CLC/TR 50083-10-1:2014

Cable networks for television signals, sound signals and interactive services - Part 10-1: Guidelines for the implementation of return paths in cable networks

1.1 General Standards and other deliverables of the EN 50083 and EN 60728 series deal with cable networks including equipment and associated methods of measurement for headend reception, processing and distribution of television and sound signals and for processing, interfacing and transmitting all kinds of data signals for interactive services using all applicable transmission media. These signals are typically transmitted in networks by frequency-multiplexing techniques. This includes for instance  regional and local broadband cable networks,  extended satellite and terrestrial television distribution networks and systems  individual satellite and terrestrial television receiving systems, and all kinds of equipment, systems and installations used in such cable networks, distribution and receiving systems. The extent of this standardization work is from the antennas and/or special signal source inputs to the headend or other interface points to the network up to the terminal input of the customer premises equipment. The standardization work will consider coexistence with users of the RF spectrum in wired and wireless transmission systems. The standardization of any user terminals (i.e. tuners, receivers, decoders, multimedia terminals etc.) as well as of any coaxial, balanced and optical cables and accessories thereof is excluded. 1.2 Specific scope of this Technical Report This document is intended to provide guidance to network designers on the issues which should be addressed, when considering the design of return paths for regional or local broadband networks. Items such as return path architecture & design, channel performance, channel planning & sources of interference, measurements, segmentation & re-segmentation, in home networks, distortion and commissioning are included. This document is not intended as a design reference but provides details which need to be addressed on individual issues relating to the design of the return path for a regional or local broadband network.

Kabelnetze für Fernsehsignale, Tonsignale und interaktive Dienste - Teil 10-1: Leitfaden für die Einrichtung von Rückkanälen in Kabelnetzen

Réseaux de distribution par câbles pour signaux de télévision, signaux de radiodiffusion sonore et services interactifs - Partie 10-1: Lignes directrices relatives à la mise en oeuvre de la voie de retour dans les réseaux câblés

Kabelska omrežja za televizijske signale, zvokovne signale in interaktivne storitve - 10-1. del: Smernice za uporabo povratnih poti v kabelskih omrežjih

Standarda EN 50083 in EN 60728 in drugi izsledki obravnavajo kabelska omrežja, vključno z opremo in povezanimi metodami za merjenje sprejema glavne sprejemne postaje, obdelavo in distribucijo televizijskih in zvočnih signalov ter za obdelavo, povezovanje in oddajanje vseh vrst podatkovnih signalov za interaktivne storitve prek vseh primernih prenosnih medijev. Ti signali se v omrežjih običajno prenašajo s tehnikami multipleksiranja frekvenc. To na primer vključuje: - regionalna in lokalna širokopasovna kabelska omrežja, - razširjena satelitska in prizemna televizijska distribucijska omrežja ter sisteme, - posamezne satelitske in prizemne televizijske sprejemne sisteme - in vse vrste opreme, sistemov in naprav, uporabljene v tovrstnih kabelskih omrežjih, distribucijskih in sprejemnih sistemih. To standardizacijsko delo med drugim zajema antene in/ali posebne vhode virov signalov v glavno sprejemno postajo ali druge vmesniške točke omrežja do vhodnega terminala opreme v prostorih strank. To standardizacijsko delo bo upoštevalo soobstoj uporabnikov radiofrekvenčnega spektra v ožičenih in brezžičnih prenosnih sistemih. Standardizacija poljubnih uporabniških terminalov (tj. uglaševalnikov, sprejemnikov, kodirnikov, večpredstavnostnih terminalov itd.) in poljubnih povezanih koaksialnih, simetričnih in optičnih kablov ter opreme je izključena.

