IBM SNA Interoperability Concepts
IBM SNA Interoperability Concepts |
|
In an SNA network, type 5 and type 2 PUs transmit and control SNA networking protocols, called logical units (LUs).
An LU is the end user's entry point into the SNA network. In SNA terminology, the end user can be a person or an application. For example, when an end user enters information into an SNA terminal, the data is passed to an LU for routing over the network to a host node. When the data reaches the host node, another end user passes it to an LU within the host for processing. In this example, the end user at the terminal is an actual person but the end user at the host node is the host application program.
In hierarchical networks, all LUs depend on the mainframe SSCP to establish and manage communications with other LUs, and are therefore referred to as dependent logical units.
As with PU types, each type of LU is identified by a number. Table A.4 identifies the LU types used in hierarchical networks, the hardware component with which each is associated, and the function of each in an SNA network.
Table A.4 LU Types Used in Hierarchical Networks
| LU Type | Component | Function |
|---|---|---|
| LU 0 | Nonstandard, user-defined component interface. | Enables the development of specialized applications. LU 0 is a general purpose LU. |
| LU 1 | IBM 3287–type printers. | Handles transmission of printer data to system and network printers. LU 1 uses SNA character string format (SCS). |
| LU 2 | IBM 3278 (3270) monochrome terminals; 3279/3179 color terminals; graphics terminals. | Defines how terminal data streams are formatted and transmitted. |
| LU 3 | IBM 3270–type printers. | Uses SNA 3270 data stream format to control the transmission of data to system and network printers. LU 3 is the most often used printing LU type. |
Note
Peer-oriented LU types, including LU 6.2, are described in "Advanced Peer-to-Peer Networking" later in this appendix.