The transport layer of the OSI model is responsible for providing end-to-end data transport, by either using a connectionless or connection-oriented protocol across an IP network. The transport protocol that's selected will depend on the application. There are several protocols in this layer, including the following:

• Reliable data protocol: Used to transfer data in a connection-oriented manner
• Stream control transmission protocol: Provides the reliable transmission of data streams that have more than one IP address 

Although there are other, less well-known transport layer protocols, the two predominant protocols are TCP or UDP, as shown in the following diagram:

UDP is connectionless and is used when data transport needs to be fast. UDP has a lightweight four-field header. Unlike TCP, UDP currently does not have any header options. However, because of the changing nature of the internet, there has been an active discussion on possibly including options for UDP, as evidenced in a draft called Transport Options for UDP, which can be found at https://tools.ietf.org/html/draft-ietf-tsvwg-udp-options-05.

TCP is a connection-oriented protocol. The eleven-field TCP header tells the story of how impressive this protocol is in its ability to ensure complete delivery of data while monitoring for congestion and providing flow control.