Advanced Replication Guide : Using advanced replication with applications : Building messages for synchronization : Requesting a reply message from the master database
  
Requesting a reply message from the master database
If the TIMEOUT in the MESSAGE FORWARD statement is not defined, the message is only forwarded to the master and the replica does not wait for the reply. In this case the reply can be retrieved with a separate MESSAGE GET REPLY call in the replica database. The syntax is:
MESSAGE unique_message_name
  GET REPLY [TIMEOUT {FOREVER | seconds }]
See also
Building messages for synchronization