In this case, subscribers need to have, on one side, computer with sound card and input-output audio hardware (speakers or headphones and microphone), on the other normal phone located anywhere in the world. The key is Gateway, which on one side is linked to telephone lines and can connect to any phone in the world. On the other side, the Gateway is linked to the Internet and can connect to any computer in the world. The server takes a standard phone signal, digitizes it (if it is not initially digital), significantly compresses it without any loss of quality, splits it and sends packets via the Internet using Internet protocol (TCP/IP). For packets coming from the Network to the telephone server and into outgoing phone line, the transaction is happening in reverse order. Both components of the operation (signal input and its exit from the telephone networks) are taking place practically simultaneously, which makes it possible to ensure full-duplex conversation.

Simplest method of IP-telephony (VOIP). To implement it requires two computers with sound cards and input-output audio hardware (speakers or headphones and microphone).