FOA Guide


Migration from CATV HFC To PON

Vladimir Grozdanovic

New services are constantly being introduced. Subscribers constantly demand greater bandwidth, higher data rates in both directions, and extremely low latency. In addition, there are constant requirements to increase the reliability of all services. As a result, some CATV service providers are converting their traditional hybrid fiber coax (HFC) networks to fiber to the home (FTTH.) Here are some of the reasons why and how it can be accomplished.



For many years, cable operators have been building and maintaining HFC (Hybrid Fiber Coax) networks. HFC is a broadband network that enables triple-play services - CATV, IPTV, Internet, telephony, etc. HFC began when AT&T developed the distributed feedback (DFB) laser, a high power laser that was capable of high frequency conversion of signals with minimal distortion. This permitted CATV operators to convert analog frequency modulation (FM) CATV signals to optical systems, allowing them to extend their CATV networks well beyond the limits of traditional coaxial cables.


About the same time, a network was developed that allowed Ethernet signals to be converted to FM and sent as data in place of a channel on a CATV system. Since Ethernet was the basis of the Internet, this allowed CATV systems to become providers of Internet service, offering much higher speeds than the telephone lines in current use and always-on service. CATV systems quickly became the dominant provider of Internet service.


This service became standardized in 1997 as DOCSIS – Data Over Cable Service Interface Specification. As the Internet grew, so did the DOCSIS standard. In order to keep up with user requirements, CableLabs, the research arm of the CATV industry has constantly upgraded the DOCSIS standard.


The DOCSIS 1.0 standard was introduced in 1997, which enabled what was then an incredible 40/10 Mbps. In the next 10 years, DOCSIS 2.0 and DOCSIS 3.0 were introduced, which significantly increased bandwidth and date rates in both directions. These two DOCSIS standards are still in use. DOCSIS 3.0 allowed a maximum of 1 Gbps downstream and 200 Mbps upstream. The DOCSIS standard upgrade, from DOCSIS 1.0 to DOCSIS 3.0 did not require major changes to the HFC network.


Generally, the changes were related to the electronics, the equipment in the head end called the CMTS (Cable Modem Termination System,) minor corrections to the coaxial part of the network (shortening of coax lines and increasing the number of optical nodes) and upgrades on the cable modem at the customer premises.


DOCSIS Standards


Production date

Downstream data rate

Upstream data rate



40 Mbps

10 Mbps



40 Mbps

10 Mbps



40 Mbps

30 Mbps



1 Gbps

200 Mbps



10 Gbps

1-2 Gbps



10 Gbps

6 Gbps


Note the biggest problem with DOCSIS HFC networks; they are asymmetrical – download speeds are generally much higher than upload speeds, which can be a problem for some user applications like video distribution and gaming.


Upgrades to DOCSIS 3.1 and future 4.0 standards require major changes in the HFC network due to frequency range expansion. In addition to replacing CMTS, major changes are required in the coaxial part of the HFC network, such as replacing passive equipment (RF splitters) and active equipment (broadband amplifiers and optical nodes). These are very big changes that many operators are not prepared for. DOCSIS 3.1 and 4.0 bring benefits but with big changes. Because of this, many cable operators are starting to build FTTH.




The passive optical network (PON) used in most FTTH networks has been present for more than 15 years. The main problems with PONs are the complexity of designing the network, especially with large numbers of subscribers and installation of large numbers of cables to subscribers. FTTH, however, enables very easy migration to new higher speed PON standards (e.g. from GPON to XGS-PON). However, once the network is built, upgrades are simply a matter of changing electronics at the head end and subscriber. By design, one can even have GPON and XGS-GPON operate simultaneously on the same network since they operate at different wavelengths.


PON Standards






1.2/0.6 Gbps

0.6 Gbps



2.5 Gbps

1.25/2.5 Gbps

Most popular


1.25/10 Gbps

1.25/10 Gbps

Rarely used


10 Gbps

10 Gbps

Most popular 10G


25/50/100 Gbps

25/50/100 Gbps



Using PONs means that subscribers are provided with reliable services with high bandwidth, high data rates in both directions and low latency. If we compare PON and HFC, all the advantages are on the side of the PON network.


Why have cable operators waited so long to convert to PONs? The reasons are generally economics. The main reason is the existing HFC network, in which they have invested a lot of money and time. Second, the cost of optical equipment was high. And finally, the cost of rebuilding or building a new cabling network.



