont) | Source MAC Addr ||-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-|| Source MAC Address (continued) ||-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-|| | | |

IEEE 802.3OSSP

|Slow Protocols Ethertype 0x8809| Subtype (10) | ITU-OUI Oct 1 ||-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-|| ITU-OUI Octets 2/3 (0x0019A7) | ITU Subtype (0x0001)* ||-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-|| Vers. |C| Reserved || |

ITU-T OUI Header

ESMC Header|-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-|| Type: 0x01 | Length | Resvd | QL ||-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-|| Future TLV #n (extension TLV) ||-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-|| |

QL-TLV

Future TLV | || Padding or Reserved || ||-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-|| FCS || + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + |

ExtensionPayload

OSSP


|-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-|

* Allocated by TSB

ITU-T SyncE: Summary Assuring The Continuity at PHY LayerAssuring The Continuity at PHY Layer

BITS/SSUBITS/SSUPRC/PRS BITS/SSU

ITU-T G.8262 (EEC) Node

SONET/SDH PHY SyncEPHY SyncE




Extension or replacement of SDH/SONET synchronization chain

(EEC) Node (EEC) Node (EEC) Node (EEC) Node

Inherit from previous ITU-T (and Telcordia) recommendations

Difference: frequency transfer path engineering will define the necessary upgrades.


upgrades.Only the NE part of the engineered timing chain needs SyncE upgrades.

Packet-Based Frequency DistributionPacket Based Frequency Distribution

Reference Clock Recovered

Clock

PSNPSN

Three key steps:Generation: from signal to packet

Transfer: packet transmission over packet network(s)


Recovery: from packet to signal

CES Frequency Recovery : ACR ModeTiming Transferred Along the CES Traffic (“in-band”)Timing Transferred Along the CES Traffic ( in band )

ATM orPacket

Network

TDM TDMAdaptive Clock Recoveryand TDM bit stream

TDM PWS IWF TDM PWS IWFATM CES AAL1

TDM sourceClock SourceService Clock

Recovered TDM timing based on the adaptive clock recovery

ATM CES AAL1 ATM CES AAL1

Note: In such mode, every individual TDM stream (Circuit

clock recovery


y (Emulation Service or TDM PWS) requires its own clock recovery.

ACR MethodsACR Methods

ITU-T Recommendation G.8261 (2008) Adaptive Clock Recovery DefinitionDefinition

“In this case the timing recovery process is based on the (inter-) arrival time of the packets (e.g., timestamps or CES packets). The information carried by the packets could be used to support this operation Two waycarried by the packets could be used to support this operation. Two-way or one-way protocols can be used.”

ACR Method One-Way Two-Way Timestampy y p

CES (SAToP, CESoPSN) X

IETF NTP (X) X X

IEEE Std 1588-2008 PTP X X X


IETF RTP X X X

Packet-Based Frequency TransferPacket Based Frequency Transfer

PSNPSN

Clock Source PEC PEC

Recovered frequency signal from packet-based timing distribution protocol (ACR)


PEC : Packet Equipment Clock

Packet-based Frequency Transfer and CESCES Independent Timing Stream

TDM TDM

IWF IWFTDM PW bit stream

Recovered TDM timing based on the adaptive clock recovery

ACR Packet StreamReference

ClockReference clock recovery

ACR Packet StreamPEC

Reference Clock

TDM TDMIWF

&PEC

IWF&

PECTDM PW bit stream


Clocking method a.k.a. “out-of-band” (here, used for CES clocking)

QuestionQuestion

What does really count for a Service Provider?Guaranteeing the quality of the timing service.


Stability and AccuracyStability and Accuracy


Source: Diagram from “Time Domain Representation of Oscillator Performance”,

Marc A. Weiss, Ph.D. NIST

Example: GSM Base StationExample: GSM Base Station

Frequency Accuracy≤ ±50ppb at base station radio interface (specified)

Turns into ≤ ± 16ppb at base station traffic interface (not specified*)

Frequency StabilityFor T1, it shall comply to G.824 traffic mask (specification; 3GPP Rel8)3GPP Rel8)

Sometimes* G.824 synchronization mask preferred

* Note: real requirements are variable as they are dependent on base station clock servo.


