Sybase Client/Server Interfaces (C/SI) includes routines and protocols for client/server communication. Replication Server uses C/SI to connect with data servers as a client. If a data server doesn’t support C/SI, you can use a Sybase gateway product, such as DirectConnect to allow Replication Server to access the data server. A gateway accepts connections from C/SI clients and, using the data server’s native interface, submits client requests to the data server for processing. When the data server returns the results, the gateway uses C/SI routines to return them to the client.