RFC 1594 defines the term Datagram as follows: “A self-contained, independent entity of data carrying sufficient information to be routed from the source to the destination computer without reliance on earlier exchanges between this source and destination computer and the transporting network.” — RFC 1594 A datagram needs to be self-contained without reliance on earlier exchanges because there is no connection of fixed duration between the two communicating points as there is, for example, in most voice telephone conversations.
RFC 1594ではデータグラムは次のように定義されている： “A self-contained, independent entity of data carrying sufficient information to be routed from the source to the destination computer without reliance on earlier exchanges between this source and destination computer and the transporting network.” —RFC 1594 電話などとは違い、2つのコミュニケーションポイント間に一定時間持続する接続が存在しないため、データグラムは以前の通信に依存せず自己完結していなければならない。