Example: BS Requirements by MTIEExample: BS Requirements by MTIE

Frequency Accuracy (Frequency Offset)

ITU-T G 823ITU T G.823Traffic Interface (MRTIE mask)

ITU-T G.823Synchronization Interface (MTIE mask)


Synchronization MeasurementsSynchronization Measurements

Phase measurementMeasure signal under test against a reference signal

Phase deviation plotTIE : Time Interval Error

Analysis


Synchronization MeasurementsStep 1 : Phase MeasurementsStep 1 : Phase Measurements

Ref.

+0.1 +0.1

Signal

-0.1 -0.2 -0.2

0

At a certain signal threshold, time stamp the edges of timing signal.

Signal edges are the significant instants.


PHY-layer signals have high frequency (e.g., 1544 kHz)

Synchronization MeasurementsStep 2 : Phase DeviationStep 2 : Phase Deviation

Phase deviation or TIE (Time Interval Error)


Synchronization MeasurementsStep 3: AnalysisStep 3: Analysis

Analysis cover different aspects of theClock (oscillator)

e.g. in free-running or holdover mode

Signal

Primary used measurement analysis are:Phase (TIE)

Frequency (fractional frequency offset)

FFrequency accuracy

MTIE

TDEV


TDEV

Analysis from Phase: Jitter & WanderAnalysis from Phase: Jitter & WanderSignal with jitter and wander present


Analysis from Phase: JitterAnalysis from Phase: JitterJitter: Filter out low-frequency components with high-pass filter

FrequencyJitter range10 Hz FrequencyJitter range10 Hz


Analysis from Phase: WanderAnalysis from Phase: WanderWander: Filter out high-frequency components with low-pass filter

FrequencyWander range 10 Hz FrequencyWander range 10 Hz


Key Stability Transfer MeasuresKey Stability Transfer Measures

Both MTIE and TDEV are measures of wander over ranges of values.

From very short-term wander to long-term wander

MTIE and TDEV analysis shows comparison to standard requirements.

Defined by ATIS/ANSI Telcordia/Bellcore ETSI & ITU-TDefined by ATIS/ANSI, Telcordia/Bellcore, ETSI & ITU T

E.g., ITU-T G.824, ANSI T1.101 or Telcordia GR-253-CORE

MTIE is a peak detector: simple peak-to-peak analysis.MTIE is a peak detector: simple peak to peak analysis.

TDEV is a highly averaged “rms”-type of calculation.


Ex: Wander Input Tolerance for DS1Ex: Wander Input Tolerance for DS1

“A stratum 3 clock in a SONET NE shall tolerate any arbitrary input reference signal having wander TDEV characteristics less than or equal to the input mask in Figure 5-15 (for an external DS1 reference).”


the input mask in Figure 5 15 (for an external DS1 reference).

Source: GR-253-CORE (2005)

Ex: SONET Clock Wander TransferEx: SONET Clock Wander Transfer

“R5-6 [61v2] When timed by any input signal whose TDEV is at or below the wander tolerance mask in Figure 4-2, the TDEV of the output signals shall be less than or equal to the corresponding wander


g q p gtransfer mask in Figure 5-6.”


Ex: Holdover Stability for Str3 ClocksEx: Holdover Stability for Str3 Clocks

In the case of variable temperature holdover stability tests, this value should be used only in calculating the fractional frequency offset limits defined by the mask in Figure 5 2


defined by the mask in Figure 5-2.


Ex: Wander Generation of SONET NEEx: Wander Generation of SONET NE

Source : Telcordia GR-253-CORE / 5.4.4.3.2 Wander Generation

Wander generation is the process whereby wander appears at the output of a clock in the absence of input wander


input wander.

