The right (straight) cable allows remarkable choices. Bill Bittencourt startled the G.fast Summit with new results from the lab and the field. They said it couldn't be done, but Calix customers are proving it is possible to use multiple DSLAMs. Instead of being limited to 16-24 G.fast customers, that can be doubled and possibly tripled. In early testing, the second DSLAM resulted in less than a 2% loss. Many North American buildings have straight cable – otherwise known as CAT1 or “station wiring” – from a distribution point to each unit. Geoff Burke explains, "In essence, what this means is that typical MDUs have insulated wiring from the Distribution Point to the unit, which greatly minimizes cross talk and loss.
Thus, given the physical isolation from cross talking pairs, multiple DPUs can be deployed without the need for cross-unit vectoring. VDSL2 and G.fast have minimal interference over in-building cabling.
My six story building has about 55 apartments, all connected to one box in the basement. If we had straight cable, every apartment could have 500-800 megabits, uncontested, from fiber to the basement.
On straight cable, each customer gets an additional 50-100 megabits because VDSL interference is minimal. Most G.fast deployments reserve (notch out) the first 19-21 MHz of prime spectrum to protect VDSL. That's proving unnecessary in these buildings.
Calix built a test bed in the laboratory, simulating a three story, 32 unit MDU building. Receiver distances were between 20 & 100 meters. (Diagram below.) The lab results confirmed what Calix customers were seeing in the field.
"Conventional wisdom was completely wrong," Bill concluded.