Tag Archives: DOCSIS 4.0

How Will Cable Companies Cope with COVID-19?

A majority of households today buy broadband from cable companies that operate hybrid coaxial fiber networks (HFC) that us some version of DOCISIS technology to control the networks. The largest cable companies have upgraded most of their networks to DOCSIS 3.1 that allows for gigabit download speeds.

The biggest weakness in the cable networks is the upload data links. The DOCSIS standard limits the upload path to me no larger than 1/8th of the total bandwidth uses – but it’s not unusual for the cable companies to make this path even smaller and offer products like 100/10 Mbps where the upload is 1/11th of the total bandwidth provided to customers.

This is not a new concern for the cable companies and the engineering folks at Comcast and other big cable companies have been discussing ways to improve upload bandwidth for much of the last decade. They understood that the need for uploading would someday overwhelm the bandwidth path provided – they just didn’t expect to get there so explosively as been done in reaction to the COVID-19 crisis.

Every student and employee trying to work from home is carving out an uploaded VPN when they connect to a school or work server. Customers are also using significant upload bandwidth when they join a video call on Zoom or other platforms. While carriers report 30–40% overall increases in traffic due to COVID-19, they are not disclosing that a lot of that increase is demand for uploading.

Cable companies are now faced with solving the upload crisis. Practically every prognosticator in the country is predicting that we’re not going to return to pre-COVID behavior. There is likely to be a lot of people who will continue to work from home. While students will return to the classroom eventually, this grand experiment has shown that’s it’s feasible to involve students in the classroom remotely, and so school systems are likely to continue this practice for students with long-term illnesses or other reasons why they can’t always be in the classroom. Finally, we’ve taught a whole generation of people that video meetings can work, so there is going to be a whole lot more of that. The day of traveling to attend a few hour meeting might be over.

There is one other interesting fact to consider when looking at a cable company upload data path. Cable companies have generally devalued the upload path quality and have assigned the upload path to the low frequencies on the cable network spectrum. Historically upload data speeds were provisioned on the 5-42 MHz range of spectrum. This is the spectrum in a cable system that experiences the most interference from things like microwave ovens, vacuum cleaners and passing large trucks. Cable companies could get away with this because historically most people didn’t care if it took longer to upload a file or if packets had to be retransmitted due to interference. But people connecting to WANs and video conferences care about the upload quality as well as speed.

One solution, and something that some cable providers have already done is to do what is called a mid-split upgrade that extend the spectrum for uploading to the 5-85 MHz band. This still includes a patch of the worst spectrum inside the cable system, but is a significant boost in the amount of upload broadband available. Depending upon the settop boxes being used, this upgrade can require some new customer boxes.

Another idea is to do more traditional node splits, meaning to reduce the number of customers included in a neighborhood node. Traditionally, node splits were done to improve the performance of download speeds – this was the fastest way to relieve network congestion when a local neighborhood network bogged down unduly in the evening. It’s an interesting idea to consider splitting nodes to relive pressure on the upload data path.

After those two idea the upgrades get expensive. Migrating to switched digital video could free up a mountain of system bandwidth which would allow for a larger data path, including an enlarged upload path. The downside of this kind of upgrade is that it moves outside of the DOCSIS technology and starts to look more like providing Ethernet over fiber. This is not just a forklift upgrade it changes the basic way the network operates.

The final way to get more upload speed would be an upgrade to the upcoming DOCSIS 4.0 standard. Everything I read about this makes it sound expensive. But the new standard would allow for nearly symmetrical data services and would let cable network broadband compete head-on with fiber network. It will be interesting to see if the cable companies view the upload crisis as bad enough to warrant spending huge amounts of money to fix the problem.

10 GB Cable Broadband?

CableLabs recently put the finishing touches on the new DOCSIS 4.0 standard – the latest standard for delivering broadband across hybrid fiber-coaxial networks. The changes are intended to make cable networks more competitive with fiber networks – although it’s unlikely that we’ll see anybody use the full capacity of the new standard.

