Table of Contents
Foreword
Abbreviations and Acronyms
Acknowledgments
Introduction
I.1. The importance of synchronization in future telecommunications networks
I.2. Purpose of this book
I.3. Differences between frequency and phase/time
I.4. From traditional TDM synchronization to new mobile applications
I.5. Structure of the book
I.6. Standardization
I.7. Bibliography
Chapter 1 Network Evolutions, Applications and Their Synchronization Requirements
1.1. Introduction
1.2. Evolution from plesiochronous digital hierarchy to optical transport networks
1.3. Migration and evolution in the next-generation networks: from time division multiplexing to packet networks
1.4. Mobile networks and mobile backhaul
1.5. Synchronization requirements in other applications
1.6. The need to define new synchronization technologies
1.7. Bibliography
Chapter 2 Synchronization Technologies
2.1. Fundamental aspects related to network synchronization
2.2. Timing transport via the physical layer
2.3. Packet timing
2.4. IEEE 1588 and its Precision Time Protocol
2.5. The concept of “profiles”
2.6. Other packet-based protocols
2.7. GNSS and other radio clock sources
2.8. Summary
2.9. Bibliography
Chapter 3 Synchronization Network Architectures in Packet Networks
3.1. The network synchronization layer
3.2. Functional modeling
3.3. Frequency synchronization topologies and redundancy schemes using SyncE
3.4. The IEEE 1588 standard and its applicability in telecommunication networks
3.5. Frequency synchronization topologies and redundancy schemes using IEEE 1588
3.6. Time synchronization topologies and redundancy schemes
3.7. Bibliography
Chapter 4 Synchronization Design and Deployments
4.1. High-level principles
4.2. MAKE or BUY network synchronization strategies
4.3. Deployment of timing solutions for frequency synchronization needs
4.4. Deployment of timing solutions for accurate phase/time synchronization needs
4.5. Bibliography
Chapter 5 Management and Monitoring of Synchronization Networks
5.1. Introduction
5.2. Network management systems and the telecommunications management network (TMN)
5.3. Synchronization Network management: the synchronization plan and protection
5.4. Provisioning and setup: manual versus automatic
5.5. Monitoring functions
5.6. Management issues in wireless backhaul
5.7. Network OS integration: M.3000 versus SNMP
5.8. Bibliography
Chapter 6 Security Aspects Impacting Synchronization
6.1. Security and synchronization
6.2. Security of the timing source
6.3. Security of synchronization distribution
6.4. Synchronization risk management
6.5. Bibliography
Chapter 7 Test and Measurement Aspects of Packet Synchronization Networks
7.1. Introduction
7.2. Traditional metrics
7.3. Equipment configuration
7.4. Reference signals, cables and connectors
7.5. Testing Synchronous Ethernet
7.6. Testing the IEEE 1588 end-to-end telecom profile
7.7. Bibliography
Appendix 1 Standards in Telecom Packet Networks Using Synchronous Ethernet and/or IEEE 1588
A1.1. Introduction
A1.2. General content of ITU-T standards
A1.3. Summary of standards
A1.4. Bibliography
Appendix 2 Jitter Estimation by Statistical Study (JESS) Metric Definition
A2.1. Mathematical definition of JESS
A2.2. Mathematical definition of JESS-w
Permissions and Credits
Biography
Index
First published 2013 in Great Britain and the United States by ISTE Ltd and John Wiley & Sons, Inc.
Apart from any fair dealing for the purposes of research or private study, or criticism or review, as permitted under the Copyright, Designs and Patents Act 1988, this publication may only be reproduced, stored or transmitted, in any form or by any means, with the prior permission in writing of the publishers, or in the case of reprographic reproduction in accordance with the terms and licenses issued by the CLA. Enquiries concerning reproduction outside these terms should be sent to the publishers at the undermentioned address:
ISTE Ltd
27-37 St George’s Road
London SW19 4EU
UK
www.iste.co.uk
John Wiley & Sons, Inc.
111 River Street
Hoboken, NJ 07030
USA
www.wiley.com
© ISTE Ltd 2013
The rights of Jean-Loup Ferrant, Mike Gilson, Sébastien Jobert, Michael Mayer, Laurent Montini, Michel Ouellette, Silvana Rodrigues, Stefano Ruffini to be identified as the authors of this work have been asserted by them in accordance with the Copyright, Designs and Patents Act 1988.
Library of Congress Control Number: 2013933689
British Library Cataloguing-in-Publication Data
A CIP record for this book is available from the British Library
ISBN: 978-1-84821-443-9
Printed and bound in Great Britain by CPI Group (UK) Ltd., Croydon, Surrey CR0 4YY
Synchronization is the bedrock of the telecommunication highways. Much like the pavement of a highway, synchronization is often taken for granted, since it is effectively invisible when it is working. But it is an enabler of many aspects of the transfer of voice and data. Some services directly require synchronization. More specifically, synchronization can optimize the use of a given bandwidth, increasing available throughput in a fixed band.
Time-and-frequency issues are rich and complex enough that they form their own discipline. Unfortunately, there are few places of study that have this unique focus as an institute unto itself. Hence, the importance of this book. There is much confusion about principles of time and frequency, in part because our human experience of time is so intriguing. Time is a major focus in human culture, in art, philosophy, and song. Yet time in science, engineering and metrology is a different thing.
