Solution to the limitations of direct links is on all devices connected to a communications network, the communication network is responsible for the data exchange.
Communication networks are often composed of several intermediate nodes, these nodes to the main data exchange, which means the data from one node to another node, until the data arrives at the destination. Common Exchange circuit-switched and packet-switched.
Introduced two Exchange technologies:
Circuit-switched: set up a dedicated communication line between two sites of Exchange. This pathway is the link between the network nodes-tail form a sequence of links. The duration of the connection, the capacity of the channel is private, even in the absence of data can be transferred, or transfer data to other sites. Circuit-switched telephone network.
Packet: packet-switched data is divided into a bunch of pieces, each packet from one node to another node finally reached their destination. Packet switch using store-and-forward mode, each switching node via a link to accept a packet and stored, and then free time to forward the packet from a suitable link to the next node. Packet-switched mode and datagram and virtual circuit divided into two. Packet switching is commonly used for communications between computers.