Editing Transport layer (section)

{{short description|Layer in the OSI and TCP/IP models providing host-to-host communication services for applications}}
{{Technical|date=March 2025}}
{{Use American English|date = March 2019}}
{{Use mdy dates|date = March 2019}}

[[File:Internet Protocol Analysis - Transport Layer.png|thumb|The transport layer in the Internet protocol stack.|alt=Four labeled stacked blocks. The blue block labeled "transport" is the second from the top.]]
{{IPstack}}

In [[computer network]]ing, the '''transport layer''' is a conceptual division of methods in the [[Abstraction layer|layered architecture]] of protocols in the network stack in the [[Internet protocol suite]] and the [[OSI model]]. The protocols of this layer provide end-to-end communication services for applications.{{Ref RFC|1122|rsection=1.1.3}} It provides services such as [[connection-oriented communication]], [[reliability (computer networking)|reliability]], [[flow control (data)|flow control]], and [[multiplexing]].

The details of implementation and semantics of the transport layer of the [[Internet protocol suite]],{{Ref RFC|1122}} which is the foundation of the [[Internet]], and the [[OSI model]] of general networking are different. The protocols in use today in this layer for the Internet all originated in the development of TCP/IP. In the OSI model the transport layer is often referred to as '''Layer 4''', or '''L4''',<ref>{{cite web|url=https://docs.oracle.com/cd/E19455-01/806-0916/6ja85398m/index.html|work=System Administration Guide, Volume 3|title=Introducing the Internet Protocol Suite}}</ref> while numbered layers are not used in TCP/IP.

The best-known transport protocol of the Internet protocol suite is the [[Transmission Control Protocol]] (TCP). It is used for connection-oriented transmissions, whereas the connectionless [[User Datagram Protocol]] (UDP) is used for simpler messaging transmissions. TCP is the more complex protocol, due to its [[stateful design]] incorporating reliable transmission and data stream services.  Together, TCP and UDP comprise essentially all traffic on the Internet and are the only protocols implemented in every major operating system. Additional transport layer protocols that have been defined and implemented include the [[Datagram Congestion Control Protocol]] (DCCP) and the [[Stream Control Transmission Protocol]] (SCTP).

{{OSI model}}