Scientific time and frequency start with a clock, a device that realizes a theoretical principle in a physical way. The underlying principle in any clock is always a law of physics that predicts circumstances in which the states of a system will repeat at a constant rate. A clock physically realizes this theoretical principle and produces this rate, or frequency, with some level of accuracy and stability. The underlying principle is a theory of physics that forces the theoretical rate of the clock to be constant by definition. Time from a clock comes by counting the states as they repeat themselves, just as counting days produces the calendar. Hence, a clock fundamentally produces a frequency, with time optionally produced by using a counter. The standard frequency is a physical quantity, equivalent to an energy. The time standard, however, is a man-made artifact. A standard frequency signal can be produced by a single device, a cesium standard. To get standard time from a clock, as opposed to time intervals, the clock must first be set, or synchronized, against a reference. Then, since the clock is at best a frequency device with some white noise on the signal, any two clocks will wander off from each other in time without bounds if they are not re-synchronized periodically, whereas the best clocks may be bounded in their native frequency differences.
So where does the time reference come from? Metrologically, the practical time standard is a weighted average of clock times from all over the world. This is produced by the International Bureau of Weights and Measures (Bureau International des Poids et Mesures – BIPM) in the forms of International Atomic Time (TAI) and Universal Coordinated Time (UTC). These time scales are produced only after the fact. Any real-time time signal can be only a prediction of what the correct time will be when it is defined later.
The result of these facts is that a system that requires only frequency can have a stand-alone device that produces the signal. But a system that requires time must compare the count of time on its local device to an external reference. This has broad implications in telecommunications systems, and in the many other systems that require some level of accurate time coordination. Not only must clocks be chosen and implemented to run properly, but their signals must be transported and measured properly.
This book describes the needs for synchronization in telecommunications networks and the current evolution of methods and standards that enable it. The challenge of supplying needed synchronization to telecommunications systems is primarily an engineering problem, not a theoretical or scientific one. Because the requisite frequency devices can be expensive, and because the necessary time synchronization must be transported, there is a need for a synchronization network. The requirements of a communications network fundamentally conflict with those of a synchronization network. The communications network ideally separates functional layers, so devices interact with other devices only one layer up or down. Synchronization requires direct access to the lowest layer, the physical layer, since synchronization, unlike data, requires a physical signal. Applications that are required to consume some form of synchronization signal can be in any layer of the communications network. Hence they must break or tunnel through the isolation of layers to get access to the synchronization signal, in violation of the layer principles of a communications network.
Alternatively, a synchronization signal can be supplied from a source external to the communications network. Receivers of Global Navigation Satellite Systems (GNSS) such as the U.S. Global Positioning System (GPS) are commonly used to provide both time and frequency synchronization. These cannot be used everywhere, however, both because of expense and because of difficulties in getting the synchronization signals where they are needed. In addition, GNSS signals are vulnerable to interference – both intentional and unintentional interference. Thus, even with GNSS signals available, a synchronization network remains essential.
As I write in 2013, synchronization in communication systems is in the midst of evolving from the role of primarily frequency synchronization to the role of precise time synchronization. The metrology community separates these two types of synchronization by calling “synchronization” in frequency the name “syntonization”, though the telecommunications community uses the word synchronization for both. The transport of networks in the late 80 s and 90 s was itself synchronous in frequency, or syntonous. With the advent of packet networks, the transport no longer needed syntonization, yet many applications and services still required various forms of either syntonization or synchronization or both.
Among other things, synchronization optimizes available bandwidth, enabling a more efficient use of the spectrum. Today, wireless networking is becoming more ubiquitous. Time synchronization is becoming essential to allow high data rates in the limited wireless spectrum. This becomes a complex engineering problem, as many different scenarios require different types of synchronization. Traditional synchronous networks still remain in use and require syntonization, while packet networks dominate all new roll-outs. Further, many size-scales of wireless networks are being deployed, from macro-cells over cities to femto-cells in a small interior of a building. These hybrid networks challenge operators to supply needed synchronization to all the requisite applications and services.
Within the context of these circumstances, this book is timely. As synchronization becomes both more complex and more necessary, there still remains a dearth of training and learning options. This book is a comprehensive effort by experts who have been developing standards and engineering devices, and employing these in real networks. It should help fill the void for those trying to negotiate the diverse and complex world of time and frequency issues in communications systems.
This book is a collaboration of major figures in the creation and use of synchronization. I will not repeat the information in the biographic, but I want to mention my appreciation and respect for this team of authors and the current effort. The authors are a mixture of standards experts, equipment building and testing experts, and operators who must implement and maintain synchronization. This book is a work of significant magnitude, involving many hours of development and coordination.
Synchronization in telecommunications is a fascinating field. It involves complex concepts and difficult engineering efforts. Concomitantly, the field creates great benefits for many users, facilitating an increasing ease for human social communications underpinned by large data transfers. In addition, synchronization facilitates large industries representing many billions of dollars. This book can take the user a long way along this river. Enjoy!
Marc WEISS
Mathematical Physicist, GPS and Telecom Sync Expert at NIST
This section lists the abbreviations and acronyms used in this book.
