Editing OSI protocols (section)

==Layer 4: transport layer==
The connection-mode and connectionless-mode transport services are specified by [http://www.itu.int/rec/T-REC-X.214/en/ ITU-T Rec. X.214 <nowiki>[</nowiki>ISO/IEC 8072<nowiki>]</nowiki>]; the protocol that provides the connection-mode service is specified by [http://www.itu.int/rec/T-REC-X.224/en/ ITU-T Rec. X.224 <nowiki>[</nowiki>ISO/IEC 8073<nowiki>]</nowiki>], and the protocol that provides the connectionless-mode service is specified by [http://www.itu.int/rec/T-REC-X.234/en/ ITU-T Rec. X.234 <nowiki>[</nowiki>ISO/IEC 8602<nowiki>]</nowiki>].
* Transport Protocol Class 0 ([[TP0 (protocol)|TP0]])
* Transport Protocol Class 1 ([[TP1 (protocol)|TP1]])
* Transport Protocol Class 2 ([[TP2 (protocol)|TP2]])
* Transport Protocol Class 3 ([[TP3 (protocol)|TP3]])
* Transport Protocol Class 4 ([[TP4 (protocol)|TP4]])
* Transport Fast Byte Protocol – ISO 14699

The transport layer transfers data between source and destination processes.  Generally, two connection modes are recognized, connection-oriented or connectionless. Connection-oriented service establishes a dedicated virtual circuit and offers various grades of guaranteed delivery, ensuring that data received is identical to data transmitted.  Connectionless mode provides only best-effort service without the built-in ability to correct errors, which includes complete loss of data without notifying the data source of the failure. No logical connection, and no persistent state of the transaction exists between the endpoints, lending the connectionless mode low overhead and potentially better real-time performance for timing-critical applications such as voice and video transmissions.