HUAWEI TECHNOLOGIES CO., LTD.
Harnessing the Power of HFC Node Facility
May 6, 2014
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Table of Contents
Abstract ...................................................................................................................................................................... 4
1 Introduction ....................................................................................................................................................... 5
2 HFC Migration Tools and Challenges .................................................................................................................. 6
2.1 Existing Tools ...................................................................................................................................... 6
2.2 Emerging Tools ................................................................................................................................... 9
2.2.1 DOCSIS 3.1 ......................................................................................................................................... 9
2.2.2 Ethernet Node.................................................................................................................................. 10
3 A Facility View of the HFC Network ................................................................................................................. 11
3.1 HFC Node Facility ............................................................................................................................. 12
3.1.1 Physical Elements ............................................................................................................................. 12
3.1.2 Service Attributes ............................................................................................................................. 13
4 The Node Facility Model .................................................................................................................................. 14
4.1 The Bandwidth Model ..................................................................................................................... 15
4.2 Downstream Bandwidth Modeling Result ....................................................................................... 17
4.3 Upstream Bandwidth Modeling Result ............................................................................................ 18
4.4 Bandwidth Modeling Summary ....................................................................................................... 19
5 Ethernet Node ................................................................................................................................................. 21
5.1 Network Maintenance Considerations ............................................................................................ 22
5.2 Power Consumption Analysis ........................................................................................................... 24
5.2.1 Overall Power Consumption Comparison ........................................................................................ 25
6 Overview of Baseband Optical Technologies ................................................................................................... 26
6.1 Comparison of Technical Parameters of GPON and EPON ............................................................... 28
6.2 TWDM-PON ..................................................................................................................................... 30
7 Summary .......................................................................................................................................................... 32
8 References ....................................................................................................................................................... 33
9 Abbreviations and Acronyms ........................................................................................................................... 33
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Figure 1 Spectrum Map Evolution between 2004 and 2014 ________________________________________________ 7
Figure 2 Spectrum Map Evolutions from 2014 to 2022 ___________________________________________________ 10
Figure 3 A Facility View of the HFC Network ___________________________________________________________ 12
Figure 4 Physical Elements of HFC Node Facility ________________________________________________________ 13
Figure 5 Service Attributes of HFC Node Facility _________________________________________________________ 14
Figure 6 Ethernet Node Facility Model ________________________________________________________________ 15
Figure 7 Downstream Bandwidth Growth Projection 50% CAGR____________________________________________ 16
Figure 8 Downstream Bandwidth Demand per Service Group @ 50% CAGR for 2015-2021 ______________________ 18
Figure 9 Downstream Bandwidth Demand per Service Group @ 35% CAGR for 2015-2021 ______________________ 18
Figure 10 Upstream Bandwidth Demand per Service Group @ 30% CGAR for 2015-2021 ________________________ 19
Figure 11 Small Cell Growth Rate in Dense Urban Areas __________________________________________________ 22
Figure 12 Core Hardware Block Diagrams of Analog Fiber Node and Digital Ethernet Node ______________________ 24
Figure 13 GPON EPON Technology Roadmaps __________________________________________________________ 28
Figure 14 GPON, XG-PON1, and TWDM-PON Coexistence _________________________________________________ 29
Figure 15 Key Technical Challenges Resolved in TWDM-PON ______________________________________________ 31
Figure 16 Coexisting TWDM-PON and GPON Deployment Scenarios ________________________________________ 31
Table 1 Existing HFC Migration Tools __________________________________________________________________ 8
Table 2 Emerging HFC Migration Tools ________________________________________________________________ 10
Table 3 Concurrency Ratio per Service Group ___________________________________________________________ 16
Table 4 Total Bandwidth Demand per Service Group in 2021 ______________________________________________ 19
Table 5 Migration Time-line per Service Group _________________________________________________________ 20
Table 6 Recommended Migration Steps toward 175HHP _________________________________________________ 20
Table 7 Recommended Migration Steps toward 60HHP __________________________________________________ 20
Table 8 Comparison of Network Maintenance Aspects of Fiber Node and Ethernet Node ________________________ 23
Table 9 Power Consumption Comparison of Analog Fiber Node and Digital Ethernet Node ______________________ 24
Table 10 Power Consumption Comparison: M-CMTS vs. Distributed Ethernet Node ____________________________ 25
Table 11 A Summary of Baseband Optical Technologies __________________________________________________ 27
Table 12 Downstream and Upstream Wavelength Bands of GPON and EPON _________________________________ 29
Table 13 Technical Parameters of GPON and EPON ______________________________________________________ 29
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Abstract
Driven by 50% CAGR in bandwidth consumption, MSOs are increasingly focused on
cost-performance of the HFC network. The unabated upward march in bandwidth demand is
expected to continue as consumers turn to higher and higher volume of IP content and services. The
trend toward Gigabit access has forever changed the broadband access competitive landscape and
the race is on for operators to seek out the lowest cost per bit solution for their access networks.
The Outside Plant (OSP) of the HFC network, specifically the coaxial plant connecting the Optical
Node to the subscribers, has seen its share of upgrades over the years but the network topologies
remain essentially unchanged. In today’s highly competitive landscape, the multi-gigabit capacity
of the coaxial plant stands as a key differentiator for the MSOs. A timely question is – how to best
capture the full performance potential of the coaxial plant?
In trying to answer this question, this paper takes a close look at the coaxial plant as modular
broadband access facilities. Along with a definition of the HFC node facility, several sizes of the
node facility are applied to a bandwidth demand projection model to determine the suitable
starting points and migration steps. A series of commercially available baseband optical
technologies are presented and compared.
As the analysis of this paper shows, the evolution of the HFC network has reached an inflection
point where a combination of baseband optical technologies and optimized Ethernet Node is fully
capable of meeting the cost-performance target and represents a promising HFC migration option.
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1 Introduction
Since the deployment of DOCSIS, MSOs have consistently maintained a competitive edge in
broadband access by adopting a series of technological enhancements including the highly
successful DOCSIS 3.0 introduced in 2008. The cycle of enhancements continues today with the
ongoing migration toward Converged Cable Access Platform (CCAP), to be followed by DOCSIS 3.1,
anticipated to start in 2016.
In recent years, a persistent shift in consumer video consumption behavior drove steady increases
in annual bandwidth demand, confirming a long-established downstream bandwidth growth rate
of 50% CAGR [1]. As growing racks of equipment were being installed in the hub to expand DOCSIS
and edge QAM capacities, it became clear that many hubs will soon reach several performance
ceilings including space, power and cooling. With the advent of CCAP, facility issues in many hubs
can be addressed at the cost of equipment swap-outs. Practical business and operational
considerations make migration toward CCAP a multi-year cap-and-grow exercise of relocating,
consolidating, and installing old and new equipment among multiple hubs. Yet questions remain
as to the longevity of an ever expanding integrated platform within the confines of the hub facility.
The steady annual growth in downstream bandwidth demand is a global phenomenon. In some
developing markets, where ARPU is significantly less, low-cost Ethernet over Coax (EOC)
technologies are being deployed to meet an extremely challenging set of business cases.
Deployment of these low-cost EOC technologies such as HomePlug AV creates a lower
performance service delivery platform in regional markets. Continue divergence of incompatible
cable access technologies will not only inhibit sharing of product and service innovations but also
significantly limit the potential for DOCSIS to scale on a global basis.
Preserving a global scale for continuous DOCSIS evolution requires a significantly lower cost
DOCSIS access platform. Couple this new price-performance target with the finite resources
available in the hub facility, the stage is set for a potential paradigm shift in HFC network
migration.
This paper examines the evolutional potential of HFC network as broadband access facilities.
These include HFC hub facility and HFC node facility. The HFC hub facility has been thoroughly
examined by the industry and the associated engineering considerations were identified as part of
the key drivers for CCAP. The focus of this paper is on the HFC outside plant, which consists of
modular HFC node facilities with a specific set of physical elements and service delivery attributes.
Several sizes of the node facility representing the core samples of HFC network are identified.
