Everything You Want to Know About Coherent Optics for Access Networks (But Were Afraid to Ask)
The cable industry has been well served by its extensive fiber deployment that took place during the initial hybrid fiber-coax (HFC) buildout. Even though cable operators have answered capacity demand through fiber node-splits in specific high demand scenarios, only recently have operators embarked on deeper-fiber roll-out strategies as part of a comprehensive long-term evolution plan.
The exponential growth in demand for capacity prompted CableLabs to explore how to best use cable’s optical infrastructure resources. This exploration led to research activities for the introduction of coherent optics in the access environment. We’re delighted to announce the publication of the book “Coherent Optics for Access Networks” by CRC Press (Taylor & Francis Group), highlighting many of CableLabs’ research activities.
The book discusses how coherent optics in the access network is re-engineered to simultaneously achieve lower complexity and higher performance afforded by the generous link margins characteristic in shorter links. This instantiation of coherent optics is not only suitable for cable access but also for telco and cellular fiber access networks.
Recent developments in the field of coherent optics for access network applications that will support point-to-point (P2P) aggregation use cases and point-to-multipoint (P2MP) fiber to the user’s passive optical network are examined. Optical industry trends as well as the conventional intensity modulation and direct detection (IM-DD) systems and newly developed advanced direct-detection architectures leveraging four-level pulse amplitude modulation format, Stokes receivers and Kramers–Krönig receivers are also presented.
This book focuses on how to adapt coherent optics technology to the access environment in ways that address major cost challenges, such as simplified transceiver design and photonic integration. An example, is the introduction of full-duplex coherent optics, which enables simultaneous bidirectional transmission on the same wavelength thereby doubling fiber’s capacity. Full-duplex coherent optics is an approach that is feasible to implement in the shorter-link-length access environment.
The book provides economical modeling for aggregation uses cases in comparison with traditional 10G IM-DD DWDM based solutions. Implementation requirements, unique to the access environment, are also provided when introducing coherent optics into access scenarios, including coexistence with existing services and security challenges. Progress on recent-specification development activities is reviewed for many industry organizations that focus on short-distance coherent optics interoperability.
In writing this book, the authors have benefitted from the numerous interactions with experts within the optical telecommunication components and systems community, in particular with the vendor and operator members that contributed to CableLabs’ point-to-point coherent optics specification. This book represents a first look of technological advances in coherent optics, in the interest of future proofing of our access networks.
Favorable coherent component cost-reduction trends are expected to continue, technological advancements will enable higher performance and simpler implementations will make coherent technology more pervasive in the access network so that exponential growth in capacity is achieved. Given the headway gained in specification generation bodies and the development progress of optical component and transceiver manufacturers focusing on shorter link distances, a future with coherent optics in the access network is upon us.
Cable Network Reliability: ProOps Platform for PNM and More!
Cable network reliability has many important dimensions, but operators are all too familiar with the significant cost of maintenance and repair, and some with the advantages of Proactive Network Maintenance (PNM). But not everyone has taken full advantage of PNM. Let’s have a look at some of the reasons for that, and what CableLabs is doing to address those needs as part of its PNM project.
The Proactive Operations Problem
CableLabs has been informally assessing the reasons why more operators don’t take advantage of the proactive gift that DOCSIS® provides: the ability to use PNM data to find problems in the network before they become impactful and costly.
It takes a lot of work to implement solid PNM solutions that keep working. A key task in operations is to make decisions based on data. That takes expertise and time. Not every operator or vendor has an expert army in place to analyze all the available operations data to find proactive maintenance work worth doing. Machine learning is anticipated to help, but it will require a lot of work to apply those techniques successfully to an operations task like PNM, and even more to develop the needed controls. Likewise, not every operator or vendor has a statistical analysis or IT army in place to build enterprise tools to automate the process of turning data into action.
Some operators need to start small with testing PNM concepts to find a solution that fits their needs. That means many operators must experiment and learn first. But that requires basic, general tools in hand before experimentation can begin.
A ProOps Platform for Everyone
Figure 1. ProOps with its elements and workers in four layers, built on CCF, on top of the network.
CableLabs created a generalized process for translating data into operations actions and applied it to PNM. Then we built the Proactive Operations (ProOps) platform to enable this process, thus making it easy for everyone to try, develop, deploy and make full use of PNM.