Following are the benefits promised by CableLabs in the DOCSIS 4.0 press release:

Speeds up to 10 Gbps. This capability isn’t quite what it seems. The current DOCSIS 3.1 standard already allows speeds up to 5 Gbps and no cable company is delivering superfast speeds because it’s not practical. The only way to achieve 5 – 10 Gbps broadband would be to remove most or all of the channels of TV signal from the system.

Cable systems could consider upgrading to speeds faster than 1 Gbps if they make another costly upgrade of migrating to IP video. Today a cable company sends all TV channels to every customer and blocks the channels that are not subscribed. An IP video system, which is used on DSL and fiber networks only sends a customer the channel they are watching. Such a migration would free tremendous bandwidth within the network but would mean replacing the cable headend and all settop boxes.

Faster Upload Speeds. DOCSIS 4.0 will be able to deliver as much as 6 Gbps upload speeds to go along with the 10 Gbps download speeds. This would allow a cable company to offer a symmetrical 1 Gbps bandwidth product – something that is not possible today and that puts cable networks at a marketing disadvantage compared to fiber. The current DOCSIS 3.1 technology provides for one-tenth of the download speed to be provided as upload – meaning a 100 Mbps download product typically has a 10 Mbps upload speed. Interestingly, many cable products today don’t even use the full 10% upload allotment and assign more bandwidth instead to download.

Improved Reliability. CableLabs is pushing higher reliability as part of the DOCSIS 4.0 upgrade. This will be done using new software they’ve labeled as Proactive Network Maintenance (PNM) that will use increased monitoring and machine learning to identify network problems earlier. However, this technology will become available with DOCSIS 3.1 as well and doesn’t require an upgrade.

Better Security. CableLabs is also touting increased security through a software suite labeled as Micronets. This will allow the cable operator to isolate different parts of the network into separate trust domains so that a problem in one part of the network doesn’t infect the rest of the network. That’s an interesting concept that would also benefit fiber networks.

Low Latency. The last touted benefit of DOCSIS 4.0 is lower latency. There is no way to improve the native latency across a coaxial cable network, so the improved latency comes as a result of a bit of smoke and mirrors. A given customer, such as a small cell site in a residential neighborhood could be given the best possible latency by giving it traffic a priority over all other traffic. This was exactly what net neutrality was supposed to protect against and residential customers in that neighborhood would likely be highly dismayed to know that connection problems are due to the cable company selling priority bandwidth to AT&T in the neighborhood.

Expanded Use of Spectrum. The extra bandwidth for DOCSIS 4.0 comes from the expansion of the frequencies used inside the coaxial cable. Coaxial networks function like a captive radio system inside of the coax and DOCSIS 4.0 expands the usable spectrum on the cable to 1.8 GHz – most cable networks today use 1 to 1.2 GHz of spectrum.

What’s not mentioned in the press releases is the cost. Expanding the spectrum likely means replacing amplifiers and possibly even power taps in the cable network. Using the new spectrum and standard means a swap-out of cable modems. It’s possible in some networks that moving to the increased spectrum will also mean replacing older or frail coaxial cable in the network.

So far, no major cable company has said that they are interested in this upgrade. However, cable companies are under increased pressure to improve upload speeds. They don’t necessarily need to move to symmetrical speeds. However, the weakness of upload bandwidth in cable networks have been highlighted as millions of people try to connect to work and school servers from home during the COVID-19 crisis – I’ve seen more demand for faster upload speeds in the last few weeks than I can ever remember in the past.

The Future of Coaxial Networks

My blog devotes a lot of time looking at fiber deployment, but since the majority of people in the US get broadband from cable companies using hybrid fiber/coaxial (HFC) technology, today’s blog looks at the next generation of changes planned for HFC.

DOCSIS 4.0. The current generation of HFC technology is DOCSIS 3.1 This technology uses 1.2 GHz of spectrum over coaxial cable. DOCSIS 3.1 has several competitive drawbacks compared to fiber. First, while the technology can deliver gigabit download speeds to customers, the dirty secret of the industry is that gigabit speeds can only be given to a limited number of customers. With current node sizes, cable companies can’t support very many large data users without sacrificing the performance of everybody in a node. This is why you don’t see cable companies pricing gigabit broadband at competitive prices or pushing it very hard.

