If networking software performs reliable data tranfer functions, then the detection of errors, and retransmission of data to recover those errors or lost data will occur in software managing this layer. The transport layer may use a variety of techniques such as a Cyclic Redundancy Check, windowing and acknowledgements. If data is lost or damaged it is the transport layer's responsibility to recover from that error.

The session layer performs the following functions

1. Communicate with the Session layer above.
2. Reassemble transport Protocol Data Units into data streams
3. Reliable protocols operating at this layer will
• Detect errors and lost data
• Recover lost data
• Manage retransmission of data.
4. Segmentation of data streams into transport Protocol Data Units.
5. Communicate with the Network layer below.

Examples of transport layer protocols include:

• Transport Control Protocol (Reliable)
• User Data Protocol (Unreliable)