Ex: Wander Generation of EEC-Option 2Ex: Wander Generation of EEC Option 2

Source : ITU-T G.8262 (EEC)Source : ITU T G.8262 (EEC)Synchronous Ethernet Equipment ClockOption 2 (1,544 kbps hierarchy)


Key OutcomesKey Outcomes

Physical layer signals can be characterized.

Recommendations exist for node clock and interface limits.

Synchronous Ethernet Equipment Clock (EEC) inherits from SONET NE clock specifications.

Th f f S E bl NE d S EThe performance of SyncE-capable NE and SyncE interface are fully specified and metrics exist.


ITU-T G.8261 CES Network LimitsITU T G.8261 CES Network Limits


Source : ITU-T G.8261 / 9.1 CES Network Limits

Wander Budget for 1544 kbps Signal for G.8261 Deployment Case 1G.8261 Deployment Case 1


The 1544 kbit/s jitter network limits shall comply with ITU-T Recommendation G.824 clause 5.1.

Monitoring ACR PerformanceMonitoring ACR Performance

How to guarantee the packet-based recovered clock quality?

Reference Clock

Recovered Clock

OK

DS1 DS1

PSN

Slave/Master/

DS1 DS1

Slave/ Client

Master/ Server ?


Packet Delay Variation is key impairment factor for timing.

Timing Measurement with PSNTiming Measurement with PSN

TIE is still a valid measurement for characterizing the packet-based servo (slave).

Oscillators and timing interfaces

How can the PSN behavior be characterized? Packet Delay Variation (PDV)

Fi h i k l PDVFirst approach is to reuse known tools to PDV analysis/measurement.

Some can be applied to PDV as to TIESome can be applied to PDV as to TIE.


Recall: Key Stability Transfer MeasuresRecall: Key Stability Transfer Measures

Both MTIE and TDEV are measures of wander over ranges of values from very short-term wander to long-term wander.

Packet flow rate vs physical rate : low & high frequency?Packet flow rate vs. physical rate : low & high frequency?

MTIE is a peak detector: simple peak-to-peak analysisPacket PDV peaks to highest delayPacket PDV peaks to highest delay.

TDEV is a highly averaged “rms”type of calculation: statistical analysis for spectral content (energy) of phase noise.

Average (mean) value over observation window


Performance MetricsPerformance Metrics

Phase (Packet Delay vs. Time)B i f ll l l ti

MTIE

Basis for all calculations

MTIE (Maximum Time Interval Error)Typically one dimensional for packet delay data

TDEV (Ti D i ti )TDEV (Time Deviation)Useful indicator of network traffic load

PhaseTDEV


Crossover Hub Switch Router

SemtechSemtech


Effect of Load on Packet DelayminTDEV

Effect of Load on Packet Delay

10 Switches, 40% Load

10 Switches, 80% Load


Key Outcomes on MetricsKey Outcomes on Metrics

One metric would not be sufficient characterizing the various possible conditions.

Reference Cl k

Recovered Cl kClock Clock

ClassificationMaster/ Server

PSN

Classification (metric)

Common, generic PSN metrics for timing performance g p

characterization?

Today, very close relationship between metric (packet


classification) and implementation specific algorithm.

Monitoring ACR PerformanceMonitoring ACR Performance

Even with (still to be agreed) metrics, other parameters will i iti l

Reference Cl k

Recovered PSN Metrics

remain critical.

PSN

Clock ClockPSN Metrics

M t i l t ti

Slave/ ClientMaster/

Server ? ?Slave implementation

Protocol parametersEvolution of : the PSN design,

Master implementation Slave implementation


the HW & SW NE configuration the traffic.