General Information

• Status: Withdrawn
• Publication Date: 05-Jun-2014
• ICS: 33.060.40 - Cabled distribution systems
• Technical Committee: CLC/TC 209 - Cable networks for television signals, sound signals and interactive services
• Current Stage: 9960 - Withdrawal effective - Withdrawal
• Start Date: 22-Feb-2023
• Completion Date: 23-Sep-2025
• Ref Project: SIST-TP CLC/TR 50083-10-1:2014 - Cable networks for television signals, sound signals and interactive services -- Part 10-1: Guidelines for the implementation of return paths in cable networks

Relations

• Replaces: CLC/TR 50083-10-1:2009 - Cable networks for television signals, sound signals and interactive services - Part 10-1: Guidelines for the implementation of return paths in cable networks
• Effective Date: 29-Jan-2023

Standards Content (Sample)

SLOVENSKI STANDARD
01-oktober-2014
1DGRPHãþD
SIST-TP CLC/TR 50083-10-1:2009
Kabelska omrežja za televizijske signale, zvokovne signale in interaktivne storitve
- 10-1. del: Smernice za uporabo povratnih poti v kabelskih omrežjih
Cable networks for television signals, sound signals and interactive services -- Part 10-1:
Guidelines for the implementation of return paths in cable networks
Kabelnetze für Fernsehsignale, Tonsignale und interaktive Dienste -- Teil 10-1: Leitfaden
für die Einrichtung von Rückkanälen in Kabelnetzen
Réseaux de distribution par câbles pour signaux de télévision, signaux de radiodiffusion
sonore et services interactifs -- Partie 10-1: Lignes directrices relatives à la mise en
oeuvre de la voie de retour dans les réseaux câblés
Ta slovenski standard je istoveten z: CLC/TR 50083-10-1:2014
ICS:
33.060.40 Kabelski razdelilni sistemi Cabled distribution systems
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

TECHNICAL REPORT CLC/TR 50083-10-1

RAPPORT TECHNIQUE
TECHNISCHER BERICHT
June 2014
ICS 33.060.40 Supersedes CLC/TR 50083-10-1:2009
English Version
Cable networks for television signals, sound signals and
interactive services - Part 10-1: Guidelines for the
implementation of return paths in cable networks
Réseaux de distribution par câbles pour signaux de Kabelnetze für Fernsehsignale, Tonsignale und interaktive
télévision, signaux de radiodiffusion sonore et services Dienste - Teil 10-1: Leitfaden für die Einrichtung von
interactifs - Partie 10-1: Lignes directrices relatives à la Rückkanälen in Kabelnetzen
mise en oeuvre de la voie de retour dans les réseaux
câblés
This Technical Report was approved by CENELEC on 2014-06-02.

CENELEC members are the national electrotechnical committees of Austria, Belgium, Bulgaria, Croatia, Cyprus, the Czech Republic,
Denmark, Estonia, Finland, Former Yugoslav Republic of Macedonia, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia,
Lithuania, Luxembourg, Malta, the Netherlands, Norway, Poland, Portugal, Romania, Slovakia, Slovenia, Spain, Sweden, Switzerland,
Turkey and the United Kingdom.

European Committee for Electrotechnical Standardization
Comité Européen de Normalisation Electrotechnique
Europäisches Komitee für Elektrotechnische Normung
CEN-CENELEC Management Centre: Avenue Marnix 17, B-1000 Brussels
© 2014 CENELEC All rights of exploitation in any form and by any means reserved worldwide for CENELEC Members.
Ref. No. CLC/TR 50083-10-1:2014 E

Contents
Foreword . 5
1 Scope . 6
1.1 General . 6
1.2 Specific scope of this Technical Report . 6
2 Normative references . 6
3 Terms, definitions, symbols and abbreviations . 7
3.1 Terms and definitions. 7
3.2 Symbols . 10
3.3 Abbreviations . 11
4 Network architecture . 13
4.1 HFC architecture . 13
4.2 Upgrade alternatives . 15
4.3 Active or passive return path . 25
4.4 In building network . 25
4.5 In home network . 25
5 Network design . 26
5.1 Considerations . 26
5.2 Return path loss, path loss difference and return path slope . 26
5.3 Noise and nonlinearity, optimizing signal levels . 31
5.4 Isolation between outlets . 33
5.5 Equalization and filtering in return paths. 33
6 Channel planning . 36
6.1 Purpose of this section. 36
6.2 Introduction . 36
6.3 Summary . 36
6.4 Considerations for channel planning . 37
6.5 Common path distortion products . 41
6.6 European upstream bandwidths . 41
6.7 Channel width . 41
6.8 QPSK/16QAM operation and channel widths . 41
6.9 Available return path spectrum (Table 8). 42
6.10 Channel plans . 43
6.11 Network radiation . 45
7 Equipment for return path implementation . 45
7.1 General . 45
7.2 Return path amplifiers . 45
8 Installation and maintenance . 48

