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About the Megabit Modem CRA-C
Megabit Modem CRA-C User Manual 3
The Megabit Modem CRA-C can be set to any one of three modes that
determine how the data rate is selected. It is important to note that rate
adaptation occurs only during startup. The Megabit Modem CRA-C will
not change its data rate while the link is up. The three startup modes are:
•
Full startup always:
In the full startup mode, the system figures out
the highest upstream and downstream data rates it can support under
the current line conditions, with a margin greater than or equal to the
configured margin. This is done during every ADSL startup attempt.
The system will always attempt a full startup where it will set a
transmission rate up to the maximum specified. It determines this rate
by assessing the signal quality data (line length and noise conditions,
for example) and the margin configuration setting. It then comes up
in the highest available rate based on this information.
•
Session startup:
In session startup mode, the system uses the data
rates set during a previous full startup, rather than re-assessing the
signal quality data. In this mode the system performs a full startup
upon every powerup or reset and would also revert back to a full
startup attempt when a session startup is not successful for 30 seconds.
•
Fixed data rate:
In a fixed-rate mode (fixed data rate), the user
programs both the upstream and the downstream data rates using the
Transceiver Configuration Menu. The user can select from available
data rates shown above. Another configuration parameter is the
startup SNR margin that is also configurable using the Transceiver
Configuration Menu. The system will attempt to come up to the
programmed data rates with a margin greater than or equal to the
configured margin. Failure to complete startup with the desired
margin results in repeated attempts to accomplish it.
When a connection is lost in any mode (the cable disconnected, for example),
the system attempts reconnection as if it has been reset.