These node facilities are then applied to a commonly referenced 35~50% CAGR downstream and
30% CAGR upstream bandwidth demand projection model to demonstrate how capacity demands
of the node facility can be met for the next seven years (2015-2021).
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2 HFC Migration Tools and Challenges
Since the fiber node became an integral part of the HFC network in 1990s, a number of HFC
performance enhancement tools have been put into practice with good results. These include
node split, spectrum expansion, and several options to improve spectrum utilization. With
increasing capacity utilization, the pace of the migration has been accelerating in the last decade.
Although each one of these currently available options is capable of achieving a certain level of
spectrum capacity gains, the cable industry came to the realization a few years ago that other
options will be necessary to meet the bandwidth demand forecast through the end of the decade.
Starting in 2012, cable industry embarked on a standardization effort, aimed at adopting
Orthogonal Frequency-Division Multiplexing (OFDM) for HFC access, with the formation of DOCSIS
3.1 working groups by CableLabs. As the first fundamental change in HFC access technologies,
DOCSIS 3.1 achieved a new milestone and forever changed the tenor of HFC migration. With the
coming introduction of DOCSIS 3.1, HFC migration has hit an inflection point where other
cost-effective options such as distributed Ethernet Node will also be leveraged to harness the full
potential of the HFC network.
2.1 Existing Tools
Among the existing migration tools, node split is utilized to specifically address the growth in
DOCSIS bandwidth demand. It was put into practice soon after the initial deployment of fiber
nodes and over the years, many larger nodes have been reduced down to the 500 to 750
household passed (HHP) range. With the introduction of DOCSIS 2.0 and 3.0, bandwidth
performance gains through higher order modulations and channel bonding created enough
headroom for bandwidth demand growth and eased the rate of additional splits toward even
smaller size nodes. However, the benefits of fiber-deep architecture including
Fiber-to-the-Last-Amplifier (FTTLA) are well understood. In recent years, node splits down to
around the 175 HHP size have also been implemented to better position the HFC network to
address competitive pressure and support future growth.
In addition to node split, several other tools are available to increase spectrum capacity and
utilization. Spectrum capacity can be expanded by physically upgrading the HFC plant to extend
the upper limit of the RF spectrum range to 750MHz, 870MHz or 1GHz. This is a major undertaking
involving extensive component upgrades. The vast majority of HFC network today have already
been upgraded to either 750MHz or 870MHz. Future migration toward the 1GHz plant will likely
be considered along with moving the US/DS split for US expansion and DOCSIS 3.1 rollout together
as a comprehensive re-engineering of the HFC network.
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Apart from spectrum expansion, other options not requiring outside plant upgrades are available
to improve spectrum utilization:
1. Analog reclamation
2. MPEG-2 to MPEG-4 AVC / HEVC conversion
3. Narrowcast video
Figure 1 is a sample spectrum usage diagram serves to illustrate a dramatic shift in HFC spectrum
allocations in the last decade.
• STB return
• DOSCIS return
• CBR voice return
• Status monitoring Analog Video
2004
Digital Broadcast
• SDV, VOD
• DOSCIS forward
• CBR voice forward
MHz 20 42 54 550 750
• STB return
• DOSCIS return
• CBR voice return
• Status monitoring
2014
Broadcast SDTV Broadcast HDTV UHDTV/ Narrowcast/ Unicast
• SDV, VOD
• DOSCIS forward
• VoIP forward
• IPTVAnalog
550 750 860 1000MHz 20 42 54
Figure 1 Spectrum Map Evolution between 2004 and 2014
Analog reclamation converts existing analog video channels to digital QAM channels to improve
spectrum utilization. For each 6MHz QAM channel, up to 12 standard-definition channels or 3
high-definition channels can be transmitted instead of a single analog channel. As part of the
analog reclamation program, Digital Terminal Adapters (DTAs) are deployed in the subscriber
premises to support standard TVs with RF input. Depending on market, the DTA is used to
convert MPEG2 to NTSC or DVB-C to PAL.
Conversion from MPEG-2 to a high efficiency encoding scheme such as MPEG-4 AVC or HEVC can
realize more than 50% bandwidth savings. Many subscription television service providers are
using MPEG-4 AVC to deliver HDTV [2] while HEVC is a key enabler for 4K Ultra HD [3]. However,
as an early adopter of HD services, MSOs are saddled with millions of MPEG-2-only digital set-top
boxes (STBs). Even though a significant number of MPEG-4 capable STBs have been deployed as
replacement units for the past several years, linear video today is still distributed in MPEG-2,
making a full transition from MPEG-2 a longer term migration option.
Migration from broadcast to narrowcast video has been extensively deployed in the forms of
switched digital video (SDV) and video on demand (VOD). Less popular linear channels are
offered through SDV while a library of video programs is offered through VOD. The number of
QAM channels used for SDV and VOD varies by markets and demographics, and in North America,
a recent reference model shows approximately 20 channels for a SDV service group and 6
channels for a VOD service group.
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SDV enabled statistical gains result in spectrum savings and allows MSOs to offer more linear
channels to keep up with growing consumer demand for more varieties of video content. For a
given SDV service group, the benefit can only be realized with a segment of channels with
intermediate popularity, between the most viewed and the least viewed. The most viewed
channels will continue to be broadcasted and the least viewed channels will only be transmitted
occasionally with low chance of benefiting from multicast. A significant portion of spectrum
savings is realized with the multicast implementation of SDV. However, in order to provide
personalization features, SDV would have to operate in unicast mode. Without multicast gains, a
significant amount of additional spectrum is required to maintain the same level of customer
experience achieved with multicast SDV.
Table 1 provides a summary of the currently available HFC migration tools described above.
Table 1 Existing HFC Migration Tools
Tools Pros Cons
Node Split Basic tool for fiber-deep migration
Doubling DOCSIS bandwidth per node
split
Reduce noise-funneling effect
Does not create more
spectrum capacity
Impact to outside plant
Splitting unbalanced nodes
require more resources
Spectrum Expansion Creates spectrum capacity
Impact to outside plant
Requires equipment upgrade
to cover expanded spectrum
range
Analog Reclamation Creates spectrum capacity
No impact to outside plant
Significant impact to
subscribers
Requires new CPE
Conversion from
MPEG-2 to MPEG-4
AVC / HEVC
Creates spectrum capacity
No impact to outside plant
MPEG-4 STBs are being
deployed
Linear video is only distributed
in MPEG-2
Migration steps include
MPEG-2 and MPEG-4 simulcast
SDV Creates spectrum capacity
No impact to outside plant
Allow addition of long tail programs
Only beneficial for
intermediate channels
Significant reduction in
spectrum capacity gains if
switched from multicast to
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unicast
VOD Creates spectrum capacity
No impact to outside plant
Limited use in linear channel
and DVR consumption
environment
2.2 Emerging Tools
There are two key emerging HFC migration tools: DOCSIS 3.1 and Ethernet Node. Both tools
deviate from the incremental enhancement path of the existing tool set by introducing mature
technologies from other telecommunications industry segments into the HFC network. As this new
class of migration tools is put into practice, other innovative tools from the global ecosystem will
surely follow.
2.2.1 DOCSIS 3.1
DOCSIS 3.1 is being developed as the next phase of HFC DOCSIS evolution specifically to address
the exponential bandwidth growth observed in the cable plant. Standard development is expected
to complete in 2014 with initial deployments targeted for 2016. Its principle goal of network
capacity optimization is achieved by supporting higher order modulations such as 4096-QAM
enabled by two technological enhancements over DOCSIS 3.0:
1. Orthogonal Frequency-division Multiplexing (OFDM), which encodes digital data on
multiple sub-carrier frequencies.
2. Low-density Parity Check (LDPC), which is a high efficiency Forward Error Correction (FEC)
technique, used in many high-speed communication standards.
DOCSIS 3.1 is designed to be backward compatible to DOCSIS 3.0 with requirement to support
MAC layer bonding of DOCSIS 3.1 and DOCSIS 3.0 PHY channels. The higher modulation order is
targeted for 4096-QAM (12 bits/Hz) with option to reach 16384-QAM (14 bits/Hz), making it
capable of supporting up to 10Gbps downstream and 1Gbps upstream capacity. The OFDM-based
technologies incorporated into DOCSIS 3.1 are widely adopted in other RF technology standards,
making DOCSIS 3.1 a significant first step toward the convergence of HFC and other access
network technologies.
