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TN3270 Server Implementation 2-17

How Session Switching Works

The LUs implemented by the TN3270 Server are dependent LUs. To route these dependent LU sessions to

multiple VTAM hosts connected to the server in the channel-attached router (rather than routing in the VTAM

hosts), the TN3270 Server implements an SNA session switch with the EN DLUR function.

Figure 2-5 illustrates how session switching works.

Figure 2-5 How Session Switching Works

To illustrate how session switching works, consider the situation in which a client’s owning VTAM is on Host A

and the client wants to reach an application on Host B:

• Without a subarea network, the client would be continuously routed from VTAM A to VTAM B. This process

causes the mainframe to expend cycles performing the routing function.

• If you migratethe host to an ICN, the subarea network still exists and the APPN functionality is now available.

Using theTN3270 Server installed on the channel-attachedrouter and the DLUR function of VTAM, the Cisco

router can session switch the user to Host B without passing through Host A.

To implement session switching, a CP-to-CP session between the two VTAMs is required. This can be achieved

three ways:

• CP-to-CP connection using the DIAL parameter and not implementing APPN on the router

Host A Host B

Applications VTAMACF/VTAM 4.2

with DLUS

CP to CP

Sessions

CIP or CNA

SNA

Session Switch

TCP/IP

RSP

TN3270

Client Workstation

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Cisco 11.0 BT Manual de usuario Pagina 17