use with ISO/IEC 8878 (SNARE) – ITU-T Rec. X.116 [ISO/IEC 10030]. This level is in charge of transferring data between systems in a network, using network-layer addresses of machines to keep track of destinations and sources. This layer uses routers and switches to manage its traffic (control flow control, error check, routing etc.) So here it takes all routing decisions, it deals with end to end data transmission. Layer 4: transport layer The connection-mode and connectionless-mode transport services are specified by ITU-T Rec. X.214 [ISO/IEC 8072]; the protocol that provides the connection-mode service is specified by ITU-T Rec. X.224 [ISO/IEC 8073], and the protocol that provides the connectionless-mode service is specified by ITU-T Rec. X.234 [ISO/IEC 8602]. Transport Protocol Class 0 (TP0) Transport Protocol Class 1 (TP1) Transport Protocol Class 2 (TP2) Transport Protocol Class 3 (TP3) Transport Protocol Class 4 (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. Layer 5: session layer Session service – ITU-T Rec. X.215 [ISO/IEC 8326] Connection-oriented Session protocol – ITU-T Rec. X.225 [ISO/IEC 8327-1] Connectionless Session protocol – ITU-T Rec. X.235 [ISO/IEC 9548-1] The session layer controls the dialogues (connections) between computers. It establishes, manages and terminates the connections between the local and remote application. It provides for full-duplex, and half-duplex or simplex operation, and establishes checkpointing, adjournment, termination, and restart procedures. The OSI model made this layer responsible for graceful close of sessions, which is a property of the Transmission Control Protocol, and also for session checkpointing and recovery, which is not usually used in the Internet Protocol Suite. The session layer is commonly implemented explicitly in application environments that use remote procedure calls. Layer 6: presentation layer Presentation service – ITU-T Rec. X.216 [ISO/IEC 8822] Connection-oriented Presentation protocol – ITU-T Rec. X.226 [ISO/IEC 8823-1] Connectionless Presentation protocol – ITU-T