The trainer is Associate Professor at Politecnico
di Milano, where he teaches telecommunications networks and
transmission networks. He was born in Milano, Italy, in
1965. In 1990, he graduated in telecommunications
engineering at Politecnico di Milano. Since 1991, he worked
on SDH and network synchronization issues, with special
regard to clock stability measurement, first with SIRTI
S.p.A (1991-1993) and then with CEFRIEL consortium
(1994-1999). In 1999, he joined Politecnico di Milano as
tenured Assistant Professor.
He has been Senior Member of the IEEE since 1999. He is
Distinguished Lecturer of the IEEE Communications Society.
He is Vice-Chair of the Transmission, Access and Optical
Systems (TAOS) Technical Committee and voting member of the
Globecom/ICC Technical Content (GITC) committee of the IEEE
Communications Society. He has been appointed Symposia Chair
of IEEE GLOBECOM 2009, Symposium Chair in ICC2004,
GLOBECOM2005, ICC2006, ICC2007, GLOBECOM2007, ICC2008, TPC
Vice-Chair of the IEEE Optical Network Design and Modelling
2005 conference (ONDM 2005) and Workshop Chair of IEEE CCNC
2008. He is Associate Editor of IEEE Communications Surveys
and Tutorials. He was appointed tutorial lecturer in IEEE
conferences ICC 2000, GLOBECOM 2002, GLOBECOM 2003 and
GLOBECOM 2005. He served on ETSI and ITU-T committees on
digital network synchronization.
He is author of about 50 papers, mostly in IEEE conferences and
journals, and of the books Synchronization of Digital Telecommunications
Networks (Chichester, UK: John Wiley & Sons, 2002; translated and
published in Russian by MIR
Publishers, Moskow, 2003) and Sistemi di trasmissione PDH e SDH
- Multiplazione (PDH and SDH Transmission Systems – Multiplexing.
Milano, Italy: McGraw-Hill, 2004). His current research interests
focus mainly on traffic modelling and optical networks.
Course Objectives
This training provides a broad overview on several topics that
are not commonly addressed in literature. In particular, the participants
will learn:
that the word “synchronization”
is used in several
contexts in telecommunications, addressing a wide spectrum
of different timing issues;
bit and byte justification techniques used
in PDH and
SDH multiplexing, emphasizing timing and jitter issues;
basic concepts such as jitter and timing
relationships
between timing signals;
timing aspects in SDH/SONET networks, such
as the main
causes of jitter in SDH/SONET networks and what are
synchronizers, desynchronizers and pointer processors;
how network synchronization issues evolved with the
telephone networks, beginning from old FDM networks up to
the latest technologies, through PDH, SDH/SONET, ATM and
mobile telephone cellular networks;
strategies and standard architectures of synchronization
networks;
principles of synchronization network planning, management,
protection and performance monitoring;
models and characterization of telecommunications
clocks;
principles of operation of clocks for synchronization
networks;
principles of Network Time Protocol (NTP);
time and frequency measurement techniques in
telecommunications, emphasizing practical aspects.
Course Overview
Network synchronization deals with the distribution
of time and frequency over a network of clocks, even spread over a
wide area. The goal is to align (i.e., synchronize) the time
and frequency scales of all the clocks, by using the
communications capacity of links among them (e.g. copper
cables, fiber optics, radio links).
Network synchronization has gained increasing importance in
telecommunications throughout the last thirty years,
especially since transmission and switching turned digital.
Actually, the quality of most services offered by network
operators to their customers is affected by network
synchronization performance.
Digital switching equipment requires synchronization to
avoid slips at input elastic stores. Plain telephone
conversations are not affected much by synchronization
slips, but circuit switched data services are indeed.
Therefore, the deployment of circuit-switched data networks
and of ISDN yielded first the need of more stringent
synchronization requirements.
Network synchronization became a thorny matter for
telecommunications operators with the deployment of SDH
(Synchronous Digital Hierarchy)/SONET networks, which posed
new and more complex requirements on the stability of
synchronization systems.
More recently, it has been also recognized that the
importance of network synchronization goes way farther than
SDH/SONET needs. ATM (Asynchronous Transfer Mode) and
cellular mobile telephone networks (GSM – Global System
for
Mobility -, GPRS – Global Packet Radio Services -, UMTS
–
Universal Mobile Telecommunications Services) are two
striking examples where the availability of network
synchronization references has been proven to affect quality
of service.
A different kind of network synchronization is the
distribution of a reference absolute time (for instance, the
national standard time) to equipment real-time clocks,
mainly to the purposes of network management
(synchronization of real-time clocks). For example, the
Network Time Protocol (NTP) is used to synchronize real-time
clocks of Internet routers and hosts via a hierarchy of time
servers and clients. Accuracy within few milliseconds
(deviation from the standard absolute time) can be achieved,
although the timing information is exchanged through normal
UDP packets affected by extremely variable delay.
A synchronization network is the facility implementing
network synchronization. Basic elements of a synchronization
network are nodes (autonomous and slave clocks) and
communication links interconnecting them. Most modern
telecommunications operators have set up synchronization
networks to synchronize their switching and transmission
equipment.
It is maybe needless to say that quality of service
degradations due to some synchronization problem look always
sudden, unexpected and of mysterious origin for almost
everybody but the (good) synchronization engineer. Rather
surprisingly, engineers with a solid expertise on the above
mentioned topics are not common. The results are quite
evident: gross mistakes in system design and management
produce quality-of-service degradations that unfortunately,
due to ignorance, are often deemed unavoidable.
