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 popular software system that allows licensed amateur radio operators to communicate with other operators or repeaters using Voice over Internet Protocol (VoIP). A unique feature of EchoLink is that it allows a user to connect via a computer or smartphone app without needing a physical radio to initiate the transmission. While systems like IRLP, D-STAR, and DMR also use the internet to link repeaters, they typically require the operator to transmit an RF signal from a radio to a local node to enter the network. EchoLink bridges the gap between purely digital devices and the RF repeater network. Therefore, if you want to talk on a distant repeater using just your smartphone or PC, EchoLink is the protocol that makes this possible.