Internet linking uses voice over IP (VoIP) to connect amateur stations that are far apart. A gateway (a node with a radio on one side and an internet connection on the other) lets a signal heard on one repeater be played out of another on the far side of the world, or from a phone with no radio at all.
A gateway is a station that connects radio to the internet.
Three long-standing systems do this for analog voice. They differ in who can join, and how you control them.
Two shapes
A node can be a repeater, a simplex radio on a gateway, or in some systems just software on a computer or phone.
A link can join two nodes, one conversation at a time, or many nodes at a hub, where everyone hears everyone. All three systems can do both in some form; each leans one way.
EchoLink, IRLP and AllStar
EchoLink
IRLP
AllStar
Need a radio?
No: PC or phone software works
Yes: a radio node
Yes for a radio node; software clients exist
Control
Software menu; DTMF from a radio
DTMF tones from the radio
DTMF commands and scripts
A node is
Software, with or without a radio interface
A dedicated computer and radio
Open-source software on a small computer and radio
Leans toward
Individual users reaching nodes and conferences
Node-to-node links and shared reflectors
Networks of many linked nodes
EchoLink is a free software system you run on a computer or phone. You register your call sign and provide proof of license; then you can connect to a gateway repeater without a radio.
IRLP (Internet Radio Linking Project) connects radio systems, such as repeaters, over the internet. Over the air, you dial a node using DTMF tones.
AllStar is built on Asterisk, open-source telephone-exchange software, so nodes can be linked together in flexible ways. Many hobbyists run one on a small computer.