ProOps translates network data into action through a framework that is not strictly enforced but is enabled and supported to better ensure effective proactive maintenance.
The steps we identify for turning network data into action are briefly as follows, moving up from the network, through data collection, and through the worker layers of ProOps in Figure 1.
- Extract Data from the Common Collection Framework (CCF)—ProOps uses CCF to extract the data it needs from the network, then applies basic analysis to translate the data into useful information.
- Analyze for Triggering—Next, the results are analyzed further to determine whether they are interesting or not; interesting results are “triggered” for deeper scrutiny. The data are looked at over time and across data sources to orient the information into context.
- Make It Actionable—Once we find the most interesting network elements to watch, we group network elements into network tasks and provide a measure of importance for the identified work.
Threshold Analysis—The best work opportunities get picked to become proactive work packages, which can be selected based on impact to customers, likelihood of becoming an emergency, and so on.
You ShOODA Get ProOps!
The steps we outline for turning network data into action—or in this case pro-action—align nicely with the well-known strategy of observe, orient, decide, act (OODA). This OODA loop, or OODA process, was created by U.S. Air Force Colonel John Boyd for combat operations. The operations of combating network failure aren’t much different! If you work as a cable operator, then you know.
ProOps is available upon request to any operator member or vendor of the CableLabs community. CableLabs supports users by helping them to deploy ProOps with an example application that shows how to configure it to a specific operator or use case, and we will help our members develop solutions in it, too. Just contact Jason Rupe to get your copy.
Our goal is to help operators provide highly reliable service, and efficient, effective operations is one proven way to do that. ProOps is the latest tool to combat network failures.
OFC: A Third of a Mile of Next-Gen Optics
For the more technically inclined, that’s 2.6 microseconds. Which is how long it would take light to travel a third of a mile through fiber optic cable. It was also the length of the show floor at OFC: The Optical Networking and Communications Conference and Exhibition, held in March in San Diego, California.
Of course, it took me considerably longer – 115,384,615 times longer, or about 5 minutes – to walk that same distance at the show. And that’s assuming I maintained a fast pace and avoided stopping for the entire distance – a feat that proved essentially impossible, given the amazing assortment of next-generation optical technology on display, as well as a large number of familiar faces around me!
The show floor hosted 683 exhibitors – too many to take in over such a short time. Among them were many of the companies that have been involved in the CableLabs P2P Coherent Optics effort, helping to blaze the trail for the use of coherent optics technology in the cable access network, in turn enabling our 10G vision. In those booths, many were showcasing products that support 100G speeds based on our PHYv1.0 specification, as well as their roadmap and plans for devices supporting 200G speeds based on our PHYv2.0 specification. Roaming the show floor, checking out exhibited products or enjoying key sessions, I kept running into many of the direct participants in our efforts, despite the fact that 15,400 people were in attendance.
It didn’t seem that I could go very far without encountering someone from a significant CableLabs contingent or one of our members, reflecting the importance of next-generation optics to the cable industry, as well as CableLabs’ strong commitment to developing new optical technologies. Our Optical Center of Excellence has been at the forefront of developing innovative approaches for applying optical technology to cable networks, such as Full Duplex Coherent Optics.
CableLabs on Display
Although CableLabs wasn’t an official exhibitor, beyond having a contingent of people present, CableLabs and cable definitely had a presence at this year’s OFC. The importance of the cable industry was mentioned during a keynote speech; Curtis Knittle participated on a panel on “Action in the Access Network” as a part of the OIDA Executive Forum, and one of our interns presented a poster as part of a collaboration with CableLabs’ Bernardo Huberman and Lin Cheng.
Another presentation from our own Mu Xu also illustrated how CableLabs is pushing the boundaries of optical technology. This presentation – titled “Multi-Stage Machine Learning Enhanced DSP for DP-64QAM Coherent Optical Transmission” and co-authored by other CableLabs thought leaders including Junwen Zhang, Haipeng Zhang, Jing Wang, Lin Cheng, Zhensheng Jia, Alberto Campos, and Curtis Knittle – was particularly noteworthy because it brought together multiple areas of next-generation technology and research going on at CableLabs.
