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
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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.
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What Will NOT Be DiscussedWhat Will NOT Be Discussed
Products and implementations
Tests and performance results
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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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HousekeepingHousekeeping
We value your feedback- don't forget to complete your online session evaluations (20 Passport points each!) after each session & complete the Overall Conference Evaluation which will be available online.
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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
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p
Problem StatementWhat and Why Do We Care About?
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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
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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
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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
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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
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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
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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
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“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
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“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.
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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!
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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
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Synchronization Equipment
Three Areas Of StudyThree Areas Of Study
External Integrated Time and Frequency ServerFrequency Server
Inter-CO/LAN (WAN)
Intra-CO, LAN
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Intra-node, -platform
Standardization DevelopmentOrganizationsOrganizationsWho’s doing what?
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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)
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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
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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
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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
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Q13/15Telcordia Timestamping
Frequency TransferDistribution of Frequency Reference
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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!
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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
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PRC : Primary Reference Clock
Source: ETSI EG 201 793 “Synchronization network engineering”
Hierarchical Physical Timing DistributionHierarchical Physical Timing Distribution
PRS : Primary Reference Source
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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
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Source: ETSI EG 201 793 “Synchronization network engineering”
Distributed Timing Network ArchitectureDistributed Timing Network Architecture
R i fReceiver for synchronization reference signal
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Source: ETSI EG 201 793 “Synchronization network engineering”
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.
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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)
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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
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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
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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
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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
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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.
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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
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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.
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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
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|-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-|
* 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
ITU-T G.8262 (EEC) Node
ITU-T G.8262 (EEC) Node
ITU-T G.8262 (EEC) Node
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.
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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)
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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
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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
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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)
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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
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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.
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Stability and AccuracyStability and Accuracy
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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.
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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)
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Synchronization MeasurementsSynchronization Measurements
Phase measurementMeasure signal under test against a reference signal
Phase deviation plotTIE : Time Interval Error
Analysis
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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.
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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)
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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
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TDEV
Analysis from Phase: Jitter & WanderAnalysis from Phase: Jitter & WanderSignal with jitter and wander present
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Analysis from Phase: JitterAnalysis from Phase: JitterJitter: Filter out low-frequency components with high-pass filter
FrequencyJitter range10 Hz FrequencyJitter range10 Hz
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Analysis from Phase: WanderAnalysis from Phase: WanderWander: Filter out high-frequency components with low-pass filter
FrequencyWander range 10 Hz FrequencyWander range 10 Hz
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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.
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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).”
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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
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g q p gtransfer mask in Figure 5-6.”
Source: GR-1244-CORE (2005)
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
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defined by the mask in Figure 5-2.
Source: GR-1244-CORE (2005)
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
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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)
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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.
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ITU-T G.8261 CES Network LimitsITU T G.8261 CES Network Limits
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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
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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 ?
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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.
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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
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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
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Crossover Hub Switch Router
SemtechSemtech
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Effect of Load on Packet DelayminTDEV
Effect of Load on Packet Delay
10 Switches, 40% Load
10 Switches, 80% Load
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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
© 2009 Cisco Systems, Inc. All rights reserved. Cisco PublicBRKAGG-3000 73
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
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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
© 2009 Cisco Systems, Inc. All rights reserved. Cisco PublicBRKAGG-3000 75
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
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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
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What about Time?French scientist B. Gitton Water Clock (1979)
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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)
© 2009 Cisco Systems, Inc. All rights reserved. Cisco PublicBRKAGG-3000 79
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?
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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
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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.
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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
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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
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Accuracy, Stability and PrecisionAccuracy, Stability and Precision
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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”
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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
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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
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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
© 2009 Cisco Systems, Inc. All rights reserved. Cisco PublicBRKAGG-3000 89
1, 2, 3, 4
Offset = ((t2 – t1)–(t4 – t3))/2Delay = ((t2 – t1)+(t4 – t3))/2
AsymmetryAsymmetry
Forward and backward delays are not identical.
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Asymmetry: A Closer LookAsymmetry: A Closer Look
Each Node and Link can introduce asymmetry.
Th i f t
© 2009 Cisco Systems, Inc. All rights reserved. Cisco PublicBRKAGG-3000 91
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
© 2009 Cisco Systems, Inc. All rights reserved. Cisco PublicBRKAGG-3000 92
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.
© 2009 Cisco Systems, Inc. All rights reserved. Cisco PublicBRKAGG-3000 93
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.
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IEEE Std 1588-2008 for TelecomChallenges of IEEE 1588-2008 applied
in Service Provider networks
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“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
© 2009 Cisco Systems, Inc. All rights reserved. Cisco PublicBRKAGG-3000 96
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
© 2009 Cisco Systems, Inc. All rights reserved. Cisco PublicBRKAGG-3000 97
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.
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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
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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
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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)
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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.
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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…
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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
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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
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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
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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
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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)
© 2009 Cisco Systems, Inc. All rights reserved. Cisco PublicBRKAGG-3000 108
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
??
?
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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 ?
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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
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Time To Conclude
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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?
© 2009 Cisco Systems, Inc. All rights reserved. Cisco PublicBRKAGG-3000 113
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
© 2009 Cisco Systems, Inc. All rights reserved. Cisco PublicBRKAGG-3000 114
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
© 2009 Cisco Systems, Inc. All rights reserved. Cisco PublicBRKAGG-3000 115
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
© 2009 Cisco Systems, Inc. All rights reserved. Cisco PublicBRKAGG-3000 116
*Free for enforced recommendations
**Free
Please Visit the Cisco Booth in theWorld of Solutions
Mobility
World of SolutionsSee the technology in action
MOB1 – Collaboration in Motion
MOB2 – Cisco Unified Wireless Network
MOB3 – Mobile High-Speed Performance g pwith 802.11n
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AppendixAcronyms
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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)
© 2009 Cisco Systems, Inc. All rights reserved. Cisco PublicBRKAGG-3000 121
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