Broadband Cable Access Networks This page intentionally left blank Broadband Cable Access Networks The HFC Plant David Large James Farmer AMSTERDAM • BOSTON • HEIDELBERG • LONDON NEW YORK • OXFORD • PARIS • SAN DIEGO SAN FRANCISCO • SINGAPORE • SYDNEY • TOKYO Morgan Kaufmann Publishers is an imprint of Elsevier Morgan Kaufmann Publishers is an imprint of Elsevier 30 Corporate Drive, Suite 400 Burlington, MA 01803 This book is printed on acid-free paper Copyright # 2009 by Elsevier Inc All rights reserved Designations used by companies to distinguish their products are often claimed as trademarks or registered trademarks In all instances in which Morgan Kaufmann Publishers is aware of a claim, the product names appear in initial capital or all capital letters Readers, however, should contact the appropriate companies for more complete information regarding trademarks and registration No part of this publication may be reproduced, stored in a retrieval system, or transmitted in any form or by any means, electronic, mechanical, photocopying, scanning, or otherwise, without prior written permission of the publisher Permissions may be sought directly from Elsevier’s Science & Technology Rights Department in Oxford, UK: phone: (þ44) 1865 843830, fax: (þ44) 1865 853333, e-mail: permissions@elsevier.com You may also complete your request on-line via the Elsevier homepage (http://elsevier.com), by selecting “Support & Contact” then “Copyright and Permission” and then “Obtaining Permissions.” Library of Congress Cataloging-in-Publication Data Large, David, 1940Broadband cable access networks : the HFC plant / David Large, James Farmer.—3rd ed p cm — (Morgan Kaufmann series in networking) Includes bibliographical references and index ISBN 978-0-12-374401-2 (alk paper) Cable television Broadband communication systems Optical fiber communication I Farmer, James II Title III Title: Broadband cable access networks, the hybrid fiber/coax plant IV Title: Broadband cable access networks, the hybrid fibre/coaxial plant TK6675.L37 2008 621.3880 57 dc22 2008034236 For information on all Morgan Kaufmann publications, visit our Web site at www.mkp.com or www.books.elsevier.com Printed in the United States 08 09 10 11 12 10 Contents Acknowledgments ix About the Authors xi Chapter Linear Broadband Distribution Systems 1.1 1.2 1.3 1.4 Chapter Introduction Coaxial Cable Amplifiers Passive Coaxial Components Power Supplies Summary .5 19 46 53 54 Coaxial Distribution System Design 57 3.1 3.2 3.3 3.4 3.5 3.6 3.7 3.8 3.9 Chapter Coaxial RF Technology 2.1 2.2 2.3 2.4 2.5 2.6 Chapter Introduction Organization of this Book The Software Applications Why This Book Introduction Carrier-to-Noise Ratio Carrier to Distortion Noise–Distortion Trade-Off System Powering Signal Level Management Signal Level Stability The Service Drop Summary 57 58 59 61 63 67 69 70 77 Linear Fiber-Optic Signal Transportation 81 4.1 4.2 4.3 4.4 4.5 4.6 4.7 4.8 4.9 Introduction Optical Basics Multimode Optical Fibers Single-Mode Optical Fibers Network Passives Linear Optical Transmitters Optical Amplifiers Optical Receivers Interactions among Transmitters, Fibers, and Receivers 81 82 87 90 99 102 110 112 114 v vi Contents 4.10 End-to-End Fiber-Optic Link Performance 117 4.11 Summary 124 Chapter Wavelength Division Multiplexing 127 5.1 5.2 5.3 5.4 5.5 5.6 5.7 5.8 Chapter 127 127 130 132 134 152 154 159 Introduction U.S Regulation of Microwave Transmission General Operational Principles Path Design Performance Calculation Link Availability Factors Summary 161 162 162 166 172 176 184 End-to-End Performance 185 7.1 7.2 7.3 7.4 7.5 7.6 Chapter Linear Microwave Signal Transportation 161 6.1 6.2 6.3 6.4 6.5 6.6 6.7 Chapter Introduction Wavelength Multiplexing: WWDM, CWDM, and DWDM Components for WDM Systems WDM-Specific Design Factors Crosstalk Mechanisms CSO Due to Transmitter Chirp Combined with Imperfect Channel Flatness Degradation in Shared-Detector, Multi-wavelength Systems Summary Introduction Quality Standards and Requirements Performance Allocations among Sections of Cable Systems Noise and Distortion Allocations in Cable Systems Typical Network Transmission Quality under Operational Conditions Summary 185 185 191 192 196 212 Upstream Issues 215 8.1 8.2 8.3 8.4 8.5 8.6 8.7 8.8 8.9 8.10 Introduction The Two-Way Node Downstream and Upstream Frequency Partitioning Group Delay of Diplex Filters Splitting the Node in the Upstream Direction Return Signal Level Issues Optional Ways to Specify Return Lasers Characteristics of Return Lasers Return Path Combining at the Headend Spurious Signals in the Return Path 215 216 217 218 219 223 230 236 239 241 Contents vii 8.11 Characteristics of a Composite Reverse Signal 8.12 Reaction of Active Components to Signal Characteristics 8.13 Common Path Distortion 8.14 Return Path Interference Mitigation Techniques 8.15 Upstream Signal Power Apportionment 8.16 Practical Level Setting 8.17 Summary Chapter Introduction Performance Parameters Requirements by Service Type Scalability Summary Introduction Architectural Architectural Summary Elements Examples 248 249 250 254 259 263 265 266 284 296 296 299 299 309 319 Emerging Architectures 321 11.1 11.2 11.3 Introduction Analog and Digital Optical Modulation Combining Analog and Digital Transmission on the Same Fiber 11.4 Bidirectional Transmission 11.5 Fiber-Deep Architectures 11.6 Classifying Fiber-to-the-Home Systems 11.7 Distance Limitations 11.8 Limitations on Analog Transmission Distance 11.9 Limitations on Digital Transmission Distance 11.10 Low-Frequency Content Removal in Digital Transmission 11.11 Summary Chapter 12 Architectural Elements and Examples 299 10.1 10.2 10.3 10.4 Chapter 11 Architectural Requirements and Techniques 265 9.1 9.2 9.3 9.4 9.5 Chapter 10 246 321 321 326 327 