3GPP | Third-Generation Partnership Project |
3GPP2 | Third-Generation Partnership Project 2 |
AAA | Authentication, Authorization and Accounting |
AAL1 | ATM Adaptation Layer 1 |
ACMA | Australian Communications Authority |
ACR | Adaptive Clock Recovery |
ADEV | Allan Deviation |
ADM | Add Drop Multiplexer |
ADPCM | Adaptive Differential Pulse Code Modulation |
ANSI | American National Standards Institute |
ATIS | Alliance for Telecommunications Industry Solutions |
ATM | Asynchronous Transfer Mode |
AVB | Audio Video Bridging |
BC | Boundary Clock |
BIPM | International Bureau of Weights and Measures |
BITS | Building Integrated Timing System |
BMC | Best Master Clock |
BMCA | Best Master Clock Algorithm |
BNC | Bayonet Neill-Concelman (connector) |
BPM | People’s Republic of China’s National Time Signal Service |
BS | Base Station |
BSC | Base Station Controller |
BSS | Base Station Subsystem |
BTS | Base Transceiver Station |
CBR | Constant Bit Rate |
CDMA | Code Division Multiple Access |
CDR | Clock Data Recovery |
CEM | (SONET/SDH) Circuit Emulation Service over MPLS (RFC5143 – obsoleted by CEP) |
CEP | (SONET/SDH) Circuit Emulation over Packet (RFC 4842 – obsoletes CEM) |
CERN | European Organization for Nuclear Research |
CES | Circuit Emulation Service |
CESoPSN | Circuit Emulation Service over Packet-Switched Network (RFC5086) |
CF | Correction Field |
CI | Characteristic Information (ITU-T Rec. G.805) |
CLI | Command Line Interface |
CNSS | Compass Navigation Satellite System |
CoMP | Coordinated Multipoint |
CPE | Customer Premise Equipment |
CPRI | Common Public Radio Interface |
CSG | Cell Site Gateway |
D/A | Digital to Analog |
DCF | Dispersion Compensating Fibers |
DCN | Data Communications Network |
DCR | Differential Clock Recovery |
DCF77 | Radio Time Service in Germany |
DNU | Do Not Use (QL value interpretation) |
DoS | Denial of Service |
DPLL | Digital Phase Lock Loop |
DS1 | Digital Signal 1 (1.544 Mbit/s) |
DSL | Digital Subscriber Line |
DSLAM | Digital Subscriber Line Access Multiplexer |
DTI | DOCSIS Timing Interface |
DUS | Don’t Use (QL value interpretation – equivalent to DNU) |
DUT | Device Under Test |
DVB-T/H | Digital Video Broadcast – Terrestrial/Handheld |
E1 | Digital signal (2.048 Mbit/s) |
E2E | End-to-End |
EEC | (Synchronous) Ethernet Equipment Clock |
eICIC | Enhanced ICIC (Inter-cell Interference Coordination) |
eLORAN | Enhanced LORAN |
EPC | Evolved Packet Core (LTE) |
EPL | Ethernet Private Line |
ESI | External Sync Interface |
ESMC | Ethernet Synchronization Messaging Channel |
ETH | Ethernet MAC Layer Network (IU-T) |
ETSI | European Telecommunications Standards Institute |
ETY | Ethernet PHY Layer Network (ITU-T) |
FCC | Federal Communications Commission |
FCS | Frame Check Sequence |
FCAPS | Fault, Accounting, Configuration, Performance and Security Management |
FDD | Frequency Division Duplexing |
FLL | Frequency Lock Loop |
FPP | Floor Packet Percentage |
GAARDIAN | GNSS Availability Accuracy Reliability and Integrity Assessment for Timing and Navigation |
GBAS | Ground-Based Augmentation System |
GE | Gigabit Ethernet |
GFP-F | Generic Framing Procedure-Framed |
GLONASS | Globalnaya Navigatsionnaya Sputnikovaya Sistema (Global Navigation Satellite System) |
GM | Grand Master |
GMP | Generic Mapping Procedure |
GNSS | Global Navigation Satellite System |
GPS | Global Positioning System |
GRI | Group Repetition Interval |
GSM | Global System for Mobile communications |
GUI | Graphical User Interface |
HL | Hop Limit |
HLR | Home Location Register |
HOL | Head Of Line |
HOLB | Head Of Line blocking |
HRM | Hypothetical Reference Model |
HRX | Hypothetical Reference Connection |
HSPA | High-Speed Packet Access |
HSS | Home Subscriber Server |
IANA | Internet Assigned Numbers Authority |
ICIC | Inter-cell Interference Coordination |
ID | Identifier or Identity Description |
IED | Improvised Explosive Device |
IEEE | Institute of Electrical and Electronics Engineers |
IETF | Internet Engineering Task Force |
IMA | Inverse Multiplex for ATM |
IP | Internet Protocol |
IP FRR | IP FastReRoute |
IPDV | Inter-Packet Delay Variation or IP Packet Delay Variation |
IRIG | Inter-Range Instrumentation Group |
IRNSS | Indian Regional Navigational Satellite System |
ITSF | International Telecom Sync Forum |
ITU | International Telecommunication Union |
ITU-T | International Telecommunication Union – Telecom |
Iu | Interconnection point between an RNC or a BSC and a 3G Core Network |
Iub | Interface between an RNC and a Node B |
IWF | Interworking Function |
JESS | Jitter Estimation by Statistical Study |
JLOC | Jammer Location |
LACP | Link Aggregation Control Protocol |
LAN | Local Area Network |
LBAS | Local Based Augmentation System |
LORAN | Long Range Aid to Navigation |
LSP | Label Switched Path |
LTE | Long-Term Evolution |
LTE-A | LTE Advanced |
Lx | Layer x |
M-CMTS | Modular Cable Modem Termination System |
MAC | Media Access Control |
