You can use DSCC to perform this task. For information, see Directory Service Control Center Interface and the DSCC online help.
Set the monitoring mode for the data source to proactive.
$ dpconf set-ldap-data-source-prop -h host -p port datasource monitoring-mode:proactive
Set the maximum time for which Directory Proxy Server detects no activity from a data source before establishing a dedicated connection.
$ dpconf set-ldap-data-source-prop -h host -p port datasource \ monitoring-inactivity-timeout:time
By default, the inactivity timeout is 120 seconds.
Configure an alert to be sent when a data source is detected as offline or online, as described in Configuring Administrative Alerts for Directory Proxy Server.