Business telephony
SIP trunk
A SIP trunk is the link connecting an organisation's telephone exchange to its operator over the internet, replacing physical lines.
It replaces a bundle of lines with a single connection whose capacity is adjusted on demand. It is the building block that made analogue lines disappear from businesses, and the one that decides whether fax still works: a trunk handling fax-over-IP transport keeps the transmission, a voice-only trunk loses it.