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Example: S-Register 6, or S6=n, defines the length of time the
modem will wait for a dial tone. In this case the acceptable
range is 3-6 (in seconds) with a default value of 5. With S6=3,
the modem will wait three seconds for a dial tone when
going off-hook before dialing the first digit of its telephone
number.
Data Communication Protocols
This can be more than a little confusing. These protocols
represent various domestic and international standards
which enhance modem performance and reliability. The
protocols are activated and controlled by a variety of
extended AT commands and S-Registers.
MNP stands for Microcom Networking Protocol and is a
protocol developed by Microcom for full-duplex, error-free
communications. This protocol detects and corrects errors
which can result from telephone line noise and other signal
distortions. There are several classes of MNP operation also
referred to as service classes. Class 5 maximizes data transfer
rate and provides compression which can significantly
increase data throughput.
The “V-Dot” standards are more numerous, but have a
single origin: the International Telecommunications Union
Telecommunications Standards Sector (formerly the
Consulting Committee for International and Telephone and
Telegraph or CCITT). Some of the lower-level standards such
as V.21 and V.22 have “domestic” equivalents as developed
by the former Bell System, also referred to as Bell standards.
The “V.Dot” standards may be summarized as shown on the
following page.
Modem Command Reference
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