TCP/IP Terminal Connectivity

Accessing mainframe applications using TCP/IP as the networking protocol requires implementing three basic components - Telnet, Telnet Clients and Servers, and TN3270/3179G emulators.

A. Telnet- Telnet is defined as a virtual terminal related application that uses TCP/IP as an underlying transport. Telnet and its facilities are a framework for establishing how terminal data streams are formatted and transported in a TCP/IP network.

B. Telnet Client and Telnet Server- A Telnet client resides on the machine that you are using. You would invoke the Telnet application on your machine and then "open" another system in the TCP/IP network. The system that you connect to via the open command would be running a Telnet server. Telnet clients and servers are standard on UNIX systems and are generally included in the various vendor TCP/IP offerings for other platforms and operating systems. This includes the IBM mainframe based offerings.

C. TN3270- TN3270 is the last component necessary for highly functional terminal access to the mainframe via TCP/IP. TN3270 stands for Telnet 3270 and is a software application that emulates 3270 devices. This software resides on each client machine and creates LU2 data that is carried to the TN3270 server via TCP/IP and Telnet. 3179G emulation is also accomplished via the same client/ server concepts and involves terminal negotiation between the client and server components.

By implementing these terminal related applications and facilities, a TCP/IP node user can access mainframe applications very transparently. Because of the windowing capabilities of all UNIX systems, and almost all other desktop operating systems, a user can be logged into multiple mainframe applications simultaneously. This single feature can raise user productivity across the board. In addition, a multi- windowed system can be logged on to applications running on systems other than the mainframe. A single workstation can have windows using TN3270 connected to mainframe applications and also have simultaneous on screen virtual terminal windows connected to applications on other systems that support Telnet and TCP/IP. The user simply moves the pointer with the mouse and "activates" the desired on-screen window and application. Figure 2 illustrates the components necessary for terminal access to mainframe applications using host based TCP/IP, Telnet client and server with TN3270.