Some challenges remain with the deployment of DOCSIS3.1 including:
1. Lower CNR of an HFC network can limit the performance of DOCSIS 3.1. For example, the
modulation order of 4096-QAM requires at least 41 dB, but the typical CNR can be
supported by current HFC is around 38-39 dB.
2. Limited spectrum is available when DOCSIS 3.1 coexists with DOCSIS 3.0 especially in the
upstream.
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Figure 2 shows a series of spectrum diagrams to illustrate how spectrum usage may evolve from
2014 to 2022. Based on recent industry discussions, only a mid-split to 85MHz is expected with the
initial deployment of DOCSIS 3.1 in 2016.
• STB return
• DOSCIS return D3.0/3.1
• CBR voice return
• Status monitoring
• STB return
• DOSCIS return D3.0/3.1
• CBR voice return
• Status monitoring
2022
2016
Broadcast SDTV Broadcast HDTV
Broadcast SDTV Broadcast HDTV UHDTV/ Narrowcast/ Unicast
UHDTV/ Narrowcast/ Unicast
• SDV, VOD
• DOSCIS forward
• VoIP forward
• IPTV
• SDV, VOD
• DOSCIS forward
• VoIP forward
• IPTV
MHz 20 85 550 750 860 1000
MHz 20 200 550 750 860 1000 >1200
• STB return
• DOSCIS return
• CBR voice return
• Status monitoring
2014
Broadcast SDTV Broadcast HDTV UHDTV/ Narrowcast/ Unicast
• SDV, VOD
• DOSCIS forward
• VoIP forward
• IPTVAnalog
550 750 860 1000MHz 20 42 54
Analog
Figure 2 Spectrum Map Evolutions from 2014 to 2022
2.2.2 Ethernet Node
Ethernet Node is a combined DOCSIS MAC and PHY solution connecting to a controller via a packet
digital optical network. Ethernet Node is designed as a dropped-in replacement for the
conventional Fiber Node and supports dedicated DOCSIS 3.0/3.1 bandwidth and legacy video
services. It originates as the Coax Media Converter Type I (CMC I) described in the C-DOCSIS
System Specification, which is a global variant of DOCSIS technology sponsored by State
Administration of Radio Film and Television (SARFT) of China and CableLabs.
Originally designed for the vertical Multiple-Dwelling-Unit (MDU) market, the Ethernet Node is
evolving to become a general purpose Fiber-to-the-Node (FTTN) solution for the migration of HFC
network. While skepticisms remain about potential operational and maintenance impacts of
embedding CMTS functions in the OSP, the role of the Ethernet Node in the longer term HFC
evolution is clear in that Ethernet Node will be the only access network element remaining in the
virtualized architecture of HFC evolution endgame.
Table 2 provides a summary of the emerging HFC migration tools described above.
Table 2 Emerging HFC Migration Tools
Tools Pros Cons
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DOCSIS 3.1 Higher modulation orders and improved
forward error correction (FEC) provide
significant B/W gains
Granular subcarriers provide better
immunity to ingress noise for higher
upstream B/W
Well-defined migration path
Higher CNR is required to
reach optimal performance
Large channel width requires a
minimum of 96MHz upstream
and 192MHz downstream
spectrum
CPE pricing will drive initial
deployment
Ethernet Node Highest cost-performance driven by the
global market Optimal solution for MDU
and rural segments
One of the few remote solutions to
realize the full potential of DOCSIS 3.1
End-to-end compatibility for the delivery
of legacy QAM video and other services
Drop-in replacement for fiber node
Synergy with FTTH rollout
The only HFC access network element to
remain in the virtualized HFC evolution
endgame
Potential impacts to OSP
operational practices
Insufficient field deployment
experience
3 A Facility View of the HFC Network
A telecommunications facility is generally defined as any part of the infrastructure of a
telecommunications network. The key components of the HFC network include the hub facility
and the node facility. A single hub facility is connected to a number of node facilities spread out
over the serving area. Telecommunications facilities are heavily regulated structures and assets.
Optimization and consolidation of existing telecommunications facilities are part of the long-term
objectives for most network operators.
The size of a hub facility is dependent on the number of household passed and varies greatly
across HFC networks. With exponential growth in bandwidth demand occurring in all markets, hub
facilities of all sizes are hitting a performance ceiling in terms of space, power and cooling. While
integrated CCAP can be deployed to address these resource issues in many medium and large hub
facilities, a solution is not quite straightforward for many smaller hub facilities. In these cases, the
logical next step is to look toward the node facility.
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Figure 3 A Facility View of the HFC Network
3.1 HFC Node Facility
With multi-gigabit bidirectional access capacity connecting to over 90% of homes in some markets,
the HFC outside plant is the crown jewel of the HFC network. The HFC outside plant has seen its
share of upgrades over the years but the plant topologies stay essentially unchanged.
HFC outside plan consists of individual coaxial plants each with a single fiber nodes connecting to a
number subscriber homes. From the fiber node down to the drop cables, the coaxial plant is a fully
powered broadband access facility with a huge potential for performance optimization. With a
minimum of 2 fibers connecting to each fiber node, it can be readily adapted to a number of fiber
access topologies.
3.1.1 Physical Elements
The HFC node facility is a coaxial plant with both active and passive elements. In addition to the
fiber node, a number of other physical elements are parts of a typical coaxial plant. These physical
elements include active components such as Trunk Amplifiers, Bridger Amplifiers, Line Extenders,
and Uninterruptable Power Supplies (UPS), as well as passive components including coaxial cable,
splitters and taps.
The physical size of the node facility is a function of HHP and serving group density. Cascaded
amplifiers are used as needed to propagate upstream and downstream RF signals at a high gain
performance while minimizing distortion. Unity gain is applied to every cable segment between
any two amplifiers and between the fiber node and the adjacent amplifiers. Unity gain is set up
and maintained with return signals arriving at each amplifier/node input port at the same level
while each amplifier/node is set to output the forward signals at the same level.
UPS provides primary and backup power to actives in the HFC node facility. Typically, UPS is
installed in an outdoor enclosure, which is either pole-mounted or ground-mounted depending on
the rules of local regulation and utilities. Most UPSs can be monitored via an embedded cable
modem (CM). HFC power consumption is a significant part of OPEX for the MSOs. Improving
overall efficiency while maintaining network reliability is a continuous tradeoff exercise as HFC
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migration continues.
Fiber Node
Trunk
AmpBridger
Amp
Line Extender
Tap
Fibers
Power Supply
Figure 4 Physical Elements of HFC Node Facility
3.1.2 Service Attributes
A finely tuned node facility with amplifiers and node set for unity gain provides the foundation for
continuing migration of the HFC network. Enhancements and innovations will continue to be
introduced to expand the service delivery capacity of the node facility. With the coming
introduction of DOCSIS 3.1, downstream and upstream bandwidth capacities available in the cable
plant will be determined by a myriad of factors driven by the DOCSIS 3.1 migration strategy. In
addition to the typical upstream/downstream spectrum split changes and spectrum expansion
toward 1GHz, DOCSIS 3.0 and 3.1 channel mix will also be part of the equation.
During this migration process, changes in spectrum assignment, as reflected by updates in channel
line-up, will be the result of a continuous trade-off exercise to meet the changing service
requirements. In addition to expanding DOCSIS bandwidth, simulcast required for QAM video also
presents a significant challenge in spectrum availability. Any change in spectrum utilization must
be coordinated with the deployment of DOCSIS 3.1 capable cable modems and gateways, as well
as other CPEs such as MPEG-4 capable STBs. The overwhelming impact of legacy CPE support has
on MSO’s migration plan cannot be overstated.
