TCP or IP Transport Layer

The Transport Layer is the fourth layer of the OSI model or the third layer of the TCP/IP model. It provides end-to-end communication services for applications running on different hosts. The two main protocols of the transport layer in the TCP/IP suite are the Transmission Control Protocol (TCP) and the User Datagram Protocol (UDP).

TCP is a reliable, connection-oriented protocol that provides guaranteed delivery of data by establishing a virtual circuit between the source and destination hosts. It breaks data into segments and sends them across the network, retransmitting lost segments as necessary. TCP also provides flow control and congestion control mechanisms to prevent network congestion and ensure reliable delivery.

UDP, on the other hand, is a connectionless, unreliable protocol that does not provide any guarantees of delivery. It simply sends datagrams across the network, without establishing a virtual circuit or checking for errors or congestion.

Applications use either TCP or UDP, depending on their requirements for reliability, speed, and overhead. For example, applications that require high reliability, such as email and file transfer, use TCP, while applications that require low overhead and speed, such as audio and video streaming, use UDP.

In addition to TCP and UDP, the transport layer also defines ports that allow multiple applications to use the same IP address to communicate over the network. Ports are identified by a 16-bit number and are used to distinguish between different applications on the same host.