328 333 336 339 342 345 346 Network Reliability and Availability 347 12.1 12.2 12.3 12.4 12.5 Introduction History and Benchmarking Definitions and Basic Calculations Effects of Redundant Network Connections Absolute versus User-Perceived Parameters 347 348 350 353 354 viii Contents 12.6 12.7 12.8 Appendix Network Analysis 356 Analysis of a Typical HFC Network 367 Summary 374 Channel Allocation 377 Glossary 385 Index 401 Acknowledgments CHAPTER Much of the material in this book is based on the transmission system portion of our previous book, Modern Cable Television Technology, Second Edition The material has been updated and expanded to reflect changes that have taken place in the broadband industry in the intervening four years As with our previous works, we freely acknowledge that we stand on the shoulders of our associates, our mentors, and those who have developed and documented cable television technology We owe a continuing debt of gratitude to those who contributed to previous books and, additionally, to those who agreed to review the proposal and scope of this current work, including Michael Adams, Vice President of System Architecture, Tandberg TV/Ericsson Group; Dan Pike, Chief Technology Officer of GCI Cable; Joseph Van Loan, Consultant and Chair of the Xtend Networks Advisory Board; and Ray Thomas, Principal Engineer, Advanced Technology Group, Time Warner Cable; Dr John Kenny, Wave7 Optics, an Enablence Technologies Company; and Dr Lamar West, Cisco Systems We are particularly indebted to Ron Hranac, who currently works at Cisco and is Senior Technology Editor of Communications Technology, for his careful review of the entire book prior to publication Additionally, specific recognition is due to many whose work is reflected in these pages more directly In most cases, the endnotes for each chapter document where the work of other authors and researchers has been quoted or characterized Additionally, we acknowledge the following: n n Figure 2.12 is based on data furnished by Howard Carnes of Antec Corporation Figure 4.6 is based on a figure in Ronald C Cotten, Lightwave Transmission Applications, September 15, 1993 (p 108) The graph is used with permission of CommScope, Inc., and Cable Television Laboratories Inc., Louisville, CO n Figures 4.10 and 4.11 are based on figures in Dogan A Atlas, “Fiber-Induced Distortion and Phase Noise to Intensity Noise Conversion in Externally-Modulated CATV Systems,” 1996 National Cable Television Association Technical Papers, April 1996 (pp 291–292) Washington, DC: National Cable Television Association n Tables 6.1 and 6.2 are adapted from material furnished by CableAML, Inc., Torrance, CA, September 5, 1997 Finally, we are indebted to the staff at Morgan Kaufmann/Elsevier for their support and encouragement, including Rick Adams, senior acquisitions editor, who identified the need for a book aimed specifically at those who work with linear distribution systems; Maria Alonso, assistant editor; and Marilyn Rash, project manager ix Glossary 389 dBmV Decibels with respect to one millivolt in a 75-ohm system The unit of RF power used in cable television work in North America In a 75-ohm system, dBmV ¼ À48.75 dBm Decibel See dB Demodulation The complementary process to modulation Recovery of information modulated onto a carrier Demodulator A device used by cable television systems to convert an RF modulated video and/or audio signal to baseband DFB laser Distributed feedback A laser technology in which the wavelength of the laser is set by the distance between reflecting surfaces at each end of the laser cavity, augmented by a grating running the length of the cavity Digital return A return path from a node to a headend, whereby the return signals are digitized and the digital signal is transmitted to the headend, where it is converted back to analog/RF form Digital television Television signals transmitted using digital techniques in which video levels are converted to digital states that approximate the original signal’s analog level As used in the consumer world, it also implies compressing the signal to minimize the transmission bandwidth required Digital video Representation of video signals in digital format It does not necessarily imply a compressed video signal Diplex filter A filter used to separate RF signals into one of two paths, based on the frequency of the signals Can also be used to combine signals that exist in different frequency bands Direct pick-up, or DPU The characteristic of a TV or VCR that a signal is picked up off-the-air in the device, creating interference with the signal being received via cable Directional coupler A three-port device for unequally dividing signal between two paths Can also be used to combine signals with more loss in one input than in the other, with the signal from the high-loss port being routed to only one of the other two ports Directivity In a tap or directional coupler, the difference in sensitivity to upstream and downstream signals, as measured at the side port Dispersion The variation of transmission velocity due to some controlling parameter; most commonly in optical transmission, as a function of wavelength (chromatic dispersion) Distribution The broadband portion of a cable television network extending from the point where the broadband spectrum is created in the same format as it will be received by subscribers (e.g., in a simple star HFC network, the distribution system starts at the input to the linear optical transmitter) DOCSIS Data-Over-Cable Service Interface Specification The formal name of the cable modem specification produced by a consortium led by CableLabs Downstream Signal flow from a headend toward subscribers DPU See direct pick-up 390 Glossary Drop The portion of the distribution plant