A full accounting and continuous updates of availability and performance level of various
resources within the node facility will be vital to the successful planning and execution of each
migration step. These monitoring and maintenance functions of the node facility can be realized
with a suite of impairment identification capabilities as provided by Proactive Network
Maintenance (PNM). Compared to the current approach of using a centralized PNM server, a
distributed implementation of PNM where data collection and analysis are dedicated to the node
facility represents a more efficient framework with an added dimension of facilitating a new set of
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localized features and innovations.
Figure 5 Service Attributes of HFC Node Facility
4 The Node Facility Model
The node facility is the principle building block of HFC network, most commonly characterized by
the number of HHP. Although the actual number of HHP per node varies significantly from more
than 1000 to less than 100 across different market segments, the vast majority of fiber nodes
today are connected to 700 or less HHP, with 500 HHP being the most prevalent. In the fiber-deep
case where trunk fibers have been extended to the last amplifier, the fiber node is connected via
passives and coaxial cable directly to the subscriber premises, making amplifier an optional
element of the node facility.
While the node facility has always been a modular extension of the hub facility since fiber node
was first deployed, the tight coupling of the two facilities driven by the centralized hub-based
solution has kept the speed of the migration within the node facility at a measured pace. With the
introduction of emerging tools and capabilities including DOCSIS 3.1 and Ethernet Node, the node
facility is becoming the focal point for the next cycle of HFC migration. Starting with the ongoing
preparation for DOCSIS 3.1 rollout, the entire cable industry is analyzing every aspect of the node
facility to seek out the most effective migration path. The clarity of the inner workings of the HFC
node facility resulting from these analyses is truly unprecedented, and will provide a sound base
for future innovations from a newly expanded ecosystem.
Figure 6 shows a block diagram of a node facility used in this model. For this modeling exercise, an
Ethernet node with embedded DOCSIS 3.1 capabilities is used. Using XG-PON1/TWDM-PON as an
example, the dual fiber connections to the hub is capable of delivering up to 10 Gbps of
downstream and 2.5 Gbps of upstream bandwidth, as well as broadcast and narrowcast QAM
video and Out-of-Band (OOB) forward and return for the support of legacy video services.
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Hub
Power
Supply
Node Facility
HHPFiber
DOCSIS MAC/PHY
PON / P2P
POWER
Mixer/AMP2
Mixer/AMP1
TX/RX WDM
Ethernet Node
HHP
Figure 6 Ethernet Node Facility Model
4.1 The Bandwidth Model
Recent data confirmed DS bandwidth continue to grow at 50% CAGR, principally driven by
increasing consumer demand for streaming video. Whether growth will continue at this rate is
subject to debate with one opinion claiming that CAGR may settle at 35% due to higher efficiency
in various aspects of streaming video. The current consensus for US bandwidth growth rate is 30%
CAGR.
There are two principal drivers for the persistent demand in downstream bandwidth:
1. Cable operators’ continuing migration toward IP video
2. Increasing popularity of over-the-top video and other applications
A recently published 50% CAGR bandwidth growth projection for the next 7 years [4] is shown in
the Figure 7. As noted in the diagram, there are two key parameters:
1. Max speed: drives bonding group size which equals to the size of the DOCSIS pipe
between the CMTS and the connected CMs.
2. Weighted average speed: drives total bandwidth needed. This is the sustained bandwidth
required per subscriber. For a given service group, the sum of weight average speed for all
subscribers are adjusted based on a concurrency ratio to determine the total amount of
bandwidth required for the service group.
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Figure 7 Downstream Bandwidth Growth Projection 50% CAGR
For the bandwidth modeling, total bandwidth needed is calculated for five sizes of service group:
700, 500, 350, 175 and 60. A take rate of 40% is used for all service groups. The weighted average
speed is roughly divided between HSI and IP video. A 10:1 oversubscription ratio is applied to HSI
bandwidth for all service groups. A 10:7 oversubscription ratio is applied to IP video bandwidth
and adjusted with a sliding scale of multicast gains based on service group size. The overall
concurrency ratios are calculated by combining the result from both services as shown in the
following formula illustrated for 700 HHP: (10Mbps*1/10+8Mbps*7/10*(1-25%))/18Mbps=29%.
Table 3 Concurrency Ratio per Service Group
Service Group Size (HHP) 700 500 350 175 60
Weighted Average Bandwidth per Home 18Mbps (10Mbps HSI + 8Mbps IP video)
Average HSI Bandwidth / Oversubscription Ratio 10Mbps / 10:1
Average IP Video Bandwidth / Oversubscription Ratio 8Mbps / 10:7
IP Video Multicast Gains 25% 20% 15% 10% 0
Concurrency Ratio 29% 30% 32% 34% 37%
While the formula used to determine the concurrency ratio is based on a set of simplified
assumptions made for this specific set of service groups, the resulting ratios shown in Table 3 are
reflective of increasing utilization of broadband access. Concurrency ratio especially with regard to
IP video has a direct impact to quality of services delivered, hence a critical consideration for MSOs.
The concurrency ratios shown here are not intended as a recommendation or to reflect any actual
implementations.
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The upstream bonding group for a typical service group size of 700HHP includes three 6.4MHz
ATDMA channels (2X64QAM and 1X16QAM), providing 80Mbps of bandwidth capacity (30Mbps
each for the two 64QAM channels and 20Mbps for the 16QAM channel). For upstream bandwidth
modeling, the 80Mbps capacity is used as the starting bandwidth demand for 700HHP. The starting
bandwidth demand for other service groups are proportionally generated based on the size of the
service group.
4.2 Downstream Bandwidth Modeling Result
The result of downstream bandwidth modeling with 50% CAGR is shown in Figure 8, which includes
bandwidth demand projection for all five service groups. Also showed in the diagram are the
bandwidth capacities of the following bonding groups representing both near-term and
longer-term options:
1. Maximum size of DOCSIS 3.0 bonding group with 32 SC-QAM channels (Annex B 6MHz,
40Mbps data rate): 1280Mbps
1. Minimum size of DOCSIS 3.1 bonding group with 32 SC-QAM channels (commercial target,
8 channels higher than the minimum of 24 SC-QAM channels specified by CableLabs) and 2
OFDM channels: 5280Mbps
Some key observations are as follows:
1. For the typical 500HHP service group, downstream bandwidth demand will exceed the
DOCSIS 3.1 bonding group capacity by mid-2018.
2. For the fiber-deep 175HHP service group, the DOCSIS 3.0 bonding group will be sufficient
until mid-2017, and with a DOCSIS 3.1 grade, bandwidth demand can be met until the end
of 2020.
20
25
30
35
40
45
2014 2015 2016 2017 2018 2019 2020 2021
700HHP
500HHP
350HHP
175HHP
60HHP
32 SC-QAM + 2x192MHz OFDM
10log(Mbps)
32 SC-QAM
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Figure 8 Downstream Bandwidth Demand per Service Group @ 50% CAGR for 2015-2021
As stated earlier, some industry observers see downstream bandwidth growth rate moderating at
35% CAGR with higher efficiency in streaming video. The result of downstream bandwidth
modeling with 35% CAGR is shown in Figure 9.
20
25
30
35
40
45
2014 2015 2016 2017 2018 2019 2020 2021
700HHP
500HHP
350HHP
175HHP
60HHP
32 SC-QAM + 2x192MHz OFDM
32 SC-QAM
10log(Mbps)
Figure 9 Downstream Bandwidth Demand per Service Group @ 35% CAGR for 2015-2021
With this model, downstream bandwidth demand of the typical 500HHP service group can be met
until later 2019, which means a node split is still required for the last 2 years of the modeling
period. On the other hand, a migration path based on the 175HHP service group begins to emerge.
With 175HHP, downstream bandwidth can be met with the 32-channel DOCSIS 3.0 bonding group
until early 2018. With a DOCSIS 3.1 upgrade, bandwidth demand can be met well into 2022.
4.3 Upstream Bandwidth Modeling Result
The result of upstream bandwidth modeling with 30% CAGR is shown in Figure 10, which includes
bandwidth demand projection for all five service groups. Also showed in the diagram are the
bandwidth capacities of the following bonding groups representing both near-term and
longer-term options:
1. Three 6.4MHz ATDMA channels (2X64QAM @6.4Mhz, 1X16QAM @6.4Mhz): 80Mbps
2. Eight 6.4MHz ATDMA channels: 200Mbps
3. Eight 6.4MHz ATDMA channels and one 24MHz OFDMA channels: 400Mbps
Some key observations are as follows:
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1. For the typical 500HHP service group, upstream bandwidth demand will exceed the DOCSIS
3.1 bonding group capacity after mid-2021.
