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Reliability

Cable-centric Reliability

Jason Rupe
Principal Architect

Aug 29, 2019

No doubt our cable industry has a unique culture of working and innovating together to solve technical issues. But there are best practices from other communities which we can build from; these practices inform how we can continue to develop toward more reliable services. By “reliable,” as it relates to service, I mean reliable, available, and resilient services, which result from reliable, available, resilient, repairable, maintainable, and highly performing cable networks, not to mention operations focused on the customers’ needs. On the other hand, specifically used, reliability refers to the probability of not experiencing failure, whereas availability refers to the expected proportion of time that something is working as intended. These are very related, but very different things. You can read more here. But when we speak generally about reliability, often many of these like concepts are relevant.

What is Unique About Cable Relating to Reliability Concepts?

For one thing, DOCSIS® networking is unique. Each version of DOCSIS technologies improved performance, but also increased the robustness of the services it supports. Error correction, profile management, pre-equalization, echo cancelers, and other technologies have enabled this performance extension, but also these advantages create separation from the impairment and service failures, allowing for maintenance before service is impacted.

Another unique advantage is Proactive Network Maintenance (PNM). The advantages of DOCSIS technologies are what make PNM possible. We use data to find impairments in the network that, left untreated, will eventually impact service. This capability affords operators the opportunity to find and remove impairments early, before the network is further damaged by degradation, and service is impacted severely. Networks can be maintained well, but also services remain available while the network is experiencing failure.

Cable operators and vendors in cable have analog radio frequency (RF) expertise with a digital mindset. The cable industry knows RF, and that knowledge has helped it get the most out of the physical layer of the network. That deep understanding of the network’s physical layer is why mitigating network failure modes is second nature, and the industry has the needed skills.

Then there’s the industry’s “laser focus.” Pushing fiber out deeper into the network can improve reliability and availability, but current technology does lack some of the PNM advantages. There is work to do, but the capabilities are there for us to develop.

What Are the Best Practices We Can Re-use?

Designing communication networks for reliability carries many best practices and experience.

  • The ability to understand and mitigate failures before deployment – We have defined PNM use cases based on the measurements we’ve been able to define in the DOCSIS specifications. Now, we must extend that work to link to failure modes, effects, and criticality analysis, and root cause analysis, to inform technology choices, measurements for management, and design for reliability.
  • Condition based maintenance – Maintenance optimization research is clear that in any practical situation it is almost always more cost efficient to base maintenance on condition information rather than age information.
  • Prognostics and Health Management (PHM) – A newer field of reliability, PHM is a lot like our PNM. PHM is a research field of study using data sources (e.g., vibration in mechanical systems, or charge time in batteries) to determine the remaining useful life of a component or system. PNM is a clear cousin to that field, so we can certainly share and gain benefit from that work.
  • Certification testing – Certifying cable modems (CMs) has improved the PNM responsiveness of CMs, and the same can be true about cable modem termination systems (CMTSs) as that part of the network begins to align.
  • Maintenance optimization – Service reliability and availability, in addition to network reliability and availability and robustness, are important focuses for the industry; they relate, but are distinct and important in their own. The network can fail while service continues to perform at a high level, so maintenance can be better planned in this situation.

Thoughts for the Future of Cable

  • More options mean more standardization – Adding more options to the technology choices allows operators to better meet the unique needs of their customer base. However, keeping it all standardized increases operability and repairability so that service is highly reliable and available.
  • Each feature needs measurements – As we add options and features to cable technologies, each option needs special measurements to assure that the feature can be managed properly. DOCSIS 4.0 technology is full of options, so we’ll need a critical eye on each to make sure those options can be operated reliably.
  • Pushing the limits of technology requires more diligence on PNM – As we rely on tighter tolerances and more complexity on issues like upstream noise, echo cancelation, and error correction, we need more information about how those perform, and more diligent PNM practice relating to them.
  • Impairments relate to capacity and network resilience – As capacity becomes a stronger focus, the impact of impairments on that capacity becomes more important, so cable network reliability is entwined.
  • As we push higher capacity to the edge, redundancy must come with it – With more capacity comes more critical services, and more impact to the lives of customers. A failure becomes more impactful as a result. Then, as the cost of a failure increases, large failures become more expensive, driving the need for more network resiliency, and thus more redundancy.

Strong Foundation, Strong Future

Building on a strong foundation of PNM and DOCSIS technologies, the cable industry has the right culture and technology foundation to take communications to a reliable future. We have lots of work to do, but we’re on the right path to do it. Here we go!


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