In this video, we will be discussing what is Datagram & Virtual Circuit and also what is the difference between datagram & virtual circuits.

What is Packet Switching?
Packet switching is a technique in which data is transferred in the form of packets to a network. Files are transferred efficiently and fast over the network and transmission delay is minimized. Data is fragmented into tiny pieces of different lengths, called Packets. At the destination, all these tiny pieces (packets) are reassembled, belonging to the same file. The packet contains control information and payload. Resources are not reserved Pre-setup is not required. 

Packet Switching is known as Store and Forward technique because when packets are switched and when a packet is forwarded each hop first stores that packet and then forward. 
This method is useful because packets may get rejected at any hop because of some reason. 
More than one path is possible between a pair of sources and destinations. 

Datagram: It is a connectionless service. The packet can use any available path to transfer data. Routing of each packet via a network is done on its own. Resources are not reserved as there is no specific channel. All destination information is stored inside the packet header. Intermediate nodes assess the packet’s header and select an appropriate link to a different node closer to the destination. Easy and cost-effective implementation. The receiver receives out-of-order data packets. 

Virtual circuit switching is a methodology to build a path between the source and the ultimate destination through which all packets will transmit. Before data transmission starts, the source and destination must approve the virtual circuit path. To make a decision, intermediate nodes which are between two places add routing entries to their routing database. 
Extra parameters, like maximum packet size, are exchanged between source and destination during call setup. Once the information is transferred successfully, Virtual Circuit is terminated.

Difference between Datagram & virtual circuit:
https://www.geeksforgeeks.org/difference-between-datagram-switching-virtual-circuit/