2. For the fiber-deep 175HHP service group, the existing 3 SC-QAM channels will be sufficient
until mid-2019. With 8 SC-QAM channels and a plant upgrade to 85MHz mid-split,
bandwidth demand can be met close to the end of 2022 without DOCSIS 3.1.
3. With node splits to 175HHP, the 85MHz mid-split upgrade can be delayed until 2019.
4. A plant upgrade to 200MHz high-split is not required for the modeling period.
10
12
14
16
18
20
22
24
26
28
2014 2015 2016 2017 2018 2019 2020 2021
700HHP
500HHP
350HHP
175HHP
60HHP
10log(Mbps)
8 SC-QAM
8 SC-QAM + 24MHz OFDMA
3 SC-QAM
Figure 10 Upstream Bandwidth Demand per Service Group @ 30% CGAR for 2015-2021
4.4 Bandwidth Modeling Summary
The primary objective of the bandwidth modeling is to determine if, how and when HFC
bandwidth demand can be met by existing and emerging migration tools. With the modeling
exercise, a template is created, which can be readily adapted to specific HFC scenarios to create a
suitable migration strategy.
Table 4 contains a summary of upstream and downstream bandwidth demands projected for each
service group at the end of 7-year modeling period in 2021. Bandwidth demands that can be
supported by the maximum bonding group size of 5280Mbps downstream and 400Mbps upstream
are also identified.
Table 4 Total Bandwidth Demand per Service Group in 2021
Service Group Size
(HHP)
700 500 350 175 60
DS Bandwidth with
50% CAGR
24.97Gbps 18.45Gbps 13.78Gbps 7.32Gbps 2.73Gbps
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DS Bandwidth with
35% CAGR
11.94Gbps 8.82Gbps 6.59Gbps 3.50Gbps 1.31Gbps
US Bandwidth with
30% CAGR
502Mbps 358Mbps 251Mbps 125Mbps 43Mbps
Other factors to consider are DOCSIS 3.1 upgrade and 85MHz mid-split upgrade. DOCSIS 3.1 is not
expected to start until 2016. Therefore, it is important to know, for each service group, when the
bandwidth demand will exceed the capacity of maximum DOCSIS 3.0 bonding group, thus
requiring a DOCSIS 3.1 upgrade. Upgrade to 85MHz mid-split or 200MHz high-split is generally
considered the next migration step leading up to, or as part of, the DOCSIS 3.1 upgrade cycle, so it
is also important to know when a mid-split upgrade becomes necessary. The timeline information
is summarized in Table 5, which also highlights the timelines on or after 2016 to illustrate alignment
with the start of DOCSIS 3.1 upgrade cycle.
Table 5 Migration Time-line per Service Group
Service Group Size (HHP) 700 500 350 175 60
DS B/W demand exceeds
D3.0 BG @ 50% CAGR
2014 2015 2015 2017 2019
DS B/W demand exceeds
D3.0 BG @ 35% CAGR
2014 2015 2016 2018 2021
Mid-split upgrade 2014 2015 2016 2019 2022
Based on the result of the bandwidth modeling analysis, it is clear a node split to 175HHP would be
necessary to meet the annual increases in bandwidth demand through 2021. Depending on the
current node size and taking into account a variety of market-specific factors, node split to 175HHP
should start between now and 2016, followed by mid-split and DOCSIS 3.1 upgrades as shown in
Table 6.
Table 6 Recommended Migration Steps toward 175HHP
Current Service Group Size (HHP) 700 500 350 175 60
Step 1: Node split to 175HHP 2014 2015 2016 N/A N/A
Step 2: Upgrade to mid-split 2018 2021
Step 3: Upgrade to DOCSIS 3.1 2018 2018 2019 2022
Alternatively, a node-split to 60HHP would defer DOCSIS 3.1 and mid-split upgrade until 2021 as
shown in Table 7.
Table 7 Recommended Migration Steps toward 60HHP
Current Service Group Size (HHP) 700 500 350 175 60
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Step 1: Node split to 60HHP 2014 2015 2016 2018 N/A
Step 2: Upgrade to DOCSIS 3.1 and mid-split 2021 2021 2021 2021 2021
5 Ethernet Node
In the past few years, there have been many discussions about the suitability of deploying
Ethernet Nodes in HFC network. Concerns were raised primarily due to the physical layer nature of
legacy cable plant and the potential operational and maintenance impacts of adding electronics in
the OSP. These are valid concerns given the history of HFC network evolution but a much different
picture emerges when the role of the Ethernet Node is considered in a comprehensive and
forward-looking context.
Although a fairly recent addition to the HFC network, the Ethernet Node is a conventional
Ethernet Bridge with a built-in media converter, extensively used in media conversion applications
in both wireless and wireline access networks. Many of these Ethernet Nodes, including Wi-Fi
access points, small cells and Fiber-to-the-Distribution Point (FTTdp) ONUs, are designed for
outdoor applications, and are built upon an evolving, mature access product platform with a
proven reliability record.
Overall, access network architecture has been trending toward incremental build-out of digital
fiber connecting to purpose-built media converters dedicated to fixed-size serving areas. This
trend is accelerating as both FTTH and wireless networks, having completed the initial phases of
deployment, are moving toward a more granular and cost-effective architecture to increase
performance and coverage. It is especially apparent in the increasing deployment of metro cells in
3G and 4G networks as illustrated in Figure 11 with one forecast predicting more than 5 million
metro cells to be shipped in 2017 [5]. The benefits of deploying metro cells in the wireless network
are well-understood to include the following:
1. Cost-effective augmentation of the macro network
2. Granular and flexible deployment to add bandwidth and coverage as needed
3. Service innovations in a distributed and localized environment
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0
100
200
300
400
500
600
700
800
900
1,000
2012Y 2014Y 2016Y 2018Y
LTE Connection HotZone LTE Capacity(Spectrum) LTE Capacity(HetNet)
1:2
Macro : Small Cell
Connected User per Macro Sector
Source: Huawei simulationDense urban area traffic forecast
1:7
1:12
Figure 11 Small Cell Growth Rate in Dense Urban Areas
Much in the same way small cell with PON backhaul augments the macro wireless network [8], the
application of Ethernet Node in the HFC network is expected to bring a similar set of benefits as a
complimentary solution to the centralized HFC architecture.
Besides being the center piece of access network evolutionary trend, the Ethernet Node also holds
an unique position in the HFC evolution path, when considered in its entirety, from the near-term
focus of enhancing bandwidth and spectrum utilization to the eventual virtualized architecture,
the Ethernet Node stands out as the only network element that will persist through the end of the
evolution cycle. Seeing it this way, it would be prudent for MSOs to evaluate various aspects of the
Ethernet Node to determine how it can be introduced into their HFC networks.
This section presents a basic impact analysis of deploying the Ethernet Node in the HFC network
by comparing network maintenance and power consumption aspects of the Ethernet Node and
Fiber Node.
5.1 Network Maintenance Considerations
Compared to traditional Fiber Node, the Ethernet Node incorporates electronics to support three
additional functions: PON/P2P ONU, Ethernet Bridge, and a simplified DOCSIS CMTS. Among these
functions, PON/P2P ONU and Ethernet Bridge are both mature technologies backed by a large
ecosystem of vendors. The only exception is DOCSIS CMTS, which has several Field-programmable
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Gate Array (FPGA)-based solutions with limited commercial chipset offerings. However, with the
coming introduction of DOCSIS 3.1, availability of CMTS chipsets is expected to improve aided by
increasing adoption of Ethernet Nodes.
From a network management perspective, the Ethernet Node is centrally managed via an access
network element, which, in the near-term, aggregates both control and data planes for the
underlying Ethernet Nodes, and operates as a virtual CCAP. For the PON based Ethernet Node, OLT
is the access network element that also provides a highly scalable fiber access concentration
platform supporting evolution toward next-generation PON technologies.
