46242853 Frequency and Time Synchronization in Packet Based Networks

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Frequency and Time Synchronization in
Packet Based Networks Packet Based Networks
BRKAGG-3000
© 2009 Cisco Systems, Inc. All rights reserved. Cisco Public Presentation_ID 1
Topic of This Session Topic of This Session
· Transmit high quality frequency and/or time reference from one or
multiple sources multiple sources…
· … to distinct consumers (applications, users, systems) with
specific synchronization requirements thru Service Provider packet
© 2009 Cisco Systems, Inc. All rights reserved. Cisco Public BRKAGG-3000 2
specific synchronization requirements thru Service Provider packet
networks.
Background Expectation Background 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.
© 2009 Cisco Systems, Inc. All rights reserved. Cisco Public BRKAGG-3000 3
What Will NOT Be Discussed What Will NOT Be Discussed
· Products and implementations
· Tests and performance results
© 2009 Cisco Systems, Inc. All rights reserved. Cisco Public BRKAGG-3000 4
Conventions Conventions
· 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.
© 2009 Cisco Systems, Inc. All rights reserved. Cisco Public BRKAGG-3000 5
Housekeeping Housekeeping
· 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.
· Visit the World of Solutions.
· Please switch off your mobile phones. Please switch off your mobile phones.
· Please be green and make use of the recycling bins
provided.
· Please remember to wear your badge at all times
including the Party.
© 2009 Cisco Systems, Inc. All rights reserved. Cisco Public BRKAGG-3000 6
Agenda Agenda
· Synchronization Problem Statement
· Overview of the Standardization Works
· Frequency Transfer: techniques and deployment q y q p y
Synchronous Ethernet
Adaptive Clock Recovery
· Challenges of Precise Time/Phase Distribution
Two-Way Transfer Time Protocols
· Overview of IEEE Std 1588-2008 for Telecom
· Conclusion & Next steps
© 2009 Cisco Systems, Inc. All rights reserved. Cisco Public BRKAGG-3000 7
p
Problem Statement
What and Why Do We Care About?
© 2009 Cisco Systems, Inc. All rights reserved. Cisco Public BRKAGG-3000 8
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&T
WiMAX
DVB-T/H
3GPP/2
Mobile user
Aggregation
Ethernet
xDSL
DSLAM
Backbone
P
PE
Peer
ISP
TDM /
ATM
P P
Femto-cell
MSE
OLT
xPON
M-CMTS
DOCSIS
Hub & Spoke or Ring
P
Internet
PE
PE
MS
A
PE
Mesh
P
VoD
Content Network
TV
SI
P
Residential
SoHO
© 2009 Cisco Systems, Inc. All rights reserved. Cisco Public BRKAGG-3000 9
P
Enterprise
Synchronization Service Synchronization Service
· Single domain vs. multiple domains
I 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/H
3GPP/2
Mobile
TV
distribution methods.
· Operators may provide synchronization services
to their customers.
Aggregation
WiMAX
Backbone
S
Mobile user
Aggregation
Ethernet
xDSL
DSLAM
Backbone
P
PE
Peer ISP
TDM /
ATM
P P
Femto-cell
UTC
PRC
MSE
OLT
xPON
M-CMTS
Hub & Spoke or Ring
P
Internet
PE
PE
MS
A
PE
Mesh
P
Content Network
Residential
SoHO
© 2009 Cisco Systems, Inc. All rights reserved. Cisco Public BRKAGG-3000 10
DOCSIS VoD TV SIP
Enterprise
UTC
PRC
Key Consumers Key Consumers
· Frequency
TDM interoperability and Co-existence: Circuit Emulation, TDM,
MSAN (MGW)
Access: Wireless Base Stations PON DSL Access: Wireless Base Stations, PON, DSL
· Time and Phase alignment
Wireless Base Stations Wireless Base Stations
SLA and Performance Measurements
BS : Base Station
© 2009 Cisco Systems, Inc. All rights reserved. Cisco Public BRKAGG-3000 11
PON : Passive Optical Network
DSL : Digital Subscriber Line
SLA : Service Level Agreement
Why Is Timing Important?
The Leading Requirements The Leading Requirements
Application Frequency
Phase Alignment
Time Synchronization
TDM t ( CES SDH
PRC-traceability, jitter & wander
TDM support (e.g. CES, SDH
transformation), Access
PRC traceability, jitter & wander
limitations
ITU-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 TDD
Phase alignment between base stations
must be < ±2.5µs
TD-SCDMA
Phase alignment between base stations
must 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 stations
from ±0.5µs to ±50µs (service degradation)
WiMAX Mobile Shall be better than ± 15 ppb
Phase alignment between base stations
must be < ±1µs must be < ±1µs
DVB-S/H//T2 SFN TBD
Cell synchronization accuracy for SFN support
must be < ± 3µs
MB SFN Service
Phase/time alignment between base stations
requirement can vary but in order of µs
© 2009 Cisco Systems, Inc. All rights reserved. Cisco Public BRKAGG-3000 12
One-way delay and jitter
Performance Measurement
To improve precision << 1 ms
for 10 to 100µs measurement accuracy
need ± 1 µs to ± 10µs ToD accuracy
GPS GPS
Use of GPS (and GNSS alternatives)
· Cost
· Limited utilization
raises some concerns:
Limited utilization
Locations
Regulatory & Politics
· Reliability
Geography
V lnerabilit Vulnerability
https://www.gsw2008.net/files/Civ%20Vulne
rabilities GSW2008 pdf
© 2009 Cisco Systems, Inc. All rights reserved. Cisco Public BRKAGG-3000 13
rabilities_GSW2008.pdf
746th Test Squadron
GPS : Global Positioning System
GNSS : Global Navigation Satellite System
“GPS provides many benefits to civilian users.