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8.1 Signal level adjustment . 48
8.2 Monitoring and measurements . 52
Annex A (informative) Interference on return path . 54
A.1 Multiple interference . 54
A.2 Impulse interference . 63
A.3 Interference from home terminals — EMC standards of home terminals . 65
A.4 Hum modulation . 66
A.5 Common path distortion (CPD) . 66
Annex B (informative) Null packet and PRBS definitions . 74
B.1 Null packet definition . 74
B.2 PRBS definition . 74
Annex C (informative) ITU DWDM grid . 75
Bibliography . 77
Figures
Figure 1 — Typical HFC topology . 14
Figure 2 — Regional network . 15
Figure 3 — Trunk-and-distribution architecture using only coaxial equipment . 15
Figure 4 — HFC system . 16
Figure 5 — Generic diagram showing the mapping of nodes and CMTS(s) to segments . 17
Figure 6 — Segment comprising a single CMTS to N optical nodes . 17
Figure 7 — Spectrum allocation bandwidth. 18
Figure 8 — Basic node architecture . 19
Figure 9 — Re-arranged feeds (two CMTS serving four nodes). 20
Figure 10 — Optical node with frequency stacking . 21
Figure 11 — Divided node . 21
Figure 12 — Return path segmentation . 22
Figure 13 — Division of the node areas using additional fibres . 22
Figure 14 — DWDM (CWDM) return path transmission . 23
Figure 15 — Digital return technology basic concept . 23
Figure 16 — Two return paths multiplexed to the transmission stream . 24
Figure 17 — Optical node segmentation . 25
Figure 18 — In house structures for transparent return path transmission . 26
Figure 19 — Example of forward (862 MHz) and return path (65 MHz) network with operating levels
for the drop and in home parts of the network . 28
Figure 20 — Example of a block diagram of return path amplifier . 46
Figure 21 — Commissioning of the forward path . 48
Figure 22 — Commissioning of the return path amplifiers using the same method as on the forward
path 49
Figure 23 — Problem when commissioning return path amplifiers following the method used for
downstream amplifiers (standard output levels) . 49
Figure 24 — Unity gain method . 50
Figure 25 — Optical reverse path . 50

Figure 26 — Optical node with reverse transmitter . 51
Figures in annexes
Figure A.1 — Typical spectrum of a return path. 54
Figure A.2 — Noise funnelling . 55
Figure A.3 — Average noise level vs. the number of subscribers and the return path frequency [19] . 56
Figure A.4 — Simplified equivalent circuit of a drop cable . 56
Figure A.5 — Screening effectiveness of a coaxial cable vs. frequency . 58
Figure A.6 — Spectrogram of noise level vs. frequency and time (example) . 60
Figure A.7 — Maximum, minimum and average noise levels vs. frequency (example) . 61
Figure A.8 — Centile analysis of noise levels vs. frequency (example) . 62
Figure A.9 — Temporal evolution of the -10 dB(mV) threshold crossing occurrence (example) . 63
Figure A.10 — Frequency evolution of the -10 dB(mV) threshold crossing occurrence (example) . 63
Figure A.11 — Illustration of impulse noise measurement according to the method described in
EN 60728-10 . 65
Figure A.12 — Example for the use of the return path frequency range . 66
Figure A.13 — Test set-up for CPD simulation . 68
Figure A.14 — Intermodulation products with 8 MHz spacing . 68
Figure A.15 — Contact resistance as function of contact pressure . 69
Figure A.16 — Upstream pass-band characterization . 70
Figure A.17 — Set-up of test signals . 71
Figure A.18 — Test set-up for passive devices. 71
Figure A.19 — Test set-up for power passing devices . 72
Figure A.20 — Thermal cycle profile . 72
Figure A.21 — Spectral response with CPD in the return path . 73
Tables
Table 1 — Summary of in home return path losses . 30
Table 2 — Calculation of return path versus temperature . 31
Table 3 — Broadcasting allocations between 5 MHz and 42 MHz . 38
Table 4 — Amateur and Citizens Band allocations between 5 MHz and 42 MHz . 39
Table 5 — DOCSIS/EuroDOCSIS symbol rates and channel widths . 39
Table 6 — Data carriers in the gaps between broadcasting bands . 40
Table 7 — Data carriers in the gaps between broadcasting, amateur and CB bands . 40
Table 8 — Available spectrum between 5 MHz and 65 MHz . 42
Table 9 — Example of a 1,6 MHz wide channel plan up to 65 MHz (avoiding CPD products) . 43
Table 10 — Example of a 3,2 MHz wide channel plan up to 65 MHz . 44
Table 11 — Permitted radiation 0,3 MHz to 30 MHz (A-Deviation for Great Britain) . 45
Table 12 — Permitted radiation 30 MHz to 68 MHz (A-Deviation for Great Britain) . 45
Table 13 — Split frequencies used in Europe . 47
Table 14 — Alarm thresholds for upstream monitoring (example). 53
Tables in Annexes
Table A.1 — European EMC standards applicable to home terminals . 65
Table B.1 — Null transport stream packet definition . 74
Table C.1 — ITU DWDM grid . 75