In a PON based system, the Ethernet Node in simply a variant of media converter developed on
top of a mature FTTN Multiple-Any-media-Unit (MxU) platform, from which Ethernet Node
inherits a complete suite of field-proven maintenance features including system recovery,
software upgrade and remote diagnostics. The addition of DOCSIS MAC and PHY functions in this
platform may appear to be a complicated proposition considering an abundant of traditional CMTS
features supported by integrated solutions. However, many of those legacy CMTS features
designed to improve scalability and performance of a centralized solution are simply not needed
for a distributed Ethernet Node designed for a small service group with up to a couple of hundred
subscribers. The simplified node-based deployment scenario makes it possible to develop Ethernet
Node as an optimized CMTS solution from the ground up. Consequently, an Ethernet Node
developed on top of a carrier-grade platform is expected to meet or exceed the reliability of
traditional fiber nodes.
Table 8 provides a summary of comparison of network maintenance aspects of Ethernet Node and
Fiber Node.
Table 8 Comparison of Network Maintenance Aspects of Fiber Node and Ethernet Node
Node Type Pros Cons
Ethernet Node
High optical power dynamic range
SNR not impacted by digital optics
More efficient RF monitoring and
analysis for automated fault
isolation and RF adjustments
Potential Impact to OSP
operational practices
Reliability may decrease because
of complex components involved.
Fiber Node
Well established maintenance
record
Mature technology with high
reliability.
No software download or
configuration actions driven by
control interface
The AM optics link is SNR aware.
No management functions unless a
special CM is embedded.
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5.2 Power Consumption Analysis
The core hardware block diagrams of analog Fiber Node and digital Ethernet Node are shown in
Figure 12. The analog Fiber Node includes O/E and E/O converter, amplifier components, and an
optional embedded CM for management; the digital Ethernet Node includes a digital optical
module which can be a P2P optical transceiver or a PON ONU, a DOCSIS PHY/MAC implemented in
FPGA or Application-specific Integrated Circuit (ASIC), and an Analog Front End (AFE) including ADC,
DAC and RF circuits. Power consumption of an actual Fiber Node or Ethernet Node will be higher
due to additional components required to support product features such as multiple RF ports.
Digital OpticalModule
PHY/MAC FPGA or ASIC
ADCEthernetFiber
DAC
RF
Analog O/E Receiver
Downstream Amplifier
Return E/O Transmitter
Managed CM(Option)
AnalogFiber
Digital Ethernet NodeAnalog Fiber Node
Figure 12 Core Hardware Block Diagrams of Analog Fiber Node and Digital Ethernet Node
As shown in Table 9, power consumption of the digital Ethernet Node is about 20W higher than
that of analog Fiber Node. The key reason is the current generation of node-specific DOCSIS
MAC/PHY chipset consumes a relatively large amount power. DOCSIS MAC/PHY in the existing
Ethernet Node solutions is digital circuits consisting of FPGA or ASIC chipset. On average, power
consumption of the FPGA device decreases 15% every year while each successive version of
commercial chipsets is expected to achieve a higher percentage of improvement in power
performance.
Table 9 Power Consumption Comparison of Analog Fiber Node and Digital Ethernet Node
Analog Fiber Node Digital Ethernet Node
Analog O/E Receiver 6W Digital Optical Module
P2P 1W
Analog E/O Transmitter 3W PON 7W
Downstream Amplifier 11W DOCSIS MAC/PHY (32x10) 22W
Managed CM (Option) 5W ADC and DAC 2W
Power Supply efficiency 85% RF Amplifier 11W
Power Supply efficiency 85%
Total Power Without CM 23.5W
Total Power P2P 42.3W
With CM 29.4W PON 49.4W
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The additional 20W of power required by each Ethernet Node is well within the overhead power
capacity of the node facility. As shown in the bandwidth modeling result, the deployment of
Ethernet Nodes is expected to be carried out together with a node split to 175HHP, which may
result in the removal of a number of amplifiers. Consider a typical amplifier consumes about 50W
of power, the additional power needed to support the new Ethernet Nodes should be more than
offset by the power saved during node split.
5.2.1 Overall Power Consumption Comparison
While the introduction of Ethernet Node has only a small impact to power consumption within the
node facility, the overall power consumption benefit of a distributed solution to both the node
facility and the hub facility is significant. Similar to the power saving benefit realized by the
introduction of I-CCAP, the amount of power savings increases as a hub is gradually converted from
the existing M-CMTS to an OLT based distributed Ethernet Node solution.
Table 10 serves to illustrate the overall power savings of an OLT based distributed Ethernet Node
solution compared to an M-CMTS solution. Using a hub with 30000 HHP as an example, power
consumption is calculated based on 700/500/350/175/60 HHP per node, each served with a 16X4
DOCSIS 3.0 bonding group. As expected, overall power savings increases dramatically with
fiber-deep service group sizes at 175 or lower number of HHP.
Table 10 Power Consumption Comparison: M-CMTS vs. Distributed Ethernet Node
M-CMTS Solution Ethernet Node Solution Total Power
Saved
700HHP Hub Chassis 1 CMTS core + 1
UEQAM + 43
TX/RX
Hub Chassis 1 OLT + 43
TX/RX
3.24kW
Total Power
Consumption
2000W +
3000W + 430W
= 5430W
Total Power
Consumption
900W +
430W =
1330W
Node Number of
Nodes
43 Node Number of
Nodes
43
Total Power
Consumption
~80W x 43 =
3440W
Additional Power
Consumption
20W over
Fiber Node
x 43 = 860W
500HHP Hub Chassis 1 CMTS core +1
UEQAM + 60
TX/RX
Hub Chassis 1 OLT + 60
TX/RX
2.9kW
Total Power 2000W + Total Power 900W +
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Consumption 3000W + 600W
= 5600W
Consumption 600W =
1500W
Node Number of
Nodes
60 Node Number of
Nodes
60
Total Power
Consumption
~80W x 60 =
4800W
Additional Power
Consumption
20W x 60 =
1200W
350HHP Hub Chassis 1 CMTS core + 1
UEQAM + 85
TX/RX
Hub Chassis 1 OLT + 85
TX/RX
2.4kW
Total Power
Consumption
2000W +
3000W + 850W
=5850W
Total Power
Consumption
900W +
850W =
1750W
Node Number of
Nodes
85 Node Number of
Nodes
85
Total Power
Consumption
~80W x 85 =
6800W
Additional Power
Consumption
20W x 85 =
1700W
175HHP Hub Chassis 2 CMTS core + 2
UEQAM + 170
TX/RX
Hub Chassis 2 OLT + 170
TX/RX
4.8kW
Total Power
Consumption
11.7kW Total Power
Consumption
3.5kW
Node Number of
Nodes
170 Node Number of
Nodes
170
Total Power
Consumption
~80W * 170 =
13.6kW
Additional Power
Consumption
20 W x 170 =
3.4kW
60HHP Hub Chassis 4 CMTS core + 8
UEQAM + 500
TX/RX
Hub Chassis 6 OLT + 500
TX/RX
16.6kW
Total Power
Consumption
37kW Total Power
Consumption
10.4kW
Node Number of
Nodes
500 Node Number of
Nodes
500
Total Power
Consumption
~80W x 500 =
40kW
Additional Power
Consumption
20 W x 500 =
10kW
6 Overview of Baseband Optical Technologies
Compared to analog optics link used to transport modulated analog signals in conventional HFC
network, baseband optical technologies offer a different set of value proposition that is
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increasingly relevant for HFC migration. One of the principle drivers for adopting digital optics is to
extend the reach of native IP content delivery pipe in the HFC network. Other benefits include
noise-immunity, plug-n-play installation, and simplified maintenance and diagnostic processes.
Short of FTTH deployment, connecting distributed Ethernet Nodes with digital optics links is an
obvious next step.
