A warm standby application is a pair of databases, one of which is a backup copy of the other. Client applications update the active database; Replication Server maintains the standby database as a copy of the active database.
The Replication Server warm standby application for Adaptive Server databases is described in the Replication Server Administration Guide Volume 2 > Managing Warm Standby Applications.
For detailed information about how Failover support works in Replication Server, see Replication Server Administration Guide Volume 2 > Configuring the Replication System to Support Sybase Failover and Replication Server Administration Guide Volume 2 > High Availability on Sun Cluster 2.2.