FTTx Networks. Technology Implementation and Operation

424 Pages·2016·16.49 MB·English

by  James Farmer, Brian Lane, Kevin Bourg and Weyl Wang (Auth.)

FTTx Networks
Technology Implementation
and Operation
James Farmer
Brian Lane
Kevin Bourg
Weyl Wang
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Dedication
We dedicate the book to the innumerable geniuses who, over
a bit more than 100 years, have built the telecommunications
industry from nonexistent to what it is today. We and others
would not be able to develop our modern fiber optic communi-
cations infrastructure were it not for these giants upon whose
shoulders we stand.
About the Authors
Jim Farmer retired in August, 2013. He has enjoyed a 45-year career in commu-
nications technology. He has held CTO responsibilities in the cable television
and FTTH industries.
He holds over 90 patents in the field of delivering video, voice, and data. He
received the 1996 NCTA Vanguard Award in Technology, was inducted into the
SCTE Hall of Fame in 1997, and was inducted into Cable Pioneers in 1998.
Formerly the President of the IEEE Consumer Electronics Society and then
editor of its newsletter for 11 years, Jim has served on the program commit-
tees for the NCTA, SCTE, and the IEEE International Conference on Consumer
Electronics, and chaired the program committee for the FTTH Council from its
inception through 2011. He was an early member of the SCTE Board of Directors
and wrote its first certification tests for set-top converters. He was active on the
NCTA Engineering Committee and participated in development of several stan-
dards and recommended practices. He has been on the FTTH Council’s Board
of Directors, was the first chair of its Technology Committee, and remained
active on the Planning Committee until his retirement. Jim is a life member of
SMPTE, a senior member of the SCTE, and a Life Fellow of the IEEE.
He coauthored two editions of Modern Cable Television: Video, Voice and Data
Communications, which won the Cable Center 2000 Cable Book Award.
Broadband Cable Access Networks was released in 2009. He has a number of
publications with the FTTH Council, NCTA, SCTE, and IEEE and has been a
columnist with several periodicals. Jim holds BSEE and MSEE degrees from the
University of South Florida.
Brian Lane has held key technology and business management positions, in
engineering, manufacturing/operations, and product management in the FTTx
industry—focused on the development and support of FTTx products and
technologies.
Brian has over 28 years of industry experience. Before getting into FTTH, he held
various engineering and management positions in real-time, embedded software
and critical systems development focusing on aircraft controls, avionics, satellite
communications, and consumer communications product development. xiii
xiv About the Authors
Brian has a Bachelor of Science in Electrical Engineering from the University
of Tennessee, Knoxville, and a Master of Science in Electrical Engineering from
the University of Texas, Arlington, where his research thesis focused on control
theory of unstable systems.
Kevin Bourg has over 20 years of industry experience in system engineering,
software development, and sales in the telecommunication industry. Kevin is
an active member of the FTTH Council Americas serving on the Technology
and Planning Committees as well as Conference Chair for the 2012 Conference
in Dallas, Texas. Kevin is a past Chairman of the Board for the Council and
continues to serve as an active Board member.
He holds a Bachelor of Science degree in Computer Science with a minor in
Business Administration from the University of Southwestern Louisiana and a
Master of Science from Southern Methodist University.
Weyl Wang has more than 20 years of industry hands-on experience in metro
transport and FTTH access broadband networks. He worked at several major
labs on WDM devices and systems. For more than 10 years Weyl had been
responsible for system testing of FTTx network equipment.
Dr. Wang holds a Ph.D. degree in Electronics Engineering from NCTU University
in Taiwan. He holds more than 10 US patents in areas of optical transport,
DWDM, OADM, switching components, and broadband access systems.
Acknowledgments
The authors are indebted to the team at Elsevier, and particularly to Amy
Invernizzi, who patiently prodded and cajoled as we missed one deadline after
another. We also appreciate the help of our reviewer, Kim Kersey, who made
the book much better with his many suggestions. And of course we thank our
families for their extra patience as we struggled to complete the project.
xv
CHAPTER 1
Introduction
PHYSICAL TECHNOLOGIES FOR COMMUNICATION
People have had communications facilities into and out of their homes for
over a century now, and in that time there have been at least three different
media technologies used. The oldest, and still widely deployed, is twisted pair
copper wire, used initially to support a single analog telephone line to the
home, now often used to also transport digital data using a technology called
digital subscriber line (DSL). As television became popular in the 1950s, compa-
nies began bringing TV signals into homes using coaxial cable from a master
antenna somewhere in the area. These were initially called community antenna
television (CATV) systems. That term is considered outdated today, because that
same coaxial cable now transports not only signals from a local antenna (in
many cases, getting a direct feed from the TV studio rather from the antenna),
but even more TV signals delivered by satellite or other means, as well as pro-
viding voice and telephony services over the same cable. The technology has
evolved from coaxial cable emanating from the central receive point (the head-
end), to hybrid fiber-coax (HFC) systems, in which fiber optic cable takes the sig-
nal part way from the headend or hub (a collection point for signals, described
later) to a node, where the signals are put on coaxial cable for the journey the
rest of the way to the subscribers’ homes.
The advantage of fiber is that its signal loss is very low compared to that of
coax, so it is possible to transport signals a very long distance without having
to amplify them. This translates into better reliability, better quality, and lower
operational expenses (op-ex). Early implementation of HFC networks (c. the
late 1980s) supplied signals to 10 to 20 thousand homes from one node. As
technology progressed and the cost of fiber optic equipment plummeted, the
size of nodes continued to shrink as fiber was moved closer to the home. Today,
