The BEGINVTAM statement block (ended with ENDVTAM) is used to define characteristics that are related to the mapping of the VTAM configuration.

A sample BEGINVTAM statement block is in Figure 1.

 BEGINVTAM                                           
   PORT 23                                           
   DEFAULTLUS TCP00001..TCP00099        ENDDEFAULTLUS
   LUGROUP LUGRP1 LUT101..LUT400..FFFXXX ENDLUGROUP
   PRTGROUP PRTGRP1 PRT101..PRT400..FFFXXX ENDPRTGROUP
   IPGROUP IPGPAY 255.255.0.0:9.8.0.0 ENDIPGROUP
   LUMAP LUGRP1 IPGPAY 
   PRTMAP PRTGRP1 IPGPAY 
   USSTCP USSTELT                                    
 ; DEFAULTAPPL TSO 
   LINEMODEAPPL TSO                                  
   ALLOWAPPL TSO* DISCONNECTABLE                     
 ENDVTAM

The capabilities of mapping within a BEGINVTAM statement block are complex and extensive. The sample used here has been kept simple to facilitate explanation of the basic concepts.

PORT 23

This statement is used to connect this BEGINVTAM block with a TELNETPARMS statement for the same port number. In other words, a connection to port 23 uses these BEGINVTAM statements as well as the TELNETPARMS statements for the same port number.

DEFAULTLUS

When a TN3270E client connects to the TN3270E server, it needs to be mapped to an LU that the TN3270E server can use to represent this client on the SNA session. If the client does not specify a specific LU, and if no other mapping statement directs a different LU to be used for this client, then an LU from this default mapping is assigned to the connection.

In this sample, the LU range from TCP00001 to TCP00099 are available as default LUs.

LUGROUP

This statement does not do any mapping. Instead, it defines a group of LUs that can be used for TN3270E terminal sessions. The FFFXXX pattern indicates that the first three characters (for example, LUT) are fixed while the remaining four characters represent a hexadecimal range.

PRTGROUP

This statement does not do any mapping. Instead, it defines a group of LUs that can be used for TN3270E printer sessions. The FFFXXX pattern indicates that the first three characters (for example, PRT) are fixed while the remaining four characters represent a hexadecimal range.

IPGROUP

Again, this statement does not do any mapping. It defines a group of IP addresses (specifically, IP addresses with a 9.8 network ID) that identify TN3270E clients (an IPGROUP is referred to as a client identifier, and there are many other client identifiers available).

LUMAP

This statement maps the LUGRP1 group of LUs to the IPGPAY group of clients. In other words, connections from the 9.8 network can only use terminal LUs from within the LUGRP1 range.

PRTMAP

This statement maps the PRTGRP1 to the same network, such that a TN3270E connection from a client on the 9.8 network can associate a printer from this group.

Note: Together, these two LUMAP and PRTMAP statements form the one-to-one mapping that is necessary for a TN3270E printer connection to utilize the ASSOCIATE command.

USSTCP

This statement specifies that the USS message 10 panel (a logon panel similar to native SNA terminals) be presented for the initial connection. If LUSESSIONPEND is coded, a client is returned to this screen after logging off from an application.

Note: Unformatted System Services (USS) messages are messages used in an SNA environment to facilitate application access. USS message 10 (often referenced as USSMSG10) is the standard logon message presented when a session is initially established. USSMSG7, as mentioned, is the standard error message presented when a command entered at a USSMSG10 screen fails to complete successfully.

DEFAULTAPPL

Note that this statement is commented out. That is because a DEFAULTAPPL and a USSTCP statement have the same function: they control where a user is directed at initial connection time. If a USSMSG10 panel is not desired, this statement could be used to direct a client to a specific application (TSO for example) at connect time.

LINEMODEAPPL

It is possible for a client to negotiate line mode when connecting to the TN3270E server. In such a situation, this setup connects the client to the TSO application.

ALLOWAPPL

This statement limits the selection of application for a TN3270E client to the TSO application only. This is a security statement to control what applications can be selected from the USSMSG10 panel.