Editing Connectionless communication

{{Short description|Network protocol with routing per packet}}
{{refimprove|date=February 2018}}

'''Connectionless communication''', often referred to as '''CL-mode''' communication,<ref name=":6">Information Processing Systems - Open Systems Interconnection, "Transport Service Definition - Addendum 1: Connectionless-mode Transmission", International Organization for Standardization, International Standard 8072/AD 6, December 1986.</ref> is a data [[transmission (telecommunications)|transmission]] method used in [[packet switching]] networks, using data packets that are frequently called [[datagram]]s, 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 in [[connection-oriented communication]]. Connectionless protocols are usually described as [[stateless protocol]]s, the [[Internet Protocol]] (IP) and [[User Datagram Protocol]] (UDP) are examples.

==Attributes==
Under connectionless communication between two network [[Communication endpoint|endpoints]], 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 are [[stateless protocol]]s because the endpoints have no protocol-defined way to remember where they are in a "conversation" of message exchanges. It has lower [[Overhead_information|overhead]] than [[connection-oriented communication]] because, in connection-oriented communication, the communicating peers must first establish a logical or physical data channel or ''connection'' in a dialog preceding the exchange of user data. It allows for [[multicast]] and [[Broadcasting (networking)|broadcast]] 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 ([[Router (computing)|router]]s, [[Network bridge|bridges]]) along the network path would be able to pre-compute (and hence [[cache (computing)|cache]]) 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.

==Architecture and implementations==
Distinction between connectionless and connection-oriented transmission may take place at several layers of the OSI Reference Model:
* [[Transport layer]]: [[Transmission Control Protocol|TCP]] is a connection-oriented [[transport protocol]]. [[User Datagram Protocol|UDP]] is connectionless.
* [[Network layer]].
* [[Data link layer]]: The [[IEEE 802.2]] protocol at the [[Logical Link Control]] sublayer of the data link layer may provide both connectionless and connection-oriented services. In fact, some [[network protocol]]s (such as [[Systems Network Architecture|SNA]]'s [[Path Control]] in its early stages) require a connection-oriented data link layer. Others (like [[Internet Protocol|IP]]) do not. (After the appearance of [[IBM Advanced Peer-to-Peer Networking|APPN]], SNA could operate on a connectionless data link service as well.)

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]], and [[Fast and Secure Protocol]] (FASP).

==References==
{{reflist}}
*{{FS1037C}}

[[Category:Network protocols]]
[[Category:Computer networking]]
[[Category:Internet architecture]]
[[Category:Internet protocols]]