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Fiber Deep Part 1: What is it?

Entertainment consumption has been shifting from linear, forcing the consumer to view the content at a time dictated by the program scheduler, to non-linear with the option to stream a vast range of content at a time and place of the viewer’s choice, and to social media platforms such as Facebook. This shift is also giving rise to increasing numbers of cord-cutters: households that cancel cable TV or other paid TV subscriptions in favor of a high speed broadband connection and over-the-top video services from the likes of Netflix, Amazon, YouTube, and Hulu.

To address these changes and the threats they present, MSO cable operators must evolve, and are evolving, their business models, service offerings, and networks. In terms of network evolution, they have an impressive number of industry initiatives to choose from. DOCSIS 3.1 evolves the Hybrid Fiber Coax (HFC) part of the network with higher order modulation (up to 4096 QAM today), increasing capacity to 10 Gbps downstream and 1-2 Gbps upstream while DOCSIS 3.1 Full Duplex enables downstream and upstream to use the same spectrum increasing upstream capacity also to 10 Gbps. Converged Cable Access Platform (CCAP) and Head End Re-architected as a Data Center (HERD) focus on the headend, with CCAP, which has already been widely adopted, bringing together the CMTS (cable broadband) and edge QAM modulator (video) functions in a single platform, while HERD seeks to virtualize these functions based on data center principles. Distributed Access Architecture (DAA), also referred to as Distributed CCAP Architecture (DCA) and Digital HFC, and with Remote PHY the most common and standardized implementation, separates the CCAP core functions and PHY (or MAC/PHY) with the core functions remaining at the headend or primary hub while the PHY function, typically but not necessarily, gets pushed deeper into the network, closer to the end-user. And then there is Fiber Deep.

Figure 1: Today’s HFC Network and Key Cable Industry Technical Initiatives

While DOCSIS 3.1 uses higher order modulation to maximize spectral efficiency and increase capacity, the problem is that coax is a shared medium with the 10 Gbps downstream and 1-2 Gbps or 10 Gbps upstream having to be shared amongst all the households sharing that coax - typically 500 homes but up to 2000. With 500 homes this works out as 20 Mbps per home. Now due to the statistical nature of internet usage, actual data rates can be significantly higher than this, but as internet usage ramps with streaming and device proliferation, oversubscription ratios are shrinking. Another approach to increasing capacity is to split the fiber node with 10 Gbps, on each of the fiber node’s ports, increasing the average capacity to between 40 Mbps (2 ports) and 80 Mbps per home (4 ports).

What Fiber Deep does is move the fiber node much closer to the customer reducing the number of homes that have to share the DOCSIS-enabled coax capacity to between 50 and 128. With a typical 64 homes, the average capacity per home with DOCSIS 3.1 would be 156.25 Mbps. However with node splitting, this average could be as high as 625 Mbps per home (4 ports), providing the ability to offer gigabit plus services to every home.

Figure 2: Fiber Deep

The other problems Fiber Deep addresses are OpEx and service availability. Fiber Deep pushes the fiber node to the point, typically within 330 meters/1000 feet of the farthest home, where there is no longer a need for Radio Frequency (RF) amplifiers, commonly referred to as “N+0” node plus zero amplifiers. A typical fiber node has 4 ports with 7 amplifiers per port, and therefore 28 amplifiers per fiber node. These amplifiers consume around 35 watts while the fiber node itself consumes around 60 watts, giving a total of 1040 watts. If we replace these with six Fiber Deep nodes at 140 watts each, we reduce consumption to 840 watts, a reduction of almost 20%.

In addition to consuming power, these RF amplifiers can fail causing service outages degrading the customer experience and increasing OpEx as the faults are reported, located, and repaired. Active devices are responsible for the vast majority of failures in an HFC network. Using the above example, we have replaced 29 active devices with 6 active devices, an almost 80% reduction.

Figure 3: Fiber Deep + DAA/Remote PHY 

For many cable operators, Fiber Deep will go hand-in-hand with DAA and Remote PHY. Benefits of this approach include reduced footprint and power consumption at the headend and simplified transport between the headend and fiber node, replacing analogue RF transport with simpler and more efficient digital technologies, such as Ethernet and OTN, which also enables higher modulation and more capacity on the coax part of the network. Furthermore, Remote PHY provides a more flexible solution for node splitting.

So to summarize, alongside DOCSIS 3.1/Full Duplex and node splitting, Fiber Deep has a key role to play in increasing cable network capacity while also reducing OpEx and maximizing service availability, especially when deployed with Remote PHY.

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