SNA Overview 437
software such as VTAM could be classified as a PU. There are five types of PUs: 5, 4, 2, 1, and 2.1.
These physical units represent actual devices and their associated resources in the SNA network:
·
PU type 5--Referred to as a subarea node, this type contains an SSCP and is usually a
mainframe.
·
PU type 4--Referred to as a subarea node, this type does not contain an SSCP and is
usually a front-end processor.
·
PU type 2--These are referred to as peripheral nodes user-programmable end nodes, and
are typically cluster controllers. PU 2 nodes provide networking services to logical units.
PU 2 nodes have greater processing capabilities than PU 1.0 nodes and are user-
programmable. They are configured with the address of the SNA PU 4 or PU 5 that
provides a boundary function. An SNA boundary function is the equivalent of the default
gateway in a TCP/IP network.
·
PU type 1--Referred to as peripheral nodes, these are not user-programmable and have
fewer capabilities than PU 2s. PU type 1s are almost always printers.
·
PU type 2.1--These PUs are used in APPN networks and can provide APPN network
node or end node functions. Even though they are APPN nodes, they still can attach to
subarea SNA networks. An example of a PU 2.1 node is the downstream physical unit
(DSPU), discussed later in this chapter.
Figure 12-3
Physical Units
IBM S/370
IBM 3745
IBM 3174
PC
PC
PC
PC
PU 2.0
PU 2.1 - Used in conjunction
with LU 6.2 for APPN
PU 5 - Manages SNA network
PU 4 - Routes SNA data intra- and inter-domain
PU 2 - Controls connected LUs
Front-end processor
HOST
VTAM
SSCP
87200333.book Page 437 Wednesday, August 22, 2001 2:53 PM