ACR Technical Challenges – SummaryACR Technical Challenges Summary

Application requirements

Client/Slave

Server/Master

C fProtocol and Protocol Configuration

NetworkNetwork Design (nodes and links)Network Design (nodes and links)

Node design

Network Traffic

Engineering Assessing & Monitoring

C i Cl


Carrier Class

Frequency Distribution Network DesignFrequency Distribution Network Design

1. PHY-layer Synchronization Distribution guarantees the quality.

2. Packet-based Synchronization Distribution for flexibility.

3. Mixing the option for getting best of both solutions.

SEC

PHY-layer methodSDH/SONET S E

PHY-layer

PHY-layer Freq Transfer

e.g. SyncE

SyncE consumer

EEC

EEC

Consumer

e.g., SDH/SONET, SyncE

PHY-layer Freq Transfer

yFreq Transfer

e.g. SyncEPacket-based

consumer

BITS/SSUBITS/SSU

EECEEC

Consumer TransferPHY-layer Freq

Transfer


BITS/SSUBITS/SSU

PRC/PRSThru BITS/SSU

Non-capable PHY Layer Synchronization Network

Packet-based method (ACR)

Frequency Distribution SummaryFrequency Distribution Summary

Timing input

EEC

ESMC & SSM-QL

Mediation functionEEC Mediation function

Relevant ITU-TSpecificationsCompliancy

SyncE Line Card

Timing output Packet-based timing protocol


What about Time?French scientist B. Gitton Water Clock (1979)


QuizQuiz

John Harrison (1693-1776) What is that?Who built them?Wh ?

Precise marine clocks

Longitude positionWhy? Longitude position

H4 (1755-1759)

H1 (1730-1735)

H2 & H3 (1737-1759)


The H4 watch's error was computed to be 39.2 seconds over a voyage of 47 days, three times better than required to win the £20,000 longitude prize.

TWTT ProtocolsWhat Specific Challenges

Does Time Distribution Introduce?


Time SynchronizationTime Synchronization

System A System BSystem A System B

timing signal recovered by system A00:01:0200:01:0100:01:00

timing signal recovered by system A00:01:0200:01:0100:01:00

tti i i l d b t B

00:01:0200:01:0100:01:00

Ex.: UTC, UTC + n x hoursGPS Time, Local arbitrary Timet

ti i i l d b t B

00:01:0200:01:0100:01:00

Ex.: UTC, UTC + n x hoursGPS Time, Local arbitrary Time

timing signal recovered by system B00:01:0200:01:0100:01:00

timing signal recovered by system B00:01:0200:01:0100:01:00

Figure xxx/G.8266 – Time Synchronization

Time synchronization is the distribution of a time reference, all the i t d d h i ti l d l t d h

tt


associated nodes sharing a common timescale and related epoch.

Absolute vs. Relative TimeAbsolute vs. Relative Time

Transmitting time reference can be absolute (from national standards) or relative (bounded timekeeping system)standards) or relative (bounded timekeeping system).

Time synchronization is one way achieving phase synchronization.


y y g p yPhase alignment does not mandate giving a time value.

Phase SynchronizationPhase Synchronization

This is not phase locking which is often a result of a PLL in a

System AReference timing signalto system A System AReference timing signalto system A

often a result of a PLL in a physical timing transfer.

Phase locking implies frequency synchronization and allows phase

System BφB

Reference timing signalto system B System B

φBReference timing signalto system B

synchronization and allows phase offset.

The term phase synchronization (or phase alignment) implies that

timing signal recovered by system Atiming signal recovered by system A

(or phase alignment) implies that all associated nodes have access to a reference timing signal whose significant events occur at the

ttiming signal recovered by system B

ttiming signal recovered by system B

gsame instant (within the relevant phase accuracy requirement).

tt


Figure xxx/G.8266 – Phase Synchronization

Time Distribution for Mobile Wireless BSTime Distribution for Mobile Wireless BS

Target from ±1µs to tens of µs (alignment between BS)

Target from ≤ ±0.5µs to tens of µs (from common reference)

Time Source


Accuracy, Stability and PrecisionAccuracy, Stability and Precision


Syntonization and SynchronizationSyntonization and Synchronization

TWTT protocol client / slave has two processes:The syntonization

The synchronization

Strictly speaking the term synchronization applies to alignmentStrictly speaking, the term synchronization applies to alignment of time and the term syntonization applies to alignment of frequency.

