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TN3270 Server Implementation 2-15

The client nailing feature of Cisco’s TN3270 Server simpliﬁes mainframe printing. If you have statically deﬁned

printersessions, itis necessaryto haveprinter LUspredeﬁned in the switched majornode. Theclient mustrequest

the name of one of these printer LUs. If the client requests the name of a printer that is already in use, then the

session request is rejected. With LU nailing, you can use the client printer ip command to deﬁne printers for a

client. LU nailing provides a better method of deﬁning printers for a client because the assignment is centrally

managed and the client cannot request an incorrect LU.

Addressing SNA Routing in Multi-Domain Environments

Anotherrequirement is theability to routetrafﬁc through the TN3270 serverto data applicationwithout routing

the trafﬁc through the VTAM, which could be on a different host. To allow this, APPN is installed on the hosts

and on the TN3270 Server router.

Note: Separate APPN code is not required on the router as the necessary code is part of the TN3270 Server. A

separate license fee is incurred for this feature.

To enable the TN3270 session to pass between the router and VTAM an LU 6.2 session pipe is established

between the DLUR, which is the Cisco router, and the DLUS, which is VTAM. Once a pair of LU 6.2 sessions

has been brought up between the DLUR and DLUS, dependent PU/LU ﬂows (SSCP-to-PU and SSCP-to-LU

sessions) are encapsulated over the LU 6.2 sessions between the DLUR and DLUS SSCP. These LU 6.2 sessions

are known as the control point (CP)-to-server pipe. In this way, SSCP services are provided from VTAM without

requiring the distribution of SSCP code or deﬁnition.

When the SNA network uses APPN and the TN3270 Server can reach multiple hosts, we recommend that you

use DLURand conﬁgure yourPUs under DLUR. You canalso use DLUR toreach a mixof APPN and non-APPN

hosts. The host that owns the PUs must be an APPN network node. When a secondary LU starts a session with

any of the APPN hosts, it can use session switching to reach that host directly. When it starts a session with a

non-APPN host, the trafﬁc is routed through the owning host.

The implementation ofDLUR/DLUS requires no changes to existing applications ordependent terminals. DLUR

requiresVTAMVersion 4.2or laterwith APPNactivated and VTAM conﬁguredas anetwork node(NN). VTAM

can be conﬁgured either a pure NN or an interchange node (ICN). To implement session switching requires

additional knowledge of the VTAM conﬁguration and the implementation of the APPN network.

How DLUR and DLUS Works

All dependent LUs, and the PUs that support them, require sessions to their owning SSCP. These sessions carry

various control messages and management requests. These messages always take the form of SSCP-to-PU and

SSCP-to-LU sessions that cannot cross domain boundaries or network boundaries. A PU serving dependent LUs

must be connected directly to its owning VTAM or to a CIP or CPA connected to that VTAM.

In addition, routing in a subarea network is always done at the subarea level. In other words, any session

involving a dependent LU must pass through the same adjacent subarea node as the SSCP-to-LU session, even if

the dependent LU happens to reside in an APPN node.

To address these restrictions, the DLUS and DLUR were created.

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Cisco 11.0 BT Manual de usuario Pagina 15