With circuit switching a（     ）path is established between two stations for communication . Switching and transmission resources within the network are（     ） for the exclusive use of the circuit for the duration of the connection . The connection is （     ）：Once it is established ，It appears to attached devises as if there were a direct connection.
Packet switching was designed to provide a moreefficient faciltiy than circult switching for（     ） data tratffic. Each packet contains some portion of the user data plus control information needed for proper functioning of the network.
A key distinguishing element of packet_switching networks is whether the internal operation is datagram or virtual circuit . With internal virtual circuits,a route is defined between two endpoints and all packets for that virtual circuit follow the（     ） route, With internal datagrams,each packet is treated independently,and packets intended for the same destination may follow different routes.