It is vulnerable however to interference and It is vulnerable, however, to interference and
other disruptions that can have harmful
consequences. GPS users must ensure that consequences. GPS users must ensure that
adequate independent backup systems or
procedures can be used when needed.”
GPS policy, applications, modernization, international cooperation February 01
Interagency GPS Executive Board
© 2009 Cisco Systems, Inc. All rights reserved. Cisco Public BRKAGG-3000 14
“The civil transportation infrastructure, seeking the
i d ffi i d ibl b GPS i increased efficiency made possible by GPS, is
developing a reliance on GPS that can lead to
serious consequences if the service is disrupted serious 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. 01
U.S. Department of Transportation
© 2009 Cisco Systems, Inc. All rights reserved. Cisco Public BRKAGG-3000 15
“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 Policy
Signed by the President of the United States on December 8, 2004, and published
December 15 2004 December 15, 2004.
© 2009 Cisco Systems, Inc. All rights reserved. Cisco Public BRKAGG-3000 16
Alternative to GPS Alternative to GPS
· As Replacement or Backup
· Alternative Radio Navigation
LORAN-C ¬ELORAN
· Atomic Clock
Cheap Scale Atomic Clock
Molecular Clock
· Network Clock
Main topic of this breakout session!
© 2009 Cisco Systems, Inc. All rights reserved. Cisco Public BRKAGG-3000 17
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-PE
N-PE
P
MSE
PE-AGG
P
© 2009 Cisco Systems, Inc. All rights reserved. Cisco Public BRKAGG-3000 18
Synchronization
Equipment
Three Areas Of Study Three Areas Of Study
External Integrated Time and
Frequency Server Frequency Server
· Inter-CO/LAN (WAN)
· Intra-CO, LAN
© 2009 Cisco Systems, Inc. All rights reserved. Cisco Public BRKAGG-3000 19
· Intra-node, -platform
Standardization Development
Organizations Organizations
Who’s doing what?
© 2009 Cisco Systems, Inc. All rights reserved. Cisco Public BRKAGG-3000 20
SDO’s Working Items SDO 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-traceability Target: High Quality Frequency: PRC-traceability
Mobile base stations
Target: Accuracy and stability of radio interface
2. Time Distribution
Purpose: get better result than with current NTP
Wi l b t ti < 1 h li t Wireless base stations: < 1 µs phase alignment accuracy
Performance measurement: minimum 100 µs accuracy
Over constrained network (Service Provider domain)
© 2009 Cisco Systems, Inc. All rights reserved. Cisco Public BRKAGG-3000 21
Over Internet, over NGN
CES : Circuit Emulation Service
MSAN: Multi Service Access Node
Technical Alternatives Technical Alternatives
· Frequency transfer
Parallel (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 ti Packet-based solutions
© 2009 Cisco Systems, Inc. All rights reserved. Cisco Public BRKAGG-3000 22
Overview and Status of SDO Works Overview and Status of SDO Works
SDO Techno Status Scope Market
G.8261(2008)
Service Provider
ITU-T
SG15 Q13
Synchronous
Ethernet
G.8262(2007)+Amend.1
G.8264(2008)
G.781 (2008)
PHY-layer
frequency transfer
Service Provider
(SP) Metro & Core
Ethernet
G 8261 (2006) CES performance
Packet-based
timing
G.8261 (2006)
Multiple working
items: profile, metrics,
modeling…
CES performance
Packet-based
frequency, phase
and time transfer
Service Provider
(SP)
IEEE
1588 PTP
IEEE1588-2002
IEEE1588-2008
No “Telecom” profile
Precise time
distribution
Enterprise: Time
SP: Frequency,
phase and time
¬ITU-T & IETF
802.1AS
Based on
PTP
Ballot
Precise time
distribution
Residential
NTP NTP
NTPv3 Standard
NTPv4: WIP (CY08)
Time distribution
Internet
SP domain
© 2009 Cisco Systems, Inc. All rights reserved. Cisco Public BRKAGG-3000 23
IETF
( )
TICTOC
NTPv5
PTP Profile(s)
New WG approved by
March 08
Frequency and
time transfer
Internet
Specific SP areas
IEEE1588-2008 and Telecom SDO’s
Relationships Relationships
ProfiNet: IEC 61158 Type10
DeviceNet: IEC 62026-3
ControlNet: IEC 61158 Type2
IETF
NTP
yp
IEC
Profiles
IETF
TICTOC
IEEE1588-
2008
(PTPv2)
IEEE
802.1AS
( )
AVB
Profile(s)
Telecom
Profile(s)
On-going
ITU-T ATIS
g g
IEEE 802.3
© 2009 Cisco Systems, Inc. All rights reserved. Cisco Public BRKAGG-3000 24
Q13/15
Telcordia Timestamping
Frequency Transfer
Distribution of Frequency Reference
© 2009 Cisco Systems, Inc. All rights reserved. Cisco Public BRKAGG-3000 25
Frequency Transfer: The Two Options Frequency Transfer: The Two Options
· Physical layer options
Ex: 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 options
Ex: 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!
