Specifications

Installation and Operation Manual Chapter 1 Introduction
ASMi-31 Ver. 3.0 Overview 1-3
ASMi-31 operates at eleven selectable synchronous data rates and at eight
selectable asynchronous data rates.
Rate Adaptation
For transmission modes at user rates less than 64 kbps the ASMi-31 modem
supports two methods of rate adaptation at the DTE interface to convert the
user rate into a constant network rate, as specified by the ISDN BRI standard.
• Proprietary RAD method, based on encapsulation of pure data into HDLC
frame (default method).
• Standard method, based on the V.110/ECMA.102 guidelines (optional).
Transmit Timing Modes
ASMi-31 supports the following transmit timing modes:
• Internal – ASMi-31 uses the internal crystal as clock source.
• External – ASMi-31 uses the internal crystal system synchronized by the
external clock coming from the DTE interface.
• Receive – Clock is recovered from the received signal.
Clock Modes
The ASMi-31 modem may be configured to operate in the master or in the slave
clock mode.
• In the slave clock mode the clock rate is recovered from the line, and the
modem must be set to LBT (loopback timing).
• In the master clock mode the modem provides the clock rate to the system
and is set to either INT (internal clock) or EXT (external clock) mode. If the
EXT clock mode is selected, the unit, after it detected and measured the
“legal” clock (clock supported by the unit), configures itself and the remote
unit at the proper data rate.
Auto External Clock Concept of ASMi-31
When the ASMi-31 modem is in EXT clock mode, it automatically switches itself to
the Auto External Clock mode. In this mode the modem identifies the correct
baud rate and synchronizes the system clock by the external clock. This condition
is called the Steady state.
The modem should pass through the following “states” or phases, two of which
are quite intricate, in order to recognize and configure itself to the external clock
i.e. to reach the Steady state:
1. Initial state: when the user selects the EXT RCV mode, the modem is switched
to Pseudo-Internal mode and sends the proper message to the remote
modem.
2. Detection state: the modem tries to detect and measure the external clock
coming from the DTE.
3. Deduction state: if the clock rate is detected as valid, ASMi-31 continues to
the next phase.