Key Benefits
Network synchronization plays a central role
in digital telecommunications. It determines the quality of most
services provided by the network operator. Nevertheless,
this subject is widely misunderstood. Neither, it may be
said that such knowledge is common among network engineers.
Actually, it is not easy to find in literature detailed
information on several network synchronization issues.
Quality of service degradations due to some synchronization
problem look of mysterious origin for almost everybody but
the (good) synchronization engineer. As a result, gross
mistakes in system design produce quality-of-service
degradations that unfortunately, due to ignorance, are often
deemed unavoidable.
Therefore, all telecommunications engineers dealing with transport
and switching network design, planning, operation and maintenance
will benefit from attending this course. In particular, companies
operating or deploying SDH/SONET transport networks, ATM networks,
fixed and mobile (GSM, GPRS, UMTS) telephone networks may be identified
as the primary target audience of this course.
The various reasons, for which these networks require good
synchronization, are well known and are summarized in A
Historical Perspective on Network Synchronization. Moreover,
a striking example of the negative impact of poor network
synchronization on the quality of service provided to the
final user is provided by paper Experimental Evaluation of
the Impact of Network Frequency Synchronization on GSM
Quality of Service During Handover, which reports
experimental results measured in a Vodaphone test plant.
This study points out how the GSM quality of service, as
perceived by the user, is negatively affected when the GSM
base stations are not synchronized: the Mean Opinion Score
of a high percentage of calls undergoing handover may become
unacceptable.
Also in IP networks, it is not uncommon to face difficult
synchronization issues. For example, consider the ITU-T Rec.
G.8261/Y.1361 "Timing and Synchronization Aspects in Packet
Networks" and the Network Time Protocol for time
distribution in the Internet.
Pre-Requisites for Participants
Basic knowledge of SDH/SONET and digital
multiplexing is recommended.
Who Should Attend?
For engineers and managers responsible for the planning,
design, and operation of networks and services
Course Outline
Introduction: synchronization processes in
telecommunications
- carrier synchronization
- symbol synchronization
- frame synchronization
- bit synchronization
- packet synchronization
- network synchronization
- multimedia synchronization
- synchronization of real-time clocks
Basic concepts about timing of digital signals
- chronosignals
- timing relationships between digital signals
- jitter and wander
Synchronous and asynchronous digital multiplexing
- taxonomy of multiplexing techniques
- primary PCM multiplex
- synchronous digital multiplexing: slip buffering
- asynchronous digital multiplexing: bit justification, justification
jitter
- plesiochronous digital hierarchies (PDH)
- synchronous digital hierarchy (SDH) and SONET
Timing aspects in SDH/SONET networks
- causes of jitter and wander in a SDH/SONET transmission chain
- synchronization processes along a SDH transmission chain
- SDH/SONET synchronizer and desynchronizer
- SDH/SONET pointer processor
- jitter and wander control in PDH/SDH networks
- SDH equipment clock
A historical perspective on network synchronization
- synchronization in analog FDM networks
- synchronization and PDH digital transmission
- synchronization and digital switching
- impact of slips on digital services
- synchronization of digital switching exchanges via PDH links
- synchronization and SDH/SONET digital transmission
- synchronization in ATM transport networks
- synchronization of mobile telephone cellular networks
Synchronization networks
- network synchronization strategies
- ITU-T Recommendations relevant to network synchronization
- synchronization network standard architectures (ITU-T/ETSI and
ANSI)
- synchronization network planning, management and performance
monitoring
- synchronization network protection: Synchronization Status Messages
(SSM)
- examples of synchronization networks
- clocks in synchronization networks: quartz and atomic clocks,
GPS
Network Time Protocol (NTP) principles
Models and characterization of telecommunications clocks
- chronosignal model and basic quantities
- basic concepts on clock quality: stability and accuracy
- autonomous clocks
- slave clocks
Phase-Locked Loop (PLL)
PLL linear model
second-order PLL
PLL performance with internal noise sources
PLL operation limits and modes
- clock stability characterization in the
frequency domain
power spectral densities
- clock stability characterization in the time domain
instantaneous frequency y(t)
classical variance of y(t)
M-samples variance of y(t)
Allan variance (AVAR)
modified Allan variance (MAVAR)
time variance (TVAR)
root mean square value of Time Interval Error (TIErms)
Maximum Time Interval Error (MTIE)
- noise types found in experimental results
power-law noise
periodic noise
background white noise due to trigger and quantization error
Telecommunications clock technologies
- quartz clocks
- atomic frequency standards: caesium beam, hydrogen MASER, rubidium,
Global -
Positioning System (GPS)
- clocks in synchronization networks
Time and frequency measurement techniques in telecommunications
- fundamentals
RF power spectral density of the chronosignal
quantities recommended by IEEE for frequency stability measurement
standard stability quantities defined by ITU-T and ETSI, estimators
time-domain and frequency-domain measures
estimating the mean frequency and frequency drift
confidence of the Allan variance estimate
distinguishing the variances of the clock under test and of the
reference clock
measurement configurations and stability quantities
impact of the sampling period on stability quantities
- measurement instrumentation
- direct digital measurement
- techniques for improving measurement sensitivity: heterodyne,
homodyne and
multiple-conversion techniques
- stability measurement on telecommunications clocks
- examples of measurement results on a SDH equipment clock