Driven by steady global FTTx deployments during the past decade, the application of baseband
optics in the access network has seen tremendous growth. With each new FTTx project,
incremental advancements were made in various deployment techniques to lower the
construction cost, which in turn enabled more projects and drove down the cost of baseband
optics and overall FTTx solutions.
Depending on market, up to 40% of the FTTx deployment is targeted for MDU, which requires
significantly higher uplink bandwidth than the SFU serving a single FTTH subscriber. The recent
trend toward Gigabit access is driving demand toward a much higher uplink capacity especially for
MDU solutions. Since baseband optics is utilized in almost all FTTx solutions, these market factors
are driving rapid development and commercialization of high-capacity next-generation baseband
optical technologies. A summary of current and future baseband optical technologies is provided
in the Table 11.
Table 11 A Summary of Baseband Optical Technologies
Technologies Capacity Cost Deployment&
Maintenance
Logical
Reach
Suitable for Ethernet Node
2.5G GPON Shared 2.5G DS
/ 1.25 G US
Low Colorless ONU,
co-existence on the
same Optical
Distribution
Network (ODN),
high scalability, easy
deployment &
maintenance
60km Limited (for <60HHP node)
10G GPON Shared 10G DS /
2.5G US
Medium 60km Yes
TWDM-PON Shared 40G DS /
10G US
Medium
to High
60km Yes
1G EPON Shared 1G / 1G Low Not
specified
No
10G EPON Shared 10G /
1G or 10G / 10G
Medium Not
specified
Yes
10G P2P Dedicated 10G
Symmetric
Medium Requires individual
trunk fibers
120km Dedicated 10G symmetric
bandwidth
10G DWDM
Ring
Up to 40/80
wavelengths
High Requires inventory
to manage colored
SFPs
120km
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6.1 Comparison of Technical Parameters of GPON and EPON
PON is the dominate baseband optical technology, accounting for 93% of FTTx deployment [6].
GPON and EPON are the two mainstream PON technologies. In 2013, worldwide EPON revenue is
about one-third of GPON [6].
At 2.4Gbps DS and 1.2Gbps US, GPON is widely deployed for FTTH in most markets as it offers
better cost-performance than 1G/1G EPON as shown in Table 13. Both XG-PON1 and 10G EPON
solutions are now available, mostly targeted for the residential MDU and various business service
applications including wireless backhaul.
Selection of a particular PON technology essentially commits the operator to a specific technology
roadmap. As shown in Figure 13, the GPON technology roadmap extends beyond XG-PON1 to
TWDM-PON, which will see initial deployment beginning in 2016 [6]. For EPON, the current
technology roadmap ends with 10G EPON. Discussion of next-generation EPON has just started
with formation of IEEE 802.3 Industry Connections NG-EPON Ad Hoc in January 2014 [7].
2004
IEEE 802.3ah
2008
ITU G.984
2009
IEEE 802.3av
2010
ITU G.987
XG-PON1
2013
ITU G.989
NG-PON2
(TWDM-PON)
1G
2.4G
10G
2.4G
1G
10G
40G
1.2G
2017?
IEEE NG-EPON
1.25G/2.5G PON
10G PON
NG PONEPON
DS US
GPON
DS US
Figure 13 GPON EPON Technology Roadmaps
Both GPON and EPON are designed to support coexistence of all standard-defined PON signals on
the same ODN. This is accomplished by utilizing different optical wavelengths for all upstream and
downstream signals. In the case of GPON, all three generations of PON signals, both upstream and
downstream, can coexist in the same ODN as shown in Figure 14.
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XG-PON1OLT
GPON ONU
WDM MUX
GPON
OLT
splitter 10G/2.5G
2.5G/1.25G
TWDM-PONOLT
Tunable 10G/2.5G
XG-PON1 ONU
TWDM-PON ONU
1577nm
1270nm
1577nm
1270nm
40G/10G
10G/2.5G
2.5G/1.25G
Hub
Figure 14 GPON, XG-PON1, and TWDM-PON Coexistence
However with EPON, the wavelength bands of 1G and 10G EPON upstream signals overlap as
shown in Table 12. In order to support 1G and 10G EPON coexistence, the upstream EPON channels
are separated in the time domain, commonly referred to as dual-rate TDMA, which also requires
the use of a dual-rate receiver in the 10G EPON OLT line card.
Table 12 Downstream and Upstream Wavelength Bands of GPON and EPON
GPON EPON
GPON XG-PON1 TWDM-PON EPON 10G EPON DS Wavelength Band 1490 nm 1575 – 1580 nm 1596 – 1603 nm 1480 – 1500 nm 1575 – 1580 nm US Wavelength Band 1310 nm 1260 – 1280 nm 1524 – 1544 nm 1260 – 1360 nm 1260 – 1280 nm
A summary of technical parameters of current-generation GPON and EPON are shown in Table 13.
Table 13 Technical Parameters of GPON and EPON
Feature GPON EPON XG-PON1 10G EPON Standard ITU G.984 IEEE 802.3 ITU G.987 IEEE 802.3av Payload Protocol Ethernet Ethernet Ethernet Ethernet Payload
Encapsulation Generic Encapsulation
Method Ethernet framing + tag Generic Encapsulation
Method Ethernet framing + tag Bandwidth (DS / US) 2.4 / 1.2 Gbps 1 / 1 Gbps 10 / 2.4 Gbps 10 / 1 & 10 / 10 Gbps Number of ONTs 32 / 64 16 / 32 32 / 64 / 128 / 256 16 / 32 / 64 / 128 / 256 32-way split Per-User
Effective DS/US B/W 71.8 / 35.9 Mbps 29 / 26 Mbps 265 / 70 Mbps 265 / 265 / 26 Mbps
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Logical Reach (km) 60 Not specified 60 / 80 Not specified Differential Reach
(km) 20 / 40 20 20 / 60 20 Wavelengths (DS /
US) 1490 / 1310 nm 1490 / 1310 nm 1270 / 1577 nm 1270 / 1310 / 1577 nm RF Overlay (DS) 1550 nm 1550 nm 1550 nm 1550 nm
Line Coding NRZ with scrambling 8b/10b NRZ with scrambling 8b/10b (asymmetric)
64b/66b (symmetric) Optics B: 25 dB PX10: 20dB N1: 29 dB PRX10, PR10: 20 dB B+: 28 dB PX20: 24 dB N2: 31 dB PRX20, PR20: 24 dB C: 30 dB PX20+: 28 dB E1: 33 dB PRX30, PR30: 29 dB C+: 32 dB E2: 35 dB Laser On / Off 25.7 ns 512 ns 25.7 ns 512 ns Framing GPON TC (125 us) 802.3 based GPON TC (125 us) 802.3 based
FEC RS(255, 239) RS(255, 239) DS: RS(248, 216), US:
RS(248, 232) RS(255, 223) Multicast Yes Yes Yes Yes PON Security AES-128 AES-128 AES-128 AES-128 QoS Ethernet & T-CONT Ethernet Ethernet & T-CONT Ethernet
OAM Ethernet, GEM,
PLOAM, OMCI Ethernet Ethernet, GEM, PLOAM,
OMCI Ethernet Protection Type B & C Not standardized Type B & C Not standardized Coexistence Yes Yes (Dual-rate TDMA) Yes Yes (Dual-rate TDMA) DOCSIS Provisioning 2014 Yes 2014 Yes
6.2 TWDM-PON
As a next-generation PON technology, TWDM-PON provides the anchor for a comprehensive GPON
technology roadmap. Compared to alternative solutions, TWDM-PON is less risky, less disruptive,
and offers the best price-performance. Within a span of few short years, through the collaboration
of key industry partners, a number of key technical challenges were solved as illustrated in Figure 15,
further demonstrating the value of a mature GPON ecosystem.