MAFE | Maximum Averaged Frequency Error |
MATIE | Maximum Averaged Time Interval Error |
MB(M)S | Multicast Broadcast (Multimedia) Services |
MBSFN | Multicast Broadcast Single Frequency Network |
MDEV | Modified Allan Deviation |
MEF | Metro Ethernet Forum |
MI | Management Information |
MIB | Management Information Base |
MinTDEV | Minimum TDEV |
MME | Mobility Management Entity |
MNO | Mobile Network Operator |
MPLS | Multi-Protocol Label Switching |
MRTIE | Maximum Relative Time Interval Error |
MS | Mobile System |
MSAN | Multi-Service Access Node |
MSC | Mobile Switching Center |
MSF | UK Low frequency time signal and standard frequency radio station based on the NPL time scale UTC(NPL) |
MTIE | Maximum Time Interval Error |
MTOSI | Multi-Technology Operations System Interface |
MTU | Maximum Transmission Unit |
MW | Microwave |
NE | Network Element |
NGN | Next-Generation Network |
NIST | National Institute of Standards and Technology (USA) |
NMS | Network Management System |
NPU | Network Processor Unit |
NS | Network Synchronization (ITU-T) |
NTP | Network Time Protocol |
NTR | Network Timing Reference |
OAM | Operations, Administration, Maintenance |
OAM&P | Operations, Administration, Maintenance and Provisioning |
OC | Ordinary Clock |
OCXO | Oven-Controlled Crystal Oscillator |
ODUk | Optical data unit of level k |
OFDM | Orthogonal Frequency-Division Multiplexing |
OLT | Optical Line Terminal (PON) |
ONU | Optical Network Unit |
OPEX | Operational Expense |
OS | Operating System |
OSC | Optical Supervisory Channel (OTN) |
OSI | Open Systems Interconnection |
OSPF | Open Shortest Path First |
OSS | Support System |
OSSP | Organization-Specific Slow Protocol |
OTDR | Optical Time-Domain Reflectometer |
OTN | Optical Transport Network |
OTT | Over-The-Top |
OUI | Organization Unique Identifier |
P2P | Peer to Peer |
PABX | Private Automatic Branch Exchange |
PAR | Project Authorization Request |
PCM | Pulse Code Modulation |
PCP | Port Control Protocol |
Probability Density Function | |
PDH | Plesiochronous Distribution Hierarchy |
PDN-GW | Packet Data Network-GateWay |
PDU | Protocol Data Unit |
PDV | Packet Delay Variation |
PHY | Physical |
PLL | Phase-Locked Loop |
PM | Packet Master |
PMC | Packet Master Clock |
PNT | Position, Navigation and Timing |
PON | Passive Optical Network |
POS | Packet over SONET (or SDH) |
ppb | Part per billion |
ppm | Part per million |
PPS | Pulse per second |
pps | Packets per second |
PRC | Primary Reference Clock |
PRS | Primary Reference Source |
PRTC | Primary Reference Time Clock |
PS | Packet Slave |
PSN | Packet-Switched Network |
PSTN | Public-Switched Telephone Network |
PTP | Precision Time Protocol |
PTSF | Packet Timing Signal Failure |
PW | Pseudo-Wire |
PWS | Pseudo-Wire Service |
QL | Quality Level |
QZSS | Quasi-Zenith Satellite System |
RAIM | Receiver Autonomous Integrity Monitoring |
RAN | Radio Access Network |
RBAS | Regional Based Augmentation System |
RF | Radio Frequency |
RNC | Radio Network Controller |
RNSS | Radio Navigation Satellite Service |
RT | Residence Time |
RTP | Real-Time Protocol |
SA | Selective Availability |
SAE-GW | System Architecture Evolution-GateWay |
SASE | Stand Alone Synchronization Equipment |
SATop | Structure-Agnostic TDM over Packet (IETF) |
SBAS | Satellite-Based Augmentation System |
SD | Synchronization Distribution (ITU-T) |
SDCM | System for Differential Corrections and Monitoring (GLONASS) |
SDH | Synchronous Digital Hierarchy |
SDO | Standardization Development Organizations |
SDSL | Symmetric Digital Subscriber Line |
SEC | SDH Equipment Clock |
SETG | Synchronous Equipment Timing Generator |
SETS | Synchronous Equipment Timing Source |
SFN | Single Frequency Network |
SFP | Small Form Factor Pluggable |
SGSN | Serving GPRS Support Node |
SG15 | Study Group 15 (ITU-T) |
SLA | Service Level Agreement |
SMA | SubMiniature Version A (connector) |
SMB | SubMiniature Version B (connector) |
SMC | SubMiniature Version C (connector) |
SNMP | Simple Network Management Protocol |
SNTP | Simple Network Time Protocol |
SOF | Start Of Frame |
SONET | Synchronous Optical Network |
SOOC | Slave Only Ordinary Clock |
SP | Service Provider |
SRTS | Synchronous Residual Time Stamps |
SSH | Secure SHell |
SSM | Synchronization Status Message |
SSU | Synchronization Supply Unit |
ST3 | QL Value for Stratum3 |
STM-N | Synchronous Transport Module (level N) |
SyncE | ITU-T Synchronous Ethernet |
S1 | Interface between an eNB and an EPC |
T-BC | Telecom-BC (boundary clock) |
T-GM | Telecom-GM (grandmaster) |
T-SC | Telecom-Slave Clock |
T-TC | Telecom-Transparent Clock |
T-TSC | Telecom-Time Slave Clock |
TAI | Temps Atomique International (International Atomic Time) |
TASI | Time Assignment Speech Interpolation |
TC | Transparent Clock |
TCO | Total Cost of Ownership |
TD-SCDMA | Time Division-Synchronous CDMA |
TDD | Time Division Duplexing |
TDEV | Time Deviation |
