In the United States, Telenet and Tymnet have been two this kind of packet networks. Neither supported host-to-host communications; within the nineteen seventies this was however the province of the exploration networks, and it will stay so for a few years.Khi công ngh??phát tri?n và c? h?i th??ng m?i thúc ??y t?ng tr??ng ??i ?ng, kh?i l??ng l?