Overview#

Transport Layer is a conceptual division of methods in the layered architecture of protocols in the network stack in the Internet Protocol Suite and the Open Systems Interconnection (OSI-Model).

Internet Protocol Suite Transport Layer#

Internet Protocol Suite Transport Layer performs host-to-host communications on either the same or different hosts and on either the Local Area Network or remote networks separated by routers.

Internet Protocol Suite Transport Layer provides a channel for the communication needs of applications. UDP is the basic Transport Layer, providing an unreliable datagram service. The Transmission Control Protocol provides flow-control, connection establishment, and reliable transmission of data.

OSI-Model Transport Layer#

Transport Layer provides the functional and procedural means of transferring variable-length data sequences from a source to a destination host via one or more networks, while maintaining the quality of service functions.

An example of a transport-layer protocol in the standard Internet stack is Transmission Control Protocol (TCP), usually built on top of the Internet Protocol (IP).

Transport Layer controls the reliability of a given link through flow control, segmentation/desegmentation, and error control. Some protocols are state- and connection-oriented. This means that the Transport Layer can keep track of the segments and re-transmit those that fail.

Transport Layer also provides the acknowledgement of the successful data transmission and sends the next data if no errors occurred.

Transport Layer creates packets out of the message received from the Application Layer. Packetizing is a process of dividing the long message into smaller messages.

OSI defines five classes of connection-mode transport protocols ranging from class 0 (which is also known as TP0 and provides the fewest features) to class 4 (TP4, designed for less reliable networks, similar to the Internet). Class 0 contains no error recovery, and was designed for use on network layers that provide error-free connections. Class 4 is closest to TCP, although TCP contains functions, such as the graceful close, which OSI assigns to the session layer. Also, all OSI TP connection-mode protocol classes provide expedited data and preservation of record boundaries. Detailed characteristics of TP0-4 classes are shown in the following table:

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« This page (revision-4) was last changed on 01-Apr-2017 17:09 by jim