© 2009 Cisco Systems, Inc. All rights reserved. Cisco Public BRKAGG-3000 26
Timing Network Engineering Principles Timing 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 signal · The 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
© 2009 Cisco Systems, Inc. All rights reserved. Cisco Public BRKAGG-3000 27
PRC : Primary Reference Clock
Source: ETSI EG 201 793 “Synchronization network engineering”
Hierarchical Physical Timing Distribution Hierarchical Physical Timing Distribution
PRS : Primary Reference Source
© 2009 Cisco Systems, Inc. All rights reserved. Cisco Public BRKAGG-3000 28
PRS : Primary Reference Source
BITS : Building Integrated Timing System
Source: Telcordia GR-436-CORE “Digital Network Synchronization Plan”
Centralized Timing Network Architecture Centralized Timing Network Architecture
PRC : Primary Reference Clock (≈ PRS)
SSU : Synchronization Supply Unit (≈ BITS)
SEC : SDH Equipment Clock
Core Network
SEC : SDH Equipment Clock
Aggregation and
Access Networks
© 2009 Cisco Systems, Inc. All rights reserved. Cisco Public BRKAGG-3000 29
Source: ETSI EG 201 793 “Synchronization network engineering”
Distributed Timing Network Architecture Distributed Timing Network Architecture
R i f Receiver for
synchronization
reference signal
© 2009 Cisco Systems, Inc. All rights reserved. Cisco Public BRKAGG-3000 30
Source: ETSI EG 201 793 “Synchronization network engineering”
Timing (Frequency) Architecture Timing (Frequency) Architecture
· Synchronization equipments
PRC (PRS) and SSU (BITS) do not belong to the Transport
network.
· SEC (SDH/SONET Equipment Clock) belong to
Transport network.
© 2009 Cisco Systems, Inc. All rights reserved. Cisco Public BRKAGG-3000 31
They are embedded in Network Element : NE.
Network Synchronization Trail Network Synchronization Trail
· Synchronization information is transmitted through the network via
synchronization network connections synchronization network connections.
· Synchronization network connections are unidirectional and
generally point-to-multipoint.
Stratum 1 level
CO
Stratum 2 level
CO
NE
(Stratum level ≥ 3)
© 2009 Cisco Systems, Inc. All rights reserved. Cisco Public BRKAGG-3000 32
CO Timing Distribution CO Timing Distribution
NE’s
External
NE’s
External
Timing
External
Timing
Input
g
Output
a.k.a.
BITS IN
Figure 4-2. Recommended BITS Implementation with SONET Timing Distribution
© 2009 Cisco Systems, Inc. All rights reserved. Cisco Public BRKAGG-3000 33
Source: Telcordia GR-436-CORE . Digital Network Synchronization Plan
PHY-Layer Transfer Summary PHY Layer Transfer Summary
PRC/PRS
SSU/BITS SSU/BITS
Intra-
office
Intra-office
Inter-office
Inter-office
NE NE NE NE NE NE
Intra-office
PRS PRS
Intra- Intra-
Inter-office
Inter-office
BITS BITS
Intra
office
Intra
office
Intra-office
© 2009 Cisco Systems, Inc. All rights reserved. Cisco Public BRKAGG-3000 34
NE NE NE NE NE NE
Network Synchronization Trail : SSM Network 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
© 2009 Cisco Systems, Inc. All rights reserved. Cisco Public BRKAGG-3000 35
This is a 4-bit field in SDH/SONET frame overhead.
· Purpose: Traceability (and help in prevention of timing loops)
Synchronization Connection Model
SSM Allows Source Traceability SSM Allows Source Traceability
Representation of the PRC p
network connection
Fault
Representation of the
synchronization network
connection in case of
f il
X
failure
Example of restoration
of the synchronization
© 2009 Cisco Systems, Inc. All rights reserved. Cisco Public BRKAGG-3000 36
PRC synchronization network connection
SSU synchronization network connection
SEC synchronization network connection
ITU-T Synchronous Ethernet (SyncE) ITU T Synchronous Ethernet (SyncE)
· PHY-layer frequency transfer solution for IEEE802.3 links
Analogy: licensed vs. unlicensed radio frequency
· Well-known design rules and metrics
Best fit for operators running SONET/SDH Best fit for operators running SONET/SDH
· Fully specified at ITU-T Working Group 15 Question 13
For both 2.048 and 1.544 kbps hierarchies p
· Expected to be fundamental to high quality time transfer
· Drawback : hardware upgrades
All timing chain shall be SyncE capable.
© 2009 Cisco Systems, Inc. All rights reserved. Cisco Public BRKAGG-3000 37
ITU-T Synchronous Ethernet Support ITU T Synchronous Ethernet Support
ITU-T G.8262 (EEC):
Synchronous Ethernet
Equipment Clock
External
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.8261
SyncE interface
Frequency
External timing
interface inputs
External timing
interface inputs
SyncE interface
jitter & wander
Frequency
distribution
traces
PLL
Synchronous
Ethernet capable
Line Card
© 2009 Cisco Systems, Inc. All rights reserved. Cisco Public BRKAGG-3000 38
Synchronous
Ethernet capable
Line Card
ITU-T G.8264
ESMC and SSM-QL
Synchronous Ethernet
capable Equipment
G.8264: ESMC G.8264: ESMC
· Ethernet Synchronization Messaging Channel
Use 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 types · Two message types
Event message sent when QL value change
Information message sent every second
· TLVs
QL-TLV is currently the unique defined TLV.
Other functions can be developed.
© 2009 Cisco Systems, Inc. All rights reserved. Cisco Public BRKAGG-3000 39
p
OSSP : Organization Specific Slow Protocol
G.8264: ESMC Format
0 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 802.3
OSSP
|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 |
| + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + |
Extension
Payload
OSSP
© 2009 Cisco Systems, Inc. All rights reserved. Cisco Public BRKAGG-3000 40
|-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-|
* Allocated by TSB
ITU-T SyncE: Summary
Assuring The Continuity at PHY Layer Assuring The Continuity at PHY Layer
BITS/SSU
BITS/SSU
PRC/PRS
BITS/SSU
ITU-T G.8262
(EEC) Node
SONET/SDH PHY SyncE
PHY 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.