This was my first year attending OFC, and I feel like I barely scratched the surface of what was there. More than anything else, I came away impressed by the impact that the CableLabs team is making on the optical industry, one that will be critical for enabling our 10G future. I’m greatly looking forward to next year.
Proactive Network Maintenance (PNM): Cable Modem Validation Application(s)
Sometimes, two apps are better than one. We now have two versions of the Cable Modem Validation Application (CMVA) available for download and use: a new lab automation version, and a data exploration version.
Thing One and Thing Two
Lab automation and certification have unique requirements, but investigation and invention require flexibility. Because the CMVA found value as a cable modem (CM) data plotter and browser on top of its original purpose as a lab testing tool, we decided there should be two versions—one focused on each use case.
Sometimes You Feel Like a DUT
The newest, most complex version of CMVA is built specifically for CM Cert-Lab testing and includes several new features and automations:
- Improved efficiency for CMVA on certification testing: CMVA now discovers OFDM/OFDMA-based topology information from the CMTS and loads all related channel configuration information automatically for testing. CMVA also synchronizes PNM SNMP SET command parameters with XCCF for better efficiency and greater control.
- Automated discovery of the active DOCSIS® 3.1 CM list: Users can easily select CMs with their test configurations automatically filled to start tests with a few clicks.
- CMVA now runs multiple PNM tests sequentially on multiple CMs in parallel with simple clicks on a single user login: The latest test reports are directly served from the CM table. Different users are handled in parallel, as previously.
- CMVA now embeds detailed testing logs into the HTML test report: The log file can be downloaded from the HTML test report. The HTML test report is portable.
- CMVA now keeps copies of raw PNM test files together with the test reports for vendor debugging references: When downloading the test reports, CMVA packages the test logs in raw text, and forms the portable HTML test report into a single archive.
- All the Acceptance Test Plan (ATP) calculation activities are placed in the log file for vendor debugging references.
- We added a function for resetting CMs remotely with one click: This is important for testing and useful for other purposes.
Figure 1: New layout for test and configuration management
Figure 2: Select CM directly from the table to start tests; the latest reports are linked directly in the table for convenience
Figure 3: The test procedures ran last time are tracked, and the configurations are automatically filled
Figure 4: Detailed test logs are embedded directly into the portable HTML test report and can be downloaded as pure text log
All these new features are important for test automation, but some of them are useful for other needs. Go nuts! But if you simply want the basic capabilities that CMVA always provided, you can still get that version.
Sometimes You Don’t
Sometimes you just want a simple way to poll a set of modems and see what you can get. The previous version is a bit simpler, but it still has the validation capabilities if you need them. So, it might be the version that can address most, if not all, of your needs. We use it for many purposes but mainly as a testing and development tool. Here are some specific use cases we’ve encountered:
- Testing ideas in the lab: The PNM Working Group InGeNeOS conducted lab testing, as reported on before, and we used CMVA to grab data from CMs under test.
- Developing applications: As we work to develop our first large-scale PNM base application, inside our prototype PNM Application Environment, we use CMVA to develop theories about how the data can be processed for automated processing.
- Building reports and documenting: So often, we need to capture what certain impairments look like, or obtain a good visualization of a PNM measurement, and CMVA makes that handy.
- Investigating issues: With CMVA, it’s a simple matter to collect data from a pool of CMs and compare the results. This helps us investigate many issues, including changes in firmware versions, CM responsiveness, and other potential issues with plant configuration, software changes and so on.
- Combined Common Collection Framework (XCCF) development and testing: As we develop new capabilities with our XCCF, we can use CMVA to validate its functionality.
If you are a user of CMVA, let us know how you have used it!
Two Can Play at That Game
Although the more complicated testing tool can be used for all these use cases and many more, some users don’t need the automation, overhead and many controls required for automated testing. When you contact us to get an updated version of CMVA, please let us know what you would like to use it for. That way, we can offer you the right version.
Forward Error Correction (FEC): A Primer on the Essential Element for Optical Transmission Interoperability
Forward error correction (FEC) has been a powerful tool in the cable industry for many years. In fact, perhaps the single biggest performance improvement in the DOCSIS 3.1 specifications was achieved by changing the FEC being used in previous versions – Reed-Soloman (RS) – to a new coding scheme with improved performance: low-density parity check (LDPC). Similarly, FEC has also become an indispensable element for high-speed optical transmission systems, especially in current coherent optical transmission age.
