Telephony

Telephony is the field of technology and services for transmitting voice communication between people over a distance. Traditional telephony uses the public switched telephone network (PSTN) based on circuit-switched connections, while contemporary telephony also includes mobile cellular networks and Voice over Internet Protocol (VoIP), which transmits voice as data packets over IP networks.

Early telephony emerged in the late 19th century with the invention of the telephone and grew through electromechanical and later electronic switching systems that connected calls via dedicated circuits. The circuit-switched PSTN developed to form a global, publicly accessible network, while mobile telephony introduced wireless access and roaming.

Key technologies include signaling and control: SS7 for PSTN call setup, routing, and features; mobile networks based on GSM, CDMA, and later LTE and 5G; packet-switched VoIP using SIP or H.323; codecs such as G.711, G.729. Gateways interconnect PSTN and IP networks, enabling calling between formats.

Current telephony trends emphasize convergence, cloud-based services, and IP infrastructure. VoIP and SIP trunking enable scalable enterprise communications; mobile networks deliver high-quality voice over LTE/5G; emergency services, security, and privacy remain important considerations. Telephony continues to evolve with features like voicemail, caller ID, conferencing, and intelligent routing.