TDF | TéléDiffusion de France (radio time service broadcasted by TDF) |
TDM | Time Division Multiplexing |
TDMA | Time Division Multiplexing Access |
TICTOC | Timing over IP Connection and Transfer of Clock (IETF WG) |
TIE | Time Interval Error |
TKS | Time Keeping System |
TLV | Type Length Value |
TMF | Telemanagement Forum |
TNC | Threaded Neill-Concelman (connector) |
TNM | Telecommunications Management Network |
ToD | Time of Day |
TSG | Timing Signal Generator |
TTL | Time To Live |
TTT | Timing Transparent Transcoding |
TWSTFT | Two-Way Satellite Time and Frequency Transfer |
TWTT | Two-Way Time Transfer (protocol) |
UDP | User Datagram Protocol |
UE | User Equipment |
UI | Unit Interval |
UMTS | Universal Mobile Telecommunications System |
US | United States |
USNO | US Naval Observatory |
UTC | Coordinated Universal Time |
UTP | Unshielded Twisted Pair (cable) |
UTRAN | UMTS Transport Radio Access Network |
Uu | Radio Interface between the UE and the NodeB |
VCO | Voltage Controlled Oscillator |
VDSL | Very High Speed Digital Subscriber Line |
VLAN | Virtual LAN (Local Area Network) |
VoIP | Voice over Internet Protocol |
VPN | Virtual Private Network |
WAAS | Wide Area Augmentation System |
WAN | Wide Area Network |
WCDMA | Wideband CDMA |
WDM | Wavelength Division Multiplexing |
WG | Working Group |
WiMAX | Worldwide Interoperability for Microwave Access |
WS | Work Station |
WSTS | Workshop on Synchronization in Telecommunication Systems |
WWWF | Radio Time Service from NIST (US) |
xDSL | x (any type of) Digital Subscriber Line |
I would like to thank Alcatel, now Alcatel-Lucent, and specially Bernard Point and Bernard Sales, who supported my work on synchronization and standardization in ITU, ETSI, IEEE and IETF.
I would like to thank Tommy Cook, CEO of Calnex Solutions, who has been sponsoring my activity in ITU-T Q13 after I retired from Alcatel-Lucent.
I want to thank all the participants of ITU-T Q13 for their work during the last decade, which allowed Q13 to address the new issues raised by the transport of synchronization in packet networks.
I want also to thank my family who supported me during my work on this book.
I would like to thank BT and specifically both Tony Flavin and Glenn Whalley for their support of my work on this book and, in the wider context, their ongoing support for the synchronization subject in general. I would also like to thank the team of professionals I work with, Greg Mason, Sean Taylor and Trevor Marwick; both Sean Taylor and Trevor Marwick have worked on the evolving SyncE/1588 technology and provided me with considerable support for which I am indebted to them.
It has been a privilege to work on the development of synchronization standards and see their evolution from concepts to finished standards and then follow their adoption into deployed networks for the benefit of all. In the 1990s, during my first term in telecoms standardization, I met many inspirational people – some are still around, Dr Ghani Abbas being one of them who taught me much. During my second term from the early 2000s, I have had the pleasure to work with many new people on this subject. I feel fortunate to have met them all and worked with many, although too many to name it is primarily the collective group in ITU-T SG15Q13, ITSF and WSTS.
I would like to thank my family who have put up with the many weeks away over the years that have been due to my standards participation. Special thanks go to my partner Jan Longthorp, who has dropped me off and collected me from many different airports and who has also put up with many broken weekends resulting from both standards participation and the subsequent writing of this book. On behalf of all the authors, I would also like to thank Jan for all the help she gave us in the final proof reading.
Finally, I dedicate this book to my parents.
I would like to very much thank my company, France Télécom Orange, for supporting this work, and all the studies that we initiated with my colleagues in Lannion. I thank in particular Jean-Paul Cornec, my predecessor representing France Télécom in ITU-T SG15 Q13, for having kindly shared his expertise when I joined the team. I also thank Pierre-Noël Favennec for his kind help in finding the publisher of this book.
I would like to acknowledge the excellent technical work that has been done over the years in ITU-T with participants of other companies that are not part of this project (but who could have been for sure without any problem), in particular, Geoffrey Garner and Kenneth Hann (there are many others, but the list would be too long …). The 7–8 year period preceding the publishing of this book has, indeed, been very fruitful in standards and is very likely one my most exciting experiences.
I obviously thank my family very much, my lovely wife Stéphanie, daughter Jessica and son Romain, for kindly supporting the hard work and the long days behind the computer writing this book or attending standardization meetings.