The other big drawback is that upload speeds on DOCSIS 3.1 are set by specification to be no more than one-eighth of the total bandwidth on the system. Most cable companies don’t even allocate that much to upload speeds.

The primary upgrade with DOCSIS 4.0 will be to increase system bandwidth to 3 GHz. That supplies enough additional bandwidth to provide symmetrical gigabit service or else offer products that are faster than 1 Gbps download. It would also allow a cable company to support a lot more gigabit customers.

The big drawback to the upgrade is that many older coaxial cables won’t be able to handle that much bandwidth and will have to be replaced. Further, upgrading to 3 GHz is going to mean replacing or upgrading power taps, repeaters, and other field hardware in the coaxial network. CableLabs is talking about finalizing the DOCSIS 4.0 specification by the end of 2020. None of the big cable companies have said if and when they might embrace this upgrade. It seems likely that many of the bigger cable companies are in no hurry to make this upgrade.

Low Latency DOCSIS (LLD). Another drawback of HFC networks is that they don’t have the super-low latency needed to support applications like intense gaming or high-quality video chat. The solution is a new encoding scheme being called low latency DOCSIS (LLD).

The LLD solution doesn’t change the overall latency of the cable network but instead prioritizes low-latency applications. The result is to increase the latency for other applications like web-browsing and video streaming.

This can be done because most of the latency on an HFC network comes from the encoding schemes used to layer broadband on top of cable TV signals. The encoding schemes on coaxial cable networks are far more complex than fiber encoding. There are characteristics of copper wires that cause natural interference within a transmission path. A coaxial encoding scheme must account for attenuation (loss of signal over distance), noise (the interference that appears from external sources since copper acts as a natural antenna), and jitter (the fact that interference is not linear and comes and goes in bursts). Most of the latency on a coaxial network comes from the encoding schemes that deal with these conflicting characteristics. The LLD solution bypasses traditional encoding for the handful of applications that need low latency.

Virtual CMTS. One of the more recent improvements in coaxial technology was distributed access architecture (DAA). This technology allows for disaggregating the CMTS (the router used to provide customer broadband) from core routing functions, meaning that the CMTS no longer has to sit at the core of the network. The easiest analogy to understand DAA is to consider modern DSLAM routers. Telephone companies can install a DSLAM at the core of the network, but they can instead put the DSLAM at the entrance to a subdivision to get it closer to customers. DAA allowed cable companies to make this same change.

With virtual CMTS a cable network takes DAA a step further. In a virtual CMTS environment, the cable company might perform some of the CMTS functions in remote data centers in the cloud. There will still be a piece of electronics where the CMTS used to sit, but many of the computing functions can be done remotely.

A cloud-based CMTS offers some advantages to the cable operator:

  • Allows for customizing portions of a network. The data functions provided to a business district can be different from what is supplied to a nearby residential neighborhood. Customization can even be carried down to the customer level for large business customers.
  • Allows for the use of cheap off-the-shelf hardware, similar to what’s been done in the data centers used by the big data complies like Google and Facebook. CMTS hardware has always been expensive because it’s been made by only a few vendors.
  • Improves operations by saving on local resources like local power, floor/rack space, and cooling by moving heavy computing functions to data centers.

Summary. There is a lot of discussion within the cable industry asking how far cable companies want to push HFC technology. Every CEO of the major cable companies has said that their eventual future is fiber, and the above changes, which each bring HFC closer to fiber performance, are still not as good as fiber. Some Wall Street analysts have predicted that cable companies won’t embrace bandwidth upgrades for a while since they already have the marketing advantage of being able to claim gigabit speeds. The question is if the cable companies are willing to make the expensive investment to functionally come closer to fiber performance or if they are happy to just claim to be equivalent to fiber performance.