© 2009 Cisco Systems, Inc. All rights reserved. Cisco Public BRKAGG-3000 41
upgrades.
Only the NE part of the engineered timing chain needs SyncE upgrades.
Packet-Based Frequency Distribution Packet Based Frequency Distribution
Reference
Clock
Recovered
Clock
PSN PSN
· Three key steps:
Generation: from signal to packet
Transfer: packet transmission over packet network(s)
© 2009 Cisco Systems, Inc. All rights reserved. Cisco Public BRKAGG-3000 42
Recovery: from packet to signal
CES Frequency Recovery : ACR Mode
Timing Transferred Along the CES Traffic (“in-band”) Timing Transferred Along the CES Traffic ( in band )
ATM or
Packet
Network
TDM
TDM
Adaptive Clock Recovery
and TDM bit stream
TDM PWS IWF
TDM PWS IWF
ATM CES AAL1
TDM source
Clock Source
Service 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
© 2009 Cisco Systems, Inc. All rights reserved. Cisco Public BRKAGG-3000 43
y (
Emulation Service or TDM PWS) requires its own clock recovery.
ACR Methods ACR Methods
· ITU-T Recommendation G.8261 (2008) Adaptive Clock Recovery
Definition Definition
“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 way carried 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 Timestamp y y p
CES (SAToP, CESoPSN) X
IETF NTP (X) X X
IEEE Std 1588-2008 PTP X X X
© 2009 Cisco Systems, Inc. All rights reserved. Cisco Public BRKAGG-3000 44
IETF RTP X X X
Packet-Based Frequency Transfer Packet Based Frequency Transfer
PSN PSN
Clock Source
PEC
PEC
Recovered frequency signal
from packet-based timing
distribution protocol (ACR)
© 2009 Cisco Systems, Inc. All rights reserved. Cisco Public BRKAGG-3000 45
PEC : Packet Equipment Clock
Packet-based Frequency Transfer and
CES CES
Independent Timing Stream
TDM
TDM
IWF
IWF
TDM PW bit stream
Recovered TDM
timing based on
the adaptive
clock recovery
ACR Packet Stream
Reference
Clock
Reference
clock recovery
ACR Packet Stream
PEC
Reference
Clock
TDM
TDM
IWF
&
PEC
IWF
&
PEC
TDM PW bit stream
© 2009 Cisco Systems, Inc. All rights reserved. Cisco Public BRKAGG-3000 46
Clocking method a.k.a. “out-of-band” (here, used for CES clocking)
Question Question
· What does really count for a Service Provider?
¬Guaranteeing the quality of the timing service.
© 2009 Cisco Systems, Inc. All rights reserved. Cisco Public BRKAGG-3000 47
Stability and Accuracy Stability and Accuracy
© 2009 Cisco Systems, Inc. All rights reserved. Cisco Public BRKAGG-3000 48
Source: Diagram from “Time Domain Representation of Oscillator Performance”,
Marc A. Weiss, Ph.D. NIST
Example: GSM Base Station Example: GSM Base Station
· Frequency Accuracy
≤ ±50ppb at base station radio interface (specified)
Turns into ≤ ± 16ppb at base station traffic interface (not
specified*)
· Frequency Stability
For 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.
© 2009 Cisco Systems, Inc. All rights reserved. Cisco Public BRKAGG-3000 49
Example: BS Requirements by MTIE Example: BS Requirements by MTIE
Frequency Accuracy
(Frequency Offset)
ITU-T G 823 ITU T G.823
Traffic Interface
(MRTIE mask)
ITU-T G.823
Synchronization
Interface (MTIE
mask)
© 2009 Cisco Systems, Inc. All rights reserved. Cisco Public BRKAGG-3000 50
Synchronization Measurements Synchronization Measurements
· Phase measurement
Measure signal under test against a reference signal
· Phase deviation plot
¬TIE : Time Interval Error
· Analysis
© 2009 Cisco Systems, Inc. All rights reserved. Cisco Public BRKAGG-3000 51
Synchronization Measurements
Step 1 : Phase Measurements Step 1 : Phase Measurements
O O O O O O O
Ref.
+0.1 +0.1
O O O O O O O
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.
© 2009 Cisco Systems, Inc. All rights reserved. Cisco Public BRKAGG-3000 52
· PHY-layer signals have high frequency (e.g., 1544 kHz)
Synchronization Measurements
Step 2 : Phase Deviation Step 2 : Phase Deviation
· Phase deviation or TIE (Time Interval Error)
© 2009 Cisco Systems, Inc. All rights reserved. Cisco Public BRKAGG-3000 53
Synchronization Measurements
Step 3: Analysis Step 3: Analysis
· Analysis cover different aspects of the
Clock (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
© 2009 Cisco Systems, Inc. All rights reserved. Cisco Public BRKAGG-3000 54
TDEV
Analysis from Phase: Jitter & Wander Analysis from Phase: Jitter & Wander
Signal with jitter and wander present
© 2009 Cisco Systems, Inc. All rights reserved. Cisco Public BRKAGG-3000 55
Analysis from Phase: Jitter Analysis from Phase: Jitter
Jitter: Filter out low-frequency components with high-pass filter
Frequency Jitter range 10 Hz Frequency Jitter range 10 Hz
© 2009 Cisco Systems, Inc. All rights reserved. Cisco Public BRKAGG-3000 56
Analysis from Phase: Wander Analysis from Phase: Wander
Wander: Filter out high-frequency components with low-pass filter
Frequency Wander range 10 Hz Frequency Wander range 10 Hz
© 2009 Cisco Systems, Inc. All rights reserved. Cisco Public BRKAGG-3000 57
Key Stability Transfer Measures 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
· MTIE and TDEV analysis shows comparison to
standard requirements.
