Which technology utilizes bandwidth above the POTS range in existing PSTN copper loops?

The correct answer is DSL, or Digital Subscriber Line, which is specifically designed to utilize the existing copper telephone lines of the Public Switched Telephone Network (PSTN). DSL technology transmits data by exploiting the bandwidth that is above the traditional Plain Old Telephone Service (POTS) range, which typically covers frequencies up to 4 kHz.

DSL achieves this by using a wider frequency range to carry higher frequencies for data transmission, thus allowing users to access high-speed Internet services while still permitting simultaneous voice calls over the same line. This dual-use capability is a significant advantage of DSL technology, as it helps maximize the utility of existing infrastructure without requiring new wiring.

In contrast, while Ethernet operates primarily over twisted-pair cabling and fiber optic cables, and is not limited to existing copper PSTN lines, it does not specifically utilize the bandwidth above POTS on those lines. ISDN, or Integrated Services Digital Network, also makes use of existing copper lines, but it does not specifically target the bandwidth above the POTS range in the same manner as DSL. Fiber optics, on the other hand, requires a completely different set of infrastructure and does not utilize PSTN copper at all, instead offering much greater bandwidth capabilities through glass or plastic fibers.