- 5 - CLC/TR 50083-10-1:2014
Foreword
This document (CLC/TR 50083-10-1:2014) has been prepared by CLC/TC 209 "Cable networks for television
signals, sound signals and interactive services".
This document supersedes CLC/TR 50083-10-1:2009.
CLC/TR 50083 10-1:2009:
a) the introduction of a new "General Scope";
b) the introduction of new upper frequency limit 85 MHz for return path as an option;
c) the introduction of some new "Terms and definitions" due to the new general scope and due to the
introduction of the extended return path frequency range to 85 MHz;
d) the deletion of Clause B.1 on "Noise power ratio";
e) the deletion of Clause B.2 on "10-tone measurement";
f) the deletion of Clause B.3 on "MER measurement".
EN 50083 is currently composed of the following parts:
— EN 50083-2, Cable networks for television signals, sound signals and interactive services — Part 2:
Electromagnetic compatibility for equipment;
— CLC/TR 50083-5-1, Cable networks for television signals, sound signals and interactive services —
Part 5-1: IP gateways and interfaces for headends;
— EN 50083-8, Cable networks for television signals, sound signals and interactive services — Part 8:
Electromagnetic compatibility for networks;
— EN 50083-9, Cable networks for television signals, sound signals and interactive services — Part 9:
Interfaces for CATV/SMATV headends and similar professional equipment for DVB/MPEG-2 transport
streams;
— EN 50083-10, Cable networks for television signals, sound signals and interactive services — Part 10:
System performance for return paths;
— CLC/TR 50083-10-1, Cable networks for television signals, sound signals and interactive services —
Part 10-1: Guidelines for the implementation of return paths in cable networks [the present document].
Attention is drawn to the possibility that some of the elements of this document may be the subject of patent
rights. CENELEC [and/or CEN] shall not be held responsible for identifying any or all such patent rights.
__________
1 Scope
1.1 General
Standards and other deliverables of the EN 50083 and EN 60728 series deal with cable networks including
equipment and associated methods of measurement for headend reception, processing and distribution of
television and sound signals and for processing, interfacing and transmitting all kinds of data signals for
interactive services using all applicable transmission media. These signals are typically transmitted in
networks by frequency-multiplexing techniques.
This includes for instance:
 regional and local broadband cable networks,
 extended satellite and terrestrial television distribution networks and systems,
 individual satellite and terrestrial television receiving systems
 and all kinds of equipment, systems and installations used in such cable networks, distribution and
receiving systems.
The extent of this standardization work is from the antennas and/or special signal source inputs to the
headend or other interface points to the network up to the terminal input of the customer premises equipment.
The standardization work will consider coexistence with users of the RF spectrum in wired and wireless
transmission systems.
The standardization of any user terminals (i.e. tuners, receivers, decoders, multimedia terminals etc.) as well
as of any coaxial, balanced and optical cables and accessories thereof is excluded.
1.2 Specific scope of this Technical Report
This document is intended to provide guidance to network designers on the issues which should be
addressed when considering the design of return paths for regional or local broadband networks.
Items such as return path architecture & design, channel performance, channel planning and sources of
interference, measurements, segmentation and re-segmentation, in home networks, distortion and
commissioning are included. This document is not intended as a design reference but provides details which
need to be addressed on individual issues relating to the design of the return path for a regional or local
broadband network.
2 Normative references
The following documents, in whole or in part, are normatively referenced in this document and are
indispensable for its application. For dated references, only the edition cited applies. For undated references,
the latest edition of the referenced document (including any amendments) applies.
EN 60728-1:2008, Cable networks for television signals, sound signals and interactive services — Part 1:
System performance of forward paths (IEC 60728-1:2007)
EN 60728-3, Cable networks for television signals, sound signals and interactive services — Part 3: Active
wideband equipment for cable networks (IEC 60728-3)
EN 60728-4, Cable networks for television signals, sound signals and interactive services — Part 4: Passive
wideband equipment for coaxial cable networks (IEC 60728-4)
EN 60728-5, Cable networks for television signals, sound signals and interactive services — Part 5: Headend
equipment (IEC 60728-5)
EN 60728-6, Cable networks for television signals, sound signals and interactive services — Part 6: Optical
equipment (IEC 60728-6)
- 7 - CLC/TR 50083-10-1:2014
EN 60728-10:2014, Cable networks for television signals, sound signals and interactive services — Part 10:
System performance for return paths (IEC 60728-10:2014)
ETSI EN 302 878 series, Access, Terminals, Transmission and Multiplexing (ATTM); Third Generation
Transmission Systems for Interactive Cable Television Services — IP Cable Modems
ETSI ES 201 488 series, Access and Terminals (AT); Data Over Cable Systems
