Exchange/RJE Manual

Exchange/RJE Components
Introduction
1–2 104698 Tandem Computers Incorporated
The Line Server The Exchange/RJE line server provides a record-oriented interface (using standard
file-system procedure calls) that is independent of the underlying communications
process, either Envoy or CP6100. The line server performs the functions required to
send and receive records over the data communications line using BSC protocols.
The command interpreter and the send/receive server (or a user-written program) use
the line server to control the data communications line and to send and receive records
over the line. When using the command interpreter, you can let the command
interpreter start and stop the line server automatically, or you can start and stop the
line server explicitly using the RJESV and TACL STOP commands. The command
interpreter can only stop temporary line servers; named line servers must be explicitly
stopped.
The line server provides a programmatic interface, which your programs can use.
When you write a program that uses Exchange/RJE, you use standard system
procedure calls to communicate with the line server. Your program passes records to
and receives records from the line server, which in turn handles the communications
with the remote system. When using the programmatic interface, you can start and
stop the line server programmatically, or you can start and stop the line server using
either the Exchange/RJE command interpreter or the RJESV and TACL STOP
commands outside of your program.
The line server uses a procedure called USER^EXIT^MODEM^SUPPORT that resides
in a user library. The user library shipped with Exchange/RJE is called RJELIB; it
contains a placeholder version of USER^EXIT^MODEM^SUPPORT that does nothing.
You can write your own user-exit procedures to control an autodial modem or
perform other special processing needed to establish a connection. For more
information on writing a user-exit procedure, see Appendix D.
The line server can be run as a NonStop process pair. If you require communications
using Exchange/RJE in a NonStop mode, you must program your own NonStop
process pair that uses the programmatic interface to communicate with and control the
line server.
The Trace Server The Exchange/RJE trace server is a diagnostic tool that captures the messages
transmitted between the line server and the underlying communications process; the
trace server records those messages in a file called the trace file. You can then format
and examine the contents of the trace file to assist in program development and in
determining the source of communications problems.
You can use the trace server with both the command interpreter and the programmatic
interface. However, in both cases, you must start the trace server using the command
interpreter. The trace server cannot be run as a NonStop process pair.