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2-8 TN3270 Design and Implementation Guide

DynamicLU allocation isthe most commonform of requestfrom TN3270 clientsemulating aTN3270 terminal.

The client is typically concerned with emulating a particular terminal type, but is not normally interested in what

LOCADDR or LU name is allocated by the host as long as a USS10 menu is presented or an LU-to-LU session is

started (via the LOGAPPL facility).

The server performs the following tasks on such a session request:

• Forms an EBCDIC string based on the model type and number requested by the client. This string is used as a

ﬁeld in a Reply PSID NMVT.

• Allocates a LOCADDR from the next available LU in the generic LU pool. This LOCADDR is used in the

NMVT.

• Sends the formatted Reply PSID NMVT to VTAM.

When VTAM receives the NMVT, it uses the EBCDIC model type and number string to look up an LU template

under the LUGROUP. An ACTLU is sent and a terminal session with the model and type requested by the client

can be established.

Note: DDDLU requires that the ISTEXCSD exit is active in VTAM. You can check to see that the DDDLU exit

is active by running this VTAM command:

D NET,EXITS

The output should say that ISTEXCSD is active and has exit ISTEXCSD in place.

LUGROUP Parameter

To use dynamic LUs, you must create and activate a VTAM LUGROUP major node, which contains the model

types and deﬁnitions for the variety of terminal types used. Each model type provides different screen functions.

The LUGROUP deﬁnition is used by the requesting LU to deﬁne terminal type settings, such as the default

logmode, mode table, and USS table.

When deﬁning an LUGROUP, itis bestto deﬁneall combinationsof modeltypes thatare typicallyfound inyour

network as well as a default model statement. The default model statement acts as a catch-all deﬁnition for

combinations not deﬁned. You do not specify a model name in the default model statement. Instead, you begin

the statement with the @ sign. The @ sign can also be used as a wildcard in other entries.

To cover all combinations of machine, model, and extension type, when creating the LUGROUP, you would

include deﬁnitions to cover the following:

• Two machine types: IBM 3278 and 3279

• Four model types: 2, 3, 4, 5

• Two extension types: 0 and S

A 0extension speciﬁes a classicTN3270 connection. The clientexpects all data to bein a TN3270 datastream.

An S extension indicates that the client expects the SSCP-to-LU data to be in SCS control code format. All

entries with an S extension to the machine type should have SSCPFM=USSSCS coded. All others should have

SSCPFM=USS3270 coded.

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Cisco 11.0 BT Manual de usuario Pagina 8