few nodes being installed serve more than 500 homes passed, with many serv-
ing even smaller numbers of homes passed.
The logical extension of HFC to the smallest node, serving one home, brings us
to the third technology, the subject of this book: fiber-to-the-home (FTTH). Typi-
cally, FTTH systems are built with only passive components from the origination
3
FTTx Networks. http://dx.doi.org/10.1016/B978-0-12-420137-8.00001-9
Copyright © 2017 Elsevier Inc. All rights reserved.
4 CHAPTER 1: Introduction
of the system to the home. This means that no power-using components are
placed in the network. With no power-using components in the network, reli-
ability is inherently better, and no provision must be made in the network for
obtaining (and paying for) power from commercial sources, and back-up power
is not needed. Hence, both capital and operational expenses are reduced, while
reliability and quality of the received signals are enhanced. Operators who have
gone from either twisted pair or HFC networks to FTTH have privately reported
operational expense savings of 75–95% compared with their old plant.
PURPOSE OF THE BOOK
This book is intended to give practical advice for successfully selecting, install-
ing, and using an FTTH network. It includes enough theory so that you will
understand what you are doing, and so that you can logically trouble-shoot
faults, but it is not intended to go deeply into the theory of how systems work.
TERMINOLOGY
If you come from a telephone background, you will call the point where sig-
nals are assembled to go to subscribers, a central office (CO). If you come from
a cable TV background, you will call it a headend. Either way, it is the point
at which communications of all types are assembled for transmission to the
customer.
If you come from a telephone background, you might call a field-mounted
terminal which converts signal formats and sends them the last distance to a
home, a digital subscriber line access multiplexer (DSLAM). If you come from a
cable telecommunications background, you will call it a hub (maybe a node
would also fit that description—we shall define both below). We shall gen-
erally use cable TV terminology, though we tend to switch back and forth. In
order to show how FTTH systems fit in, it is useful to show a high-level view
of a modern cable TV HFC system, while understanding that this description
could be of a telephone system with data and video.
Fig. 1.1 illustrates a high-level HFC system as it might be applied in a large
metropolitan area. A primary headend gathers most or all TV content, and may
be the interface point for data and voice services. An optional secondary head-
end, which mirrors the functions of the primary headend, may be placed in a
geographically different part of the metropolitan area, so that if a disaster, such
as a fire, occurs at the primary headend, the secondary headend can take over.
The headend(s) are linked using fiber optic cables, to hubs, which may serve
10,000–20,000 customers. The hub may include certain data and maybe voice
equipment, and will typically convert signals to the RF-modulated format
Terminology 5
FIGURE 1.1
Metropolitan HFC network.
needed on the coaxial cable. The RF signals are in turn modulated onto optical
carriers in optical transmitters. The output of these transmitters differs from that
which you may have experience with for transmitting data. Rather than trans-
mitting a digital signal, represented by light ON for a binary 1 and OFF for a
binary 0 (or vice versa), the optical transmitter of Fig. 1.1 is a linear (analog)
transmitter capable of transmitting a wide spectrum of RF signals (typically
from 54 to 1002 MHz or more in North America), each signal carrying one of
several types of content: One 6MHz (8MHz in many parts of the world) chan-
nel may carry one analog video signal (declining in use), or multiple digital
TV signals, or time division multiplexed data including voice. These signals are
assigned a frequency band, and many such signals can coexist at one time on
one fiber optic transmitter.
The optical transmitter puts signals described above onto a fiber optic cable,
which traverses most of the distance to a neighborhood to be served. At the
neighborhood, a node demodulates the optical signal, turning it back into the
RF-modulated carriers which went into the optical transmitter. From here,
the signals are transported to homes through coaxial cable. RF amplifiers are
usually needed to overcome signal loss, which loss may be attributed to two
mechanisms. Each time a tap is used remove some signal power to serve one
or more homes, conservation of energy dictates that less power is available to
go further downstream to other homes. The second mechanism is loss in the
coaxial cable itself, which can be significant. If the signal level gets too low,
then analog channels get noisy (“snow” in the picture). If the digital signal gets
6 CHAPTER 1: Introduction
FIGURE 1.2
Typical hub serving PONs.
too low in amplitude, the picture or data disappears, with just a small signal
level range where the picture breaks up.
Upstream signals are all RF-modulated carriers, returned over the coax by using
lower frequencies on the coax (typically 5–42 MHz in North America). At the
node they are modulated onto an optical carrier by an upstream transmitter,
and then transmitted to the hub, usually on a dedicated fiber, but sometimes
on the same fiber used for downstream, but on a different wavelength.
Many areas of the world use other transmission standards. In many locations,
RF channels are 8 MHz wide rather than the 6 MHz used in North America, and
carry upstream signal at frequencies up to about 65 MHz, with downstream sig-
nals being carried from about 85 MHz up. For many years there has been talk
in North America about changing our split between upstream and downstream
frequencies, but momentum and the market are hard things to overcome.
COMMON FTTH SYSTEMS
An HFC network may be contrasted to the most common type of FTTH system,
called a passive optical network (PON). The PON starts at the hub (taking a lead
from the example HFC system above), and serves, commonly, 32 homes. Some
systems may serve 64 homes, and future systems are expected to serve more
homes.
Fig. 1.2 illustrates one of the hubs of Fig. 1.1, but this hub serves a number of
PONs. Each PON is defined by a single fiber strand feeding a passive optical
splitter, which may be located in one place as shown, or which may be distrib-
uted. Each splitter serves, typically, 32 homes, with some serving 64 homes.
There is interest in serving more homes per PON as the technology permits.