between the tap and the individual subscriber’s home DWDM Wavelength division multiplexing in which the optical carriers are spaced 50 to 200 GHz apart (about 0.4 to 1.6 nm) EDFA Erbium-doped fiber amplifier The most common technology used to construct optical amplifiers for cable systems Egress A measure of the degree to which signals from the nominally closed coaxial cable system are transmitted through the air Also known as signal leakage EIA Electronic Industries Alliance A trade organization in Washington that represents companies that manufacture electronic equipment EIRP Effective isotropic radiated power The total power supplied to an antenna, multiplied by the gain of the antenna in a certain direction Elevation (A) The number of feet that a location is above mean sea level (AMSL) (B) The number of degrees by which an antenna is tilted upwards from a horizontal plane Error correction In data transmission, the technique of adding extra bits to a transmitted signal, with the extra bits being used to detect and correct errors in the transmission Ethernet A popular layer-2 protocol used for interconnecting data equipment Express feeder An untapped coaxial line between two amplifiers in the coaxial portion of an HFC distribution system External modulation A method of modulating a fiber-optic transmitter by operating the laser at a constant output level, and sending the output through an external modulator Extinction ratio In a binary laser transmitter, the ratio between the maximum light output in one binary state, to the minimum light output on the other binary state Fabry–Perot laser A laser technology in which the wavelength of the laser is set by the distance between reflecting surfaces at each end of the laser cavity Failure rate The per-unit average rate at which a group of similar devices will randomly fail during their normal service life Usually expressed in fraction, percentage per year, or parts per million (PPM) FCC Federal Communications Commission The governmental body in the United States that oversees telecommunications In other countries, the corresponding body may be called the Department of Communications or may be part of a Ministry of Posts, Telegraph and Telecommunications F-Connector The RF connector commonly used to attach drop cables to taps and other devices FDM Frequency division multiplexing The process of combining signals modulated on carriers of differing frequencies to create a signal spectrum for transmission or optical modulation Feeder The portion of the coaxial subnetworks that starts at an amplifier fed by an express feeder or trunk and supplies signals directly to subscriber taps Glossary 391 Filtering In communications, usually refers to the transmission of power in some frequency range(s) combined with the nontransmission of power in other frequency range(s) In computer use, may also refer to the elimination of certain types of information, with passage of other types Flat loss The loss in a cable plant that is not a function of frequency Typically, taps and attenuators have flat loss, as contrasted to coaxial cable, whose loss is approximated as being proportional to the square root of frequency FM/AM conversion FM to AM conversion A type of distortion to a modulated signal, in which frequency modulation is translated into amplitude modulation Forward Downstream transmission of cable signals Forward error correction (FEC) In data transmission, a process by which additional data are added; that is, are derived from the payload by an assigned algorithm It allows the receiver to determine whether certain classes of errors have occurred in transmission, and in some cases, allows other classes of errors to be corrected Fourier series A mathematical expression relating the time domain representation of a periodic waveform with the frequency domain representation It shows that any periodic waveform may be expressed as a series of harmonically related sine and cosine waves (Sine and cosine waves have the same shape, but are shifted in phase by 90 ) Frequency agile The ability to operate on more than one frequency (but not simultaneously) Frequency response The gain as a function of frequency through a system or device, relative to the defined ideal In the case of a cable distribution system, this is also known as peak-to-valley response or P/V Fresnel zone In a microwave path, this describes a hypothetical ring centered on the path such that the distance from transmitter to ring to receiver is one-half wavelength longer than the distance from transmitter to receiver FSAN Full service access network A standard for passive optical networks based on ATM FTF Fiber-to-the-feeder A distribution architecture in which fiber nodes feed coaxial feeder lines without any intervening coaxial trunk links FTTC Fiber-to-the-curb A distribution architecture in which directly fiber-fed termination units are shared by a number of dwellings FTTC implies fiber to within a few thousand feet of the home, with DSL being used to carry data from there to the home FTTH Fiber-to-the-home A delivery technology in which signals are delivered from the headend to the home completely in the optical domain GE-PON Gigabit Ethernet passive optical network Also known as EPON (Ethernet passive optical network) or EFM (Ethernet in the first mile) A protocol for FTTH developed by the IEEE It is used extensively in Asia and in other parts of the world It features symmetrical wire rates of 1.25 Gb/s GPON Gigabit passive optical network A protocol for FTTH developed by the ITU and the announced next generation of technology to be deployed by Verizon 392 Glossary Features a downstream wire speed of 2.488 Gb/s and an upstream wire rate of 1.244 Gb/s Group delay Generally, the deviation from linear phase shift versus