Layer 5, the Session Layer, allows two applications on different computers to open, use, and close a connection called a session.
The Session Layer is responsible for managing this dialogue.
session A highly structured dialog between two workstations.
Layer 2, the Data Link Layer, sends data frames from the Network Layer to the Physical Layer. A data frame is like a vehicle, in which the data are the people, or cargo, who ride inside the vehicle across the network.
data frame An organized, logical structure in which data can be placed. Two other models, also layered, tend to pop up in descriptions of network architectures.
Systems Network Architecture (SNA)
Transmission Control Protocol/Internet Protocol (TCP/IP) reference model
Transmission Control Protocol/Internet Protocol (TCP/IP) reference model An Internet-related network architectural model.
SNA was originally designed around the mainframe/terminal relationship, but was later modified, in a specification known as Advanced Program to Program Communications (APPC), to include minicomputers and personal computers.
Advanced Program to Program Communications (APPC) The SNA mainframe communication model was modified in a specification known as APPC to include minicomputers and personal computers.