Remote PHY (also known as R-PHY, R PHY, and RPHY) is popular among service providers because it does an effective job of alleviating the rack space, power, and cooling constraints in the hub of a network. It does this by separating out the PHY layer and redistributing it out to the fiber node. CableLabs created the Remote PHY specifications that have become the standard for the industry. But this begs the question as to why there are constraints in the hub in the first place.
It’s due to the insatiable appetite of subscribers for bandwidth to support services such as 4k and IP video and other bandwidth intensive offerings. Add to this the fact that most households and businesses now have multiple devices accessing a network at any given time, and it becomes obvious why providers are rushing to provide gigabit speed services to the home and an increasing number of businesses.
For this to happen, an exponential number of node splits are required to reduce the size of the downstream service groups. In some cases, increasing the number of nodes by a multiple of 5-10 over the next five years. While this can increase speeds, it also creates new problems in the head-end or hub. More space/power/cooling capacity are required in the hub to accommodate the exponential number of nodes splits. Remote PHY relieves these issues.
Learn what VIAVI is doing to support the transition to Remote PHY in this 3-minute video!
Stephen Hardy: The show floor at SCTE Cable-Tec Expo is, of course, the place to go to see the latest technology innovations. I'm Stephen Hardy, Editorial Director of Broadband Technology Report and Program Director for the 2018 Diamond Technology Reviews. Here at the booth of the VIAVI Solutions speaking to Dave Hering, Senior Product Line Manager at VIAVI. Dave, the XPERTrak earned four diamonds in this year's Diamond Technology Reviews Program. What can you tell me about the product?
David Hering: So, the XPERTrak system was built from the ground up to help operators really solve the problems that matter the most. And this was done by integrating our PNM solutions with our monitoring and service assurance solutions, so that it's very clear to operators what are the problems, which are really impacting their subscribers. And they can then go to the appropriate node, troubleshoot the node, and then take advantage of the PNM tools to see those low-hanging problems, which aren't problems today, go ahead and clean those up. And that can reduce a truck roll and it really provides a way to change the process that the operators are using to go through and maintain the plant to do so with greater efficiency.
Stephen Hardy: So, among those features and benefits, what do you see as being unique about XPERTrak?
David Hering: What's unique and what won us the award this year is the ability to go through and integrate different data sources. VIAVI saw an inflection point in the industry with Remote PHY where the probes which you would place in the hub to go through and do things like monitoring and signal leakage and sweep, those are no longer appropriate because you don't have RF going back to the hub. So, the solution uses software agents in place of probes to go through and do things like the return sweep and the spectrum monitoring and live spectrum displays and communicate that information back to the field instruments.
Stephen Hardy: So, of course, Remote PHY is a major topic of discussion here at Cable Tech Expo. What else is VIAVI doing to support the transition to Remote PHY?
David Hering: So, Remote PHY creates some different struggles for operators in that the normal boundaries between work groups has really changed. You see lots of contract labor being used for different things, for example doing the fiber runs. So, if you look at the overall process of setting up the Remote PHY device, you start in the hub, you have to do work in the field with a fiber, you actually have to turn the RPD on, and you have to test everything all along the way just like we have done with business services traditionally to make sure that everything will run properly.
David Hering: VIAVI has a suite of tools to manage all that from assurance solutions [XPERTrak] to the hand-held [HFC test] instruments. And it has software that sits over the top [StrataSync] that lets the different work groups be coordinated with one another and perform very consistent, reliable processes.
Stephen Hardy: Great. Thank you, Dave. For Broadband Technology Report, I'm Stephen Hardy.
Distributed Access Architectures
Remote PHY is part of a larger family of technologies called distributed access architectures (DAA) that alleviate congestion in the hub. In general, DAA technologies such as Remote PHY, R-MACPHY, and R-CCAP virtualize and move certain aspects of a network out of the hub and closer to subscribers.
Hubs are evolving from housing row after row of specialized equipment and RF splitting/combining networks, into potentially nothing more than a small collection of optical switches and routers (akin to a mini data center). R-MACPHY and R-CCAP have been adopted to some extent by the cable industry but Remote PHY is the most popular to-date due to its early adoption by established network equipment vendors and early CableLabs standardization.
Advantages of Remote PHY
Besides reducing space/power/cooling requirements in the hub, Remote PHY also eliminates the analog optical link and replaces it with a commodity digital 10G Ethernet link. This provides distinct advantages for a network moving forward. A digital link is easier to set up, taking less time to deploy. The link is more reliable, requiring less maintenance and manpower in the future. Significant signal to noise ratio (SNR) gains are also achieved using digital optical links versus the old amplitude modulated links, potentially enabling higher modulation orders for DOCSIS 3.1 downstreams.
