You can specify a connect identifier in the connect string when you start the Data Pump Import utility. The connect identifier can specify a database instance that is different from the current instance identified by the current Oracle System ID (SID). The connect identifier can be an Oracle*Net connect descriptor or a net service name (usually defined in the tnsnames.ora file) that maps to a connect descriptor. Use of a connect identifier requires that you have Oracle Net Listener running (to start the default listener, enter lsnrctl start). The following is an example of this type of connection, in which inst1 is the connect identifier:
impdp hr@inst1 DIRECTORY=dpump_dir1 DUMPFILE=hr.dmp TABLES=employees
Import then prompts you for a password:
Password: password
The local Import client connects to the database instance identified by the connect identifier inst1 (a net service name), and imports the data from the dump file hr.dmp to inst1.
Specifying a connect identifier when you start the Import utility is different from performing an import operation using the NETWORK_LINK parameter. When you start an import operation and specify a connect identifier, the local Import client connects to the database instance identified by the connect identifier and imports the data from the dump file named on the command line to that database instance.
Whereas, when you perform an import using the NETWORK_LINK parameter, the import is performed using a database link, and there is no dump file involved. (A database link is a connection between two physical database servers that allows a client to access them as one logical database.)
Oracle Database Administrator's Guide for more information about database links
Oracle Database Net Services Administrator's Guide for more information about connect identifiers and Oracle Net Listener