G.fast is an acronym for Fast Access to Subscriber Terminals and its main purpose is just that--to get higher speeds from digital subscriber lines (DSLs). It is modeled on Very-high-bit-rate digital subscriber line 2 (VDSL2) which was designed to get high-speed data over the copper telephone wires already in older buildings (VDSL2 was defined as standard ITU-T G.993.2 in 2005.) The only thing exotic about G.fast is its promise of 200-to-500 megabit per second speeds for DSL.
It seems the spectral efficiency without bonding (1 pair) is 5.7 bps/Hz, while with bonding (2 pairs) it is 10 bps/Hz. What's the catch? Distance (70m vs. 30m)? I would still not expect such a big difference.
I asked your question ("What's the catch?") to the Bell Labs experts and this is what they said: "Distance is one part of the answer; we're also doing some undisclosed optimizations to get the most out of the 2-pair/30m case."
What are the engineering and design challenges in creating successful IoT devices? These devices are usually small, resource-constrained electronics designed to sense, collect, send, and/or interpret data. Some of the devices need to be smart enough to act upon data in real time, 24/7. Are the design challenges the same as with embedded systems, but with a little developer- and IT-skills added in? What do engineers need to know? Rick Merritt talks with two experts about the tools and best options for designing IoT devices in 2016. Specifically the guests will discuss sensors, security, and lessons from IoT deployments.