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How I invented the datagram

The term datagram appeared first within the project CYCLADES, a packet switching-network created in the early 1970s, and was coined by Louis Pouzin by combining the wordsdata and telegram. CYCLADES was the first network to make the hosts responsible for the reliable delivery of data, rather than the network itself, using unreliable datagrams and associated end-to-end protocol-mechanisms.

“The inspiration for datagrams had two sources. One was Donald Davies’ studies. He had done some simulation of datagram networks, although he had not built any, and it looked technically viable. The second inspiration was I like things simple. I didn’t see any real technical motivation to overlay two levels of end-to-end protocols. I thought one was enough.”

These concepts were later adopted for the creation of the [Internet Protocol (IP) and other (now deprecated) network protocols like e.g. (AppleTalk) or (Xerox Network Systems).

A datagram or packet 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.

Datagram is opposite of Virtual circuit

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.”

Datagram service is often compared to a mail delivery service, the user only provides the destination address, but receives no guarantee of delivery, and no confirmation upon successful delivery.

Datagram service routes datagrams without first creating a predetermined path. There is also no consideration given to the order in which it and other datagrams are sent or received. In fact, many datagrams in the same group can travel along different paths before reaching the same destination.

The Internet Protocol defines standards for several types of datagrams.

For this invention Louis Pouzin had the following prizes:

- ACM SIGCOMM 1997

- IEEE Internet 2001