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COURIER HIGH SPEED MODEMS
CHAPTER 7. SYNCHRONOUS OPERATIONS
OVERVIEW
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. The user's device is often called a
terminal, even if
it
is a powerful personal computer.
NOTE: The term DTE in the following discussion means Data
Terminal Equipment, the end-to-end equipment involved in data
communications. DTE denotes your terminal or computer and
the remote computer.
Data Rate Synchronization
During synchronous operations, transmit and receive clocks at
both ends of the phone link control the precise timing of the data
flow. The communications equipment at the remote DTE (the
modem and network software) and your modem and DTE must
all handle the data at the same speed.
Protocol Compatibility
The devices at both ends of the link must also use the same
protocol. These devices are exclusive of the Courier modem,
which is transparent during synchronous communications. The
Courier's V.42 and MNP error control capabilities are not used.
The link protocol may be SDLC (Synchronous Data Link Con-
trol), HDLC (High-Level Data Link Control), BISYNC (Binary
Synchronous Control) or another protocol determined by the
mainframe manufacturer. These protocols format the data into
blocks or frames, add control information, and usually provide
error control.
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 (not a
personal computer) designed for a particular network, you
probably need only set the Courier properly before calling or
Synchronous Operations
7-1
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