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Optics in Cable TV Networks

LightCounting Releases a Research Note

 

LightCounting has published a Research Note titled “Optics in Cable TV Networks” based on interviews and presentations that took place at the Cable-Tec Expo conference and exhibition held in Denver, Colorado in October 2017, hosted by the Society of Cable TV Engineers (SCTE). This newsletter is an excerpt from the Research Note.

MSOs going “Fiber Deep” to increase bandwidth

Along with the move to DOCSIS 3.1, cable companies are evolving their network architecture, adopting a ‘Fiber Deep’ architecture, which is simply moving to smaller optical nodes, to make more bandwidth is available on the coaxial portion of the network serving the homes connected to a given optical node.



The traditional hybrid-fiber-coax (HFC) networks transmit an RF signal over fiber to a remote optical node, and from there the signal goes over coaxial cable through several RF amplifiers, in cascade, until ultimately reaching the subscriber’s home.  One optical node in an HFC network may serve a neighborhood of 500-2500 homes. 

A Fiber Deep upgrade increases capacity to the subscribers, and thereby extends the useful life of the Hybrid Fiber Coax network. By extending fiber closer to subscribers homes, the average size of the optical nodes serving area shrinks to 50-150 homes, and eliminates all the cascaded RF amplifiers from the coaxial portion of the network. And of course, moving from 500 homes per node in HFC networks to 50 homes per node in Fiber Deep means that as many as ten-times more nodes – and transceivers – are needed in Fiber Deep networks, which is positive news for suppliers of optical components.

Unfortunately the transition to Fiber Deep also created a congestion problem on the Cable Modem Termination System (CMTS) side of the network, as each new node consumed another port on the CMTS headend unit. To alleviate space and power issues in the headend, a further evolution of the cable architecture was developed and is now being deployed: the Distributed Access Architecture or DAA. A key feature of this development is that the physical layer (either PHY or MAC-PHY) of a CMTS or Converged Cable Access Platform (CCAP) is moved down to the remote node, which are then called ‘remote PHY nodes’ or ‘R-PHY nodes’, often abbreviated as RPD.  Moving the PHY layer from headend to node cannot be accomplished using analog optics, so moving to DAA also necessitates moving to digital optics on the headend to remote node link. In practical terms, R-PHY nodes are also Fiber Deep nodes, though they are separate concepts.

In a nutshell, cable networks are transitioning away from using low volumes of analog optics and toward using many more standardized digital optics.

DAA networks will require lots of 10G SFP+ transceivers

R-PHY nodes have two SFP+ ports, one for connectivity to the headend, and the other for redundancy or daisy-chaining to another R-PHY node. 10G SR and LR transceivers are almost universally used in these nodes today.  If all of the 116 million US housing units are eventually passed by a cable network, with an average optical node size of 100 households, and if each headend-node link has two SFP+ ports, then roughly 2.2 million transceivers will be deployed. (116 million homes/100 homes/node*2 transceivers/node). This is a rough estimate, because, in practice, the number of ports per node depends on factors such as node redundancy, segmentation configuration, downstream vs. upstream, etc.

All remote node optics must meet either the e-Temp or i-Temp specification for operating temperature range. One conference speaker noted that temperatures inside a typical aluminum remote node housing have been measured as high as 170 degrees F, which is about 77 degrees C.  This extended temperature requirement is the same as that required for mobile fronthaul transceivers. One vendor told LightCounting that they have received requests from MSOs for temperature performance beyond the iTemp range, to 90 degrees C or more.

The Research Note also provides information on several related topics, including 10G tunable transceivers being developed for the cable TV market, how 100Gbps transceivers may be used in future cable networks, and how cable MSOs and equipment makers have adapted PON technologies for cable networks.

LightCounting subscribers can access the full research note by logging into their accounts at www.LightCounting.com/Login.cfm

The use of optical transceivers in wired and wireless access networks will be covered in greater detail in the forthcoming LightCounting report “Next Generation Access Optics”, slated for publication by the end of November 2017.  The report includes a five-year forecast of transceivers used in mobile fronthaul, backhaul, and in Fiber-to-the-X networks, broken out by speed, reach, technology, and color.  For more information, contact  George@LightCounting.com or see https://www.lightcounting.com/Access.cfm.



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LightCounting is a leading optical communications market research company, offering semiannual market updates, forecasts, and state-of-the-industry reports based on its analysis of primary research with dozens of leading module, component, and system vendors as well as service providers and other users. LightCounting is the optical communications market’s first choice source for the accurate, detailed, and relevant information necessary for doing business in today’s highly competitive environment. For more information, visit: www.LightCounting.com or follow us on Twitter at @LightCounting.