Network Addressable Unit (NAU)

SNA describes three significant network addressable units: LUs, PUs and CPs. Each one plays a vital role in setting up connections among systems in an SNA network. These are further explained as follows:

• System services control points: SSCPs offer services for handling a network or a subnetwork (usually in a mainframe). Control points (CPs) control SNA nodes in addition to their resources. Generally, CPs are differentiated from PUs for the reason that CPs decide which actions have to be taken, whereas PUs induce actions to take place.
  
  The SSCP of the SNA is a good example of a CP. An SSCP could be the CP located in a PU 5 node or an SSCP as employed according to an SNA access technique, like the Virtual Telecommunications Access Method (VTAM).


• Logical units: LUs are a logical set of services that can be accessed from a network. LUs work as end-user access ports in an SNA network. With LUs, users can access the network resources. LUs also control the data transmission between the end users.


• Physical units: PUs are a mix of software and hardware that handle the links to other nodes. PUs are used to control and keep track of connected network links as well as other network resources related to a specific node. SNA access techniques, like the VTAM, are used to implement PUs on hosts. Moreover, network control programs can be used to implement PUs within communications controllers.