ETSI ES 202 488 series, Access and Terminals (AT); Second Generation Transmission Systems for
Interactive Cable Television Services — IP Cable Modems
3 Terms, definitions, symbols and abbreviations
3.1 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
NOTE As far as possible the available terms and definitions are taken from IEC 60050 series and are repeated below. The relevant
IEV-numbers or other references are given in rectangular brackets after the definition text.
3.1.1
CATV networks
regional and local broadband cable networks designed to provide sound and television signals as well as
signals for interactive services to a regional or local area
Note 1 to entry: This was originally defined as Community Antenna Television networks.
3.1.2
common path distortion
intermodulation distortion of downstream signals, mainly due to nonlinearities found at metallic junctions
Note 1 to entry: The distortions are manifest as a series of beats (caused by analogue downstream channels) or a band(s) of noise
(caused by digital downstream channels) most noticeably in the upstream path. CPD may also be present in the downstream path, but
since it adds with other downstream distortions (i.e. CTB and CSO), caused by active components, it is difficult to differentiate between
the two. The nonlinear behaviour found at passive junctions may be due to a number of reasons including corrosion, typically from
exposure to the elements, dissimilar metals, contact pressure, and junctions involving connectors contaminated with carbonaceous
materials.
3.1.3
downstream direction
direction of signal flow in a cable network from the headend or any other central point (node) of a cable
network towards the subscriber
[SOURCE: EN 60728-10:2014, modified]
3.1.4
extended satellite television distribution network or system
distribution network or system designed to provide sound and television signals received by satellite receiving
antenna to households in one or more buildings
Note 1 to entry: This kind of network or system could be eventually combined with terrestrial antennas for the additional reception of
TV and/or radio signals via terrestrial networks.
Note 2 to entry:  This kind of network or system could also carry control signals for satellite switched systems or other signals for
special transmission systems (e.g. MoCA or WiFi) in the return path direction.
3.1.5
extended terrestrial television distribution network or system
distribution network or system designed to provide sound and television signals received by terrestrial
receiving antenna to households in one or more buildings
Note 1 to entry:  This kind of network or system could be eventually combined with a satellite antenna for the additional reception of
TV and/or radio signals via satellite networks.
Note 2 to entry: This kind of network or system could also carry other signals for special transmission systems (e.g. MoCA or WiFi) in
the return path direction.
3.1.6
forward path (downstream)
physical part of a cable network by which signals are distributed in the downstream direction from the
headend or any other central point (node) of a cable network towards the subscriber
[SOURCE: EN 60728-10:2014, modified]
3.1.7
gateway
functional unit that connects two computer networks with different network architectures
EXAMPLES LAN gateway, mail gateway.
Note 1 to entry:  The computer networks may be either local area networks, wide area networks or other types of networks.
[SOURCE: IEC 60050, IEV 732-01-16 – definition altered and original Note 2 turned into the present
"EXAMPLES" paragraph]
3.1.8
headend
assembly of equipment feeding signals into a cable network from local or external sources, including
equipment for reception and signal processing
[SOURCE: IEC 60050, IEV 723-09-11, modified – definition altered]
Note 1 to entry:  The headend may, for example, comprise antenna amplifiers, frequency converters, combiners, separators and
generators.
3.1.9
hub
local area distribution point for the insertion and recovery of two-way narrowcast signals such as
DOCSIS/EuroDOCSIS with broadcast transmissions from the headend in the RF domain (frequency
multiplexing)
3.1.10
hybrid fibre coaxial network
HFC network
cable network which comprises optical equipment and cables and coaxial equipment and cables in different
parts
[SOURCE: EN 60728-10:2014]
3.1.11
individual satellite television receiving system
system designed to provide sound and television signals received from satellite(s) to an individual household
Note 1 to entry:   This kind of system could also carry control signals for satellite switched systems or other signals for special
transmission systems (e.g. MoCA or WiFi) in the return path direction.
3.1.12
individual terrestrial television receiving system
system designed to provide sound and television signals received via terrestrial broadcast networks to an
individual household
Note 1 to entry:  This kind of system could also carry other signals for special transmission systems (e.g. MoCA or WiFi) in the return
path direction.
3.1.13
ingress noise
noise which is caused by electromagnetic interference into cable networks. Its power decreases with
increasing frequency. It is permanently present but slowly varies in its intensity as a function of time
[SOURCE: EN 60728-10:2014]
3.1.14
local broadband cable network
network designed to provide sound and television signals as well as signals for interactive services to a local
area (e.g. one town or one village)

