Layer 4 The Transport Layer

The transport layer is responsible for segmenting upper-layer applications and establishing end-to-end connections between devices. Other transport layer functions include providing data reliability and error-free delivery mechanisms. Information at this layer is processed in what are commonly known as segments. Examples of transport layer protocols include the following:

■ Transmission Control Protocol (TCP)

■ Real-Time transport protocol (RTP)

■ User Datagram Protocol (UDP)

RTP has some important properties of a transport Layer-4 protocol; however, it also runs on end systems. RTP differs from transport protocols like TCP in that it (currently) does not offer any form of reliability or a protocol-defined flow/congestion control. IP voice is an example of RTP operating at Layer 4 of the OSI model.

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