2. X-Windows based 3270 and 3179G client emulators that use TCP/IP as the transport into the mainframe.

There are two approaches that provide the TCP/IP to VTAM interface, or SNA "entry point", for this I/O Concepts solution set - mainframe resident TCP/IP and SNA Gateway solutions. Figure 4 illustrates the mainframe resident TCP/IP approach. In this case the TN3270/3179G client on the UNIX system connects to the TN3270 server on the mainframe and the terminal data is passed to VTAM via LU definitions that are assigned to the TCP/IP stack application.

Figure 5 illustrates an SNA Gateway approach. In this case, the TCP/IP protocol stack is running on a system that provides services into SNA without using mainframe host resources. The TN3270/3179G client connects to the TN3270 server in the Gateway system and the LU2 data is given to VTAM then on to the application.