Finally, I dedicate this book to my father.
First and foremost, I would like to thank my wife Zsuzsanna for her support and patience during the many months involved with the preparation of this book. Words are not enough to express my gratitude to her for accommodating my absences during the many standards meetings where much of the content of this book was honed and refined. My children Fanni, David and Ben also deserve thanks for putting up with my travels.
Much of the content of this book has been developed over the many years of collaboration with my other colleagues in various companies and standards bodies, particularly the ITU-T and COAST-SYNC. I am very thankful for the privilege to work with so many bright and talented people.
I would like to also thank my coauthors for the opportunity to participate in this truly collaborative effort.
Finally, I would like to dedicate this book to the memory of my parents.
I would like to thank the Q13/15 attendees, most coauthors, who, in 2005, welcomed the first “packet guy”, and to Marc Weiss who provided me with extended help for this book.
I would like to thank Cisco as a company for promoting thought leadership and providing me with the opportunity to meet and collaborate with so many great talents and individuals. I also thank all my managers (Axel Clauberg, Cedrik Neike, Art Feather, Jane Butler, Chip Sharp and Russ Guyrek) who trusted me in supporting this work.
I would like to particularly recognize Stewart Bryant as an early and staunch supporter and Leonid Goldin as a faithful partner on synchronization for years. I must express my profound gratitude to my very first mentor Jean Guylane, long before my tenure at Cisco.
I would like to thank my four beloved sons and daughters who have, through their patience, strongly contributed to this book. Special thanks go to my wife Marie for her love and support over the years.
I dedicate this book to my parents.
I would like to thank my lovely wife Kim, beautiful daughters Haley and Oliva, and my parents Francois and Monique for their support and looking after me during those long evenings and weekends while I was spending time with my other wife “the Computer”.
Special thanks go to Dr James Aweya, an outstanding mentor who taught me so many things. I also thank Bob Mandeville from Iometrix for the opportunity he provided me, as well my previous colleagues at Huawei Technologies and to this great university that was once called Nortel.
I would like to thank Integrated Device Technology (IDT), my coworkers, specially my former manager Jim Holbrook, and my current manager Louise Gaulin for their support of my work on this book. I would also like to thank IDT for its support of the standards activities.
It has been a pleasure to work with several colleagues from different companies at the ITU-T and IEEE standards meetings, and ITSF, ISPCS and WSTS workshops. Over the years, several colleagues became very good friends. I feel very fortunate to work with such a great group of people. I would also like to thank John Eidson who provided me with advice while writing this book.
Special thanks go to my loving family, my husband Claudio and sons Nicholas and Thomas. Their support throughout my career was fundamental for my development, with so many weeks away from home participating in standards meetings, and many weekends writing this book. I also would like to thank my sisters Celi and Ivani, and my brother Fabio for their support. I dedicate this book to my father (in memory) and to my mother.
I wish to thank all the people who have supported me working on this book. They include my company, Ericsson, which has given me the opportunity to take part in this project and has provided with great support over the many years in my participation in the standardization activities, and in particular my current manager, Roberto Sabella, and Ghani Abbas whose experience in the standardization activities has often been a great help; all colleagues, especially those I have met during the ITU-T Q13/15 meetings, and who during these years have inspired me and with whom I often have established extraordinary relationships; and my loving family – my son Dante, daughter Emma Vittorina and wife Elin – who have supported me in this project.
Moreover, I wish to remember the Fondazione Ugo Bordoni and, in particular, Domenico De Seta, with whom more than 20 years ago I started to learn about synchronization in SDH systems.
Finally, I would like to dedicate this book to the memory of my parents, Giovanni and Vittorina.
Exchanging digital data has always required some level of synchronization: the receiver of a telecommunication system must correctly acquire the “rhythm” or frequency of the bits sent by the transmitter in order to recover the data correctly. But synchronization within a telecommunications network has a much wider scope than between a transmitter and receiver on a local link: the delivery or distribution of a common timing reference across a telecommunications network is required for various network applications to ensure proper network operation. This timing distribution effectively becomes a network within a network. In many cases, this distribution follows the same path across a network as the data. However, in some cases the data may flow across the network but the timing will flow from a central point to the edge and only follow the same path for part of the distribution, typically at the edge. Ideally engineering the synchronization network should take place at the same time as engineering the network to carry data. However, this is not always the case.
Synchronization is often thought of for time division multiplexing (TDM) based fixed line voice and data-based infrastructure networks. However, few realize the importance that synchronization plays in allowing various applications to work correctly, one such application that is gathering pace is the increase in mobile telecommunications through long-term evolution (LTE). For instance, in mobile telephony, the synchronization requirements of the air interface are critical. How would wireless mobile (based on technologies such as global system for mobile communications (GSM), code division multiple access (CDMA) and LTE) communications work without synchronization? Clearly it would not and Quality-of-Service issues would arise if it were not considered.
Quality-of-Service and synchronization have always had close links. This has been true in the TDM world where accurate synchronization is required to limit the occurrence of slips.
Synchronization is still needed today and in future for mobile applications and networks:
– to stabilize the radio frequencies used by the mobile base station;
– to allow efficient spectrum usage;
– to avoid radio interference between neighboring cells;
– to allow seamless hand over between cells.
Poor synchronization within a telecommunications network may have important impacts on the end user:
– The communication can degrade (voice communication can become inaudible).
