Another step in the HFC network’s evolution.

Cable TV subscribers are demanding services that strain the capacity of today’s networks. At the same time, MSO and cable TV network operators are looking for ways to increase revenue. Operators also are driving lower operating costs. At the heart of solving those issues is a common solution – changing the network – and there are myriad options and methods to do so. One emerging technology solution co-exists with today’s HFC network, enables more bandwidth, decreases operating expenses and moreover, preserves investment – the micro-node.

Selected options for bandwidth expansion
Table 1: Selected options for bandwidth expansion in cable TV networks.
Source: ABI Research 2007 – CATV Bandwidth Expansion Solutions.

As noted below, subscribers, competitors, and cable TV network operators themselves contribute to the push for progress.


  • Quickly embraced HDTV and are clamoring for more channels
  • Are calling for more interactive services such as VOD and gaming
  • Increased use of third-party services such as downloads of online videos and hosted VoIP services.


  • Primarily telephone companies that offer video services along with data and voice, primarily using low-operational cost, high bandwidth passive optical networks (PON).

MSO/cable TV network operators themselves are:

  • Expanding bandwidth to satisfy customers’ service demands
  • Protecting their revenue base from competitors
  • Driving operating expenses ever lower
  • Seeking to increase revenue in the lucrative business services market.

Addressing those concerns is a daunting task indeed, but cable TV operators are up to the challenge, and the vendor community offers a host of solutions. Table 1 from ABI Research identifies some of the choices available.

Typical HFC architecture
Figure 1: Typical HFC architecture.

Regardless of the methods and technology chosen, it is clear that operators must alter the network in some way. As services evolve, the advantages of pushing fiber deeper in the distribution network become more and more distinct. Many cable TV network operators have decided that an FTTx or deep fiber strategy is their architecture of the future. However, the high cost of migration to FTTx leaves many operators reconsidering deployment timing.

Also troubling, a number of the solutions summarized in Table 1 result in stranded investment as FTTx is deployed. Operators are looking for an affordable migration plan that does not waste past investments and is a permanent solution.

There is an emerging technology that allows them to do just that. It is a deep fiber architecture based on the use of a per-subscriber node called a “micro-node.” The micro-node concept is to extend fiber to (or nearly to) the subscriber premises where a low-cost transceiver performs the optical-electrical conversion.

Unlike traditional FTTx solutions, the micro-node preserves today’s transport protocols and modulation formats (DOCSIS, DAVIC, QAM, QPSK, etc.). Moreover, a micro-node architecture remains open and protocol/modulation format agnostic. The network operator retains the ability to implement a new distribution technology without abandoning the fiber or the micro-node.

To further explain, Figure 1 illustrates a typical HFC configuration. Figure 2 illustrates the micro-node deep fiber architecture. In this network, coax between the node and subscriber is replaced by fiber terminated at the subscriber location with a micro-node transceiver. The result is a fiber optic network extending from the headend to the subscriber’s home or curb.

Micro-node architecture
Figure 2: Micro-node architecture.

For simplicity, Figure 2 illustrates a micro-node network completely replacing the node and coax distribution plant. Most real-world deployments leave the HFC node in place for some time while selectively extending fiber deeper into the subscriber base. Both HFC and micro-node architectures co-exist during the transition; over time, the node and coax are fully replaced.

This implementation presents several interesting advantages, but before exploring those it is important to recognize that the outside plant changes. Fiber is extended to or almost to the subscriber residence. This article focuses on the technical/architectural aspects of the micro-node approach along with identifying costs savings opportunities. Quantitative economics of the solution will be addressed separately.

The advantage of a micro-node strategy is that the network operator gains the benefits of a deep fiber or fiber-to-the-subscriber network without the enormous costs of changing distribution technologies. Deploying a micro-node architecture establishes a layer 1 fiber infrastructure that supports traditional RF and DOCSIS with the potential to support other layer 2 protocols. For example, traditional FTTH protocols such as gigabit Ethernet PON (GEPON) and gigabit PON (GPON) can coexist on the layer 1 network with the current RF channel lineup and DOCSIS. The investment in HFC is not abandoned, and a foundation for network protocol evolution is created. With a micro-node strategy, the access network of the future is deployed not with an expensive “forklift upgrade” but as an incremental investment when and where needed.

HFC vs. micro-node architecture fiber usage
Figure 3: HFC vs. micro-node architecture fiber usage.

Increased bandwidth per subscriber. As the ultimate in node-splitting, the micro-node architecture can be constructed to cost-effectively serve many customers or as few as one subscriber. Bandwidth may be allocated and balanced on a per-user basis using a micro-node network that offers single-subscriber granularity. The net effect is that higher bandwidth per user is enabled. That means additional revenue when subscribers sign up for faster data service tiers or bandwidth-hogging applications such as gaming and video-on-demand (VOD). It also lays the foundation for business-class data services, which are discussed later in this article.

Micro-node transceivers can support up to 1.1 GHz bandwidth and beyond, enabling another bandwidth increase method. By extending the traditional 870 MHz ceiling to 1.1 GHz, an additional 230 MHz is available for more HD channels, more data services, and emerging services such as VOD, time-shifted television, gaming, and other interactive services. While it is necessary for headend equipment and customer premise equipment (CPE) to also support 1.1 GHz, using a micro-node architecture avoids upgrading amplifiers and other network equipment for the additional bandwidth.