Defined by ATIS/ANSI Telcordia/Bellcore ETSI & ITU-T Defined 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.
© 2009 Cisco Systems, Inc. All rights reserved. Cisco Public BRKAGG-3000 58
Ex: Wander Input Tolerance for DS1 Ex: 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).”
© 2009 Cisco Systems, Inc. All rights reserved. Cisco Public BRKAGG-3000 59
the input mask in Figure 5 15 (for an external DS1 reference).
Source: GR-253-CORE (2005)
Ex: SONET Clock Wander Transfer Ex: 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
© 2009 Cisco Systems, Inc. All rights reserved. Cisco Public BRKAGG-3000 60
g q p g
transfer mask in Figure 5-6.”
Source: GR-1244-CORE (2005)
Ex: Holdover Stability for Str3 Clocks Ex: 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
© 2009 Cisco Systems, Inc. All rights reserved. Cisco Public BRKAGG-3000 61
defined by the mask in Figure 5-2.
Source: GR-1244-CORE (2005)
Ex: Wander Generation of SONET NE Ex: 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
© 2009 Cisco Systems, Inc. All rights reserved. Cisco Public BRKAGG-3000 62
input wander.
Ex: Wander Generation of EEC-Option 2 Ex: Wander Generation of EEC Option 2
Source : ITU-T G.8262 (EEC) Source : ITU T G.8262 (EEC)
Synchronous Ethernet Equipment Clock
Option 2 (1,544 kbps hierarchy)
© 2009 Cisco Systems, Inc. All rights reserved. Cisco Public BRKAGG-3000 63
Key Outcomes Key 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 E · The performance of SyncE-capable NE and SyncE
interface are fully specified and metrics exist.
© 2009 Cisco Systems, Inc. All rights reserved. Cisco Public BRKAGG-3000 64
ITU-T G.8261 CES Network Limits ITU T G.8261 CES Network Limits
© 2009 Cisco Systems, Inc. All rights reserved. Cisco Public BRKAGG-3000 65
Source : ITU-T G.8261 / 9.1 CES Network Limits
Wander Budget for 1544 kbps Signal for
G.8261 Deployment Case 1 G.8261 Deployment Case 1
© 2009 Cisco Systems, Inc. All rights reserved. Cisco Public BRKAGG-3000 66
The 1544 kbit/s jitter network limits shall comply with ITU-T Recommendation G.824 clause 5.1.
Monitoring ACR Performance Monitoring 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
?
© 2009 Cisco Systems, Inc. All rights reserved. Cisco Public BRKAGG-3000 67
Packet Delay Variation is key impairment factor for timing.
Timing Measurement with PSN Timing 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 PDV · First approach is to reuse known tools to PDV
analysis/measurement.
Some can be applied to PDV as to TIE Some can be applied to PDV as to TIE.
© 2009 Cisco Systems, Inc. All rights reserved. Cisco Public BRKAGG-3000 68
Recall: Key Stability Transfer Measures Recall: 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 analysis
Packet PDV peaks to highest delay Packet 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
© 2009 Cisco Systems, Inc. All rights reserved. Cisco Public BRKAGG-3000 69
Performance Metrics Performance 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
Phase
TDEV
© 2009 Cisco Systems, Inc. All rights reserved. Cisco Public BRKAGG-3000 70
Crossover Hub Switch Router
Semtech Semtech
© 2009 Cisco Systems, Inc. All rights reserved. Cisco Public BRKAGG-3000 71
Effect of Load on Packet Delay
minTDEV
Effect of Load on Packet Delay
10 Switches, 40% Load
10 Switches, 80% Load
© 2009 Cisco Systems, Inc. All rights reserved. Cisco Public BRKAGG-3000 72
Key Outcomes on Metrics Key Outcomes on Metrics
· One metric would not be sufficient characterizing the
various possible conditions.
Reference
Cl k
Recovered
Cl k Clock Clock
Classification
Master/
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 Public BRKAGG-3000 73
classification) and implementation specific algorithm.
Monitoring ACR Performance Monitoring 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
Clock
PSN Metrics
M t i l t ti
Slave/
Client
Master/
Server
?
?
· Slave implementation
· Protocol parameters
· Evolution of : the PSN design,
· Master implementation
· Slave implementation
© 2009 Cisco Systems, Inc. All rights reserved. Cisco Public BRKAGG-3000 74
the HW & SW NE configuration
the traffic.
ACR Technical Challenges – Summary ACR Technical Challenges Summary
· Application requirements
· Client/Slave
· Server/Master
C f · Protocol and Protocol Configuration
· Network
Network 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 Public BRKAGG-3000 75
Carrier Class
Frequency Distribution Network Design Frequency 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 method
SDH/SONET S E
O PHY-layer
PHY-layer
Freq Transfer
e.g. SyncE
SyncE
consumer
O
EEC
EEC
Consumer
e.g., SDH/SONET, SyncE
PHY-layer Freq
Transfer
O
y
Freq Transfer
e.g. SyncE
Packet-
based
consumer
BITS/SSU BITS/SSU
EEC
EEC
Consumer
Transfer
O
O
PHY-layer Freq
Transfer
© 2009 Cisco Systems, Inc. All rights reserved. Cisco Public BRKAGG-3000 76
BITS/SSU BITS/SSU
PRC/PRS
Thru BITS/SSU
Non-capable PHY Layer Synchronization Network
Packet-based method (ACR)
Frequency Distribution Summary Frequency Distribution Summary
Timing input
EEC
ESMC &
SSM-QL
Mediation function
EEC
Mediation function
Relevant ITU-T
Specifications
Compliancy
SyncE Line
Card
Timing output
Packet-based
timing protocol
© 2009 Cisco Systems, Inc. All rights reserved. Cisco Public BRKAGG-3000 77
What about Time?
