Retrains and Rate Re-negotiation
Retrains and rate re-negotiations can be initiated (1) by the other
modem, (2) by an AT command, and (3) automatically, by the modem.
Two measures of transmission quality manage retrains and rate renegotiation:
signal quality and frame error rate (FER). Frame error rate is the measure
of transmission quality used when the modem can determine the received signal
FER. When the modem cannot determine the FER, signal quality is the basis
for retrain and rate re-negotiation attempts.
The general procedure for automatic retrain and rate re-negotiation is the
following. If signal quality falls below the acceptable level during a call
or the FER goes too high, the modem should try a retrain. If the retrain
does not improve the signal quality or reduce the FER, then the modem tries
to reduce the line speed by a rate re- negotiation. If the FER improves
to an acceptable level, then a rate re-negotiation to attain a faster line
speed is recommended, provided the current DTE speed is appropriate for
the next higher line speed.
The modem does not change its line speed if either of the following conditions
apply:
a) it is in a synchronous mode (&Q1, &Q2, or &Q3 selected)
and transmit clock is supplied by the
DTE (&X1) or
b) the modem is using V.14 asynchronous-to-synchronous conversion.
Retrain
Rate Re-negotiation
Automatic Rate Re-negotiation
Interface Leads
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