frequency through a circuit or network This can occur due to reflections in a network It is also a property of many practical filters that signal power near the edge of the passband are delayed in traversing the filter, with respect to signals away from the edge This gives rise to waveform distortion, which can damage both analog and digital signals Hard cable, sometimes called hard line An informal term applied to the solidjacketed coaxial cable used in the coaxial distribution portion of a cable system ahead of the subscriber tap Also applied as an adjective to that portion of the distribution system HDTV High-definition television Television with significantly more picture information (resolution) than that provided by a good NTSC or PAL television signal While the definition of HDTV is nonspecific, it usually implies about twice the resolution in both the horizontal and vertical direction, and wide aspect ratio Headend The point at which all programming is collected and formatted for placement on the cable system HFC Hybrid fiber-coax A network for transmitting signals modulated onto RF carriers, which consists of RF carriers modulated onto optical carriers and transmitted on fiber-optic cable, followed by transmission of the RF carriers on coaxial cable medium The majority of cable plants built since the early 1990s use this architecture High pass filter A filter that passes all frequencies above its cutoff frequency, but not below HRC Harmonically related coherent A method of establishing picture carriers on a cable plant, such that all carriers are harmonics of a single fundamental frequency close to MHz Hub A point in a distribution system where signals are converted to the form used to transmit them to subscribers If a hub system is used, typically each hub will supply signals to a number of nodes IEEE Institute of Electrical and Electronics Engineers A professional organization of technologists interested in all aspects of electrical engineering IIN Interferometric intensity noise Noise in an optical link caused by the mixing of direct and doubly reflected signals in the optical detector diode Image response The response of a tuner to signals in a portion of the spectrum separated from the IF by the local oscillator frequency, but on the wrong side of the local oscillator Index of refraction The ratio of the speed at which light is transmitted in a vacuum to its speed in a material It is a property of any material that can transmit light Ingress Over-air signals that are inadvertently coupled into the nominally closed coaxial cable distribution system Glossary 393 Internal modulation A method of modulating a fiber-optic transmitter by directly varying the bias current on the laser diode with the modulating information IRC Incrementally related coherent A method of establishing picture carriers on a cable plant such that all carriers are spaced MHz apart based on a master oscillator, but the carrier frequencies are offset 1.25 MHz from harmonics of MHz Isolation In a tap or directional coupler, the difference between the amount of signal coupled to the side port and the directivity JEC Joint Engineering Committee A joint committee (no longer active) of the EIACEMA and the NCTA that developed several standards in use by the two industries, such as the ANSI/EIA-542 band plan Laser In the context of cable systems, the device used to convert electrical signals to optical signals LE Line extender A single-input, single-output amplifier used to boost signals in a coaxial distribution plant Long loop ALC Long loop automatic level control A technique practiced in most systems using upstream RF transmission The headend measures the RF level from each upstream transmitter and signals the upstream transmitter at the home to increase or decrease its power output until the correct level is received at the headend Low pass filter A filter that passes all frequencies below its cutoff frequency but none above Luminance, or luma Referring to the black and white portion of the television signal, as opposed to the chrominance (color) and aural (sound) portions MER Modulation error ratio A measurement of the quality of a digital modulated signal, which defines the average error between the proper location of all points in the constellation and their actual location Microreflections Small reflections occurring within both the coaxial distribution and drop portions of a cable plant They can lead to impaired analog reception, group delay, and errors in digital signals Modal dispersion In a multimode fiber, the variation of transmission time among the various possible paths for the light Modulation The process of imposing information on an RF carrier by varying some parameter of the carrier The parameters that can be varied are amplitude, frequency, or phase Modulator A device used by cable television systems to convert a baseband video and/or audio signal from baseband to the RF channel on which it is to be transmitted MPEG Motion Picture Experts Group A group that developed standards for digital decompression of television pictures The second generation of this standard, MPEG-2 is used for transmission of digital television in all parts of the world that have introduced such transmission MPEG-4 is a newer standard being deployed in certain applications 394 Glossary MPEG-2 The set of digital video decoding rules that form the basis of off-air and cable TV digital video transmission MPEG-4 An advanced set of digital video decoding rules The basic MPEG-4 is intended to provide for very low data rate transmission of less than entertainment-grade video MPEG-4 level 10 (also known as AVC, advanced video coding) is intended for entertainment-grade video Compare with MPEG-2 MSO Multiple system operator A company that owns