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SNA | Tech Info Home Page |

Systems Network Architecture (SNA)

SNA is a hierarchical network architecture, introduced by IBM in 1974 to facilitate communications between mainframes.

SNA Network Structure -

SNA has 3 parts, the System Services Control Point (SSCP), the Physical Units (PUs) and the Logical Units (LUs). These parts of the SNA network consist of the mainframe also known as the host system running VTAM software, a communications controller, also known as the fron-end processor (FEP), a cluster controller and the printers/terminals.

Cluster controllers can be either local (directly connected to the mainframe) or remote.

The SNA Server operates in a Client-Server environment as a Server, to a workstation which is the client. SNA Server handles the LU-to-LU connections with the host mainframe on behalf of the workstations.

Link Services are added during setup ( or afterward ) to allow the server to communicate with the mainframe. Logical connections are then established between the Link Services connection acting as a PU 2 and the mainframe connection acting as a PU 5.
and reside on top of the Link Services.

A LU connection is configured for 3270 access and  which can support up to 254 LUs. LUs are associated with sessions.

The security is configured by adding the NT user account to the SNA server subdomain and then assigning the account to the appropriate LU.

On the mainframe side, a VTAM definition must be established for every SNA Server connection.


SNA Hierarchy

Host - PU 5.

The mainframe is the PU 5 device at the top. Only one can exist and it hosts the SSCP (System Services Control Point).

Communication Controller - PU 4

It runs ACF and NCP.

Peripheral Nodes

1) cluster controller Node
....(can be SNA server acting as PU 2.0 or 2.1 device)
2) terminal node

End-User Components

Terminals and printers, 3270 LUs

SNA Network Layers





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