French scientist B. Gitton
Water Clock (1979)
© 2009 Cisco Systems, Inc. All rights reserved. Cisco Public BRKAGG-3000 78
Quiz Quiz
John Harrison (1693-1776)
· What is that?
· Who built them?
Wh ?
Precise marine clocks
Longitude position
· Why?
Longitude position
H4 (1755-1759)
H1 (1730-1735)
H2 & H3 (1737-1759)
© 2009 Cisco Systems, Inc. All rights reserved. Cisco Public BRKAGG-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 Protocols
What Specific Challenges
Does Time Distribution Introduce?
© 2009 Cisco Systems, Inc. All rights reserved. Cisco Public BRKAGG-3000 80
Time Synchronization Time Synchronization
System A
System B
System A
System B
timing signal recovered by system A
00:01:02
00:01:01 00:01:00
timing signal recovered by system A
00:01:02
00:01:01 00:01:00
t
ti i i l d b t B
00:01:02
00:01:01 00:01:00
Ex.: UTC, UTC + n x hours
GPS Time, Local arbitrary Time
t
ti i i l d b t B
00:01:02
00:01:01 00:01:00
Ex.: UTC, UTC + n x hours
GPS Time, Local arbitrary Time
timing signal recovered by system B
00:01:02
00:01:01
00:01:00
timing signal recovered by system B
00:01:02
00:01:01
00:01:00
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
© 2009 Cisco Systems, Inc. All rights reserved. Cisco Public BRKAGG-3000 81
associated nodes sharing a common timescale and related epoch.
Absolute vs. Relative Time Absolute 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.
© 2009 Cisco Systems, Inc. All rights reserved. Cisco Public BRKAGG-3000 82
y y g p y
Phase alignment does not mandate giving a time value.
Phase Synchronization Phase Synchronization
· This is not phase locking which is
often a result of a PLL in a
System A
Reference timing signal
to system A
System A
Reference timing signal
to system A
often a result of a PLL in a
physical timing transfer.
Phase locking implies frequency
synchronization and allows phase
System B
φ
B
Reference timing signal
to system B
System B
φ
B
Reference timing signal
to system B
synchronization and allows phase
offset.
· The term phase synchronization
(or phase alignment) implies that
timing signal recovered by system A timing 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
t
timing signal recovered by system B
t
timing signal recovered by system B
g
same instant (within the relevant
phase accuracy requirement).
tt
© 2009 Cisco Systems, Inc. All rights reserved. Cisco Public BRKAGG-3000 83
Figure xxx/G.8266 – Phase Synchronization
Time Distribution for Mobile Wireless BS Time Distribution for Mobile Wireless BS
Target from ±1µs to tens of µs (alignment between BS)
O
Target from ≤ ±0.5µs to tens of µs (from common reference)
O
O
O
Time Source
O
O
O
O
O
O
© 2009 Cisco Systems, Inc. All rights reserved. Cisco Public BRKAGG-3000 84
Accuracy, Stability and Precision Accuracy, Stability and Precision
© 2009 Cisco Systems, Inc. All rights reserved. Cisco Public BRKAGG-3000 85
Syntonization and Synchronization Syntonization and Synchronization
· TWTT protocol client / slave has two processes:
The syntonization
The synchronization
· Strictly speaking the term synchronization applies to alignment · Strictly 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 i · The 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 ) i · The 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”
© 2009 Cisco Systems, Inc. All rights reserved. Cisco Public BRKAGG-3000 86
synchronization is making the wall-clocks equal .
TWTT Protocols
NTP vs PTP Message Exchange NTP vs. PTP Message Exchange
As part of time recovery, there’s always a frequency recovery process.
Master
time
Slave
time
t
Timestamps
known by slave
PTP
Usual unidirectional Usual unidirectional
ACR protocol ACR protocol
t
1
t
2
t
2
t t
t-ms
Sync
Follow_Up
pp
t
t
3
t
1
, t
2
t
1
, t
2
, t
3
t-sm
Delay_Req
NTP
t
4
t
1
, t
2
, t
3
, t
4
Delay_Resp
© 2009 Cisco Systems, Inc. All rights reserved. Cisco Public BRKAGG-3000 87
1 2 3 4
TWTT Protocol Basics
Basic NTP Message Exchange Basic NTP Message Exchange
SERVER
CLIENT
Server time = Ts Client time = Tc = Ts + offset
“Real” T
2
= T
1
+ “Real” Delay
Offset = ((T
2
- T
1
) - (T
4
- T
3
))/2
Server time = Ts Client time = Tc = Ts + offset
Timestamps
known
But… Delay = ((T
2
- T
1
)+(T
4
- T
3
))/2
Time_REQ
T
1
T
2
by client
T
1
T
CS
Time_RESP
2
T
3
T
1
, T
2
, T
3
, T
4
T
SC
© 2009 Cisco Systems, Inc. All rights reserved. Cisco Public BRKAGG-3000 88
T
4
Assumption := symmetry!
TWTT Protocol Basics
Basic PTP Message Exchange Basic PTP Message Exchange
MASTER SLAVE
Master time = T
M
Slave time = T
S
= T
M
+ offset
Ti t
Offset = T
S
- T
M
t
1
Timestamps
known by
slave
Delay
t
2
t
1
, t
2
SYNC
Offset + Delay = A = t2 – t1
t
3
Delay
t
2
t
1
, t
2
, t
3
Delay - Offset = B = t
4
– t
3
t
2
= t
1
+ Offset + Delay
Delay_Req
Delay_Resp
t
4
t
1
, t
2
, t
3
, t
4
t
4
= t
3
- Offset + Delay
© 2009 Cisco Systems, Inc. All rights reserved. Cisco Public BRKAGG-3000 89
1
,
2
,
3
,
4
Offset = ((t
2
– t
1
)–(t
4
– t
3
))/2 Delay = ((t
2
– t
1
)+(t
4
– t
3
))/2
Asymmetry Asymmetry
· Forward and backward delays are not identical.