Th t / d l / li t l k h h th iThe master/server and slave/client clocks each have their own time-base and own wall-clock and the intent is to make the slave/client “equal” to the master/server.

Th ti f f h i ti ( t i ti ) iThe notion of frequency synchronization (or syntonization) is making the time-bases “equal”, allowing a fixed (probably unknown) offset in the wall-clocks. The notion of time synchronization is making the wall-clocks “equal”


synchronization is making the wall-clocks equal .

TWTT ProtocolsNTP vs PTP Message ExchangeNTP vs. PTP Message Exchange

As part of time recovery, there’s always a frequency recovery process.

Mastertime

Slavetime

t

Timestampsknown by slave

PTP

Usual unidirectional Usual unidirectional ACR protocolACR protocol

t1

t2t2

t t

t-msSync

Follow_Up

pp

t

t3

t1, t2

t1, t2, t3

t-smDelay_Req

NTPt4

t1, t2, t3, t4

Delay_Resp


1 2 3 4

TWTT Protocol BasicsBasic NTP Message ExchangeBasic NTP Message Exchange

SERVER CLIENT

Server time = Ts Client time = Tc = Ts + offset

“Real” T2 = T1 + “Real” DelayOffset = ((T2 - T1) - (T4 - T3))/2

Server time = Ts Client time = Tc = Ts + offset

Timestamps known

But… Delay = ((T2 - T1)+(T4 - T3))/2

Time_REQ T1

T2

by client

T1T CS

Time_RESP

2

T3T1, T2, T3, T4

T SC


T4

Assumption := symmetry!

TWTT Protocol BasicsBasic PTP Message ExchangeBasic PTP Message Exchange

MASTER SLAVEMaster time = TM Slave time = TS = TM + offset

Ti t

Offset = TS - TM

t1

Timestamps known by slave

Delay

t2 t1, t2

SYNC Offset + Delay = A = t2 – t1

t3

Delay

t2

t1, t2, t3

Delay - Offset = B = t4 – t3 t2 = t1 + Offset + Delay

Delay_Req

Delay_Resp

t4

t1, t2, t3, t4

t4 = t3 - Offset + Delay


1, 2, 3, 4

Offset = ((t2 – t1)–(t4 – t3))/2Delay = ((t2 – t1)+(t4 – t3))/2

AsymmetryAsymmetry

Forward and backward delays are not identical.


Asymmetry: A Closer LookAsymmetry: A Closer Look

Each Node and Link can introduce asymmetry.

Th i f t


There are various sources of asymmetry.

Sources of AsymmetrySources of Asymmetry

Link Link delays and asymmetry

Asymmetric (upstream/downstream) link techniques

Physical layer clockPhysical layer clock

NodeDifferent link speed (forward / reverse)

Node design

LC design

E bl d f tEnabled features

NetworkTraffic path inconsistency


p y

Interface speed change

TWTT: Summary of Sources of ErrorTWTT: Summary of Sources of Error

Asymmetry: introduce a mean time-error. timefrequency

Also transit delay variation (a.k.a. PDV or packet jitter): The standard deviation of the time-base and time-error error will increase with increasing time-delay variation in the path(s) between g y p ( )master and slave.

Inaccuracy of the slave time-baseAny frequency offset and/or frequency drift will color the measurementsAny frequency offset and/or frequency drift will color the measurements.

The standard deviation of the time-base and time-error error will decrease with increasing rate of packet exchange between master and slaveand slave.

Increasing the averaging time does reduce the standard deviation of the time-base and time-error error.


Provided the quality of the oscillator is commensurate with the (long) time constant!

Two Way Time Transfer ProtocolsSummary and Introduction to IEEE Std 1588Summary and Introduction to IEEE Std 1588

Basis of all packet time transfer protocols (NTP, IEEE1588) is the two way time transfer mechanism.

