Exchange/RJE Manual

Operational Features
Introduction
104698 Tandem Computers Incorporated 1–7
3780-emulation mode supports the compression of multiple consecutive blanks
during send operations if you so specify. During receive operations, compressed
blanks are automatically expanded by the line server.
2780-emulation mode does not support the compression of multiple consecutive
blanks during send operations, nor does it expand compressed blanks during
receive operations.
2780-emulation mode automatically appends an EM (end-of-media) character to
the end of records less than 80 bytes long. The use of the EM character can be
suppressed if you so specify.
3780-emulation mode does not use the EM character.
Choosing Between 2780- and 3780-Emulation Modes
The choice of which emulation mode to use, 2780 or 3780, is often determined by the
setup and programming of the remote system. For example, if the remote system is
expecting to communicate with a 2780 data communications terminal, you should
select 2780-emulation mode.
If you have a choice of which emulation mode to use, the larger block size of 3780-
emulation mode may result in better throughput over the data communications line,
all other factors being equal.
The choice of emulation mode will also affect CPU resources. Each ITB and ETB
generates an interrupt; each interrupt requires CPU time. 2780-emulation mode uses
ITB to separate records and therefore will generate an interrupt for each record. 3780-
emulation mode does not use ITB and generates an interrupt for each block. 2780-
emulation will generate more interrupts than 3780-emulation mode, assuming more
than one record per block.
Block Mode The three block modes described below allow you to send and receive larger record
sizes than those supported in either 2780- or 3780-emulation mode. As is the case with
2780- and 3780-emulation mode, the choice of which block mode to use is often
determined by the setup and programming of the remote system.
Three variables control the mode of operation: BLOCKSIZE, BLOCKING, and
terminal-type (2780 or 3780).
After you have started the line server, you cannot change the values for BLOCKSIZE
and BLOCKING; you can change the value for terminal-type each time you
connect to the line server.
You may use all three block modes from either the Exchange/RJE command
interpreter or the programmatic interface:
From the command interpreter, specify values for BLOCKSIZE and BLOCKING in
the RJECIR or SET command; specify the value for terminal-type in the
CONNECT command.
From the programmatic interface, specify values for BLOCKSIZE and BLOCKING
in the RJESV command; specify the value for terminal-type in SETMODE 41.