- 9 - CLC/TR 50083-10-1:2014
3.1.15
(network) segment
part of a cable network comprising a set of functions and/or a specific extent of the complete cable network
[SOURCE: EN 60728-10:2014]
3.1.16
network termination unit
NTU
equipment for access to the cable network connected between home network interface (HNI) and system
outlet
3.1.17
node
point in a cable network where two or more links are interconnected
[SOURCE: IEC 60050, IEV 715-08-06, modified – definition altered]
3.1.18
Optical Modulation Index
OMI
index which is defined as:
φ - φ
h l
m =
+
φ φ
h l
where
φ is the highest and φ is the lowest instantaneous optical power of the intensity modulated optical
h l
signal. This term is mainly used for analogue systems
[SOURCE: EN 60728-10:2014, modified]
Note 1 to entry:  This definition doesn’t apply to systems where the input signals are converted and transported as digital baseband
signals. In this case the terms modulation depth or extinction ratio defined in 2.6.79 and 2.7.46 of IEC/TR 61931:1998 will be used. A
test procedure for extinction ratio is described in EN 61280-2-2.
3.1.19
regional broadband cable network
network designed to provide sound and television signals as well as signals for interactive services to a
regional area covering several towns and/or villages
3.1.20
return path (upstream)
physical part of a cable network by which signals are transmitted from any subscriber, connected to the
network, to the headend or any other central point (node) of a cable network
[SOURCE: EN 60728-10:2014, modified]
3.1.21
upstream direction
direction of signal flow in a cable network from a subscriber towards the headend or any other central point
(node) of a cable network
[SOURCE: EN 60728-10:2014, modified]