more than one separate cable system MTBF Mean time between failure A measure of the average time interval between circuit restoration from a previous failure and the onset of the next failure in a network MTTR Mean time to restore A measure of the average time required to restore proper network/circuit operation after a failure Multimode An optical fiber that supports more than one transmission path and thus has a transmission delay whose uncertainty increases with length, thereby limiting bandwidth Multipath A condition in which an over-the-air signal may reach a receiver via more than one path from a transmitter, leading to degraded reception Applies to all transmission systems and frequencies Multiplex Use of a single data path for more than one set of data Multiplexing The combining of multiple independent signals into one signal path for transmission Cable systems operate in a frequency multiplexing mode, in which signals at different frequencies are combined in one signal path Another example is time division multiplexing, where multiple signals share the same path but are segregated in terms of time A third example is wavelength division multiplexing in which signals modulated on different optical wavelengths share use of a single fiber Mux See multiplex NCTA National Cable & Telecommunications Association A trade organization that represents companies in the cable television industry NID Network interface device One of many names for a box on the side of the house that contains any required interfaces between a telephone line, FTTH, or cable plant, and inside wiring Node (A) The portion of a coaxial cable plant served from one optical receiver (B) The equipment that receives the linearly modulated FDM spectrum, converts it back to RF form, and transmits it into one or more of the coaxial distribution legs Noise Generally defined as undesired signals in a transmission channel In television, the term is commonly applied to broadband thermal noise excluding discrete carriers and distortion products Noise figure The ratio, expressed in dB, of the noise produced by a device over and above the thermal noise produced in a matched resistor at the input to that device Higher noise figure devices require a higher signal level to deliver a given signal-to-noise ratio Glossary 395 NPR Noise power ratio A method of specifying the quality of a transmission path by loading it with noise, eliminating the noise in a narrow band, and measuring the amount of noise filled in by the transmission path NTSC National Television Systems Committee An entity that developed the analog TV system used in North America and elsewhere There were actually two NTSCs: the first developed the monochrome transmission system and the second added color OpenCable A set of industry standards intended to define the next-generation digital consumer devices used by the cable TV industry, encourage supplier competition, and create a retail hardware platform OpenCable has now been rebranded as tru2way OMI Optical modulation index A measure of how much optical modulation is applied to a laser It is usually stated in terms of how much of the range from the laser’s quiescent bias point to cutoff is taken up by the signal The OMI may be expressed in terms of per channel or composite signal P/V Peak-to-valley The peak-to-peak variation in the frequency response of a cable distribution network relative to the ideal response curve PacketCable A set of interoperable interface specifications for delivering advanced, real-time multimedia services over two-way cable plant PacketCable is built on top of DOCSIS Passband The frequency or wavelength region passed by a filter Passive A component that handles signals, but which requires no power of its own Examples are taps and power inserters Peak-to-average ratio In data transmission, the ratio, usually expressed in dB, between the peak power of a signal and the average power Phase noise A distortion in which a carrier signal is subjected to random variations in phase Pilot A signal on the distribution plant that is used either as a level or as a frequency reference In some cases, the pilot is one of the normal analog picture carriers that has been so designated PMD Polarization mode dispersion In an optical fiber, a measure of the transmission time as a function of the orientation of the E-field of the light relative to the fiber POE Point-of-entry Equipment that is placed between the drop and inside wiring of a dwelling and which processes some or all of the signals for specific services One application is cable telephony where the POE device interfaces standard analog in-home wiring to the RF distribution system See NID Polarization An expression of the orientation of the electric field in a radiated RF signal or an optical signal in single mode fiber PON Passive optical network An all-optical network that consists of nothing more than fiber-optic cable and splitters Port A logical construct through which data are transferred from one process to another 396 Glossary Power inserter A passive device used to add ac power to the center conductor of a coaxial cable for the purpose of powering active devices Power pack In a cable system, the module within an amplifier station (or other active equipment) that receives the power multiplexed with the RF signals on the distribution system and creates the voltages required by the station’s internal circuits Power supply In a cable system, the device that receives power from the utility, processes it for use in the cable system, and inserts it into the coaxial plant through a power inserter Predistortion A technique for reducing distortion in a linear transmission system by intentionally generating distortion at the transmit end; this distortion will be canceled by