LU 6.2 API Application Programmer's Reference Guide (30294-90008)

Chapter 1 21
The SNA Network and LU 6.2 API
Systems Network Architecture (SNA)
Figure 1-2 Type 2.1 Nodes in an SNA Network
NOTE The APPC subsystem on MPE XL allows the HP 3000 to function as a
Type 2.0 or Type 2.1 node. On MPE V, however, the HP 3000 functions
only as a Type 2.0 node. For more information on Node Type 2.1, see the
APPC Subsystem on MPE XL Node Manager’s Guide.
Logical Units (LUs)
A Logical Unit (LU) is the set of data communication functions
required by an end user in an SNA network. In SNA, an end user is
defined as the ultimate destination of data. So, an end user can be a
peripheral device (like a printer or a terminal) or an application
program. A Logical Unit is like a port through which an end user sends
and receives data.
Just as different node types define how machines will communicate,
different Logical Unit types define how end users will communicate
across the network. Since different peripheral devices use different
communication protocols and data formats, SNA assigns an LU type to
each kind of peripheral. For example, an LU Type 2 (LU.T2) describes
the communication protocols and data format for any terminal that
uses the IBM 3270 data stream.
Logical Units can communicate only with other Logical Units of the
same type. An application on the mainframe that will exchange data
with an LU.T2 terminal must have its own Type 2 Logical Unit through
which to transmit and receive data. Figure 1-3 shows a logical mapping
between a terminal at a remote location and an application on the
mainframe computer.