Subscriber equipment unchanged
Figure 4: Subscriber equipment unchanged.

Headend architecture and distribution protocols remain intact. In Figures 1 and 2, note that the headend architecture and distribution protocols remain the same for either application. That ensures both traditional HFC and micro-node networks peacefully coexist, sharing the same standard headend network. Thus micro-node implementations are done more easily and at the discretion of the network operator, addressing high-priority situations today while leaving others for more appropriate times.

Increased fiber productivity. Both upstream and downstream signal paths are carried on a single fiber by using passive wave division multiplexing (WDM) technology in the headend. Compared to the traditional two-fiber approach of HFC (Figure 1), a micro-node architecture effectively doubles the number of fibers available between the headend and node/splitter location. Figure 3 illustrates the difference in fiber usage.

Reduced operational expenses. As micro-node architectures replace traditional HFC, active electronics are removed from nodes and other field locations. Expensive sweep testing, certification, proofing, and FCC and CLI testing are eliminated as deep fiber is implemented. Field powering costs for both installation and kilowatt-hour usage are eliminated as well. Smaller enclosures can be used for splices and housing passive elements, reducing equipment costs and easing right-of-way and aesthetics concerns.

Troubleshooting and maintenance are simplified, again lowering operational expenses. Industry studies have shown FTTH operating costs to be as low as 8 percent of those for an HFC network.1 Those savings come from fewer points of failure in the network along with the higher reliability of a deep fiber/FTTH network. While some may quibble with the amount of savings, industry consensus is that the costs of operating an FTTH network are significantly less than HFC.

Subscriber equipment is unchanged. With a deep fiber micro-node architecture, customer premises equipment such as set-top boxes and cable modems remain in place and intact. Communications between headend and CPE products are unaffected as well; micro-node deployment is transparent to network protocols.

Operational practices are unaffected. Because headend and subscriber premises equipment are unchanged, operational practices and back office procedures are unaffected. Subscribers and subscriber support personnel can continue with familiar methods and equipment even though migrating to a micro-node architecture. Beyond just simplicity, deploying an enhanced network without retraining the customer support staff means real savings.

Additional business-class services enabled. Some businesses demand data services and bandwidth that overburden the capabilities of DOCSIS. The micro-node deep fiber architecture is the foundation for solving that problem. It enables an overlay system that adds bandwidth with rich SLA-quality Ethernet services. By installing an optical line terminal (OLT), optical network terminal (ONT), and WDM using the existing fiber infrastructure as shown in Figure 5, both TDM and Ethernet business and backhaul services can be added incrementally and cost-effectively. The FTTx overlay operates on different wavelengths than the micro-node so that RF communications are unaffected.

Ingress noise reduction. Unterminated coax in subscriber locations has long been a source of uncontrolled ingress noise for HFC systems. Since these endpoints are continuously connected to the HFC network, the noise floor of the return path is raised by the sum of the noise from all unterminated endpoints. This often results in the lower 10 MHz of the 5-40 MHz upstream band being unusable for data services.

Micro-node transceivers operate in burst mode to avoid wavelength contention on the fiber optic network. They transmit only when the cable modem is sending data. Therefore, the micro-node transmitter effectively isolates unterminated endpoints except during transmission. Only one transceiver operates at any given time, allowing ingress noise from that location only during the transmission period. There is no summing of ingress noise from multiple locations, thereby creating a lower noise floor than HFC. Since the micro-node return path operates in burst mode and the HFC return path is in a continuous “on” state, they do not share return path receivers. Thus, any network section with a micro-node immediately sees the full benefits of lower noise, which is sufficient to improve CMTS performance along with reclaiming the 5-15 MHz band previously lost to noise.

Business service overlay
Figure 5: Business service overlay.

In the never-ending realm of network evolution, HFC operators are looking for ways to expand network capabilities and reduce operating costs. Many, if not most, foresee deep fiber networks as the next major plateau for service delivery architectures. However, wholesale replacement of existing HFC systems is prohibitively expensive, and the revenue-generating services to support that scale of investment are not yet sufficiently mature or widespread to justify such expenditure.

Nevertheless, HFC networks are straining under the current demand, creating a need for a solution that is cost-effective in today’s service environment while moving the network toward an FTTx architecture without stranding investment. Micro-node technology solves that problem.

Micro-node architectures work with existing headend and subscriber premises equipment such as cable modems and set-top boxes. They offer the benefits of node splitting and node balancing with a deep fiber strategy that paves the path to an FTTx network. And unlike FTTx systems, the micro-node does not require the operator to change fundamental distribution protocols, giving the operator an evolutionary approach to FTTx.

Micro-node technology allows the network operator to deploy and immediately generate revenue from enhanced capabilities without making any changes in their service delivery methodology. Should the operator decide to change from their current distribution protocol to something else, the investment in fiber and the micro-node remains intact.

The unique layer 1 design of the micro-node means that investments are protected, deployments are scalable and co-exist with current HFC technology, operating practices remain intact, subscriber equipment is unchanged, maintenance expenses drop, ingress noise is controlled, and more bandwidth is enabled per subscriber for additional revenue.

1. John Browse, “Fiber Access Network – A Cable Operator’s Perspective,” presented at ITU-T All Star Network Access Workshop, Geneva, June 2-4, 2004.