– The throughput of data connections in the networks can reduce.
– The network’s connections (in the case of the internet) might even be totally lost.
– In the case of mobile communications, hand over between cells could fail and quality of experience degrade.
Ensuring a proper design for a synchronization network should therefore not be underestimated when considering these potential impacts.
One of the problems faced by the network engineers responsible for building suitable synchronization architectures is that synchronization is not necessarily a well-known or even a well-understood topic within telecommunications. Many engineers may have a limited knowledge about the subject and may feel uncomfortable with existing synchronization technology. Equally, there are also many engineers who have no knowledge on the subject at all and no basis on which to develop their understanding of new synchronization technology in the packet world.
Now, with the evolution toward new packet-based technology and consequently new synchronization technologies, a review of some of the key principles and concepts of synchronization and timing is useful. This is especially useful when applying synchronization to new packet-based technologies to understand how they work and where they apply, how they can be tested and what challenges may exist from a network design or operational management perspective.
Dissemination of such knowledge is critical for subject areas such as synchronization that are not common or well understood, but even more so when these new technologies are being considered in new network architectures. Like any subject area, spreading a proper understanding takes time but has wider and longer-term benefits.
Synchronization design and the vagaries around the subject is often a specific discipline that is practiced by a relatively few individuals on a day-to-day basis. These individuals tend to be experts that sit in a wide range of companies within the telecoms and associated industries. For example:
– Large network operators will often have a few individuals who understand the issues across their deployed technologies and scale of operations. When these operations cover many different types of voice and data applications and span tens or hundreds of thousands of elements, supporting many millions or even billions of dollars in revenue, it becomes apparent that the scale of this challenge can be large and the risk under failure conditions is high.
– Systems vendors will have experts in designing and integrating synchronization capabilities within their products and may well have expertise in designing these products into some aspects of the synchronization network.
– Silicon vendors will have experts in designing and integrating their components into the various systems.
– Other organizations may well have a small group of experts, for example these could be test houses or consultancies. A few specialist companies also make it their business to design specific synchronization-related products or provide expert consultancy or both.
However, it is worth knowing that the number of people worldwide with a fair knowledge in the industry is probably in the order of a few thousand (and could actually be below a thousand) and this drops to only a couple of hundred who have real knowledge of how synchronization is designed into real networks and how the industry is evolving. At events such as International Telecom Synchronization Forum (ITSF) and Workshop on Synchronization in Telecommunication Systems (WSTS) through the late 2000s, typically between 70 and 120 experts attended each year. The experts actively involved in standardization results in an even lower number: in 2003, the expert question in the International Telecommunications Union (ITU) dealing with synchronization had less than 10 experts dealing with the subject and even in 2013 at most it will be 45.
Some of the disciplines that are involved in synchronization require the engineer to:
– have a good understanding of the overall network architecture and the different technologies that make this architecture;
– understand how these technologies work (certainly at a high level) but in some cases to some depth;
– have an appreciation of digital networking;
– have a detailed understanding of analogue technology and some of the factors affecting oscillator performance and other clock components;
– have an understanding of the services carried and the performance requirements. Also how they may be degraded and what may degrade them to sort out potential synchronization problems from the normal service problems;
– have an understanding of how to test for synchronization problems in live networks and for lab-based evaluation. The engineer also needs to understand how the various pieces of test equipment work and what may influence the results, for example a badly tuned reference oscillator;
– understand the standards and what can and cannot be achieved in terms of architecture, technology and performance;
– take the network architecture that has often been developed to carry services without any thought to synchronization and work out how to add synchronization for the services that often have a demanding commercial criteria;
– have an understanding of packet networks and packet technology in the world of NGNs.
There are probably more, but hopefully the reader can see that the synchronization engineer while being a specialist in the field of synchronization also needs, to a certain degree, to be a “jack of all trades”. That is they have a wide base of knowledge that can practically be applied. In many cases, although synchronization knowledge can be acquired through study, it will often be learnt over many years of dealing with practical problems of design, problem resolution and testing.
One thing that should be clearly stated is that the content within this book is the work of many experts over many years. Much of this work has become codified within standards and has obviously been based on contributions to standards bodies such as ITU-T throughout the years, for example public switched telephone network (PSTN) synchronization in the 1980s, then synchronous digital hierarchy (SDH) technology and its respective synchronization in the 1990s. On the more recent technologies, these contributions have been from an increasing group of experts that now regularly attend ITU-T. The authors of this book have attempted to distill this collective knowledge and translate it into an up-to-date body of work. Some of this work is the authors’ own work and other aspects are based very much on the work of others distilled into a consensus view by the ITU-T process with an attempt by the authors to translate this into a useful reference source.
There may be many reasons why a reader may find this book useful:
– It brings interested engineers very much up to date with the latest technology on this topic.
– It provides some useful guidance based on the latest standardization.
– It provides a handy reference for expert engineers who need to check technical aspects on the latest technology.
This book aims to provide some clarity to the subject and highlight the importance of synchronization so that the subject is not forgotten, or considered only at a very late stage, or poorly designed inside an overall network architecture, especially in the packet network world.
As discussed earlier, experts in the subject of synchronization tend to be fairly rare, with the non-expert in the subject split between those that know the requirement for synchronization and timing exists, and those that do not. This book will have something for the non-expert readers as well and should clarify and build on their existing telecoms knowledge or provide a base on which to explore the subject further. This should help to demystify some aspects of synchronization.
