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442 Chapter 12: SNA Technology
NOTE
When a 3270 terminal accesses an application on the host computer, a PLU-SLU session is
established.
Establishing a LU-LU Session
As mentioned previously, end users or terminals access the network through logical units. For
example, a 3270 terminal communicates with the mainframe via Logical Unit-Logical Unit
(LU-LU) sessions that are controlled by the SSCP. A secondary logical unit (SLU) initiates the
session. A primary logical unit (PLU) activates the session.
Let's look at what must happen for LU-LU session establishment. Figure 12-7 depicts this
concept. It is explained in the following steps:
1
The SLU, a cluster controller in this example, requests a session with a PLU on the host.
2
The SLU sends a LOGON to the SSCP. The LOGON is a request that a LU-LU session
be established between the SLU and PLU.
3
The SSCP contacts the PLU with session parameters.
4
The SSCP sends an initiate to the PLU, which asks the PLU to activate a session with the
SLU.
5
The PLU establishes the LU-LU session with the SLU.
Figure 12-7
LU-LU Session Establishment
IBM 3X74
Mainframe
Primary logical unit -
VTAM
SSCP
1. Secondary logical unit sends requests to the SSCP for a session
with the primary logical unit
2. SSCP and primary logical unit (VTAM) establish session parameters
3. Primary logical unit (VTAM) establishes session with the secondary logical unit
Secondary
logical unit
1
2
3
87200333.book Page 442 Wednesday, August 22, 2001 2:53 PM