© 2009 Cisco Systems, Inc. All rights reserved. Cisco Public BRKAGG-3000 90
Asymmetry: A Closer Look Asymmetry: A Closer Look
· Each Node and Link can introduce asymmetry.
Th i f t
© 2009 Cisco Systems, Inc. All rights reserved. Cisco Public BRKAGG-3000 91
· There are various sources of asymmetry.
Sources of Asymmetry Sources of Asymmetry
· Link
Link delays and asymmetry
Asymmetric (upstream/downstream) link techniques
Physical layer clock Physical layer clock
· Node
Different link speed (forward / reverse)
Node design
LC design
E bl d f t Enabled features
· Network
Traffic path inconsistency
© 2009 Cisco Systems, Inc. All rights reserved. Cisco Public BRKAGG-3000 92
p y
Interface speed change
TWTT: Summary of Sources of Error TWTT: Summary of Sources of Error
· Asymmetry: introduce a mean time-error.
time
frequency
· 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-base
Any frequency offset and/or frequency drift will color the measurements Any 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 slave and 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 Public BRKAGG-3000 93
Provided the quality of the oscillator is commensurate with the (long)
time constant!
Two Way Time Transfer Protocols
Summary and Introduction to IEEE Std 1588 Summary 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 ti · IEEE1588 incorporates some in-network correction
mechanisms to improve the quality of the transfer.
· IEEE1588 has the concept of asymmetry correction · IEEE1588 has the concept of asymmetry correction.
But the correction values are not dynamically measured - they
need to be statically configured.
© 2009 Cisco Systems, Inc. All rights reserved. Cisco Public BRKAGG-3000 94
IEEE Std 1588-2008 for Telecom
Challenges of IEEE 1588-2008 applied
in Service Provider networks
© 2009 Cisco Systems, Inc. All rights reserved. Cisco Public BRKAGG-3000 95
“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 Public BRKAGG-3000 96
PTP Version 2 PTP 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 Public BRKAGG-3000 97
· Multiple possible values or range of values, TLVs (possible
extensions), …
PTP Device Types PTP Device Types
· Five basic types of PTP devices (“clocks”)
Ordinary clock (master or slave)
Boundary clock (“master and slave”)
End-to-end Transparent clock End-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 mode clock mode.
· One-step mode breaks IEEE/OSI/IETF/ITU layers.
© 2009 Cisco Systems, Inc. All rights reserved. Cisco Public BRKAGG-3000 98
Basic PTP Message Exchange Basic PTP Message Exchange
MASTER SLAVE
Master time = T
M
Slave time = T
S
t
1
Timestamps
known by
slave
t
2
t t
SYNC
MS_Delay
t
3
SM Delay
t
1
, t
2
, t
3
t
1
, t
2
Delay_Req
Delay_Resp
t
4
SM_Delay
© 2009 Cisco Systems, Inc. All rights reserved. Cisco Public BRKAGG-3000 99
t
1
, t
2
, t
3
, t
4
Quality of the Timestamp Quality of the Timestamp
MASTER SLAVE
MAC/PHY
MAC/PHY
µP
µP
t
SYNC
t
1
t
t
1
Need to inject the
timestamp into the
payload at the
Timestamps
known by
slave
t
2
t
2
payload at the
time the packet
gets out.
t
1
, t
2
Delay_REQ
t
3
t
4
t
3
t
1
, t
2
, t
3
Delay_RESP
t
4
t t t t
© 2009 Cisco Systems, Inc. All rights reserved. Cisco Public BRKAGG-3000 100
y_
Hardware assistance necessary to prevent insertion of errors or inaccuracies.
t
1
, t
2
, t
3
, t
4
Follow Up Follow_Up
MASTER SLAVE
MAC/PHY
MAC/PHY
µP
µP
SYNC()
Timestamps
known by
slave
t
1
t
2
Follow_Up(t
1
)
Two-step clock
mode
Vs.
t
1
, t
2
t
2
Delay_REQ()
t
4
t
3
One-step (a.k.a.
“on-the-fly”)
clock mode
t
1
, t
2
, t
3
Delay RESP(t
4
)
© 2009 Cisco Systems, Inc. All rights reserved. Cisco Public BRKAGG-3000 101
y_ ( )
t
1
, t
2
, t
3
, t
4
Timestamp Generation Model Timestamp 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.
© 2009 Cisco Systems, Inc. All rights reserved. Cisco Public BRKAGG-3000 102
· Need to classify a packet as timing packet.
Telecom Timestamp Generation Issues Telecom Timestamp Generation Issues
· If IEEE 1588-2008 is not planned node to node, with
every node IEEE 1588 aware and in unique every node IEEE 1588 aware and in unique
domain…
· Multiple interface types p yp
IEEE 802.3, ITU-T G.709, …
· Multiple interface frequencies
10GE, 100GE, STM64, STM192…
· Multiple encapsulations
Ethernet, IP
MPLS, MPLS-TP, PBT…
© 2009 Cisco Systems, Inc. All rights reserved. Cisco Public BRKAGG-3000 103
IEEE Std 1588-2008 Clocks IEEE Std 1588 2008 Clocks
· BC and TC aims correcting delay variation into intermediate nodes
between OCs between OCs.
· Can correct link asymmetry if known.