TWTT consists of a time transfer mechanism and a time delay “radar”time delay radar .

Assumes path symmetry and path consistency.

IEEE1588 i t i t k tiIEEE1588 incorporates some in-network correction mechanisms to improve the quality of the transfer.

IEEE1588 has the concept of asymmetry correctionIEEE1588 has the concept of asymmetry correction.But the correction values are not dynamically measured - they need to be statically configured.


IEEE Std 1588-2008 for TelecomChallenges of IEEE 1588-2008 applied

in Service Provider networks


“This standard specifies: a) The Precision Time Protocol, and b) The node, system, and communication properties necessary to support PTP “necessary to support PTP.

IEEE Std 1588-2008


PTP Version 2PTP Version 2

A set of event messages consisting of:

A set of general messages consisting of:consisting of:

- Sync

- Delay_Req

consisting of:- Follow_Up

- Delay_Resp

- Pdelay_Req

- Pdelay_Resp

- Pdelay_Resp_Follow_Up

- Announce

M- Management

- Signaling

Transmission modes: either unicast or multicast (can be mixed)

Encapsulations: L2 Ethernet, IPv4, IPv6 (others possible)

Multiple possible values or range of values TLVs (possible


Multiple possible values or range of values, TLVs (possible extensions), …

PTP Device TypesPTP Device Types

Five basic types of PTP devices (“clocks”)Ordinary clock (master or slave)

Boundary clock (“master and slave”)

End-to-end Transparent clockEnd-to-end Transparent clock

Peer-to-peer Transparent clock

Management node

All five types implement one or more aspects of the PTP protocol.

OC Master, BC and TC running either in one-step or two-step clock modeclock mode.

One-step mode breaks IEEE/OSI/IETF/ITU layers.


Basic PTP Message ExchangeBasic PTP Message ExchangeMASTER SLAVE

Master time = TM Slave time = TS

t1Timestamps known by slave

t2t t

SYNCMS_Delay

t3

SM Delayt1, t2, t3

t1, t2

Delay_Req

Delay_Resp

t4

SM_Delay


t1, t2, t3, t4

Quality of the TimestampQuality of the TimestampMASTER SLAVE

MAC/PHY MAC/PHYµP µP

tSYNC

t1

t

t1Need to inject the timestamp into the payload at the

Timestamps known by slave

t2t2payload at the time the packet gets out.

t1, t2

Delay_REQ

t3

t4

t3 t1, t2, t3

Delay_RESP

t4

t t t t


y_

Hardware assistance necessary to prevent insertion of errors or inaccuracies.

t1, t2, t3, t4

Follow UpFollow_UpMASTER SLAVE

MAC/PHY MAC/PHYµP µP

SYNC() Timestamps known by slave

t1

t2Follow_Up(t1)

Two-step clock modeVs. t1, t2

t2

Delay_REQ()t4

t3

One-step (a.k.a. “on-the-fly”) clock mode t1, t2, t3

Delay RESP(t4)


y_ ( )t1, t2, t3, t4

Timestamp Generation ModelTimestamp Generation Model

Need to timestamp timing packet from timestamp point.Need to timestamp timing packet from timestamp point.

Timestamp point shall be identical at ingress and egress.Location is not so important if consistent.


Need to classify a packet as timing packet.

Telecom Timestamp Generation IssuesTelecom Timestamp Generation Issues

If IEEE 1588-2008 is not planned node to node, with every node IEEE 1588 aware and in uniqueevery node IEEE 1588 aware and in unique domain…Multiple interface typesp yp

IEEE 802.3, ITU-T G.709, …

Multiple interface frequencies10GE, 100GE, STM64, STM192…

Multiple encapsulationsEthernet, IP MPLS, MPLS-TP, PBT…


IEEE Std 1588-2008 ClocksIEEE Std 1588 2008 Clocks

BC and TC aims correcting delay variation into intermediate nodes between OCsbetween OCs.

