IBM 6400i Setup Manual page 327

Summary of LU Types and Representative IBM Products
LU type 3
An LU type 3 is for an application program that communicates with a single
printer using the SNA 3270 data stream. Another name for this connection is
Data Stream Extended (DSE). This type of connection will not support the
SCS data stream and may be used when no host controls are to be sent to
the printer. An example of printers that may use this method of connection are
4230, 3912, 6400, 3930, and others.
LU type 4
LU type 4 is is seldom used today. It is used for (1) an application program
that communicates with a single or multiple-device data processing or work
processing workstation in an interactive, batch data transfer, or distributed
data processing environment (for example, an LU for an application program
that uses CICS/VS and communicates with an IBM 6670 Information
Distributor); or (2) logical units in peripheral nodes (for example, two 6670's)
that communicate with each other. The data stream is the SNA Character
String (SCS) for data processing environments and Office Information
Interchange (OII) Level 2 (a precursor of DCA) for word processing
environments.
LU type 6.1
An LU type 6.1 is for an application subsystem that communicates with
another application subsystem in a distributed data processing environment.
An example of an LU type 6.1 is an application program that uses CICS/VS
and communicates with an application program that uses IMS/VS.
LU type 6.2
An LU type 6.2 supports sessions between two applications in a distributed
data processing environment. The data stream is either the SNA General
Data Stream (GDS), which is a structure-field data stream, or a user-defined
data stream. LU 6.2 session provide communication between (1) two PU type
5 nodes (host resource-owning VTAM), (2) a PU type 5 node and a PU type
2.1 node, and (3) two PU type 2.1 nodes. Examples (1) VTAM-to-VTAM
communication, or an application program that uses CICS/VS and
communicates with another application program that uses CICS/VS, (2) An
application program which uses VTAM and PSF/MVS communicating with an
IBM 3820, 3935, or PSF/2; or (3) Two iSeries Host Systems communicating in
APPC mode.
LU type 7
An LU type 7 is for an application program and a single display workstation in
an interactive environment. An example of an LU type 7 is an application
program in an iSeries communicating with a 5250-type terminal. The data
stream is the 5250 data stream.
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