Leased-Line Restoration and Dial Backup
The dial backup process is started by one of the following:
1. Loss of carrier on an established connection.
2. Failure to establish an Automatic Connection.
3. Inability to complete a retrain.
Failure to manually establish a leased-line connection through AT commands
does not start dial backup.
When a leased-line connection fails, the modem checks the value of S61.
If, S61=0 the modem enters idle state. If S61=1-255, the modem checks the
value of S62. If S61=1 to 255, the originating modem retries the leased
line a maximum of S61 times. After the leased line has been retried S61
times unsuccessfully, the dial backup process begins. S62 determines the
number of seconds allowed for each leased-line retry.
The originating modem performs dial backup by dialing the number stored
in location 0 of its phone book. If no dial-up connection is established,
it retries the leased line. After the number of allowable successive failures
in this cycle of alternately trying to establish a dial-up connection and
retrying the leased line, the modem quits attempting the dial-up call and
retries the leased line until user intervention.
The answer modem, which had ignored dial-up calls while a leased-line connection
was in progress or being established, begins monitoring both the dial-up
line and the leased line when the leased line fails. It accepts either a
dial-up call after S0 rings or a leased-line retry.
If a dial-up connection is established, the modem retries a leased-line
connection after S62 minutes.
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