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Connectionless communication, often referred to asCL-mode communication,[1] is a datatransmission method used inpacket switching networks, using data packets that are frequently calleddatagrams, in which each data packet is individually addressed and routed based on information carried in each packet, rather than in the setup information of a prearranged, fixed data channel as inconnection-oriented communication. Connectionless protocols are usually described asstateless protocols, theInternet Protocol (IP) andUser Datagram Protocol (UDP) are examples.
Under connectionless communication between two networkendpoints, a message can be sent from one endpoint to another without prior arrangement. The device at one end of the communication transmits data addressed to the other, without first ensuring that the recipient is available and ready to receive the data. Some protocols allow for error correction by requesting retransmission.
Connectionless protocols arestateless protocols because the endpoints have no protocol-defined way to remember where they are in a "conversation" of message exchanges. It has loweroverhead thanconnection-oriented communication because, in connection-oriented communication, the communicating peers must first establish a logical or physical data channel orconnection in a dialog preceding the exchange of user data. It allows formulticast andbroadcast operations in which the same data are transmitted to several recipients in a single transmission.
In connectionless transmissions the service provider usually cannot guarantee that there will be no loss,error insertion, misdelivery, duplication, or out-of-sequence delivery of the packet. However, the effect of errors may be reduced by implementing error correction within an application protocol.
In connectionless mode, there is less opportunity for optimization when sending several data units between the same two peers. By establishing a connection at the beginning of such a data exchange the components (routers,bridges) along the network path would be able to pre-compute (and hencecache) routing-related information, avoiding re-computation for every packet. In connection-oriented communication, network components can also reserve capacity for the transfer of the subsequent data units of a video download, for example.
Distinction between connectionless and connection-oriented transmission may take place at several layers of theOSI Reference Model:
Notable connectionless protocols are:Internet Protocol (IP),User Datagram Protocol (UDP),Internet Control Message Protocol (ICMP),Internetwork Packet Exchange (IPX),Transparent Inter-process Communication,NetBIOS, andFast and Secure Protocol (FASP).
This article incorporatespublic domain material fromFederal Standard 1037C.General Services Administration. Archived fromthe original on 2022-01-22.