FEC is an effective digital signal processing method that improves the bit error rate of communication links by adding redundant information (parity bits) to the data at the transmitter side so that the receiver side then uses the redundant information to detect and correct errors that may have been introduced in the transmission link. As the following figure shows, the signal encoding that takes place at the transmitter has to be properly decoded by the receiver in order to extract the original signal information. Precise definition and implementation of the encoding rules are required to avoid misinterpretation of the information by the receiver decoding the signal. Successful interoperability will only take place when both the transmitter and receiver follow and implement the same encoding and decoding rules.
As you can see, FEC is the essential element that needs to be defined to enable the development of interoperable transceivers using optical technology over point-to-point links. The industry trends are currently moving toward removing proprietary aspects and becoming interoperable when the operators advocate more open and disaggregated transport in high-volume short-reach applications.
When considering which FEC to choose for a new specification, you need to consider some key metrics, including the following:
- Coding overhead rate— The ratio of the number of redundant bits to information bits
- Net coding gain (NCG)— The improvement of received optical sensitivity with and without using FEC associated with increasing bit rate
- Pre-FEC BER threshold— A predefined threshold for error-free post-FEC transmission determined by NCG
Other considerations include hardware complexity, latency, and power consumption.
One major decision point for FEC coding and decoding is between Hard-Decision FEC (HD-FEC) and Soft-Decision FEC (SD-FEC). HD-FEC performs decisions whether 1s or 0s have occurred based on exact thresholds, whereas SD-FEC makes decisions based on probabilities that a 1 or 0 has occurred. SD-FEC can provide higher NCG to get closer to the ideal Shannon limit with the sacrifice of higher complexity and more power consumption.
The first-generation FEC code, standardized for optical communication, is RS code. RS is used for long-haul optical transmission as defined by ITU-T G.709 and G.975 recommendations. In this RS implementation, each codeword contains 255 code word bytes, of which 239 bytes are data and 16 bytes are parity, usually expressed as RS (255,239) with the name of Generic FEC (GFEC). Several FEC coding schemes were recommended in ITU-T G. 975.1 for high bit-rate dense wavelength division multiplexing (DWDM) submarine systems in the second-generation of FEC codes. The common mechanism for increased NCG was the use of concatenated coding schemes with iterative hard-decision decoding. The most commonly-implemented example is the Enhanced FEC (EFEC) from G.975.1 Clause I.4 for 10G and 40G optical interfaces.
At the 100 Gbps data rate, CableLabs has adopted Hard-Decision (HD) Staircase FEC, defined in ITU-T G.709.2 and included in the CableLabs P2P Coherent Optics Physical Layer v1.0 (PHYv1.0) Specification. This Staircase FEC, also known as high-gain FEC (HG-FEC), is the first coherent FEC that provides an NCG of 9.38 dB with the pre-FEC BER of 4.5E-3. The 100G line-side interoperability has been verified in the very first CableLabs’ Point-to-Point (P2P) Coherent Optics Interoperability Event.
At the 200 Gbps data rate, openFEC (oFEC) was selected in CableLabs most-recent release of P2P Coherent Optics PHYv2.0 Specification. The oFEC provides an NCG of 11.1 dB for Quadrature Phase-Shift Keying (QPSK) with pre-FEC BER of 2E-2 and 11.6 dB for 16QAM format after 3 soft-decision iterations to cover multiple use cases. This oFEC was also standardized by Open ROADM targeting metro applications.
Although CableLabs has not specified 400G coherent optical transport, the Optical Interworking Forum (OIF) has adopted a 400G concatenated FEC (cFEC) with soft-decision inner Hamming code and hard-decision outer Staircase code in its 400G ZR standard; this same FEC has been selected as a baseline proposal in the IEEE 802.3ct Task Force. This 400G implementation agreement (IA) provides an NCG of 10.8 dB and pre-FEC BER of 1.22E-2 for coherent dual-polarized 16QAM modulation format specially for the Data Center Interconnection (DCI).
The following table summarizes performance metrics for standardized FEC in optical fiber transmission systems.
CableLabs is the first specification organization to demonstrate 100G coherent optics interoperability with a significant level of participants. Please register for our next coherent optics interoperability testing.
