IBM 3708 Description page 77

SNA Sessions
Before communication can begin between a host application and the 3708, a set of
logical SNA connections, called sessions, must be established to control the exchange
of data and control information.
At the host system, the access method provides the System Services Control Point
(SSCP) function for all sessions that are established with the 3708. The SSCP
maintains information that allows an application to establish and maintain a session
with a 3708. For 3708 operations, the host always contains the Primary Logical
. Unit (pLU), and the 3708 always contains the Secondary Logical Unit (SLU).
The sessions that must exist between the host system and the 3708 before an
application program and the 3708 can exchange information are the following:
SSCP-PU (access method-3708 Physical Unit
(PU»
SSCP-PLU (access method-host program)
SSCP-SLU (access method-3708 SLU)
PLU-SLU (host program-3708 SLU) (referred to as LU-LU).
The following sections discuss the sessions individually and identify how they are
established and terminated. The SNA commands that establish and terminate the
sessions are identified. SNA commands are discussed in detail under "SNA
Commands" on page 3-15.
SSCP-PU Session
Before establishing the SSCP-PU (access method-3708 Physical Unit) session, the
physical transmission connection to the host must be established.
The SSCP-PU session must be established before the SSCP-SLU or LU-LU sessions.
When the network operator activates a specific 3708, the access method issues an
ACTPU command to the 3708. A predefined start procedure for the access method
may also request the activation of specific 3708 network conversion units. The
SSCP-PU session is the first session established between the host system and the
3708.
The SSCP-PU session is terminated when the network operator deactivates the 3708.
When all SSCP-LU sessions for the network conversion unit have been terminated,
the access method issues a Deactivate Physical Unit (DACTPU) command that
terminates the SSCP-PU session.
SSCP-Secondary LU Session
When the SSCP-PU session is established, an activate command is issued by the
access method to establish the SSCP-SLU session. The access method issues an
Activate Logical Unit (ACTLU) command for the appropriate SLU or SLUs in the
3708. The SSCP-SLU session must be established before the LU-LU session.
The SSCP-SLU session is terminated when the access method sends a DACTLU
command to the specified 3708 SLU.
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IBM 3708 Description