Which of the following protocols enables an amateur station to transmit through a repeater without using a radio to initiate the transmission?
Why EchoLink is VoIP software that runs on a computer or smartphone, so a licensed operator can log in over the internet and key a distant repeater or link node without any RF transmitter of their own. The audio travels over the internet to the node, which then transmits it on the air. This is why EchoLink requires license validation before an account is activated.
Watch out IRLP is the tempting one because it also links repeaters over the internet, but IRLP is strictly node-to-node: every user must access the system with a real radio. D-STAR and DMR are digital voice modes, not internet access methods.
EchoLink = echo from your PC or phone; IRLP = radio link only.