AM3270/TR3271 Reference Manual

2 Overview of AM3270 and TR3271
086705 Tandem Computers Incorporated 2–1
This section introduces:
The Tandem access methods AM3270 and TR3271
The subsystem components
What Are AM3270 and
TR3271?
AM3270 and TR3271 are Tandem’s implementations of IBM’s 3270 BSC protocols.
The AM3270 Access Method supports communications with IBM 3270 terminals that
are connected to one or more byte-synchronous 3271 cluster controllers. Under this
access method, one data communications process controls a single byte-synchronous
line.
The TR3271 Tributary Access Method provides communications with IBM mainframes
where the Tandem system appears to be one or more 3270 terminals connected to one
or more byte-synchronous 3271 cluster controllers. Under this access method, one
data-communications process controls a single byte-synchronous line.
When Are They Used? These access methods are used in the following ways:
AM3270
The AM3270 communications subsystem allows Tandem application programs to
access individual 3270-compatible devices connected to a Tandem system through a
non-switched, byte-synchronous, multipoint communications line. The multipoint
line can consist of multiple IBM 3270-family cluster controllers, each controller
configured with 3270-family terminals and printers.
With AM3270, application programs can issue file system requests to a terminal or
printer on an AM3270 line without concern for low-level communications-related
requirements such as control unit and device address, record size, and message
blocking.
These are the general characteristics of the AM3270 communication subsystem:
Supports general and specific polling capabilities
Adds communication protocol-related information to outbound messages
Strips communication protocol-related information from inbound messages
Permits standard line-at-a-time access to printers on a multipoint line
Allows interactive access from Tandem applications and utilities.
TR3271
The TR3271 communications subsystem allows a Tandem system to connect to an IBM
host as a 3270 controller and associated devices. With TR3271 the Tandem equipment
emulates one or more IBM 3270 cluster controllers in a remote 3270 byte-synchronous
environment. TR3271 is commonly used as to programmatically respond to screen
messages that are normally destined for IMS or CICS™ terminals.