The P2P Coherent Optics Specification of the Future, Available Today
Today, CableLabs is announcing another addition to our family of Point-to-Point Coherent Optics specifications: The Physical Layer 2.0 (PHYv2.0) specification. This new specification defines interoperable point-to-point (P2P) coherent optics links running at 200 Gbps (200G) on a single wavelength.
Just 9 months ago, in July of 2018, CableLabs announced the release of the P2P Coherent Optics Physical Layer 1.0 (PHYv1.0) specification, which defines operation at 100 Gbps (100G) on a single wavelength. The PHYv1.0 specification is designed to support rapid product development, ensuring the availability of interoperable products quickly. That quick availability was born through the interoperability event we held this past December, in which 9 different suppliers participated and demonstrated 100G interoperability.
In other words, the specification of the Now
The PHYv2.0 specification, on the other hand, is designed to leverage an emerging new generation of silicon and the resulting devices, which are anticipated to arrive by 2020. Those new devices will double the capacity of the cable access network, consume less power, and lower the cost per bit delivered. All on the network that already exists today.
This is the specification of the Future: A future that’s coming very quickly
Further, this new specification is a key part of another future that’s coming soon: the 10G future recently unveiled by the cable industry. P2P coherent optics running at 100G – and now 200G – allows cable operators to leverage the fiber they’ve already deployed to support that future vision as cost effectively as possible by greatly increasing the capacity of their existing hybrid fiber coax (HFC) networks. That, in turn, enables the enhanced services and experiences envisioned as a part of the 10G future.
Whether the connection to the customer is wired or wireless, at some point all of those network connections need to be aggregated together. The CableLabs suite of coherent optics specifications – now highlighted by the PHYv2.0 specification, defining interoperable 200G operation – will serve as a critical piece of enabling our interconnected future. Fill out the form below for more information.
Preparations for Full Duplex DOCSIS® Technology are Marching Along
Built on the successful completion of CableLabs’ DOCSIS 3.1 specification, Full Duplex (FDX) DOCSIS® technology (now a part of DOCSIS 4.0 technology) is a key component of the 10G platform that will significantly elevate the level of services available to consumers using existing cable broadband networks. With FDX DOCSIS technology (now a part of DOCSIS 4.0 technology), the same frequencies are simultaneously used for both upstream and downstream traffic, virtually greatly increasing the capacity of the coaxial cable. More capacity means lower latency and speeds of up to 10 Gbps for downstream traffic and up to 6 Gbps for upstream traffic. Cable broadband users will be much more satisfied with services, leading to greater customer retention and the ability to attract new customers.
Field Testing Analysis
In the past year, CableLabs has thoroughly scrutinized FDX DOCSIS technology (now a part of DOCSIS 4.0 technology) in the field. Test equipment and engineers have flown around North America performing analysis on real cable broadband networks, including both a newly constructed plant and coaxial cable that was installed back while I was in college (that coax is well past voting age…). Volumes of data were collected, such as technical parameters on various configurations and various weather conditions: data from real networks in the real world.
And it works. The testing results were positive and in line with expectations, and products built to the specifications are expected to deliver the higher symmetrical bit rates associated with full duplex operation. Now, coaxial cable networks won’t be a limiting factor in getting to full duplex and the next generation of broadband services.
Now that CableLabs has developed FDX DOCSIS specifications (now a part of DOCSIS 4.0 technology), members can move forward with this exciting technology. Members can further benefit from the Kyrio testing services that provide all the engineering expertise and lab equipment needed for testing FDX DOCSIS (now a part of DOCSIS 4.0 technology). All the operator has to do is identify network segments where the work is to be performed.
What’s Coming in 2019
Getting back to the lab (which is a lot dryer and warmer than some of the outside plant scenarios where CableLabs has worked), CableLabs is:
- Hosting lab activities to support the development and interoperability of FDX DOCSIS (now a part of DOCSIS 4.0 technology) products
- Bringing back important discoveries from the field testing into the labs to support testing in real-world situations and scenarios.
- Building the lab infrastructure needed to rigorously analyze performance and reliability in a variety of configurations
CableLabs and the cable industry are continuing to advance cutting-edge developments in cable broadband networks to remain ahead of consumer demand. The focus is on developing innovative network technologies, as well as defining optimal network architectures that provide the necessary capacity and performance in each network segment for multi-gigabit services today and in the future.
