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What the term means
IBM’s z/TPF documentation, in its “Basic SNA terms and concepts” material, states: “A network addressable unit (NAU) is a resource managed by the communications system.” The same material describes the NAU as the origin and/or destination of transmitted information, and says each NAU has a unique network name that is translated into a unique address.
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Because the definition is architectural, the term applies to SNA resources. It is not a generic label for every device on a network.
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Network name and network address
An NAU involves two identifiers that do different jobs:
- Network name is the symbolic identifier that users and operators refer to.
- Network address identifies the resource within SNA addressing. IBM’s z/OS Communications Server glossary describes an SNA network address as having subarea and element fields.
IBM documentation treats the network address as a distinct concept from the NAU itself, which is why the two should not be used interchangeably.
Types of NAU depend on the IBM product context
IBM’s lists of NAU types are not identical across its documentation. Compare the two sources below before quoting a list.
| Source | Types listed | Context noted in the source |
|---|---|---|
| z/OS Communications Server Glossary | Logical units (LU), physical units (PU), system services control points (SSCP) | Also describes the subarea and element structure of SNA network addresses. |
| Basic SNA terms and concepts (z/TPF) | SSCP, PU, LU, control point | States that node and NAU have the same meaning in that documentation. |
If you need to explain the taxonomy, name the product documentation you are drawing on rather than presenting one list as universal.
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When comparing NAU types, the most useful axis is the role each resource plays in the network:
- Management: the SSCP, which manages resources within its domain.
- Physical-resource representation: the PU, which represents a physical node to the network.
- Application communication: the LU, through which end users and application programs communicate.
This grouping is a general orientation to SNA roles; the exact responsibilities of each type are defined in the IBM product documentation for the system you are working with.
How NAUs exchange data: sessions
NAUs communicate through sessions. IBM’s z/TPF terminology states that two NAUs must be formally connected before data can be exchanged, and that this formal connection is called a session.
- One NAU requests a connection to another NAU.
- The two NAUs are formally connected, which creates a session.
- Data is exchanged between the NAUs within that session.
The first step describes the general sequence in SNA terms; the mechanics of how a session is requested and activated depend on the product and configuration in use.
When an NAU has more than one address
IBM’s historical SNA publication, SNA Concepts and Products, notes that an LU may have multiple addresses to support parallel LU-LU sessions. This is architectural background. It is not a general rule that applies to every current configuration, so check the documentation for your own product and release before relying on it.
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Where you will see the term
IBM Personal Communications documents an NAU_ADDRESS parameter whose meaning is tied to the specific release. Read that parameter’s entry for your release before assuming how it is applied.
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What an NAU is not
- An NAU is not an IP address. SNA addressing and IP addressing are separate systems.
- An NAU is not simply any computer or network-connected device. Only resources that SNA manages and addresses in this way are NAUs.
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