Which of the following protocols enables an amateur station to transmit through a repeater without using a radio to initiate the transmission?

EchoLink is a unique VoIP-based amateur radio system because it allows licensed operators to connect to repeaters using a computer, tablet, or smartphone application. This means an operator can initiate a transmission over the internet without needing a physical two-way radio at their location. While systems like IRLP (Internet Radio Linking Project) strictly require an RF (radio frequency) connection on both ends of the link, EchoLink explicitly supports PC-to-radio or app-to-radio connections. D-STAR and DMR are digital radio modes that also typically require a radio to initiate a local RF transmission.