USRobotics V.34 - Manual (Page 166)

COURIER HIGH SPEED MODEMS
Synchronous Operations F-1
APPENDIX F. SYNCHRONOUS AND
DEDICATED AND LEASED LINE OPERATIONS
SYNCHRONOUS APPLICATIONS
Synchronous mode is required for users who need to call, or
receive calls, from a
Host computer of a large network. The
Host is usually a mainframe. There are two ways the Courier
can operate in synchronous mode:
• Selecting the ITU-T standard V.25 bis protocol, which
formats data in HDLC or character-oriented frames.
This method is used by mainframe operators and
synchronous terminal users.
V.25
bis acts as an interface between the mainframe and
modem, sending synchronous responses. An
asynchronous device or a "dumb" terminal is used to
configure the modem before it dials out in synchronous
mode.
• Dedicating a PC as a synchronous device by installing
the proper hardware and software so it can
communicate with a mainframe. The modem is
configured and dials out in asynchronous mode, then
switches to synchronous mode once a connection is
made.
NOTE: HST modulation is not supported for synchronous
communications.
GENERAL REQUIREMENTS
Courier modems in asynchronous mode adapt to many condi-
tions of remote asynchronous modems. But synchronous
connections to a mainframe require strict adherence to specific
operating parameters. If you are operating a terminal designed
for a particular network, you probably need only set the Courier
properly before calling or answering.