Any engineer involved in synchronization will be familiar with the challenges faced when service is failing or Quality-of-Service metrics are declining and the first response is that “it must be the synchronization”. It is true synchronization is sometimes to blame. However, there are many other issues that can cause problems that look as though they are synchronization related. Certainly unfamiliarity with the topic does not help. However, the subject of synchronization essentially revolves around the simple concept of distribution of accurate frequency, time or phase from point A to point B. Some of the detail behind this is complex, but in reality it can be divided into areas that can be explained with simple clarity and intuitive examples which hopefully this book will achieve. The danger is that oversimplification misses certain aspects of the topic or creates yet further misunderstanding.
All synchronization designers have seen “The Good, The Bad and The Ugly” – to use the title from the Sergio Leone spaghetti western film starring Clint Eastwood – in terms of network synchronization designs. Sometimes bad and ugly designs are created through necessity or inherited from previous work; they may have resulted through network migration or are determined through architecture or are sometimes driven by expedient commercial needs. This book cannot comment on those reasons, but what it can do is talk about the approach taken in the development of synchronization standards, which is the key starting point in creating good reusable synchronization designs that have a solid technical foundations and are proven to interwork correctly and stand up commercially (i.e. in both capital investment terms and operation costs). Standardization provides a key coordinating framework around which equipment and their respective interfaces can be specified, network limits can be appropriately designed and how architectures can be created to meet the various performance requirements using an agreed set of design rules. This book, written by a group of people deeply involved in the standardization process of recent synchronization technologies developed over the last decade, attempts to clarify these results.
The authors have all been in various standards bodies and contributed to the development of these new synchronization technologies developed over the last decade by the ITU Telecommunication Standardization Sector (ITU-T), such as Synchronous Ethernet or Precision Time Protocol version 2 (PTPv2) telecom profiles based on IEEE Standard 1588-2008.
As indicated, one of the objectives of this book is to describe the state-of-the-art of these technologies and what can and cannot be achieved with them. It also aims to show how the standards that have been developed should be used and understood. It further discusses the evolving needs for synchronization in a 21st Century telecoms environment and illustrates some of the challenges related to synchronization and its evolution.
Another important goal of this book is to help dispel a few myths sometimes stated or answer questions sometimes asked in the telecom industry, such as:
– synchronization is only for legacy networks;
– synchronization is not needed when migrating toward Internet Protocol (IP) networks;
– Global Positioning System (GPS) is sufficient when synchronization is needed;
– Precise Time Protocol (PTP)/IEEE 1588 is the best solution for synchronization over packet networks;
– PTP is more precise than Network Time Protocol (NTP);
– why synchronize the Ethernet physical layer?
This book, as the title indicates, addresses Synchronous Ethernet and IEEE 1588 as it is used in telecom networks. This book helps to understand how and why Synchronous Ethernet technology was developed, and how it can interwork with existing SDH-based synchronization networks.
Likewise with IEEE Standard 1588-2008 (“1588v2”, or “PTPv2”), this book will also provide up-to-date information about this new technology that has been developed, when it can be applied to telecoms networks, and explain the concept of “profiles” and the different PTP telecom profiles developed or under development at the ITU-T. It will explain how to use these standards, the limitations and possible combinations. It will also show how this can be linked with Synchronous Ethernet technology when moving from simple end-to-end (E2E) frequency-based transport to very high precision time and phase transport.
The synchronization world has – like any technology area – many concepts or terms that can be used and are also misused or even used interchangeably. For example, where only frequency is concerned, the oscillators and associated filtering within equipment are collectively called a clock, but these clocks traditionally do not tell the time. However, in the context of next-generation synchronization, clocks will have some concept of a time base or transfer time. Hence timing can now also mean phase and time. Similarly, the term synchronization is often called timing but tends to mean frequency synchronization. However, again in the next-generation synchronization network, timing can now also mean phase and time. Similarly, new terminology previously not associated with traditional synchronization networks will also be introduced.
An attempt will be made to clarify some of these terms and put them into propercontext within the packet-based world these technologies will exist. For example, this book will describe the concepts of packet delay variation (PDV), a term that is often called jitter in the data world. Although both can be measured over time, the jitter in packet networks tends to represent a “maximum value” when PDV is associated to a “variation over time”, which is much more important to understand for timing recovery and can be analyzed and metrics developed to quantify. Some discussion will also take place on PDV metrics and their importance in the context of timing recovery in packet-based systems. Jitter, as a term when used in this book, is the strict definition of jitter when applied to synchronization.
Every synchronization specialist has probably felt at least once in their working career that the telecoms world is split into three groups, those who have no idea that the subject of synchronization exists, those who do have a vague idea that it exists – but know little about it, prefer to ignore or have a dangerously vague understanding of the topic and those who are involved in the subject. The synchronization world tends to be a small technical world that does not have a large body of written technical information published and books on the subject are relatively rare (see [BRE 02, SHE 09]) compared to some specializations. This book aims to help to fill the gap. Regardless of the reasons for reading this book, be it for information, for reference, to aid learning of a new subject or refreshing and enhancing knowledge on the subject and bringing oneself up to date with new concepts and technology, the authors hope that this book will be of value.