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Putting the “Why” in Remote PHY

- October 13, 2017 - 3 Comments

As cable operators continue to look at facing the ever-increasing onslaught of data demand from subscribers, we must ask ourselves, “Is there a better way to do things?” We all have heard the unofficial definition of “insanity” as “doing the same thing over and over and expecting a different result,” we can’t just keep going forward blindly doing things like node splits forever as it is not a sustainable practice doing it the way it has been done for the last 5-10 years .

Invoking a New Thought Process

Step back and look at the problems we are facing and what we can actually change. So often, the industry gets so caught up in the low level “geek factor” of all the great products and technologies developed, that we forget to ask ourselves, “What problem am I actually solving?  Am I deploying this because it is new and cool or does it make sense to solve an actual problem now or one we know is coming in the near-term future?”

One of those technologies with lots of buzz right now is Remote PHY (RPHY). It is one of a few competing technologies that live in the arena of cable Distributed Access Architectures (DAA). At its most basic, root definition, RPHY takes the QAM modulation/demodulation portion of the CMTS and separates it to a location outside of the CMTS. This function will now typically be handled directly in an HFC node in the field or a “shelf” type unit located in a hub or cabinet. The connection between the CMTS and the Remote PHY Device (RPD) is traditional Ethernet.  But we are not here to talk about the broad technology that makes up RPHY. More importantly, we need to talk about what the benefits are and what problems it can solve.

It is important to first start by identifying some of the more pervasive problems that an HFC operator is currently facing. The number one question is “How will I deal with the ongoing, massive expansion of data bandwidth?” There is not a single operator in the US that is immune to dealing with this, but how the problem manifests for each operator can be very different.

Let Us Explain

Take the case of a rural operator that has multiple serving territories covered by multiple Headends/hub sites. Typically, each of these sites would end up with its own CMTS due to distance limitations of RF Optics performance and the DOCSIS protocol. Many times, in the past, we might have been able to get away with smaller CMTS at these locations due to a lower bandwidth demand. If we want to start slowing down node splits by employing forward-looking technology that is more efficient with RF spectrum like DOCSIS 3.1, this may require deploying a brand new, potentially larger CMTS that is capable of the protocol. This could become quite expensive. What if instead, we could centralize the functions of the CMTS and use nearly any type of IP network to interconnect to the sites in order produce the DOCSIS carriers via a RPHY shelf? If we can connect the sites to an existing network, leased wavelength or even a data circuit, we can run Remote PHY. From this example alone, we can see benefits of hardware reduction, power savings, support cost reduction and operational ease of only having a single CMTS. Not to mention achieving the goal of deploying the more forward-looking technologies that you set out to do which may have otherwise been too costly.

On top of this example, here are a few more benefits that we can see from Remote PHY:

  • By taking the RF QAM generation out of the CMTS, it turns the platform into an IP in and IP out piece of equipment. This typically allows the CMTS platform the ability to handle more bandwidth through it if it has the proper backplane and processing capability. This, in turn, allows an operator not to have to deploy as many individual CMTS units as in the past, thus saving valuable rack space, power, cooling and common control hardware along with management time and support and maintenance contracts.
  • By moving the PHY layer of the CMTS potentially out to the node, you can have a compounding effect on how much more efficient DOCSIS 3.1 is. DOCSIS 3.1 will run at higher modulation orders when SNR gets higher. When you take out any or all the typical RF Optical link and turn it into a digital IP link, you end up removing a sizable component of the SNR that can, in turn, lead to the higher modulations. Thus, having the capability of being able to push more data through the same amount of RF spectrum as before.
  • When looking at making an outside plant architecture change of cascade reduction of anything smaller than what the operator has today all the way down to Node + 0, the potential number of transmitters and receivers needed could potentially become overwhelming from a space and powering standpoint. In contrast, Remote PHY uses high-density Ethernet switching in place of an RF combining network and the Ethernet links in place of the RF optical links. This offers the potential to greatly reduce the space considerations needed.
  • There are another two benefits of using Ethernet as the transport for Remote PHY. The first is the ability to now potentially mesh the RPHY transport into an already existing long haul and/or metro IP network. This allows for a great efficiency of getting two benefits out of the same IP transport network. The second benefit of using Ethernet is the ability to gain the potential for true redundancy further out into the network due to the resiliency of many IP protocols.

Many of these benefits were realized recently by a customer of Cisco and CCI Systems that deployed a fully converged CMTS and video deployment (CCAP) over Remote PHY into a serving territory that needed to now have 1 Gbps/s services utilizing DOCSIS 3.1. This operator needed to provide all their services for voice, video, and data over a single leased circuit. This proved to be a perfect application for Remote PHY as it allowed the operator to garner much greater efficiency in density of their CMTS, minimized the footprint of gear needed to be deployed in the serving territory and increase the modulation profile of the DOCSIS 3.1 carriers that were implemented, thus giving the operator more data throughput in the same amount of RF spectrum.

CCI Systems worked with the operator from beginning to end on the project, starting with listening to the needs to understand the problem to solve. It was quickly determined that Remote PHY would provide the operator the best technical and financial solution for not only this opportunity, but also for the future for growth. CCI Systems then completely designed and procured the entire end to end solution including the CMTS, IP switching architecture, video ingestion and delivery, Outside Plant nodes and passives (N+0), and any OSP facilities needed like cabinets and powering. Moving to the delivery phase, CCI deployed the entire solution while working very closely with the customer staff so they would be able to quickly take over the solution for day to day operations.

From a solution perspective, CCI and the operator relied on multiple platforms from Cisco. The Cisco cBR-8 was used as the CMTS platform along with the GS7000 node to provide the Remote PHY delivery in the plant. Cisco switching was utilized for aggregation of the Ethernet network.  CCI also integrated multiple other 3rd party items to complete the entire solution from Headend to outside plant.

Do you want to know more about the end result of example presented above? CCI and Cisco will be on-hand all week at the SCTE Cable Tec Expo in Denver, CO to discuss RPHY options with operators. Visit booth #1319 to speak directly with blog author, Todd Gingrass, regarding your network’s challenges and future demands and better understand what solution is right for you.


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    Great perspective Todd!

  1. Well explained Todd! Looking forward to SCTE CABLE Tec Expo in Denver. See you there!

  2. Excellent Article and Well Explained!