the real distortion of the network PSK Phase shift keying In data transmission, a modulation format that depends solely on differences in phase of a modulated signal to convey information QAM Quadrature amplitude modulation A digital modulation method in which the value of a symbol consisting of multiple bits is represented by amplitude and phase states of a carrier Typical types of QAM include 16 QAM (4 bits per symbol), 32 QAM (5 bits), 64 QAM (6 bits) and 256 QAM (8 bits) QoS Quality of service Techniques for ensuring the delivery of data in a reliable and timely manner QPSK Quadrature phase shift keying A digital modulation method in which the state of a 2-bit symbol is represented by one of four possible phase states Quadrature At right angles In transmission, often used to express independence between two signals Rain fade In a terrestrial or satellite microwave link, signal loss due to absorption and reflections caused by rain drops within the signal path Reflectometer A device used to determine the location of a fault in a cable by propagating a signal down the cable and reading any signal reflected May be used for RF or optical transmission Refraction The process by which optical signals are transmitted through the interface between two dissimilar materials See index of refraction Reliability The probability that a component or network will survive for some interval of time, therefore is inversely proportional to its failure rate Return loss A measure of the amount of incident power that is reflected back toward the opposite end of a cable from a termination or other discontinuity in the characteristic impedance of the cable Reverse See upstream RFoG Radio frequency over glass A form of FTTH being developed within the SCTE that features RF modulation only of optical carriers in both directions, to and from the home RIN Relative intensity noise A measure of the residual internal noise modulation of an optical transmitter RIN often limits the attainable C/N of RF signals transmitted through an optical link Glossary 397 Ring network An architecture in which terminal points are connected in a continuous ring and each terminal is connected to both of its neighbors SBS Stimulated Brillouin scattering A mechanism that limits the amount of optical power at a single wavelength that can be transmitted through an optical fiber Scattering In an optical network, scattering is any process by which light is briefly delayed, and then retransmitted Forward scattering causes an overall slowing of the signal (see index of refraction), while scattering in other directions leads to signal loss and, sometimes, distortion SCTE Society of Cable Telecommunications Engineers A professional organization of technologists interested in cable telecommunications technology SDM Space division multiplexing The simultaneous use of the different physical portions of a network (e.g., nodes) to carry different signals at the same frequencies SDV Switched digital video A method of delivering video programming whereby a given program stream is only delivered to any given service group when at least one member of the group requests it Set-top converter Also known as a set-top terminal A device used with a subscriber’s TV to allow reception of programs It may tune channels the TV does not tune and may include descrambling circuitry It also may include a digital decoder and auxiliary functions such as an electronic program guide Shot noise In an optical link, noise at the optical receiver that is caused by the statistical variation in the arrival of photons Signal level In analog television work, the RMS level of the picture carrier measured over the occupied bandwidth of the signal, during sync tips In digital communications as practiced by the cable industry, it is the average level of the modulated signal or the level that would be read on a thermocouple-type RF power meter Signal-to-noise (S/N) ratio In video work, the ratio between the video signal amplitude and the noise power measured in a reference bandwidth Many variations in the definition of “signal” and “noise” exist, and the reader must exercise care that the definitions in use are accurately conveyed Single mode fiber Optical fiber that supports only a single transmission path and thus offers a better-defined transmission delay Skin effect The tendency of RF signals to travel near the surface of conductors Spectrum analyzer A piece of test equipment used to plot amplitude versus frequency Splitter A device having three or more ports, used to divide RF signal equally between two paths, without regard for the frequency of the signal Can also be used to combine two signals SPM Self-phase modulation In an optical fiber, incidental phase modulation at high optical levels caused by variation of the index of refraction with the instantaneous power level of the optical signal 398 Glossary SRL Structural return loss A measure of the degree to which signals are reflected from a length of cable as a function of frequency SRS Stimulated Ramon scattering A mechanism in fiber cable that caused transfer of power from a shorter wavelength to a longer wavelength if the wavelength separation is within a certain range Standard definition Loosely defined, the picture definition associated with analog NTSC video or with digital video formats that yield roughly equivalent resolution Stopband The frequency or wavelength region rejected by a filter Supertrunk In a cable system, the signal transportation link used to connect the point where the FDM signal complex is created to local coaxial distribution networks In an HFC network, linearly modulated optical links are used, but other systems use AML microwave or coaxial supertrunks Tap The component installed in the distribution cable that diverts a