SIP

SIP (Session Initiation Protocol) is the signaling protocol that establishes, modifies, and terminates communication sessions over IP networks: it's what makes a softphone ring, what negotiates the call between two parties, what transfers it and hangs it up. An open standard from the 1990s (IETF), it became the common language of internet telephony — every VoIP call you make is, somewhere, a SIP handshake.

Its concrete consequence for a business: SIP telephony decouples the number from the hardware. A SIP account is identified by an address (sip:name@domain) and works on any device — physical handset, mobile app, software switchboard — and with any compatible carrier. In France, the phased closure of the switched telephone network (the historic PSTN) has definitively moved business lines to SIP: the question is no longer whether you switch, but with which carrier.