Along with the announcement of faster download speeds, the company is claiming new upload speeds of as much as 200 Mbps – at least for the 2 Gbps plan. The press release made it sound like all upload speeds would be increased by five to ten times the existing speeds, and today’s blog looks at what it would take for a cable company to increase upload speeds across the board.
Interestingly, the same press announcement said that Comcast would be introducing DOCSIS 4.0 in 2023, at least for some business customers. That’s an announcement that has me scratching my head. Comcast just announced a successful test for DOCSIS 4.0 in January of this year. To be able to go from a lab prototype to production units in less than two years would be extraordinary. The normal time to market for a major new technology is five or six years. I’m skeptical about the announcement and wonder if this is aimed at Wall Street more than any actual technology plan. The company has been asked non-stop about DOCSIS 4.0 for several years, and maybe this announcement is taking advantage of that hype. Comcast could hold a field trial of the new technology next year and still meet this promise.
But cable companies have another option to get faster upload speeds. A cable network is essentially a captive radio network inside of the coaxial cable. Cable networks don’t all have the same total bandwidth, and most of the big cable company networks have total bandwidth of either 1 GHz or 1.2 GHz. The total bandwidth has to be shared between video channels and broadband.
Most existing cable companies have allocated bandwidth between download and upload using something called the sub-split. This assigns a relatively small amount of frequency between 5 MHz and 42 MHz for upload. On top of being a small swath of throughput, this is also the part of the spectrum that suffers from external interference. This combination results in both relatively slow upload speeds and also variable speeds due to interference – something most cable customers are aware of.
There are two additional configurations for allocating upload speeds. A mid-split configuration uses the spectrum between 5 MHz to 85 MHz for upstream. In a high-split, the upload is enhanced by using the spectrum up to 204 MHz. DOCSIS 4.0 will provides multiple options for upload bandwidth with possible spits at 300 MHz, 396 MHz, 492 MHz, and 684 MHz.
If Comcast is going to improve bandwidth in the near future, it will have to implement one of the larger DOCSIS 3.1 splits. There is a cost for moving to a different split. There must first be enough room available for video channels and download bandwidth. It can be expensive if the entire bandwidth of the network must be increased. That can mean replacing amplifiers and other outside electronics, and even some coax. In most cases, the existing customer modems would need to be replaced unless already configured to accept the different split.
At the recent SCTE Cable-Tec Expo, CommScope, Vecima, and CableLabs said there are plans for a different upgrade path for the DOCSIS 3.1 higher splits. They are claiming new ‘turbocharged’ modems that will add more effective upload bandwidth capability. I’ve not heard of any field trials of the new modems, and perhaps this is what Comcast has in mind by the end of 2023.
Cable companies are sensitive about the marketing advantage that faster upload speeds give to fiber and even to slower technologies like FWA cellular wireless. It’s hard to know if the Comcast announcement foreshadows big improvements next year or was just a way to signal to Wall Street that cable companies are working towards improved bandwidth. It’s inevitable that faster upload bandwidth is coming – the big questions are when and how much faster.