You can learn more about Full Duplex DOCSIS technology (now a part of DOCSIS 4.0 technology) and the 10G platform by clicking below.
Proactive Network Maintenance (PNM): Are You InGeNeOS?
I love a good acronym! InGeNeOS™ is an acronym built from Intelligent General Next Operations Systems. It’s the name of a CableLabs working group that solves Proactive Network Maintenance (PNM) issues for the cable industry, and it might be for you.
What’s So InGeNeOS about PNM?
The InGeNeOS group focuses on discussing, inventing, building and sharing network operations tools and techniques from the data made available from DOCSIS® systems, including the CM, CMTS and test devices. Other CableLabs working groups focus on DOCSIS specifications, and the SCTE Network Operations Subcommittee Working Group 7 focuses on network operations training material. The InGeNeOS group connects these two worlds and turns the network information into capabilities that engineers and technicians can use to maintain services. We turn DOCSIS system information into solutions that identify, diagnose and sometimes automatically correct network problems—often before the customer notices. When these tools get good enough, they can become proactive. Thus, we often refer to this group as the PNM Working Group (WG). See why we put it into an acronym?
Don’t Just Think—Do!
This group doesn’t merely ponder PNM solutions; it is very active in several ways:
- Developing best practices for PNM solutions—We just started an effort to document PNM best practices in a DOCSIS 3.1 environment.
- Guiding specifications development for emerging technologies—For example, although Full Duplex (FDX) DOCSIS technology is not yet deployed, we know it must be fully ready when it is, and that includes being operationally supportable.
- Sharing experiences, both problems and solutions—Many working group participants work maintenance problems at operator companies, or for operators, so they bring problems to the working group to get ideas for causes and resolutions.
- Testing theories in the lab—Once we develop theories about the causes of problems in the field, we reproduce the theorized conditions in the lab to confirm the cause. We can also calibrate measurements, test methods for detection and develop new PNM tools and methods based on these tests.
This developing, defining, knowledge sharing and testing help operators reduce costs and improve service reliability by improving their network maintenance operations. All these are just examples of what we do. If you have ideas that might fit within this framework, keep reading.
So You Think You’re InGeNeOS?
Operators in—and vendors supporting—the cable industry can easily benefit from joining the InGeNeOS group:
- If you are a cable operator and a CableLabs member, consider this your invitation to join.
- If you are a cable operator but not a member, this is a very good reason to become a member.
- If you are a vendor, all you need to do is sign the NDA and IPR.
In any case, contact Jason Rupe to join the InGeNeOS group.
Proactive Network Maintenance: Where Is Common Data Collection Going Next?
Welcome to 2019, and the future of Proactive Network Maintenance (PNM)! As CableLabs’ PNM solutions mature, we look toward developing a framework for PNM that everybody can use.
On December 21, 2018, CableLabs released the Combined Common Collection Framework (XCCF) version 2.0. This new version includes several enhancements, including refactoring to make it easier to work with and tuning to support new use cases. If you are in the PNM club and receive the monthly reports, you’ve seen some of these enhancements over the past 6 months:
- In July, the XCCF team solved many encountered cable modem (CM) stability issues associated with polling. We also created methods to purge and maintain files in the cache, and to allow better load management.
- In August, we added additional scalability enhancements, multiple formats for outputs, listing abilities, read or write (RW) and read-only (RO) strings, and we introduced code to support the new 10th PNM measurement.
- As of September, the XCCF includes a data archiver function to allow users to manage and save space on the application program interface (API).
- As of October, the XCCF includes a method to manage host machine performance, as well as the ability to separately manage read and write strings. We have also significantly optimized query time and further hardened and enhanced it for greater performance as part of the Gridmetrics™ project.
- In November, the XCCF team added improved CM polling, a few back-end improvements, a CM events driver and better spectrum analysis handling in a new driver.
- In December, final touches to version 2.0 of the XCCF included an ability to receive traps from CMs and converged cable access platforms (CCAPs), and store them. A considerable amount of code was refactored to decouple data storage from the rest of the code so that users can swap out the data storage with their favorite database or alternative method.
