|  | 1.4 |
Host Layers (the Upper 4 Layers of the OSI Model)
| 1.4.2 | Transport Layer
The transport layer (Layer 4) is responsible for transporting and regulating the flow of information from source to destination reliably and accurately. Its functions include: connection synchronization flow control error recovery reliability through windowing The transport layer (Layer 4) enables a user's device to segment several upper-layer applications for placement on the same Layer 4 data stream, and enables a receiving device to reassemble the upper-layer application segments. The Layer 4 data stream is a logical connection between the endpoints of a network, and provides transport services from a host to a destination. This service is sometimes referred to as end-to-end service. As the transport layer sends its data segments, it also ensures the integrity of the data. This transport is a connection-oriented relationship between communicating end systems. Some of the reasons for accomplishing reliable transport are as follows: It ensures that senders receive acknowledgement of delivered segments. It provides for retransmission of any segments that are not acknowledged. It puts segments back into their correct sequence at the destination device. It provides congestion avoidance and control. One of the problems that can occur during data transport is overflowing buffers on receiving devices. Overflows can present serious problems that result in data loss. The transport layer uses a method called flow control to solve this problem.