This header is often only sent at the beginning of an application operation. This provides function call exchange between host operating systems and software layers. It defines the format of data being sent and any encryption that may be used. The Session layer defines how data conversations are started, controlled and finished. The messages may be bidirectional and there may be many of them, the session layer manages these conversations and creates notifications if some messages fail.
Indications show whether a packet is in the middle of a conversation flow or at the end.
Only after a completed conversation will the data be passed up to layer 6. This layer is resonsible for the ordering and reassembly of packets that may have been broken up to travel across certain media. Some protocols in this layer also perform error recovery. After error recovery and reordering the data part is passed up to layer 5. This layer is responsible for the delivery of packets end to end and implements a logical addressing scheme to help accomplish this.