CableLabs is using the XCCF for several use cases, including PNM, Gridmetrics™, Profile Management, LTE ingress detection and general network monitoring needs. We envision several use cases beyond those already identified and have demonstrated effectiveness for many of these:
- CM testing: This is the purpose of the Cable Modem Validation Application (CMVA). We found it useful for validating chip and CM builds for PNM, for modem testing in an operator’s lab setting, and for streamlining testing such as the acceptance test plan (ATP) for certification. We also found it useful for the next use case.
- Developing PNM methods: The convenience of the CMVA, coupled with XCCF, makes it useful for a lot of basic data visualization needs, including experimenting with detecting impairments. The PNM working group used it to capture output from testing while reproducing observations from the field and discovering the effectiveness of some measurement methods. CableLabs is using it to guide our development of the next use case.
- PNM ApplicatioN Environment (PNMANE): CableLabs will be developing an environment for PNM applications that sit on top of XCCF.
- Gridmetrics™: XCCF collects machine data, so why not collect voltage measurements from power supply modems? We did exactly that, and it works very well. Now, operators can use their network to monitor power levels they receive, and thus provide out-of-band measurement of the power grid to support power companies.
- Profile management: The profile that a CM uses dictates much of the quality of experience that a customer enjoys. XCCF collects the information needed from the network to enable optimizing the profiles that the CMs use, thus enhancing service performance and experience.
- LTE ingress detection: Spectrum analysis and receive modulation error ratio (RxMER) data, as well as other PNM measures, can reveal ingress, including LTE. CableLabs has a method for detecting these issues, which can inform not only PNM activity but also the placement of small cells, and report on overall network health for such an endeavor.
- General network monitoring and operations: Northbound data collection on any network device is possible in the same manner as supported by XCCF. A whole world of possibilities exists here. Fortunately, the XCCF is suited to evolve to new methods of machine data collection and is set to protect the network from over-polling, too.
- Service protection automation in Software Defined Networking (SDN): Many SDN solutions lack access to the network data required to adjust network conditions for an automated response to network impairments and other conditions. The XCCF can provide useful information northbound to applications that can protect against failures, develop traffic engineering solutions or analyze and define solutions for network risk.
We expect use cases to drive how we support the XCCF into 2019, and this is where you all come in.
Please comment below or contact us to share your use cases and experiences with using the XCCF and CMVA, or where your PNM needs are headed. Many operators and vendors have requested access to download and install the XCCF, as well as CMVA, and we hope and expect that everyone has been getting good use out of them.
CableLabs needs feedback to continue supporting projects, so we need your input. Please let us know how you’ve been using the XCCF or CMVA, particularly how you’ve gained value for your company or the industry overall. Anything you can share is helpful, no matter how brief or minor you might think it is. Your input will help drive future development of XCCF, CMVA and our current efforts, including PNMANE.
The Profile Management Application: Optimizing DOCSIS® 3.1 Networks
Cable operators are broadly deploying DOCSIS 3.1 technology around the world. Operators in North America and Europe have announced gigabit service offerings that use the technology across their footprint. In this blog, I focus on techniques by which operators can boost the capacity and robustness of their existing DOCSIS 3.1 network.
Introducing Toolsets for Optimizing the DOCSIS 3.1 Network
DOCSIS 3.1 specifications introduced orthogonal frequency division multiplexing (OFDM) technology to the access network. In DOCSIS 3.0 and prior technologies, a single-carrier downstream channel (6 MHz) would be configured with just the one modulation order (say, 256-QAM). The DOCSIS 3.1 technology divides a wider (e.g. 192 MHz) channel into a number of small subcarriers spaced at 25 kHz or 50 kHz apart, creating up to 7600 subcarriers. These subcarriers can be individually configured to operate at a different modulation order, anywhere from 256-QAM, to 1024-QAM, all the way to 4096-QAM.
A specific configuration of modulation orders for every subcarrier in the OFDM channel is known as a “profile.” A cable modem termination system (CMTS) can use multiple profiles on a channel; profiles differ in the modulation orders assigned to each subcarrier.
Different modems experience the network in different ways. Some modems may have a noisier environment, whereas others see a relatively clean plant. The figure shows an example of the interference seen by a modem in part of the OFDM channel.
Profiles allow the channel to operate at a higher modulation order in clean parts of the spectrum and then go down to more robust modulation orders when there is any interference present. The idea with multiple profiles is to have the CMTS use different profiles for such different groups of cable modems. This allows the operator to reach two goals:
- minimize transmission errors on the network and
- maximize network capacity.
