Exchange/SNA Manual

1 Introduction
104700 Tandem Computers Incorporated 1–1
Exchange/SNA provides batch data communications between Tandem systems and
IBM host systems in a Systems Network Architecture (SNA) environment.
Exchange/SNA provides batch data communications by emulating—in software on
the Tandem system—an IBM 3770-type SNA Multiple Logical Unit (MLU) terminal.
From the point of view of the host system with which Exchange/SNA is
communicating, Exchange/SNA looks like an IBM 3770-type SNA MLU terminal,
such as an IBM 3777 Model 3 or 4.
To understand Exchange/SNA and its place in an SNA network, it is helpful to
understand the basic features of the IBM 3770-type SNA MLU terminals that
Exchange/SNA emulates. The following subsections describe the basic features of
these terminals.
IBM 3770 SNA MLU
Terminals
The IBM 3770 SNA MLU terminals are a family of batch data communications
terminals that IBM introduced in the early 1970s. These terminals are used for remote
job entry (RJE) applications. Typically, the terminals are used to submit a job from a
remote site to a central host system for processing. When the host has completed the
job, the output is transmitted back to the terminal for printing at the remote site.
Devices Supported The IBM 3770 SNA MLU terminals support the following types of input and output
devices:
Card readers
Printers
Card punches
Diskette storage units
Console keyboard and display
Card Readers
Card readers are the main input device used by the IBM 3770 SNA MLU terminals.
The card readers read cards for transmission to the host system. Generally, a deck of
cards contains Job Control Language (JCL) commands and data for the host system.
The JCL specifies the job to be performed and the data supplies any information
required by that job.
Printers
Printers are the main output device used by the IBM 3770 SNA MLU terminals.
Output from the host system is sent to a printer attached to an IBM 3770 SNA MLU
terminal for printing at the remote site. Generally, the output to be printed is the
output produced by a job submitted earlier from the same remote site.