portion of the downstream distribution signal and splits it to feed two to eight individual subscribers In the reverse direction, it combines the signals from subscribers and inserts them into the upstream direction of the distribution cable TCP Transmission control protocol A connection-oriented, layer-4 protocol often used with IP to transmit data Includes various mechanisms to enhance the probability that a packet will arrive TDM Time division multiplex A data transmission method in which a number of individual digital datastreams share a transmission channel, each occupying the channel for a portion of the total time TDMA Time division multiple access A data transmission method in which a number of individual transmitters in different locations share a transmission channel, each occupying the channel for a portion of the total time TDR Time domain reflectometer A device that measures the quality of a transmission line by transmitting a pulse, then measuring signals reflected as a function of time The reflections indicate the distance to the point of reflection TDRs can operate in either the electrical RF domain or in the optical domain Telcordia The current name of what was formerly known as BellCore, now a privately owned body that sets standards used in the telephone industry TEM Transverse electric and magnetic A description of the normal field configuration for signals transmitted through coaxial cables Transition region The frequency or wavelength region(s) of a filter that are between the passband and the stopband Trap A passive coaxial component inserted in series with a drop line that blocks transmission of a specific frequency or range of frequencies Used to block or enable specific channels or to tailor the services available in homes Trunk (A) The untapped portion of a coaxial distribution network Trunk links are typically operated at lower levels than distribution links to minimize distortions (B) An amplifier module used in the trunk portion of a coaxial distribution system (C) An amplifier station that contains a trunk module It may Glossary 399 also contain a bridger module if creating a distribution leg at that location is desired Unavailability The fraction of time that a network or channel is unavailable for use See availability UPC Ultra-polished connector An optical connector that minimizes loss and reflections by careful preparation and polishing of the fiber end, and alignment with the mating fiber Upstream Signal flow from subscribers toward a headend UTP Unshielded twisted pair A data cable consisting of one or more twisted pairs without shielding See Cat Video In television work, this term is reserved to mean a baseband electrical signal that conveys information regarding picture content Visual An adjective implying an RF or IF carrier that is modulated with a video signal VOD Video-on-demand A video service that allows users to select the program and exact start time interactively In some embodiments, it allows VCR-like control of the playback (e.g., pause, rewind, fast-forward) Wavelength The distance traveled through a transmission medium by an RF or optical signal in a time equal to the inverse of the frequency (e.g., for a 1-GHz signal, the distance traveled in ns) It is equal to the speed of propagation in the medium divided by the frequency Wavelength dispersion In an optical fiber, the variation in transmission time as a function of the wavelength of the light W-curve The variation of subscriber perceptibility of interfering signals in an analog television channel as a function of frequency within the channel boundaries So called because of the shape of the curve, caused by extreme sensitivity to interfering signals occurring near the visual and chrominance carriers WDM Wavelength division multiplexing The use of an optical fiber to simultaneously carry signals at different wavelengths Can also refer to a wavelengthsensitive device used to combine and separate optical signals at different wavelengths Wire rate The actual data rate at which a signal is transferred on an interface, including all overhead XMOD Cross-modulation A type of distortion in which the amplitude modulation of one signal causes incidental amplitude modulation to another signal XMOD is an odd-order distortion This page intentionally left blank INDEX Above ground level, 169 Above mean sea level, 169 Active fiber-to-the-home systems, 332–333 Air dielectric, 16 Allocation channel, 377–383 constant power density method of, 255 performance, 191–192 Aluminum shields, 9, 16 Amplifiers bidirectional, 35f broadband random noise, 19 design choices for, 38–41 distortion See Distortion distribution, 41, 41f drop, 76, 300 erbium-doped fiber, 111, 111f, 341 error, 45 failure rate for, 361 feed-forward, 45–46 gain, 43f, 44 gain-flattened optical, 132 group delay variation, 34–35 hum modulation, 36–38 input circuits, 42 low-noise, 165 noise generated by, 20 operating dynamics of, 42–45 optical, 110–112, 132 optical noise, contribution by, 341 optimum gain, 44 parallel hybrid, 45 power/radiofrequency separation in, 37f power supply for, 36, 64f push-pull, 45 radiofrequency line, 26 signal loading, 43f, 44 stability of, 34–35 transimpedance, 113–114, 325 trunk, 40, 40f Amplitude-modulated microwave links, 180–182 channel combinations, 164t–165t distortion calculations, 175 frequency relationships in, 163t indications for, 161 low-noise amplifiers, 165 multipath, 176–177 operational principles of, 162–165 path, 166 azimuth of, 167–168 clearances, 168–171 end coordinates for, 166 factors affecting the availability of, 176–180 Fresnel zone calculations, 168–169, 171 K factor, 170 length of, 166–167 multipath, 176–177 performance calculations using, 172 rain fade effects, 177–180, 181f–182f vertical clearances, 169–171 