Exchange/RJE Manual

Underlying Communications Subsystems
Introduction
1–4 104698 Tandem Computers Incorporated
Underlying
Communications
Subsystems
Exchange/RJE uses one of two underlying communications subsystems to handle
some of the BSC protocols and the interface with the data communications line. These
two communications subsystems are:
Envoy with a byte-synchronous controller
CP6100 with a 6100 communications subsystem
Which one your system uses depends on your particular installation. From the point
of view of using Exchange/RJE, it makes no difference which one you use. The
Exchange/RJE line server handles all communication with the underlying
communications subsystem and hides the differences between the two from you and
your programs. You can, for example, set up a command file or write a program on a
system that uses Envoy and then move the command file or program to a system that
uses CP6100, and the command file or program will work with no changes.
There are differences in the SYSGEN definitions for Envoy lines and CP6100 lines, and
in how the two types of lines are managed. However, these differences are apparent
only outside of Exchange/RJE.
Data Communications
Lines
Both Envoy and CP6100 support two types of data communications lines: EBCDIC
lines and ASCII lines. The line type, EBCDIC or ASCII, refers to the code used for the
BSC control codes. An EBCDIC line uses EBCDIC for the BSC control codes, and an
ASCII line uses ASCII for the BSC control codes. Note that the line type does not limit
the type of data that can be sent over the line. The line type simply determines the
code that is used to control the line.
A data communications line is defined as an EBCDIC or an ASCII line during system
generation. The Tandem system and the remote system must assign the same type to
the same data communications line. No communication is possible if the Tandem
system and the remote system do not use the same code for the BSC control codes.
Controlling
Exchange/RJE
You can control Exchange/RJE in two ways:
Through commands, using the Exchange/RJE command interpreter.
Through file-system procedure calls, using the Exchange/RJE programmatic
interface.
Both the Exchange/RJE command interpreter and programmatic interface operate in
each of the following modes:
2780-emulation mode
3780-emulation mode
Block mode
Block mode allows you to send and receive larger records than are supported in
either standard 2780- or 3780-emulation mode.