The same concept applies to upstream OFDMA channels, where one can create upstream profiles for the channel, to increase reliability and throughput.
The Profile Management Application (PMA) Solution
If there are say 4 OFDM channels per port, 10 ports per line-card, and 10 line-cards on a CMTS, then there could be easily over a couple of million subcarriers requiring a specific configuration! This represents an immense configuration challenge which cannot be solved manually. This problem is made more difficult because profiles are not typically “one size fits all,” but rather they need to be tailored to the set of cable modems on the channel, the interference on the channel, and they also need to adjust to plant changes over time. The question then becomes: What is the most efficient method for automating the creation of multiple profiles to maximize robustness and capacity?
I am pleased to announce that CableLabs has met this tremendous challenge with the introduction of the Profile Management Application (PMA). The PMA creates a set of optimal profiles for each channel and assigns profiles to modems. And the PMA accomplishes this dynamically by proactively reading data collected from the network. The PMA can create optimized modulation profiles periodically, as well as backup profiles in case of errors. It can also intelligently decide when to roll out profile changes to the network. A single PMA instance can create and configure profiles for a number of CMTSs in a short period of time and help the operator understand the data capacity of each channel.
How It Works—PMA Architecture and Algorithms
CableLabs released a PMA Technical Report that describes the PMA architecture, use cases, and interface definitions. We also developed data models (YANG) and protocols to facilitate the design of a software application to configure and manage modulation profiles.
Determining the optimal set of modulation profiles to use on a DOCSIS 3.1 channel is a task for intelligent software, given the number of modems, the number of subcarriers and the differences in signal quality across the channel each modem experiences. This CableLabs paper on profile management algorithms describes methods to optimally compute the profiles. The paper also introduces a metric indicating the capacity gain a set of profiles obtains compared with running all traffic at 256-QAM. The key idea is to use clustering algorithms to group modems that have similar signal-to-noise signatures across the channel and then design a profile for each group. The PMA algorithm searches for the best set of profile definitions to maximize the overall capacity and at the same time keeps the individual profiles robust to observable interference patterns.
Some of the information that a PMA needs to compute the profiles includes the channel information from a CMTS, list of modems and network signal quality metrics (mainly, each modem’s per subcarrier RxMER data). Also using performance data (e.g., codeword error rates), a PMA can further refine the profiles.
How It Works—Deployment
A PMA field deployment would include the following:
- Data Collection: A centralized server is needed for modems and CMTSs to upload signal quality data. Operators can use the CableLabs DOCSIS Common Collection Framework (DCCF) to implement this.
- PMA: Using the data collected, this application creates optimized profiles per channel. It configures these profiles on the CMTS, assign CMs to profiles and can initiate performance tests.
- CMTS: Configures profiles for the individual channels, assigns the modulation profiles to CMs and ultimately sends/receives data using the profiles.
- CMs: Cable Modems use the profiles defined and assigned by the CMTS to receive/send data.
What’s Next? PMA Software Available
CableLabs has developed network-deployable software that operators can integrate and use within their DOCSIS 3.1 access network. This PMA solution can use the data generated by the network devices and create optimized OFDM/OFDMA profiles while considering different capabilities supported across CMTS platforms. The software is capable of calculating profiles for a channel with around 200 CMs in ~30 msecs using a single CPU process, so it is easily scalable across an operator’s network. Many operators are testing and planning PMA deployment using this solution framework. PMA is available via CableLabs C3. Contact us to try it out. (Watch for an upcoming video blog on this topic.)
Gains from PMA
A PMA will help increase the throughput per cable modem and maximize network capacity by optimizing the bit-loading of the subcarriers within a channel. Designing profiles around noisy areas in the plant make the system operation more robust. The bandwidth gains in running a well-designed set of profiles can be anywhere from 15% to 40% capacity increase on a channel, compared with running the whole channel at 256-QAM. This can translate to a solid 200 to 400 Mbps extra capacity on each OFDM channel! This enables an operator to match growing bandwidth demands and defer potential node-splits and new equipment costs.
With this profile management technology, operators can realize the full potential of their DOCSIS 3.1 network, by minimizing transmission errors and maximizing the data capacity of the OFDM/OFDMA channels.
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