Can correct link asymmetry if known.

Ref. Clock

Ordinary Slave

Ordinary Master

ClockRecovered Clock

TC BC

Transparent Clock

Boundary Clock


IEEE Std 1588-2008 BCIEEE Std 1588 2008 BC

Equivalent to NTP Stratum (>1) Server

Can help on scalability when using unicast.

Issue: time dispersion? BC slave function is critical.

Ordinar O di Ref. Clock

Recovered Clock

Ordinary Slave

Ordinary Master

BC

Boundary

BC

Boundary


Boundary Clock

Boundary Clock

IEEE Std 1588-2008 TCIEEE Std 1588 2008 TC

TC calculates Residence Time (forward / reverse intra node delays)delays).

TC are supposed to be transparent but: One-step clock issuep

Path consistency

Ordinar O di Ref. Clock

Recovered Clock

Ordinary Slave

Ordinary Master

Transparent Transparent

TC TC


Transparent Clock

Transparent Clock

IEEE1588-2008 Transparent ClocksResidence Time and Correction FieldResidence Time and Correction Field

PreambleEvent message payload Network

protocolheadersCorrection

field

PreamblePTP message payload Network

protocolheadersCorrection

field

Message at ingress Message at egress

++

Residence time bridgeIngress Egress

- +Ingress timestamp Egress timestamp


About Telecom ProfilesAbout Telecom Profiles

Telecom profiles will require matching the consumer requirements to the network design and behaviornetwork design and behavior.

It will involves a set of IEEE Std 1588-2008 parameters as such asMessages

Options and TLVs

Mode of transmission

Values (e.g., message rates)

Specification of new timestamp points (telecom encapsulation)

But Service Providers will also needMetricsMetrics

Node characterization

New Node modeling (IEEE Std 1588-2008 document includes some sort of clock modeling)


modeling)

Support of new routing functions (e.g. traffic engineering)

…

Monitoring the PerformanceMonitoring the Performance

How to guarantee the recovered clock quality?

PSN

Ref. Clock

Recovered Clock

Slave/ Client

Master/ Server? ?

PSNClockTC BC

??

?


IEEE 1588-2008 (PTPv2) In A NutshellIEEE 1588 2008 (PTPv2) In A Nutshell

IEEE Std 1588-2008 is actually a “toolbox”.

The protocol can use various encapsulations, transmission modes, messages, parameters and parameter values…

Multiple “Clocks” are defined: OC (slave/master) BC TC P2P TCMultiple Clocks are defined: OC (slave/master), BC, TC P2P, TC E2E, with specific functions and possible implementations.

IEEE 1588-2008 added the concept of PTP profile.

Moreover, IEEE1588 recommendations are not sufficient for telecom operator operations.

Node characterization, interoperability, performance and metrics…

What does “support of IEEE 1588” mean ?


Time Distribution TWTT Technical Challenges – SummaryTWTT Technical Challenges Summary

Application requirementspath symmetrypath symmetryClient/Slave

Server/Master

1 88 2008 &hardware assistancehardware assistance

path consistencypath consistency

IEEE 1588-2008 Boundary & Transparent Clocks

Protocol and Protocol Configuration

NetworkDesign, Traffic, Nodes

Node design includes BC & TC

Engineering


Time To Conclude


Challenges for Sync ArchitecturesChallenges for Sync Architectures

Timing is a new service many networks shall have to support.

Different solutions are necessary to cover disparate requirements, network designs and conditions.

Physical layer solutions required to upgrade routers and switches.y y q pg

Packet-based solutions are more flexible but less deterministic.

Whatever the timing protocol, it must deal with the same network t i tconstraints.

How can the network better support timing service?Hardware upgrade?Hardware upgrade?

Software functions?

Metrics and characterizations?


ConclusionConclusion

Technical alternatives are known.

Their pros & cons are also known.