performance calculation, 182 carrier-to-thermal-noise calculation, 174–175 distortion, 175 power budget calculation, 172–174 sample, 173t signal path definition for, 172 receivers, 165 simplicity of, 162–163 transmitters, 165 U.S regulation of transmission, 162 Amplitude shift keying, 342 Analog optical modulation, 321–323 Analog receivers, 325–326 Analog shared ring, 308, 309f Analog signals carrier-to-noise ratio for, 193–194, 197 FCC rules for, 187t–188t Note: Pages numbers followed by “f” denote figures; those followed by “t” denote tables 401 402 Index Analog-to-digital converters, 222–223 Analog transmission, 326–327 distance limitations for, 339–341, 340f, 342f Analog transmitter, 323–325 Angle-polished connectors, 100–101, 101f ANSI/SCTE 105, 189 Architecture, 265 for broadcast video services, 284–286 for interactive video services, 289–290 for narrowcast video services, 287 for on-demand video services, 289–290 for packet data services, 290–292 scalability of, 296 service-based requirements for, 284–296 for utility monitoring and control services, 295–296 for voice-grade telephony services, 292–295 ATM passive optical network, 335 Attenuation in bent fibers, 95 as function of characteristic impedance, 10–11 as function of frequency, 7–9 as function of temperature, 9–10 methods of, return, 252–253 single-mode optical fibers, 92, 93f Attenuators, 67, 102, 233 return, 252–253 return path interference mitigation by moving of, 254 August mean radio refractivity, 170 Aural carrier frequency, 191 Automatic gain and/or slope control circuits, 69 Automatic gain control, 36, 227–230 Automatic level control, long-loop, 224, 226–228, 260, 262 Availability, 353 See also Network reliability and service availability Azimuth, of amplitude-modulated microwave link path, 167–168 Backbone, 310 Bands, 127–128, 129b Bandwidth downstream RF, 266–267 efficiency of, 272–274 limitations on, 267 per customer, 269–272 upstream RF, 267–269 Bidirectional amplifier, 35f Bidirectional transmission, 327 Bit error rate, 103, 103f, 123, 235, 236f, 245, 280–281 Block conversion, 220–221, 270 Block tilt, 43 Bridger, 40, 40f Brillouin scattering, stimulated, 95–96, 97f, 339–340, 340f Broadband combiner, 131 Broadband passive optical network, 335 Broadband random noise, 19 Broadcast digital video services, 282 Broadcast video services, 284–286 Cable coaxial See Coaxial cable fiber-optic, 362–363 Cable antenna relay service, 162 Cable area network, 310–311, 311f Cable television systems advances in, hybrid fiber/coax plant, 1–2 outage of, 349 reliability and availability of, 349–350 Carrier to distortion, 59–61 Carrier-to-noise ratio, 20, 34, 192–193, 197–198 analog signals, 193–194, 197 calculation of, 155, 174–175, 192 contributors to, 174–175 degradation of, 42, 44 digital signals, 194, 197 noise power ratio vs., 234–235 total link, 117–118 Carrier to thermal noise, 174–175 Cascade amplifier operating levels, 62 maximum attainable, 62 noise and, 63f Cascaded reflections, 208f Index 403 C-Band, 128 C/CSO ratio, 24, 26, 97 degradation of, 98, 99f self-phase modulation effects on, 98 CEA–542, 199 CEA–23-A, 189 Centralized powering, 64 Channel allocation, 377–383 Characteristic impedance, 6–7 attenuation as function of, 10–11 average, 12 Chirp, 107, 132, 234, 343–344 with dispersion, 107–108 with imperfect channel flatness, 152–154 Choke, 51 Chromatic dispersion, 93–94, 343 Clipping, 120–124, 199–200 in frequency domain, 248–249 Coarse wavelength division multiplexing, 128, 221 Coaxial cable, advantages of, attenuation See Attenuation basics of, 6f characteristic impedance of, 6–7 construction of, drop, 16–18, 17f–18f, 72 failure rate, 363 feeder, 16 hard-line, 16 selection of, 15–18 structural return loss, 12–13 theoretical size limitation of, 11–12 time domain reflectometry, 13–15 trunk, 16 wavelength of, 11 Coaxial distribution legs, 304–305 Coaxial distribution systems, 57, 77–78, 300–302 amplifiers See Amplifiers area size for, 301 nodes, 311 See also Nodes powering strategies, 301–302 RF bandwidth, 300–301 Code division multiple access, 273 Coding gain, 273 Common path distortion, 242, 249–250 Competitive access providers, 307 Component failure rates, 351 amplifiers, 361 calculation of, 367 connectors, 362 determination of, 360–364 fiber-optic cable, 362–363 headend, 363–364, 366 hubs, 366 network interface devices, 363 optical receivers, 361 optical transmitters, 361 passive devices, 362 power supplies, 361 rack-mounted equipment, 363–364 splitters, 362 taps, 362 terminal equipment, 363 Composite intermodulation noise, 33–34, 199 Composite reverse signal, 246–247 Composite second-order distortion, 24–25, 157–158, 231 from chirp combined with imperfect channel flatness, 152–154 from chirp interacting with dispersion, 107–108 degradations, 119 distribution of, 199 self-phase modulation effects on, 97 Composite third-order distortion, 32–33, 157–159, 231 Composite triple beat distortion, 26–32, 194–196 Connectors angle-polished, 100–101, 101f cleaning of, 101–102 difficulty in improving, 100 failure rate for, 362 ultra-polished, 100–101, 101f Constant bit rate, 275 telephony, 293–294 Constant power density, 255 Copper, Corrosion, 249–250 Couplers directional, 46–48, 47f Wilkinson, 48 .. .Broadband Cable Access Networks This page intentionally left blank Broadband Cable Access Networks The HFC Plant David Large James Farmer AMSTERDAM... paper) Cable television Broadband communication systems Optical fiber communication I Farmer, James II Title III Title: Broadband cable access networks, the hybrid fiber/coax plant IV Title: Broadband. .. feeder cable, whereas 20 dB is considered adequate for drop cable The absolute impedance should be within Æ2 to ohms for trunk and distribution cables and Æ5 ohms for drop cables.3 2.2 Coaxial Cable