DOCSIS 3.1 vs FTTH
By Dean Stoneback, Senior Director, Engineering & Standards for SCTE/ISBE
Since the completion of the DOCSIS 3.1 specification, there has been a lot of discussion about whether DOCSIS 3.1 or Fiber To The Home (FTTH) is the best option for service providers. In the broadband communications industry, the majority of homes are serviced by coaxial cable connections. The networks enabling those connections are called Hybrid Fiber Coax (HFC) networks because they contain a fiber feed to the neighborhood and then use coaxial cable to transport signals through the neighborhood to the homes. Since fiber equipment has become less expensive, most recent greenfield deployments utilize fiber all the way to the home. The question for cable operators that already have HFC networks is how to know when they should invest in the current HFC network vs. deploying fiber all the way to the home. The creation of DOCSIS 3.1 has made this choice more difficult because DOCSIS 3.1 enables 10 Gbps services to the home over HFC networks. With such high throughput available, why would an operator ever need to replace the HFC network with FTTH? However, since upgrades from existing DOCSIS 2.0 or 3.0 equipment to DOCSIS 3.1 equipment are not cheap, should operators skip DOCSIS 3.1 and go directly to FTTH?
The first step in answering the DOCSIS 3.1 vs. FTTH question is to realize that it’s the wrong question! DOCSIS is a transport technology (protocol), which is a method to carry information across a network. FTTH is an architecture, which is a physical network structure that connects multiple locations. Other examples of transport technologies are EPON, GPON, and Ethernet, and other examples of architectures are HFC, RFoG, and PON. Specific transport technologies can be used on some architectures but not on others. For instance, one could use any version of DOCSIS (including DOCSIS 3.1) over an RF over Glass (RFoG) architecture to deliver broadband services to homes over fiber. In this case, it’s not DOCSIS 3.1 vs. FTTH—it’s DOCSIS 3.1 and FTTH!
Instead of asking DOCSIS 3.1 vs. FTTH, the correct questions to ask are what architecture is needed and what transport technologies can operate over that architecture. Although the questions are interrelated, they need to be explored separately. For instance, if an operator is not facing serious bandwidth competition in its existing services areas, that operator might choose to deploy EPON in new areas and slowly migrate existing areas to EPON over many years. If an operator is facing bandwidth competition but has limited capital, then DOCSIS 3.1 could make more sense, delivering higher speeds while delaying the more expensive FTTH transition. To deliver FTTH in the future, such an operator might decide to eventually switch to EPON, or the operator might keep its DOCSIS 3.1 network and add some RFoG. If an operator is facing extreme bandwidth competition, the operator might want to go directly to EPON.
The decision process is certainly not easy, but cable operators have the good fortune of having many tools at their disposal. DOCSIS 3.1 enables state-of-the-art speeds to be delivered over HFC networks. DOCSIS Provisioning of EPON (DPoE) allows EPON to be operated with the same back office as a DOCSIS network. RFoG enables FTTH with HFC back office and HFC consumer premises equipment. Broadband providers have many options. To make the most sense of all these choices, I suggest checking out the training available to the industry at www.scte.org/courses.
(Dean Stoneback is Senior Director, Engineering & Standards for SCTE/ISBE)