Nothing prevents using packet-based solutions.

fBut packet-based solutions need further work.

Timing network engineeringRulesRules

Experience

Monitoring

ChallengesCost-efficiency : TCO considerations

M lti d i t f


Multi-domain transfer

Next StepsNext Steps

Frequency transfer can be achieved.

Time transfer needs to be improved.Sub-millisecond is a reachable target.

Sub-microsecond objective is challenging.

Next StepsNetwork element functions and metrics

Protocol “profile”

Architecture

Combining packet-based timing protocol functions with routing capabilities


p

Some ReferencesSome References

ITU-T* : http://www.itu.int/rec/T-REC-G/eG.803, G.823, G.8261, G.8262, G.8264, G.781

Telcordia : http://telecom-info.telcordia.com/site-cgi/ido/index.htmlGR-253-CORE, GR-1244-CORE, GR-436-CORE

ETSI : http://pda.etsi.org/pda/queryform.aspeg_201 793-010101 (2000) Synchronization network engineering

IEEE Std 1588 2008IEEE Std 1588-2008http://www.ieee.org/web/publications/standards/index.html

IETF**NTP : http://www.ietf.org/html.charters/ntp-charter.html

TICTOC : http://www.ietf.org/html.charters/tictoc-charter.html


*Free for enforced recommendations

**Free

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AppendixAcronyms


AcronymsAcronymsACR : Adaptive Clock Recovery

AVB : Audio Video Bridging

BITS : Building Integrated Timing System

OLT : Optical Line Terminal (PON)

OSSP : Organization Specific Slow Protocol

PDV : Packet Delay VariationBITS : Building Integrated Timing System

BS : Base Station

CDMA : Code Division Multiple Access

CES : Circuit Emulation Service

DSL : Digital Subscriber Line

DTI : DOCSIS Timing Interface

PDV : Packet Delay Variation

PON : Passive Optical Network

PPS : Pulse Per Second

PRC : Primary Reference Clock

PRS : Primary Reference Source

PSN : Packet Switched Network

DVB : Digital Video Broadcast

DVB-T/H : DVB Terrestrial / Handheld

ESMC : Ethernet Synchronization Messaging Channel

FDD : Frequency Division Duplexing

GNSS : Global Navigation Satellite System

GPS : Global Positioning System

PTP : Precision Time Protocol

QL : Quality Level

SDO : Standardization Development Organizations

SDSL : Symmetric Digital Subscriber Line

SEC : SDH Equipment Clock

SFN : Single Frequency NetworkGPS : Global Positioning System

GSM : Global System for Mobile communications

IPDV : Inter-Packet Delay Variation

IRIG : Inter Range Instrumentation Group

LORAN : LOng Range Aid to Navigation

LTE : Long Term Evolution

SFN : Single Frequency Network

SLA : Service Level Agreement

SP : Service Provider

SSM : Synchronization Status Message

SSU : Synchronization Supply Unit

SyncE : ITU-T Synchronous Ethernet

MAFE : Maximum Averaged Frequency Error

MATIE : Maximum Averaged Time Interval Error

MB(M)S : Multicast Broadcast (Multimedia) Services

MBSFN : Multicast Broadcast Single Frequency Network

M-CMTS : Modular Cable Modem Termination System

MSAN : Multi Service Access Node

TDD : Time Division Duplexing

TDEV : Time DEViation

TDM : Time Division Multiplexing

TD-SCDMA : Time Division – Synchronous CDMA

TIE : Time Interval Error

TWTT : Two Way Time Transfer (protocol)


MSAN : Multi Service Access Node

MRTIE : Maximum Relative Time Interval Error

MTIE : Maximum Time Interval Error

NGN : Next Generation Network

NTP : Network Time Protocol

TWTT : Two Way Time Transfer (protocol)

UTC : Coordinated Universal Time

UTMS : Universal Mobile Telecommunications System

WCDMA : Wideband CDMA

WIP : Work In Progress

frequency and time synchronization in packet based networks

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