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NOTE
NOTE
On type 2.1 nodes (which can be APPN nodes), the control point provides
PU services in addition to providing other services (see "Control Points").
Two type 2.1 nodes (such as SNAplus2 nodes) can communicate directly,
without requiring the services of a host to establish communications.
Logical Units
Each SNA node contains one or more logical units (LUs). An LU provides
a set of functions that are used by TPs and end users to provide access to
the network. LUs communicate directly with local TPs and devices.
SNA defines several types of LUs, each optimized for a specific class of
applications. LUs of different types cannot communicate with each other,
but LUs of the same type can communicate even though they reside on
different kinds of systems.
For example, a TP running on a workstation that uses the HP-UX
operating system can communicate with a TP on an AS/400 computer as
easily as it can with a TP on another HP-UX workstation, as long as both
TPs use the same LU type.
SNAplus2 supports the following LU types:
LU 6.2 (for APPC, 5250 and CPI-C)
LU 6.2 supports program-to-program communication
in a distributed data processing environment. The LU
6.2 data stream is either an SNA general data stream
(GDS), which is a structured-field data stream, or a
user-defined data stream. LU 6.2 can be used for
communication between two type 5 nodes, a type 5
node and a type 2.0 or 2.1 node, or two type 2.1 nodes.
(Type 2.1 nodes can serve as APPN nodes.)
This LU type provides more functions and greater
flexibility than any other LU type. Unless you are
constrained by existing hardware or software, LU 6.2 is
the logical choice when developing new applications.
Only LU 6.2 can provide independent LU functions.
LU 3 (for 3270 printing)
LU 3 supports application programs and printers using
the SNA 3270 data stream.
Chapter 1
SNA Terms and Concepts
Basic SNA Concepts
33
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