New FTTH network

Building a completely new FTTH network is one of the most common ways of migrating from HFC to FTTH. Rather than converting the current HFC over to FTTH which would disrupt service for many users, overbuilding the cable plant with new fiber is generally a better solution. A FTTH PON solution requires completely different network, an optical line terminal (OLT) in Headend, building an optical network (ODN – Optical Distribution Network) and migration of subscribers from the old to the new network (replacement of CPE equipment and home network connection (optical network terminal, ONT). Cable operators usually use GPON (OLT with GPON service boards) or parallel GPON and XG(S)-PON standards.


Installation of the appropriate OLT with the appropriate service boards is required. The OLT can be of different capacities, depending on the number of subscribers to be connected. The number of subscribers on a PON port depends on several factors, such as the PON standard, distance, and provision for future expansion of subscribers in a geographic area.


The design of the cable plant will probably follow the design of the current cable plant, overbuilding on aerial cables and pulling additional cables into current underground ducts. The construction of the FTTH cable plant can be realized in the traditional way (fusion splicing of optical fibers) or using pre-terminated solutions (optical cables with connectors). The use of pre-terminated solutions significantly reduces realization time.


Operators can build a completely new ODN or sometimes use parts of an existing HFC network. In order to save time and money, most cable operators want to use what is available  from the existing HFC network. If there are dark fibers in existing optical cables, the construction of the feeder segment of the new network may be simplified. This reduces costs, shortens the time of realization, and the quality is the same as long as the fibers are in good condition.


If there are not enough dark fibers in the existing optical cables, cable operators have the options of installation of new feeder cables, reconfiguring the network to a remote OLT solution and/or replacement of old optical nodes with new optical nodes with WDM modules.


Generally, FTTH construction reuses the same poles, pipes, manholes, handholes, and optical cables. This significantly reduces the time and cost of a new network. This is very important since there may be delays and problems obtaining new building permits.

Convert HFC to PON

The coaxial components of the HFC network (optical nodes, broadband amplifiers, different boxes and cabinets, and coaxial cables - RG11, RG6, etc.) must be replaced for conversion to a PON. However, on that part of the network, cable operators can use poles, conduits, handholes and manholes for the FTTH network.


Building a fiber optic distribution and drop segment is necessary. Special boxes and cabinets are required for housing optical splitters. If possible, boxes for splitters, as well as cables, are installed on the same poles or existing manholes or handholes.


In indoor applications, such as multi-dwelling buildings, distribution and drop cables should use existing pipes in the walls or special metal or plastic channels. It is important that the network is built according to all the rules and that the aesthetics of the building are not damaged.


Once construction is completed, the service provider will  have two parallel networks - the old HFC network and the new FTTH network.  The migration of subscribers from HFC to FTTH can then be gradual and  planned in stages.


When the FTTH technician connects the subscriber (migrating from HFC to FTTH), the drop cable is installed and the coaxial cable (most often RG11) may be reoved. Most drop cables are available with factory-installed connectors (plug & play solution), which enables quick connection. One end of the drop cable is connected to the last optical splitter on the network, while the other end of the drop cable ends at the ONT. Cable modem and coaxial network may then uninstalled. This is the procedure for each and every subscriber. Only when all subscribers migrate from HFC to FTTH, then the HFC network can be completely uninstalled.


Vladimir Grozdanovic is a graduate electrical engineer for telecommunications with more than 10 years of experience in access networks (HFC and FTTH) in large cable operators in Serbia (SBB and Jotel).

Technical Information on FTTX  From The FOA Online Guide
FTTH Introduction  
FTTH Architectures
FTTH in MDUs (Multiple Dwelling Units)  
FTTH PON Standards, Specifications and Protocols  
FTTH Design    
FTTH Installation 
FTTH Customer Premises Installation  
FTTH Network Testing  
FTTH Case Studies: Do-It-Yourself FTTH  
FTTH Project Management
Migration from GPON to XG(S)-PON  
Migration from CATV HFC To PON  

The Fiber Optic Association Fiber To The Home Handbook: For Planners, Managers, Designers, Installers And Operators Of FTTH - Fiber To The Home - Networks
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The Fiber Optic Association Fiber To The Home Handbook
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