Client/Server Laboratory 4


When you want to access a remote server you need an access component on your workstaton or your PC. Some examples are the browser, the telnet client, and the ftp client.

It is possible to access OS/390 using a telnet client or an ftp client. Most frequently however, a “3270 client” is employed. Using the 3270 communication protocol it connects your workstation to an OS/390 subsystem called the "Communication Server" .

The 3270 communication protocol is an extension of the telnet protocol and uses telnet port 23 on the server side. Most people call a 3270 client a "3270 Emulator" .

In some cases the 3270 protocol is used only to establish a connection. Subsequently a Java applet is downloaded. Any further communication occurs within a browser; the 3270 protocol is emulated using the http protocol. The applet is either stored locally or downloaded on demand.

Quite a few companies sell 3270 emulators.

For Linux / Unix we recommend the x3270 emulator (oder the c3270 command line version). Both are open source and still need compiling on the target platform (unpack, make, ... ). It is also included in many popular Linux Distributions (e.g. SuSE 7.3 Professional). To use it, just call x3270 and connect to IP address , port 23.

For Windows, quite a few companies offer a free 30 or 60 day evaluation copy. Search Google for “3270 emulator”. We liked very much the „Jet3270 Emulator“ sold by Platypus Partners. We also recommend the "QWS3270" emulator ( An older freeware version of QWS3270 is readily available on the Web. With Google use the following search argument "QWS3270 download -plus site:edu" , and you will find any number of download locations. You can also download it from our Website. A short instruction notice explains how to install it.

"Personal Communication" and "Host on Demand" (HOD) are IBM products. HOD is also available on our server. Send us an e-mail if you want to use it.

All our tutorials can be done with any 3270 emulator, including x3270 or QWS 3270.

If you want to use our system, and after you have installed a 3270 client on your PC or workstation, you need a User ID plus Passwort to access our system. There are two alternatives.

You may login (OS/390 uses the terms logon and logoff) to Internet Address "" (or and port = 23. You use one of the three User IDs "gast1" , "gast2" , or "gast3" and the passwords "gast1", "gast2", or "gast3". Because this service is frequently misused we have to shut it down from time to time. Send us a note if you have problems

This will severely limit your access rights (OS/390 controls this with the help of “RACF” user profiles). You will be able to allocate a partitioned data set under TSO and ISPF (Tutorial 1). You can edit, compile and execute Programs in several languages (e.g. in C, Cobol ,Java, or REXX), see Tutorials 1 and 2. You also should be able to write a simple Java servlet without database access using Unix System Services .

When allocating a partitioned data set you should select a name of the type GASTI.XXX.YYY(ZZZ) . GASTI should be identical with your user ID, while the values "XXX", "YYY" und "ZZZ" may be arbitrary alphanumeric strings no longer than 7 characters.

If this wets your appetite you may contact us for extended access rights. Send an email to

You find detailed and easy to use tutorials on the next page. Tutorials 1 – 5 will provide some basic knowledge in how to use an OS/390 system. They are on the same level as the c-shell, vi-editor and make file facilities under Unix. We have developed a number of additional tutorials that teach e-business related functions, like writing Java applications using the Eclipse Integrated Development Environment (IDE) , DB2 access with JDBC or DB2Connect, or accessing CICS COMMAREA via the MQSeries CICS gateway. We are also working on Enterprise Java Beans and Web Services under z/OS.

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