Defining a VTAM APPN network

Definitions are put together in the ATCSTRxx in VTAMLST and by defining various VTAM major nodes.

Defining data sets and VTAM startup JCL

The first step for implementing APPN on a mainframe is to define the data sets used for APPN checkpointing and to update the VTAM startup JCL.

i//* DATA SETS FOR APPN DATABASE CHECKPOINTING
//DSDB1 DD DSN=SYS1.DSDB1,DISP=SHR
//DSDB2 DD DSN=SYS1.DSDB2,DISP=SHR
//DSDBCTRL DD DSN=SYS1.DSDBCTRL,DISP=SHR
//TRSDB DD DSN=SYS1.TRSDB,DISP=SHR

Creating definitions in ATCSTRxx

Define the APPN node type. You need to assign the role of VTAM as an APPN node; that is, either a network node (NN) or an end node (EN). Do this by coding the NODETYPE parameter. The two possible values are either NN or EN. To define VTAM as a network node, code the following:
```
NODETYPE=NN
```
Assign the control point name (CPNAME). The same parameter used for subarea networking (SSCPNAME) is used for APPN. To assign CPNAME1 as the control point in ATCSTRxx, code:
```
SSCPNAME=CPNAME1
```
Assign a network ID (NETID). The same parameter used for subarea networking (NETID) is used for APPN. To assign NET1 as the network ID in ATCSTRxx, code:
```
NETID=NET1
```
Specify the level of high performance routing support. VTAM can support either automatic network routing (ANR) or rapid transport protocol (RTP). The HPR parameter specifies which functions of HPR, either ANR or RTP, or both, are implemented by VTAM. To indicate that VTAM provide RTP-level HPR support, specify:
```
HPR=RTP
```
HPR=RTP is the default.
Specify the default link type. For a VTAM type 2.1 node the CONNTYPE parameter determines whether connections to adjacent type 2.1 nodes are established as a low-entry networking (LEN) node (with no APPN support) or attempted as an APPN connection. To specify that the connection be attempted as an APPN connection, code:
```
CONNTYPE=APPN
```
Specify CP-CP support. The CPCP parameter specifies whether VTAM supports CP-CP sessions with adjacent type 2.1 node. To specify that CP-CP sessions be supported on all connections to adjacent type 2.1 nodes code:
```
CPCP=YES
```
The CONNTYPE and CPCP parameters can be overridden on the physical unit definition statement as illustrated in the following example:
```
PU1 PU ADDR=01,
       ISTATUS=ACTIVE,
       CONNTYPE=APPN,
       CPCP=YES
```
Define VTAM as the central directory server (CDS). If you want to define VTAM as a central directory server, use the CDSERVR start option. You do not need to define anything on the other network nodes. The other network nodes find out about the existence of the central directory server through normal topology exchanges. To define VTAM network node as a central directory server, code:
```
CDSERVR=YES
```
Control security. To reduce the burden of static definitions, VTAM permits dynamic definitions of physical units, logical units, and adjacent APPN nodes. In the mainframe environment, many installations are reluctant to allow dynamic definitions of VTAM resources. The DYNADJCP parameter controls whether adjacent control points are allowed to be created dynamically. To disable the dynamic definition of adjacent control points, code:
```
DYNADJCP=NO
```
The BN=YES start option is used to define VTAM as an extended border node (EBN). VTAM EBNs must also be NNs.
IVTAM is defined as an ICN or MDH, then SORDER is used to control the order these networks are searched.

Defining VTAM major nodes

Define the adjacent control point major node. If DYNADJCP in ATCSTRxx is defined as NO, the ADJCP major node defines the adjacent control point that can establish a CP-CP session with this VTAM.
```
ADJCP1 VBUILD TYPE=ADJCP
CP1    ADJCP
EBN1   ADJCP  NETID=NET2
```
Create a network node server list for end node. To create a network server for an end node, code a NETSRVR major node. The major node list the network nodes that are part of the network node server list.
```
NETSRVR1 VBUILD  TYPE=NETSRVR
CP1A     NETSRVR NETID=NETA
CP2A     NETSRVR NETID=NETA
         NETSRVR
```
In the last entry, the nameless NETSRVR entry allows the end node to select any other known adjacent network node that meets the defined criteria as its network node server.