27 September - 30 September 2010
(Mon - Thu) 4-day Instructor-Led , 0900-1700 Dar es Salaam, Tanzania
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 issues of
synchronization in Next-
Generation 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 for 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. Today, the migration of operators
to the packet-
switched Next-Generation Network (NGN) poses newer and even
more
difficult problems of network synchronization.
Therefore, since the �90s, the
international standard
bodies ITU-T and ETSI have been defined new synchronization
standards, based on modern criteria, which specify more
stringent and
complex requirements than traditional ones. On 2004,
moreover, the
ITU-T has started to develop a new set of Recommendations,
specifically
for synchronization on packet-switched networks.
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.
The various reasons, for which these
networks require
good synchronization, are well known. 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", IEEE GLOBECOM 2003, 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 and NGN,
synchronization plays a
key role. Since 2004, the ITU-T has been developing a new
set of
Recommendations, specifically for synchronization on
packet-switched
networks (for example, ITU-T Rec. G.8261/Y.1361 "Timing and
Synchronization Aspects in Packet Networks"). Let us also
notice the
Network Time Protocol for time distribution in the Internet.
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 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.
In particular, after having attended
this course,
participants should:
Know all main aspects
related to synchronization
of telecommunications networks
Be able to avoid mistakes in
synchronization
network design, planning and operation
Be able to understand
technical documentation
from equipment and system suppliers
Be capable of interacting
effectively with product
managers of equipment and system suppliers, avoiding
misunderstandings that may yield additional costs
Possess adequate knowledge
to assess actual
synchronization requirements for their networks.
Pre-Requisites for Participants
For best understanding and enjoyment of some topics of this
tutorial, basic
knowledge of SDH/SONET systems and digital multiplexing is
recommended.
Who Should Attend?
This course has been designed primarily for the technical
personnel of
telecommunications operators, service providers and
equipment suppliers.
This may include, but not exclusively, system engineers,
network planners,
designers and engineers in charge of system testing, operation,
maintenance and customer support.
Not only practitioners or new-to-the
job should attend
this course, but also senior personnel with expertise in the
field will
discover several enlightening aspects and will benefit from
attending it. The
richness and depth of course topics cover a wide spectrum of
practical and
theoretical issues in a wide range of applications.
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 in
Next-Generation
Networks
issues and strategies
ITU-T standards
architectures and
methods for
synchronization over packet 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