3.2 Symbols
The following graphical symbols are used in the figures of this Technical Report. These symbols are either
listed in IEC 60617 or based on symbols defined in IEC 60617:
Symbol Function Symbol Function
Optical transmitter forward Optical transmitter return
E O
path path
O E
Optical receiver forward Optical receiver return
O E
path path
E O
Analogue-Digital Converter Digital-Analogue
Converter
ADC DAC
Multiplexer De-multiplexer
De-
[IEC 60617-S01626] [IEC 60617-S01626,
MUX
modified]
MUX
Attenuator (fixed)
[IEC 60617-S01244]
A
Tap-off (n ports) Multi-tap (n ports) with
…. …. terminated feeder line
1 1
…. ….
n n
Splitter
Distribution network
Combiner
(in the reverse direction)
Amplifier, one-way Amplifier, two-way
[IEC 60617-S01239] [IEC 60617-S00433]

- 11 - CLC/TR 50083-10-1:2014
Symbol Function Symbol Function
Low-pass filter High-pass filter
[IEC 60617-S01248] [IEC 60617-S01247]

Diplexer Band-pass filter
[IEC 60617-S01249]
Fibre cable Multiplier
Equalizer System outlet
SO
Sinewave Generator Headend
G
HE
Network termination unit Cable modem termination
system
NTU CMTS
AC power supply Returnpath transmitter
Return
Tx
Test Receiver Test transmitter
Test Test
Rx Tx
3.3 Abbreviations
For the purposes of this document, the following abbreviations apply.
AC Alternating current
ADC Analogue-to-digital converter
ALSC Automatic level & slope control

AM Amplitude modulation
BNI Building network interface
BNTU Building network termination unit
C/NLD Carrier to non-linear distortion ratio
CATV Community antenna television
CB Citizens band
CF Centre frequency
CMTS(s) Cable modem termination system(s)
CPD Common path distortion
CPE Customer premises equipment
CSO Composite second order
CTB Composite triple beat
CW Continuous wave
CWDM Coarse wavelength division multiplex
DAC Digital-to-analogue converter
DAVIC Digital Audio Visual Council
DC Direct Current
DeMUX De-multiplexer
DFB Distributed feedback (laser)
DOCSIS Data-over-cable service interface specification
DS Downstream
DVB Digital video broadcasting
DWDM Dense wavelength division multiplex
EDFA Erbium doped fibre amplifier
EMS Element management system
EuroDOCSIS European data-over-cable service interface specification
EUT Equipment under test
FM Frequency modulation
FP Fabry-Perot (laser)
FSK Frequency shift keying
HE Headend
HF High frequency
HFC Hybrid-fibre-coax
HNI Home network interface
IP Internet protocol
ISF Ingress suppression filter
MDU Multiple dwelling unit
MER Modulation error ratio
MUX Multiplexer
NGN Next generation network
- 13 - CLC/TR 50083-10-1:2014
NLD Non-linear distortion
NPR Noise power ratio
NTU Network termination unit
OMI Optical modulation index
PID Packet identifier
PIM Passive intermodulation
PMD Polarization mode dispersion
PRBS Pseudo random bit sequence
PSTN Public switched telephone network
QAM Quadrature amplitude modulation
QPSK Quadrature phase shift keying
RF Radio frequency
RP Return path
Rx Receiver
SBC Session border controller
SDH Synchronous digital hierarchy
SDU Single dwelling unit
SIP Session initiation protocol
SIR Signal to ingress ratio
STB Set-top box
SUT System under test
Tx Transmitter
US Upstream
VOD Video on demand
VoIP Voice-over-IP
VSB Vestigial side-band
4 Network architecture
4.1 HFC architecture
Access networks today are required to carry a multitude of different services. As a result, network engineers
and architects are challenged to build infrastructures that are able to deliver these new services.
CATV networks, using HFC technologies have become the standard for providing both broadcast and
interactive services. In an HFC network the forward path and return path portions are closely linked together.
Where needed, for a better understanding, both portions will be considered in this document. This document
will however focus primarily on return transmission. The return path portion of such networks is related to the
corresponding standard document (EN 60728-10). The return path frequency range of such networks
(Figure 1, network portion between reference points) is typically specified up to a maximum frequency range
of 5 MHz to 65 MHz; (other frequency ranges, e.g. 5 MHz to 85 MHz, may apply).

