Digital Telephone


The public switched telephone network (PSTN) has gradually evolved towards digital telephony which has improved the capacity and quality of the network. End-to-end analog telephone networks were first modified in the 1960 by upgrading transmission networks with T1 carrier systems, designed to support the basic 3 kHz voice channel by sampling the bandwidth-limited signal voice analog and encoding using PCM. While digitization allows wideband voice on the same channel, the improved quality of a wider analog voice channel did not find a large market in the PSTN.

Subsequent transmission methods such as SONET fiber optic transmission and more advanced digital transmission. Although the systems support multiplexed analogue exists several voice channels on a single carrier analog transmission, digital transmission has a lower cost and more channels multiplexed on the transmission medium. Today, the final instrument often remains analog but the analog signals are typically converted to digital signals at the interface (service area (SAI), central office (CO), or other aggregation point. Carriers digital Loop (DLC) place the digital network ever closer to the customer premises, relegating the analog local loop to legacy status.