To start database replication, you can enter the Replicate After_
    Journal Start command on both the standby node and the master
    node. Although you can initiate replication operations on either
    node, Oracle Corporation recommends that you start replication on
    the standby node before you start it on the master node. This is
    because replication activity does not begin until:

    o  The standby database creates the network connection

    o  The master database attaches to the network connection

    o  The master and standby databases are synchronized with regard
       to committed transactions

                                   NOTE

       If you used the Replicate After_Journal Configure command
       to preconfigure the master and standby database attributes
       (see the Replicate_After_Journal_Commands Configure Help
       topic), you can invoke a single Replicate After_Journal
       Start command to start replication operations on both the
       master and standby databases.