DOCSIS 3.1 vs. PON

This post has generated some great buzz on other platforms and is worth sharing again.

There is a perception that the only way broadband cable can compete with the likes of CenturyLink, Google Fiber, and others, is to adopt a fiber-to-the-home (FTTH) network architecture. Before accepting this perception as reality, one should first consider the networks of these competitors.

Legacy telephone networks were built with twisted-pair copper cable, which is approaching the hundred-year mark in some cases. Digital subscriber line (DSL) technology has enabled competitors with telephone company roots to provide high-speed Internet access over these copper legacy networks. Yet, DSL technology appears to be nearing its limits, and practical delivery of data rates that approach 1 gigabit per second (Gbps) is unachievable. Realizing this dilemma, Verizon began replacing their copper networks with FTTH over a decade ago; CenturyLink and other comparable companies have followed suit.  Google Fiber is building their networks from scratch, so choosing FTTH network architecture makes sense.

The common denominator among these competitors is their networks are obsolete or non-existent. There is no debate that an entire network built with fiber-optic cable is the way to go if you are building a network from scratch or replacing a legacy copper wire network. However, in addition to fiber-optic cable, FTTH architecture requires in-network installation of optical line terminators (OLT), optical distribution network (ODN) devices, and optical network units (ONU).

The hybrid fiber/coax (HFC) network architecture, used by broadband cable in conjunction with Data Over Cable Service Interface Specification (DOCSIS), has many years of useful service left. Operators currently using DOCSIS 3.0 to provide high-speed Internet access have elements in place to provide downstream data rates of 1 Gbps. With the certification of DOCSIS 3.1 modems and cable modem termination systems (CMTS), downstream data rates over 10 Gbps are feasible. Each version of DOCSIS is compatible with previous versions. This compatibility means customers experience minimal disruption when a migration to the next version is necessary.

Conversion from HFC/DOCSIS network architecture to PON/FTTH architecture requires a “forklift” approach- the old network and its elements will have to be lifted out and replaced with the new network elements. This requires operating two parallel networks until all customers are successfully transferred to the new network. In addition to replacing the coaxial cable with fiber-optic cable, the CMTS will need to be replaced by an OLT and DOCSIS modems/gateways replaced by ONUs.

Any concern of DOCSIS becoming obsolete should be minimal.  DOCSIS was developed to leverage the flexibility of HFC networks.  Each version adds features and value that have enabled the broadband cable industry to be the leading provider of high-speed Internet access. Compared to switching to PON/FTTH, DOCSIS is less disruptive for customers and the expense to migrate to it is relatively incremental.


Michael Spence has been working on the carrier side of the broadband cable industry as an account executive, sales manager, corporate trainer, performance coach, and technical trainer.  Michael credits his industry knowledge to the hundreds of brilliant engineers and network innovators he has been privileged to learn from.

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