HP-UX SNAplus2 R7 Administration Guide

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SNA Terms and Concepts

Basic SNA Concepts

The root of the tree (at the top of the diagram) is the computer controlling the network. The branches are the

communications links from the host to the other computers in the network (terminal controllers); the leaves (at the

bottom of the diagram) are the terminals or printers attached to these computers, which are accessed by users.

The traditional subarea SNA set-up described here enables the users to use the resources of a single host system.

The terminals provide only simple data entry and display functions to and from the terminal controller; the terminal

controller is responsible for handling SNA communications between the terminals and the host.

The terminal controller and its terminals can be replaced by an SNA node using a product such as SNAplus2. From

the host’s point of view, the node appears as a terminal controller. However, it provides the users with additional

functions, such as the ability to access more than one host system and facilities for customizing screen displays. In

addition, SNAplus2 runs on HP-UX computers that can also be used for other tasks not related to SNA (unlike the

terminal controller, which is used solely for communications with the host).

Node Types in a Peer Network

Peer networks do not classify nodes hierarchically, as is done in a subarea network. Exchanges with other nodes

are not controlled by a host or other centralized processor. Instead, any node can establish communication with any

other node.

A peer network is composed of type 2.1 nodes. The nodes in a peer network can serve the following roles:

• APPN network nodes (NNs) identify the locations of network resources, determine routes for sessions between

these resources, route sessions, and serve end nodes (EN) and low-entry networking (LEN) nodes directly

attached to the network node. The domain of an APPN network node consists of itself and any end nodes for

which it provides network services.

• APPN end nodes can access remote resources without requiring that those resources be conﬁgured on the end

node. An end node can communicate with adjacent nodes on its own, but requires the services of a network

node server to access nonadjacent nodes. The domain of an APPN end node includes only itself.

• APPN branch network nodes allow the APPN network to be separated into branches to simplify its topology

and reduce network management overheads. They provide network node functions to end nodes in a branch

separated from the main APPN network, while acting as end nodes in the main network itself. For more

information, see Section 1.3.5,

Branch Extender.

• Low-entry networking nodes (LEN nodes) are type 2.1 nodes that do not support APPN functions. They can

communicate with adjacent nodes in an APPN network, but do not participate in the APPN network. In a LEN

node, all potential sessions with remote LUs must be predeﬁned, either speciﬁcally or through a single default

entry indicating that all remote LUs reside in an adjacent network node that can be accessed using a certain

link. The domain of a LEN node includes only itself.

For more information about peer-oriented node types, see Section 1.3.1, APPN Node Types.

1.2.3 Connectivity

For two nodes to communicate, each node must have a combination of hardware and software that supports data

ﬂow between the nodes. The hardware component consists of an adapter at each node and the transmission medium

that connects the two adapters. The software component provides control of the hardware and the data exchanged

over it.

Each node connected to a network has one or more link stations, which are the hardware and software in a node

that control data ﬂow to a speciﬁc adjacent node. To establish communication between two adjacent nodes, one of

the link stations must ﬁrst activate the link between the nodes.

1.2.4 Transaction Programs

Programs that exchange information across the SNA network are called transaction programs (TPs).

Following are examples of application programs that can include SNA TPs:

• Emulation programs