But old style phone regulations often require network operators to maintain and expand obsolete copper wires and TDM (time division multiplexing) switching technologies.

FORBES: "Phone" Is Just an App; Why Regulate It?

His work in this area would outline many of the fundamental principles required for digital communications, especially in regard to required sample rates and bandwidth limitations, and build upon previous ideas, like Time Division Multiplexing and early facsimile machines.

ENGADGET: Primed: digital audio basics Mobile