Ref.
Clock
Ordinary
Slave
Ordinary
Master
Clock
Recovered
Clock
TC
BC
Transparent
Clock
Boundary
Clock
© 2009 Cisco Systems, Inc. All rights reserved. Cisco Public BRKAGG-3000 104
IEEE Std 1588-2008 BC IEEE 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
© 2009 Cisco Systems, Inc. All rights reserved. Cisco Public BRKAGG-3000 105
Boundary
Clock
Boundary
Clock
IEEE Std 1588-2008 TC IEEE Std 1588 2008 TC
· TC calculates Residence Time (forward / reverse intra node
delays) delays).
· TC are supposed to be transparent but:
One-step clock issue p
Path consistency
Ordinar
O di
Ref.
Clock
Recovered
Clock
Ordinary
Slave
Ordinary
Master
Transparent Transparent
TC TC
© 2009 Cisco Systems, Inc. All rights reserved. Cisco Public BRKAGG-3000 106
Transparent
Clock
Transparent
Clock
IEEE1588-2008 Transparent Clocks
Residence Time and Correction Field Residence Time and Correction Field
Preamble
Event message payload Network
protocol
headers
Correction
field
Preamble
PTP message payload Network
protocol
headers
Correction
field
Message at ingress Message at egress
+
+
Residence time bridge Ingress Egress
- +
Ingress timestamp Egress timestamp
© 2009 Cisco Systems, Inc. All rights reserved. Cisco Public BRKAGG-3000 107
About Telecom Profiles About Telecom Profiles
· Telecom profiles will require matching the consumer requirements to the
network design and behavior network design and behavior.
· It will involves a set of IEEE Std 1588-2008 parameters as such as
Messages
Options and TLVs
Mode of transmission
Values (e.g., message rates)
Specification of new timestamp points (telecom encapsulation)
· But Service Providers will also need
Metrics Metrics
Node characterization
New Node modeling (IEEE Std 1588-2008 document includes some sort of clock
modeling)
© 2009 Cisco Systems, Inc. All rights reserved. Cisco Public BRKAGG-3000 108
modeling)
Support of new routing functions (e.g. traffic engineering)

Monitoring the Performance Monitoring the Performance
· How to guarantee the recovered clock quality?
PSN
Ref.
Clock
Recovered
Clock
Slave/
Client
Master/
Server
?
?
PSN
Clock
TC
BC
?
?
?
© 2009 Cisco Systems, Inc. All rights reserved. Cisco Public BRKAGG-3000 109
IEEE 1588-2008 (PTPv2) In A Nutshell IEEE 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 TC Multiple 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 ?
© 2009 Cisco Systems, Inc. All rights reserved. Cisco Public BRKAGG-3000 110
Time Distribution
TWTT Technical Challenges – Summary TWTT Technical Challenges Summary
· Application requirements
path symmetry path symmetry
· Client/Slave
· Server/Master
1 88 2008 &
hardware assistance hardware assistance
path consistency path consistency
· IEEE 1588-2008 Boundary &
Transparent Clocks
· Protocol and Protocol Configuration
· Network
Design, Traffic, Nodes
Node design includes BC & TC
· Engineering
© 2009 Cisco Systems, Inc. All rights reserved. Cisco Public BRKAGG-3000 111
Time To Conclude
© 2009 Cisco Systems, Inc. All rights reserved. Cisco Public BRKAGG-3000 112
Challenges for Sync Architectures Challenges 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 t constraints.
· 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 Public BRKAGG-3000 113
Conclusion Conclusion
· Technical alternatives are known.
· Their pros & cons are also known.
· Nothing prevents using packet-based solutions.
f · But packet-based solutions need further work.
· Timing network engineering
Rules Rules
Experience
Monitoring
· Challenges
Cost-efficiency : TCO considerations
M lti d i t f
© 2009 Cisco Systems, Inc. All rights reserved. Cisco Public BRKAGG-3000 114
Multi-domain transfer
Next Steps Next Steps
· Frequency transfer can be achieved.
· Time transfer needs to be improved.
Sub-millisecond is a reachable target.
Sub-microsecond objective is challenging.
· Next Steps
Network element functions and metrics
Protocol “profile”
Architecture
Combining packet-based timing protocol functions with routing
capabilities
© 2009 Cisco Systems, Inc. All rights reserved. Cisco Public BRKAGG-3000 115
p
Some References Some References
· ITU-T* : http://www.itu.int/rec/T-REC-G/e
G.803, G.823, G.8261, G.8262, G.8264, G.781
· Telcordia : http://telecom-info.telcordia.com/site-cgi/ido/index.html
GR-253-CORE, GR-1244-CORE, GR-436-CORE
· ETSI : http://pda.etsi.org/pda/queryform.asp
eg_201 793-010101 (2000) Synchronization network engineering
· IEEE Std 1588 2008 · IEEE Std 1588-2008
http://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 Public BRKAGG-3000 116
*Free for enforced recommendations
**Free
Please Visit the Cisco Booth in the
World of Solutions
· Mobility
World of Solutions
See the technology in action
MOB1 – Collaboration in Motion
MOB2 – Cisco Unified Wireless Network
MOB3 – Mobile High-Speed Performance g p
with 802.11n
© 2009 Cisco Systems, Inc. All rights reserved. Cisco Public BRKAGG-3000 117
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© 2009 Cisco Systems, Inc. All rights reserved. Cisco Public BRKAGG-3000 119
Appendix
Acronyms
© 2009 Cisco Systems, Inc. All rights reserved. Cisco Public BRKAGG-3000 120
Acronyms Acronyms
· ACR : 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 Variation · BITS : 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 Network · GPS : 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 Public BRKAGG-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

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