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Most of the guidelines in this document are also valid for legacy networks, consisting only of an RF
distribution networks. To enable interactive services the CATV network shall be made “bidirectional” by
adding diplex filters and active or passive return path hardware. The return path portion in the RF distribution
network is to be considered active, when at least one amplifier station is equipped with a return path amplifier
module; otherwise it should be considered as passive.
It is assumed that in the HFC network optical links are feeding optical nodes, which are followed by the RF
coaxial distribution network. It is also assumed that the trunk and distribution networks are subdivided in
nodal areas, which provides a more reliable and manageable topology. Greater reliability is achieved due to
the fact that an interruption in the signal path will at most affect only the nodal area. It is also more
manageable because upgrades and interventions need not be extended over the whole network, but can be
performed on a “per nodal area” and therefore phased as needed.
The subdivision into nodal areas has an additional benefit of providing serving zones that can be managed
individually and provides greater flexibility with regards to traffic capacity and capacity planning. At the
subscriber site typically a network termination unit (NTU) is connected to the reference point of the given
home network interface (HNI). An NTU (network termination unit) provides the necessary interfaces to the
system outlets.
In practice real networks are more extensive and sophisticated. Therefore the issues to be considered have
to be broadened to include possible multiple headends, hubs, cascaded optical links and interfaces for
service interconnection. Several serving zones could be combined to connect with a regional broadband
network by means of (a) transport network(s) (Figure 2). Different technologies are available for the transport
networks. If the distance is short an RF analogue transport network may be used. For longer distances
optical transport may be employed using, either at 1 310 nm or 1 550 nm optical links.
NOTE At 1 550 nm the fibre attenuation is lower than at 1 310 nm and also optical amplification of the signals using optical amplifiers
(EDFAs) is possible.
For long distances and high data rates high speed digital transport standards e.g. SDH, Gigabit Ethernet,
10 Gigabit Ethernet are possible transport technologies.

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Figure 2 — Regional network
4.2 Upgrade alternatives
4.2.1 Introduction
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Figure 3 — Trunk-and-distribution architecture using only coaxial equipment
The HFC architecture is typically derived by means of traditional trunk-and-distribution architectures as
shown in Figure 3. During any upgrade often some of the amplifiers are replaced by optical nodes and
connected by two-way optical fibre links directly to the local headend (see Figure 4).

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Figure 4 — HFC system
In an early phase of any upgrade 500 to 5 000 homes passed per optical node is a typical starting value for
network engineers. A “segment” serving between 500 and 20 000 homes passed consists of several optical
nodes and is configured to handle the initial data requirements. However, with the potential requirements of
future services, and increased number of connections, there is usually a need to increase the upstream data
capacity either by the use of smaller segment sizes (fewer optical nodes per segment) or by adding more
data channels. As a result a single segment could be served by one or more downstream
DOCSIS/EuroDOCSIS channels together with the associated upstream channels.
One of the tasks for network engineers is to connect optical nodes to any termination system, in a way which
guarantees the required bandwidth to all subscribers. Most networks have been configured with a single
segment (500 to 20 000 homes passed) being served by a single downstream feed together with a single
upstream feed (Figure 6). The downstream feed typically carries a single DOCSIS/EuroDOCSIS QAM
channel with the associated upstream link carrying between 1 and 6 upstream RF channels.
Figure 5 shows a theoretical segment for interactive traffic. This segment can consist of a number of nodes
and be served by a number of CMTS units. On “day 1” a single CMTS may serve 6 or 8 optical nodes. As
traffic requirements increase this may change to a single CMTS serving a single optical node and eventually
say 4 CMTS units feeding a single node. This process is known as “re-segmentation”.
Further options and considerations for re-segmentation are given in the following sections.

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NOTE 1 Only one segment is shown in the diagram for clarity.
NOTE 2 As protection against equipment failures is of paramount importance, more segments, hubs and CMTS cards are added as
required for the number of homes passed, penetration and traffic requirements.
Figure 5 — Generic diagram showing the mapping of nodes and CMTS(s) to segments
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