HP-UX SNAplus2 R7 Administration Guide

SNA Terms and Concepts
Basic SNA Concepts
Session Types
SNAplus2 is primarily concerned with the following types of sessions:
LU-LU sessions
In order for two TPs to communicate, the LUs that support the TPs must first establish an LU-LU session.
In general, a session is established when a TP in one SNA node tries to communicate with a TP in another
node and no existing session between the LUs on the two nodes is available.
SSCP-LU sessions
A dependent LU (see Section 1.2.7,
Sessions) must have an active SSCP-LU session with an SSCP on a type
5 node before it can have a session with an LU in the subarea network. Once an SSCP-LU session is active,
a dependent LU can solicit an LU-LU session.
SSCP-PU sessions
Before an SSCP-LU session can be established, the PU controlling the LU must have an active SSCP-PU
session with an SSCP on a type 5 node. The SSCP-PU session is used to pass control data and network
management data between the PU and SSCP.
CP-CP sessions
In an APPN network, adjacent nodes establish CP-CP sessions. These sessions are used to search for a
resource in the APPN network and to maintain topology information (see Section 1.3.2, APPN Control Point).
Logical Unit Attributes for Sessions
Logical units have attributes that determine how they interact during LU-LU sessions. These attributes are determined
by the architecture of SNA. LUs can be primary or secondary, and dependent or independent.
Primary and Secondary LUs
To establish a session, one LU requests session activation by sending a BIND request to another LU:
• A primary LU is the LU that sends the BIND request for a given LU-LU session.
• A secondary LU is the LU that receives the BIND request.
Peer networks do not use a fixed hierarchy of nodes and do not have predetermined primary or secondary LUs.
Note
In a peer network, an independent LU that is participating in multiple sessions (see Section
1.2.7, Sessions) can act as a primary LU for one session and a secondary LU in another.
Dependent and Independent LUs
All type 0, 1, 2, and 3 LUs are dependent LUs. Type 6.2 LUs can be configured as either dependent or independent
LUs.
• A dependent LU (also known as an SSCP-dependent LU) requires the services of an SSCP to establish a
session with another LU. An SSCP-LU session must be established before a dependent LU-LU session can be
established.
A dependent LU can be in session only with LUs on an SNA host. Because of this restriction, dependent LUs
usually use subarea networks (also known as host-mediated networks). However, the dependent LU requester
(DLUR) function enables session traffic from dependent LUs to flow over APPN networks. For more information
about DLUR, see Section 1.4, Accessing Subarea Networks from APPN Networks.
A dependent LU on a peripheral node is always the secondary LU.
• An independent LU can establish sessions with other independent LUs without the aid of an SNA host. LU 6.2
is the only LU type that can be independent.
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