In practice, SNA and LU6.2 use only layers 4 through 6. In this tutorial, we'll describe the functions and features these layers provide. Before continuing, let's define logical unit, and its hardware-specific counterpart, the physical unit. In SNA parlance, PUs are physical systems or nodes connected to each other via cabling. PUs are also known as Node Types, or NTs.
Logical units are electronic entities connected by sessions.
Just as there are five PUs, there are five LUs, including LU6.2, that make SNA network resources, including disk files and processing cycles, available for application software. In essence, LU6.2 acts as an interface, or protocol boundary, between SNA and an end user's application. PU2.0, also known as 3270 terminal emulation, is the protocol most often used to connect personal computers into an SNA network. PU2.0 also lets other devices on an SNA network access a mainframe by emulating a cluster controller.