ExpressConnect for Oracle is an embedded library loaded by Replication Server for Oracle replication.
ExpressConnect for Oracle (ECO), which is available with Replication Server Options 15.5 and later, provides direct communication between Replication Server and a replicate Oracle data server. ECO eliminates the need for installing and setting up a separate gateway server, thereby improving performance and reducing the complexities of managing a replication system.
See the ExpressConnect for Oracle Installation and Configuration Guide in Replication Server Options 15.6 product documentation.