The reverse path is finally getting some love


(It’s about time!)

One of our industrial obsessions is the state of the “upstream” or “reverse” path -- the passageway that moves digital stuff away from you / your house. “Two-way” communications can’t exist without it. Mostly, and until recently, the reverse path moved relatively tiny things: Your side of a phone call, or your click, to request a web page. Little things, compared to what barrels down the “downstream” / “forward” path, to you. 

The relative dearth of stuff moving upstream from our devices, out to the Internet, is exactly why it hasn’t been an issue, so far, that the reverse path is a tiny 5 percent of total available capacity -- or about 100 Megabits per second, total. Nor that it’s located in a quirky, noisy corridor of RF spectrum (down at the bottom, between 5-52 MHz.)

But! Raise your hand if you have a WiFi connected webcam in your home/business. Probably two, right? One inside (to spy on the dog when you’re at work), one outside (to see who’s at the door.) Webcams generate video streams; video is big. Facetime, WhatsApp, and all other WiFi/IP-sourced video chat applications fall into this same category. It’s a category called “too much of this could cause upstream congestion.” 

Which is why more and more operators are doing the unthinkable: Widening the upstream path. Why did it used to be unthinkable? Lots of reasons -- the expense (high, if done in isolation); the operational impact (heavy); the fact that the spectrum right “above” it (above 54 MHz) used to be occupied (and thus protected) by off-air broadcast television. 

These days, operators thinking about taking fiber deeper, for instance, are using the occasion to also widen the upstream -- some up to 85 MHz, others to 200 MHz. Plus, the next phase of the DOCSIS spec (after 3.1) involves “full duplex” technologies, which enable equivalent throughput, upstream and downstream. 

So, at long last, that skinny, stepped-on signal path is getting some respect. ​