At one time, the term network meant the set of serial lines used to attach dumb terminals to mainframe computers. Other important networks include the voice telephone network and the cable TV network used to disseminate video signals.
Concerning about how to forward some packet or frame from source to destination.
It is a connectionless protocol, which means that we can directly send the packet to the switch without establishing the connection. Hosts need to compete with each other to get the slot in the switch so that the packet could be sent out to the destination. In the packet, we need to specify the destination addess, while making use of the forwarding table, to know which port we are going to send the packet to.
It is a connection-oriented protocol, which means that in order to deliver the packet to the other host, it will first try to establish the connection, then send the packet, and finally close the connection. There’re mainly two kinds of VC, wihch are Permanent VC and Switching VC. The former one is usually set by the network administrator to maintain a long-lived connection, which is kind of like the physical cable connection, while the latter one is just like the definition.
It will number the established link between host and switch, or switch and switch, so that the connection could be remembered. Thus, it don’t need to include the destination address in the packet bit, rather it would only need the VCI [Virtual Circuit Identifier].
The well-known usages of this tech include X.25 network, Frame Relay, Asynchronous Transfer Mode (ATM) and virtual private networks (VPN).