Overview#Packet (or Datagram) is a formatted unit of data carried by a Packet switching network.
Packet consists of control information and user data, which is also known as the payload. Control information provides data for delivering the payload, for example: source and destination network addresses, error detection codes, and sequencing information. Typically, control information is found in Packet headers and trailers.
communications links that do not support Packet, such as traditional point-to-point telecommunications links (Circuit switching), simply transmit data as a bit stream. When data is formatted into Packet, packet switching is possible and the bandwidth of the communication medium can be better shared among users than with circuit switching.Datagram are generally the same. Some folks will be define a Packet as any data on a Reliable protocol or Unreliable protocol where a Datagram is used only on a Unreliable protocol. We generally see the two used interchangeably.