The 10G Ethernet link creates an economical path for providers to add new services in the future. If an operator needs to spawn an FTTH connection to a high-usage customer or small business, this can be accomplished very economically with 10G Ethernet already nearby. The digital link also allows for longer fiber runs in a network enabling greater flexibility in collapsing hub sites. Finally pushing fiber deeper into the plant via DAA is directionally aligned with N+0 plans to support future Full-Duplex DOCSIS (FDX) rollouts.
R-PHY Challenges for Testing
Deploying Remote PHY creates some unique challenges for testing. Specifically, R-PHY removes the RF feed from the hub, which also removes the possibility for the use of dedicated test and monitoring gear in these locations. This change has a direct impact on actions such as return path monitoring, sweep and transmitting leakage tagger signals.
Remote PHY also has the potential of introducing timing issues between the MAC and PHY layers as R-PHY separates the previously co-located MAC and PHY layers. The separation of the creates distance between the two making it more difficult to keep the timing in sync. If precision timing protocol (PTP) messages are delayed for any reason, timing sync can be thrown off, and as a result, upstream packets from different modems collide and create upstream BER. Troubleshooting is difficult for technicians that don’t have the right knowledge and tools to recognize this type of issue.
Fiber has long been a part of the HFC, but distributed access architectures like R-PHY are rapidly accelerating the deployment of advanced fiber technologies like dense wavelength division multiplexing (DWDM) as fibers are migrated from analogue optical links to digital Ethernet links.
Turning up R-PHY nodes will require the certification or validation of the fiber physical layer links feeding the new R-PHY nodes to ensure that newly activated DWDM wavelengths route correctly from hub to node through any optic MUX/deMUX (optic combiner/splitter) and that the DWDM channels supporting the various R-PHY nodes are present and with the correct optic power levels. This applies equally to newly laid fiber and existing analogue fibers, after all those existing fibers may have been carrying light previously but not at these new DWDM wavelengths.
DWDM networks are more complicated to install, troubleshoot, and maintain versus previous technologies and require new equipment to support. The other fiber-related challenge created by R-PHY is the need for many more technicians to be equipped and skilled to work with fiber due to the massive increase in deployed fiber. The migration of 10G Ethernet from hubs/headends out into the field creates similar challenges. No longer is this a niche technology understood by just a handful of hub/headend engineers, maintenance tech’s must now be trained and equipped to properly maintain and troubleshoot 10G Ethernet.
Remote PHY has also created a proliferation of NEMs in the market giving providers more choices, but also creating confusion and complexity around testing. Many NEMs offer point-solution testing tools that only partially support other vendors' gear. This means technicians must be trained and equipped with a wider mix of testing combinations to accurately maintain and troubleshoot the situation they may face on any given day.
Leveraging the Remote PHY Unit
Virtualization of certain aspects of the hub for Remote PHY obviously has its challenges but also creates advantages moving forward. The R-PHY unit (RPU) can now assume several roles including monitoring the upstream RF, supporting the field find and fix for technicians, and enabling return sweep including real-time field meter interaction. It also provides the downstream RF tagging needed for leakage monitoring and troubleshooting systems.
For Remote PHY, Ethernet test gear designed for CATV is used to validate new R-PHY device turn-ups and troubleshoot timing issues for Remote PHY nodes that split the MAC and PHY layers. Virtualizing the upstream spectral analysis capabilities previously handled by hub-mounted hardware into the RPU enables continuity of these critical capabilities in a Remote PHY environment.
The RPU can further be leveraged to transmit and receive sweep telemetry signaling with existing field sweep meters, enabling a common sweep process between legacy and Remote PHY nodes. In this case, the technician uses the same process and meter regardless of the node type or service provision gear in use, effectively insulating the technician from the underlying complexity. Leakage tagger functionality is also virtualized into Remote PHY nodes to enable this critical plant maintenance capability in this new virtualized environment.
Testing and Monitoring Solutions for Remote PHY
VIAVI has developed the OneExpert CATV field instrument and the XPERTrak monitoring solution for networks that are deploying R-PHY and other DAA technologies. The OneExpert CATV tester has the ability to test both legacy and virtualized environments while also automating tests and displaying the pass/fail results on a dashboard. XPERTrak simplifies the transition to R-PHY by enabling continuity of critical test capabilities including interoperation with deployed VIAVI field meters for return sweep and ingress remediation.
For the fiber element in R-PHY the 4100 series DWDM OTDR module with Smart Link Mapper (supported on the T-BERD/MTS 2000, 4000V2 & 5800), OCC-56C DWDM Optical Channel Checker and not forgetting fiber inspection tools such as the P5000i (also supported by the T-BERD/MTS platforms) or FiberChek Probe provide everything needed to deploy, certify and troubleshoot new or existing fiber links for DWDM services.
To gain more in-depth knowledge about Remote PHY read, “Remote PHY Architectures: Operational Challenges and Opportunities”. More detailed information regarding sweep testing for Remote PHY and DOCSIS 3.1 can be found in the application note, “Sweeping in an Evolving Network”.
Short on time? There are two great webinars that can help. “Remote PHY: Problems Solved, and Problems Created by DAA” and, “Exploring Distributed Access Architectures” will get you up to speed in no time.
