ORLANDO -- Finally! Someone is going to see what it takes to widen cable’s upstream path.
At last week’s SCTE Cable-Tec Expo here, attendees burrowed into an opening session featuring engineers from mid-sized operators. Massillon Cable general manager and technical operations manager Kelly Rehm made this understated but momentous declaration: “One of the projects we’re working on next year is to go to 85 Megahertz, to improve the return path.”
In the hall, an audible murmur: “Did he say what I think he said?”
Trust me: If ever you want to raise the energy level in a room full of cable engineers, ask them when they’re going to widen the upstream. Answers like, “Hopefully not in my lifetime” tend to follow.
It’s nearly a religious debate. Why? Widening the upstream is a big deal, operationally and technically. The common refrain is, it’s not for the faint of heart.
Plus, technologists and bandwidth watchers submit, the need for more upstream capacity isn’t as dire as the need for more room in the downstream, so far. That 50% yearly growth rate in broadband usage that we keep hearing about is a downstream phenomenon only.
Of all the IP-connected devices you use (smartphones, tablets, PCs, connected TVs), most activities that eat up bandwidth are downstream — towards you.
Streaming video is a classic example. Until we’re using our digital, IP gadgetry to, say, video-conference through the cable modem (as opposed to FaceTime-ing through the cellular network), or to send live video streams, it’s less of an issue.
Cable upstream basics: Spectrally slender, cable’s upstream path (which also goes by the “return” or “reverse” path) represents a scant 5% of total available bandwidth. Because of where it sits (between 5 MHz and 42 MHz), it’s riddled with different types of noise — much of it generated inside the home.
Just as you slow down when driving on a road pocked with potholes, transmitting upstream traditionally required modulation sturdiness, more so than boffo speeds.
In conversations about the new DOCSIS 3.1 specification, also unveiled here, MSOs said they would phase new, higher-order modulation and forward-error correction techniques into the downstream first. Then, if the need arises, they’ll have the tools they need to expand the upstream as well.
That’s why Massillon’s decision to experiment with widening the upper boundary of the reverse path, to an 85-MHz “mid-split,” is a big deal. Finally, we’ll see what it really takes to get ready for a wider upstream. Go Massillon!
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