virtual circuit and datagram networks connection, connection-less service 데이터그램 네트워크 → connectionless service virtual-circuit network → connection service Network layer vs Transport layer (ex: Internet) Network layer vs Transport layer Host-to-host Service Process-to process Only one Choice(인터넷 프로토콜) Connection(TCP) and Connectionless(UDP) End-system and NW Core Implementation End-system Only Ab..