The TNSNAMES.ORA configuration file needs a TNS entry to point to this remote database. At the minimum, that entry should look like the following:
ISGDB3 = (DESCRIPTION = (ADDRESS_LIST = (ADDRESS = (PROTOCOL = TCP)(HOST = sjomir.eng.stsj.jafa.com)(PORT = 10000)) ) (CONNECT_DATA = (SERVICE_NAME = ISGDB3) ) )
It is my convention that the TNS alias name is the same name as the SERVICE_NAME parameter. But the TNS alias can be anything you choose. Once you have the TNS alias defined, you can use it in the userid/password@tns_alias construct to connect to a remote database.