LU 6.2 API Application Programmer's Reference Guide (30294-90008)

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1 The SNA Network and LU 6.2 API
Systems Network Architecture (SNA)
IBM has established a set of protocols that govern communication
between various types of machines and applications. This set of
protocols is called Systems Network Architecture (SNA).
SNA is an architecture designed to be independent of specific software
or hardware. In SNA, machines and applications are defined only in
terms of the functions they perform. Each machine or node in an SNA
network has a node type, which is determined by the set of data
communications functions it performs. For example, a Type 5 node is a
mainframe or host computer. Any machine that performs the data
communication functions defined by SNA for a mainframe computer
can act as a Type 5 node in an SNA network.
In the past, IBM has focused on centralized data processing, where data
is kept in one central location (usually a mainframe computer), and
remote processors use the data communication network to access the
data. Figure 1-1 shows a typical IBM network, with a centralized
mainframe that serves smaller processors in remote locations. An
HP 3000 serves as a remote processor in the IBM environment.
At the central location, the mainframe computer and the
communications controller work as a unit to send and receive data.
The communications controller helps the mainframe manage
communication with the remote locations so that the mainframe has
more power to process and manage data. A communications controller
is a Type 4 node.
At each of the remote locations, a cluster controller multiplexes
several terminals or other peripheral devices to a single data
communication line, making efficient use of the line between the cluster
controller and the mainframe. A cluster controller is a Type 2 node. The
HP 3000 functions as a Type 2 node.