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OLT module v14 XFP+EDFA+Mux/Demux
+ +
4 XFP Modules Optical
Amplifier
Mux/Demux
Tunable filter
Tunable laser
ONU Module v2:10G SFP+ with Tunable Rx/Tx
ONU Module v1:TF+TL
World’s first 4- in-1 OLT
integrated module
World’s first 10G SFP+
ONU module for
TWDM -PON
IntegrationIntegrated into BOSA
Technical Challenges: Small Size tunable BOSA(SFP+) Low cost tunable transmitter and tunable receiver Wavelength calibration and alignment
OLT Module v2
Technical Challenges: Limited space to accommodate Tx, Rx,
Mux/Demux , optical amplifier Burst mode optical amplification ASE noise impact on ONU registration Crosstalk of four channels
Figure 15 Key Technical Challenges Resolved in TWDM-PON
The mixed residential and business application of PON network as illustrated in Figure 16 is an
important part of network planning strategy to maximize ROI. Despite increase in upstream traffic,
service evolution driven by consumer behavior continues to demand higher downstream
bandwidth. Support for asymmetric bandwidth is a market requirement supported by the entire
ecosystem, which translates to higher cost for symmetric PON solutions. Symmetric bandwidth is
an important part of business service offering but with typical service tiers ranging from 50Mbps to
200Mbps, a relatively small percentage of business subscribers can easily be covered by
multi-gigabit asymmetric PON solutions.
Figure 16 Coexisting TWDM-PON and GPON Deployment Scenarios
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A single TWDM-PON OLT port provides 40Gbps DS and 10Gbps US bandwidth over a single ODN. In
a mature FTTx deployment, each ODN is expected to connect directly to both residential and
business subscribers, as well as a number of cell backhaul and FTTN locations. For the vast majority
of FTTN applications serving less than a couple of hundred subscribers per node, this level of
uplink capacity is sufficient to support bandwidth demand growth well into the next decade. With
commercial launch anticipated in 2016, TWDM-PON positions GPON network for future growth
and solidifies GPON as the technology of choice for many operators.
7 Summary
As demonstrated by the modeling result, HFC bandwidth demand for the next 7 years can be met
with a combination of node split, mid-split upgrade and DOCSIS 3.1 upgrade. Most would agree
these migration steps can be carried out with either centralized or distributed solutions depending
on prevailing conditions. Less obvious is the macro trend of an accelerating transition toward a
distributed architecture in the access network.
HFC coaxial plants each consisting of hundreds or more modular node facilities are ready to be
optimized. However, industry continues to focus on improving the efficiency of hub facilities to
maintain flexibility of a physical layer outside plant. This least disruptive approach appears to be
perfectly rational. But a closer examination of the competitive landscape presents a different view.
Within many node facilities, digital fibers are being installed by competing wireline and wireless
operators offering services to the same pool of potential subscribers. The exponential growth in
bandwidth demand is being addressed with innovations in both DOCSIS and FTTx solutions.
Economies of scale continue to drive better performance, reliability, and pricing for the FTTx
Ethernet Node solutions, most of which are tailored for service delivery over other access media
today.
With the introduction of OFDM, DOCSIS 3.1 represents the first major step toward the
convergence of cable access and other telecommunications networks. Adoption of Ethernet Node
is another step down this convergence path toward better economies of scale. There is little
debate about fiber being the future-proof access medium. Newly validated business cases are
accelerating FTTx network build-out and continue to tip the balance in favor of the larger scale.
Now is the opportune time for MSOs to plan for the coming convergence of HFC node facility and
packet digital optical network. The value of Ethernet Node as one of the emerging HFC migration
tools is underscored by the strategic implication it would bring to the HFC network.
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8 References
[1] Howald, Dr. Robert L, ARRIS. Breathing New Lifespan into HFC: Tools, Techniques, and Optimizations,
Cable Show Spring Technical Forum
[2] http://advanced-television.com/2012/04/19/research-mpeg-4-drives-operator-investment/
[3] http://www.cnet.com/news/broadcom-chip-ushers-in-h-265-and-ultrahd-video/
[4] Virtualizing CCAP: Developing a Distributed Access Architecture, a Light Reading Webinar
[5]http://www.prnewswire.com/news-releases/mobile-experts-latest-small-cell-market-forecast-predicts-carrie
r-grade-small-cells-will-outnumber-consumer-femtocells-in-2016-200211811.html
[6] PON, FTTH, and DSL Aggregation Equipment and Subscribers Market Share, Size, and Forecasts: 4Q13 /
CY13 Edition, Infonetics Research
[7] http://www.ieee802.org/3/ad_hoc/ngepon/email/msg00012.html
[8] C. Ranaweera, M.G.C. Resender, K.C. Reichmann, P.P. Iannone, P.S. Henry, B-J. Kim, P.D. Magill, K.N.
Oikonomou, R.K. Sinha, and S.L. Woodward. Design and Optimization of Fiber-Optic Small-Cell Backhaul
Based on an Existing Fiber-to-the-Node Residential Access Network
9 Abbreviations and Acronyms
ADC Analog-to-Digital Converter
AES Advanced Encryption Standard
AFE Analog Front-end
AM Amplitude Modulated
ASE Amplified Spontaneous Emission
ASIC Application-specific Integrated Circuit
ATDMA Advanced Time Division Multiple Access
AVC Advanced Video Coding
BOSA Bi-directional Optical Sub-assembly
CAGR Compounded Annual Growth Rate
CBR Constant Bit-rate
CCAP Converged Cable Access Platform
C-DOCSIS China DOCSIS
CM Cable Modem
CMC Coax Media Converter
CNR Carrier-to-Noise Ratio
CPE Customer Premises Equipment
DAC Digital-to-Analog Converter
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DOCSIS Data over Cable Service Interface Specifications
DSL Digital Subscriber Line
DTA Digital Terminal Adaptor
DVB-C Digital Video Broadcasting - Cable
DVR Digital Video Recorder
E/O Electrical-to-Optical
EOC Ethernet over Coax
EPON Ethernet Passive Optical Network
FEC Forward Error Correction
FPGA Field-programmable Gate Array
FTTdp Fiber-to-the-Distribution Point
FTTH Fiber-to-the-Home
FTTLA Fiber-to-the-Last-Amplifier
FTTN Fiber-to-the-Node
FTTx Fiber-to-Anything
GEM Gigabit-capable Passive Optical Network Encapsulation Method
GPON Gigabit-capable Passive Optical Networks
HD High Definition
HDTV High Definition Television
HEVC High Efficiency Video Coding
HFC Hybrid Fiber Coaxial
HHP Household Passed
HSI High-speed Internet
I-CCAP Integrated CCAP
IP Internet Protocol
IPTV Internet Protocol Television
LDPC Low Density Parity Code
MAC Media Access Control
M-CMTS Modular Cable Modem Termination System
MDU Multiple Dwelling Unit
MxU Multiple-Any-media-Unit
MPEG Motion Picture Experts Group
MSO Multiple-system Operator
NG-EPON Next-generation EPON
NG-PON2 40-Gigabit-capable Passive Optical Network
NRZ Non-return-to-zero
NTSC National Television Standards Committee
ODN Optical Distribution Network
O/E Optical to Electrical
OFDM Orthogonal Frequency-Division Multiplexing
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OMCI Optical network termination Management and Control Interface
ONU Optical Network Unit
OOB Out-of-Band
OPEX Operating Expenses
OSP Outside Plant
P2P Point-to-Point
PAL Phase Alternate Line
PHY Physical Layer
PLOAM Physical Layer Operations, Administration and Maintenance
PNM Proactive Network Maintenance
PON Passive Optical Network
QAM Quadrature Amplitude Modulation
RF Radio Frequency
ROI Return on Investment
RS Reed-Solomon
SARFT State Administration of Radio Film and Television
SC-QAM Single Carrier QAM
SDTV Standard Definition Television
SDV Switched Digital Video
SFP Small Form-factor Pluggable
SFU Single Family Unit
SNR Signal-to-Noise Ratio
STB Set-top Box
T-CONT Transmission Container
TDMA Time Division Multiple Access
TF Tunable Filter
TL Tunable Laser
TWDM-PON Time and Wavelength Division Multiplex Passive Optical Networks
UEQAM Universal Edge QAM
UHDTV Ultra High Definition Television
UPS Uninterruptable Power Supplies
VOD Video on Demand
VoIP Voice over Internet Protocol
XFP 10 Gigabit Small Form Factor Pluggable
XG-PON1 10-Gigabit-capable Passive Optical Network
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