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Short R-PHY Video Interview
Alan: Hi, I'm Alan Breznick from Light Reading. We're here in Atlanta at SCTE Cable-Tec Expo. We're at the VIAVI booth. And I'm talking to Koji Okamoto. Hi Koji.
Koji: Alan, nice to see you.
Alan: Good to see you again. So both at your booth and all around the show, we're hearing a lot about Remote PHY and DAA and general. What's your prospective on roll outs that you're seeing and the impact it's going to have on plant maintenance?
Koji: Yes, so it's obvious that it's everywhere right now. I'll say compared to two years ago and last year -- two years ago it was just about the more conceptual stage. Last year was focused on development. This year I see more actual testing of the real devices. And then we've really seen the trial going on, and towards the end almost. In the next two months or so. And I'll see probably pretty good sizable chunks start coming out in the major operators rolling out next calendar year.
Alan: So 2019's a big year?
Koji: Yeah, I think so. Because it hasn't really deployed yet so our operators are all looking at the how you're going to operationalize this. A big piece of this is changing from the analog to digital optics and there's many changes that happen based upon it, so they're trying to work out all that stuff first.
Alan: So what will the impact be of all these Remote PHY rollouts on planned maintenance?
Koji: Yeah, so biggest thing is they just lose the visibility into the RF coming back from the fields. Which is still the operational maintenance technician needs it to do their job every day.
Koji: And this transition happens in next, probably, 10 years. So, 10% of networks could be DAA and then 90% could be something else. So you need to gracefully transition this over without giving the technicians a completely different workflow so they can migrate over between those two points.
Koji: So, we created a more virtual solution then start embedding a test agent into the DAA so that allow us to see these critical parameters in order for them to maintain their network and troubleshoot and so on.
Alan: Okay, so given all that, what is VIAVI doing to help support operators through these Remote PHY transitions?
Koji: Other piece, on top of just the portion I mentioned is mostly the DAA facing to the customer side. There more impact actually going backward, as well, in a technology perspective. Now the field guys needs to start testing the fiber and more ethernet. So, that's a big deal. That's a new transition. So technology wise, that's a big influence. The other intangible impact, the disruptiveness that we are seeing, is organizational boundaries.
Koji: So, what's happening is you just separated the CMDS functioning into two pieces. Used to be into the hub site. You move the RF portion, for example and you move PHY into the node. And then the MAC piece could be on the data center.
Koji: So it used to be owned by, let's say, the field technicians and the head and the hub technicians. Now, some are going to data centers. So, if it doesn't work, what work group is responsible for it 'cause you separate the functioning into two locations.
Koji: So, organizations are not built to troubleshoot today. So we are helping them to figure out how to be able to segment the problems with more virtual agents throughout the network for ethernet testing, for example. As well as the fiber mode integrity testing between the hub site to the DAA.
Koji: And the other piece of this, the operators are asking us is they want to have flexibility in deploying a different type of vendor and architecture because every vendor has this advantage in what they do best. And depending on their current architect, they start picking and choosing.
Koji: So, the challenge is how would the operator manage multi-architectural and multi-vendor scenario. So we created the alliance program with us and all the NEMs and enable the inopability so the operator can really have the way to manage the multi-vendor scenario much better based upon the strength of each of the NEMs have.
Alan: Right. And you haven't really had to do that before.
Alan: It hasn't been multiple vendors like this before.
Koji: Yeah. It's correct. And then the biggest piece of this is you lose the visibility of this testing, so operators needs these to operationalize. They can't deploy Remote PHY devices without having a way to maintain and manage. And they weren't doing a consistent way across all the vendors. So we are here to help them to basically bridge between those points in the test site and in the old NEMs.
Alan: Okay. And besides the vendors, how about managing all the contractors?
Koji: Okay. That's a great question, too, because a lot of contractors do a lot of work on this deep fiber work.
Koji: So we're finding out that quite a bit of the contractors really need the help on the fiber testing piece of it. And on the ethernet portion because now it becoming the fiber which is the physical layer and then now you're going to have ethernet on top.
Koji: So all this testing needs to be managed in terms of the processes. So, A, I would like this contractor do test X, Y, Z. So you have a way to control what's being done. And so we worked quite hard in the last three years or so to get the vision of cloud-enabled test systems such that all the data from either the RF side of the fence or ethernet or fiber can move up into the cloud to enable the operator to manage both contractors as well as the direct work group in a very consistent way.
Alan: So now operators will be able to manage both multiple vendors and multiple contractors.
Koji: Yes. And we're finding out, some of the major operators rolled out some of the deep fiber and FTTH. When they did not have these processes enabled, we saw as much as 30 to 40% noncompliance after they were built. Which is huge cost. So, now going back and redoing all these tests, which could have been done in the first place.
Alan: Right. Okay, Koji, always a pleasure.
Koji: No, thank you. I appreciate your time.